this work was performed by the jet propulsion laboratory, 5th pim 1... · rca, and ti the...

"This work was performed by the Jet Propulsion Laboratory, California I nstitute of Technology , under NASA Contract NAS7-100 for the U.S. Energy Research and Development Administra tion, Division of Solar Energy.

"The JPL Low-cost Silicon Solar Array Project is f unded by ERDA and forms part of the ERDA Photovoltaic Conversion Program to initiate a major effort toward t he development of low- cost s olar arrays ."

ENERGY RESEARCH AND DEVELOPMENT ADMINISTRATION SOLAR PHOTOVOLTAIC CONVERSION PROGRAM LOW-COST SILICON SOLAR ARRAY PROJECT

5th PROJECT INTEGRATION MEETING JANUARY 17-18, 1977

5101-18

JET PROPULSION LABORATORY • CALIFORNIA INSTITUTE OF TECHNOLOGY • PASADENA, CALIFORNIA

CONTENTS

I. OVERVIEW AND CONCLUSIONS

A. Narrative of Events

B. Interaction of PIM with ERDA Review

C. Project Summary of Results

II. TASK RESULTS

A. Silicon Material Task (Ralph _Lutwack)

B. Large Area Silicon Sheet Task (John Zontendyk)

C. Encapsulation Task (W. F. Carroll)

D. Automated Array Assembly (W. A. Hasbach)

E. Large Scale Procurement Task (Ed Sequeira)

F. Operations Task (L. N. Dumas)

G. Engineering Task (Ron Ross)

III. PRESF.NTATION SUMMARIES

A. Project Analysis and Integration

B. Economics and Industrialization Task

C. Engineering Task

D. Silicon Material Presentation

E. Battelle Columbus Laboratories

F. Springborn Laboratories/DeBell & Richardson

G. Encapsulation Presentation

H. Texas Instruments Presentation

I. RCA Presentation

J. Motorola Presentation

K. Uniform Costing Presentation

L. Project Price Goal

APPENDIX: AGENDA

V

I-1

I-1

I-2

1-2

II-1

II-1

II-2

II-4

Il-6

Il-7

II-9

II-14

III-1

III-2

III-7

III-13

III-19

III-35

III-45

III-49

III-55

III-63

III-69

III-71

A-1

I. OVERVIEW AND CONCLUSIONS

A. NARRATIVE OF EVENTS

The Fifth LSSA Project Integration Meeting was held January 17 and 18, 1977, at the San Diego Hilton Hotel. There were logical advantages in holding the quarterly meeting in sequence with the ERDA Semiannual National Solar Photovoltaic Review, and these dictated the specific location and schedule.

1. Meeting Objectives

The Objectives of the Fifth PIM were:

(a) To integrate the LSSA Project technical plans and activities.

(b) To assess Project activities in the areas of higher efficiencies, costs, economics, and manufacturing.

(c) To exchange technical data at the working level.

(d) To provide an overview of LSSA Project technical plans and status.

2. Meeting Activities

Two major topics were covered in the Fifth PIM; these were cost versus efficiency and manufacturing processes for solar cells and solar arrays.

All participants convened jointly Monday morning, January 17, for a·brief presentation concerning the P_rogram/Project status. Concepts for cost and efficiency tradeoffs were presented subsequently, arid the various aspects and definitions used in the tradeoff process were discussed. Detailed presentations were then made on System/Module Interactions, Module Efficiency Optimization, and Task-level Influences. Monday afternoon the Tasks, including Operations and Engineering, held Intra-/Inter-Task sessions. Efficiency of cells and arrays was the primary subject of each of these sessions.

Tuesday morning a key general session was held in which the ERDA program status was delineated by L. Magid and M. B. Prince, and manufacturing processes for solar cells and solar arrays were discussed in detail by contractors. Tuesday afternoon Intra- and Inter-Task.sessions were held essentially to review problems, status, and cost effects of requirements.

A concluding general session was held in the late afternoon which reviewed the highlights of the meeting and ended with ERDA comments and the LSSA Project summary.

A copy of the agenda is in the Appendix.

I-1

B. INTERACTION OF PIM WITH ERDA REVIEW

The location and timing sequence for the Fifth Project Integration Meeting, as detailed above, provided an opportunity for interaction between the LSSA Project meeting and ERDA Program activities. The administrative results of this scheduling were to minimize travel requirements and, more importantly, to facilitate the dissemination of information for the participants of two wide, but related, sectors of interest in the field of solar voltaics.

The Tuesday session was a joint meeting that provided an opportunity for attendees to gain further insight into LSSA Project functioning. The LSSA Project contractors were also invited to attend the continuation of the Program Review Mee~ing sessions on Wednesday and Thursday, January 19 and 20.

C. PROJECT SUMMARY OF RESULTS

The prime objective of the LSSA Project is to focus its activities on the development and procurement of solar cell arrays that are compatible with photovoltaic power systems which have minimum system life cycle costs. To date, the Project efforts have concentrated on minimizing the manufacturing costs of arrays. The Project recognizes, however, that an array manufactured for a minimum system life cycle cost is not necessarily identical to an array that has a minimum manufacturing cost. Consequently, as system life cycle analyses and data are obtained, the Project will alter, if necessary, the emphasis of its activities, so that module designs and costs are complementary with optimal system designs and costs.

The generation and compilation of this information will require an integration of the activities and experience of all Program participants during the next few years. As part of that effort, JPL has initiated studies of concepts that need to be examined, such as: system design tradeoffs and solar cell module efficiency optimization.

The results of these studies are some methods for minimizing array costs. An archetypal model was devised for system tradeoff assessments. Module efficieµcy was defined in terms of its component efficiencies, and methodologies for assessing cost effectiveness versus module efficiencies were illustrated. The relationship between cell efficiency and module efficiency was clarified. Studies involving the optimization of costs versus other parameters will continue to be discussed at future integration meetings.

Based upon the 12-month studies of cell and module fabrication by Motorola, RCA, and TI the $0.50/watt Project goals probably is achievable (given the achievement of material cost goals) without a major technological breakthrough or invention. However, evolution of today's module manufacturing techniques, adaptation of some semiconductor technology, and the continuance of LSSA technology developments are required. The application of today's technology even without complete automation could reduce the cell fabrication costs to within a factor of three of those required to meet the 50¢/watt goal. It is estimated that these costs could be further reduced to meet the goal by the use of new improved technology and automated mass production. A present concern

I-2

relative to meeting the goal is the cost of the module materials, including module structure, encapsulants, silicon, and contact metals.

The costing methodology for evaluating the economics of new silicon refinement processes as developed by Lamar University is compatible with the Project costing methodology developed at JPL. Further integration activity between the two is expected.

I-3

II. TASK RESULTS

The Intra- and Inter-Task meetings reflected the Project meeting directives and concentrated on cost versus efficiency and on solar cell/array manufacturing processes. The continued discussions and feedback generated in these meetings are expected to influence the evolution of activities and speed overall progress toward Project Goals.

Summaries of task results were determined in part by the open discussion periods in each of these meetings. These tend to produce effective results, essentially because of their frankness and the immediate exchange of information.

A. SILICON MATERIAL TASK (Ralph Lutwack)

Two Silicon Material Task meetings were held. The topic of the first was "Standardization of Economic Analyses of Process Developments." The formal presentations were by the team of Professors Miller and Yaws of Lamar University. The procedures being used under the JPL contract were illustrated with discussion of the analyses of the Battelle development of the process for the Zn reduction of SiCl4. (The steps of these procedures have been described in the Lamar quarterly reports.) The additional considerations of incorporating normal contingencies for undeveloped designs, of environmental protection, and of materials of construction were emphasized. Special attention was given to the declaration th~t each process will have peculiar economically sensitive factors and consequently that the use of generalized extrapolations in economic analyses may lead to grossly incorrect results. This conclusion was vigorously suppo~ted in the discussions. An action item of this meeting was that a document presenting the format and the strategic values to be used in all of the economic analyses of the Silicon Material Task will be prepared by Lamar University and JPL.

The second meeting consisted of status reports on a group of contracts for process developments. The first was a description by W. Breneman of Union Carbide effort to develop a process for producing SiH4. The primary items were (1) a discussion of the SiH4 redistribution reaction and (2) a presentation of the flow chart for the mini-plant, which is designed for an output of about 5 kgm per day. Dr. R. Elbert and J. Rexar then described the second effort by Union Carbide, the development of a method for producing Si from SiH4 using either a free space reactor or a fluidized bed reactor. The presentations were devoted almost entirely to results obtained for the free space reactor in an 18 month company sponsored program. This reactor has been operated at 500 - 600°C to determine rate and yield data; the product is a fine powder.

Dr. J. Blocher discussed the progress on the Battelle contract to develop the process for the reduction of SiCl4 by Zn in a fluidized bed reactor. The mini plant, designed for an output of 200 gm per hour will be operated to determine rate and yield data and to study problems such as that with the condenser subsystem. The design of an experimental production facility capable of an output of 25 MT per year is underway; a preliminary flow sheet was shown.

Kinetic studies and descriptions of deploymerization reactions, as deduced from mass spectroscopy information, were the central points of the presentation

II-1

by Dr. W. Ingle of Motorola. The results of an economic analysis of the process for the reaction of SiF4 with metallurgical grade Si and the use of the SiF2 transport were given for a 2000 MT per year plant; the product cost was $7.01 per kgm Si.

Progress in the contract with Texas Instruments for a study of the use of a plasma reactor for the C reduction of Si0

2 was given by R. Roques. Several

elements of the effort were summarized: thermodynamic calculations, a temperature diagram for the plasma device, and a statistical analysis program.

The final presentation was by M. Fey.of Westinghouse. He described the contract to develop the process for the reduction of SiCl4 by Na, Mg, or H2 using an arc heater. The thermochemical analyses, which showed reactions using Na and H2 to be favorable and Zn to be unfavorable, were discussed. In the case of Zn, the instability of AnClz at high temperatures and unsatisfactory mass and energy balances were noted. Other aspects of the first phase, including preliminary analyses of the reactant injection systems, were discussed.

B. LARGE AREA SILICON SHEET TASK (John Zontendyk)

The Large-Area Silicon Sheet Task participated in three Intertask sessions during the 5th PIM.· Representatives of the Task concerned with various sheetgrowth techniques met with representatives of the Silicon Materials Subtask on Effects of Impurities and Prof. B. Chalmers of Harvard University for a discussion of the effects of impurities on crystal growth, under the chairmanship of T. Digges, on Monday afternoon. At the same time, under the chairmanship of G. Cumming, there was a joint session with representatives of the Automated Array Assembly Task on sheet characteristics/cell fabrication interactions. Tuesday afternoon, the Task participated in a meeting with Task 4 and large-scale production on the same general subject, with emphasis on manufacturing processes.

In the meeting with Silicon Material Task, discussions were held on the effect of constitutional supercooling on the growth (solid-liquid) interface during solidification. The two major impurities that might produce constitutional supercooling were identified as carbon and oxygen. Professor Chalmers believed constitutional supercooling to have minimal effects in the growth processes funded by JPL. The thermal gradients in the various processes were thought to exert an order of magnitude effect greater than supercooling effects. However, there was no definition ·of anticipated structural defects as the results of fast growth rates.

The question of the impact on constitutional supercooling of impurities which might be permitted in solar grade material was not resolved. However, the fast growth processes such as ribbons would be impacted more by constitutional supercooling than would ingot growth such as Czochralski and HEM.

The second Monday session, with Task 4, resulted from recent emphasis on understanding relationships between chemical and crystal imperfections of lowcost crystal-growth processes and the relationships to solar-cell fabrication. For this session, Dr. G. Schwuttke of IBM was invited to discuss aspects of lowcost silicon sheet structure and electrical properties and their influence on cell fabrication. Dr. Schwuttke's discussion was limited to the studies IBM has

II-2

conducted to categorize defect states in the three main crystal types: Czochralski, shaped ribbon growth (CAST, EFG), and web dendritic.

In CAST ribbons, grain boundaries and dislocations are the principal native defects, and are believed responsible for reduced lifetime and degraded solarcell performance. These defects are being carefully studied at IBM using electron microscope (TEM and EBIC) and MOS capacitance lifetime measurements. IBM has observed that cells fabricated from ribbon materials with defined imperfection densities have a predictable perfon,1ance range. Technical details are available in IBM quarterly and monthly reports from the latter part of.CY76.

Dr. Schwuttke also commented briefly on the problems of maintaining crystallinity in Cz crystals.grown at rates approaching maximum. This is important to the extent that growth rate is a limiting factor for the Cz process. It should be added to the problem list with slicing, polishing, and limitations on crucible usable·life.

His concluding comments were concerned with web-dendritic growth. He spoke favorably of the material-conserving nature of the process and its high degree of crystalline perfection, which could contribute to both cost-effectiveness and performance.

A general discussion ensued during which TI and Mobil Tyco asserted that cell-fabrication techniques now used on Cz single-crystals (although better understood than any other cell-fabrication technology) may not yield highefficiency cells when applied to cell materials grown by low-cost sheet technology. IBM indicated·that CAST cells of 10% efficiency have been made using the same techniques that yield 15-16%-efficient cells from·cz ig9ts.

Certain participants in this session expressed interest in determining the necessary purity level for silicon material from which low-cost sheet will be grown. Thd discussion emphasized the need for joint efforts by the two Tasks in processing sufficient quantities of low-cost sheet, from the more mature technologies such as ribbon and web, under controlled conditions to better understand the effects of impurities, dislocations, ·growth rates, and other conditions which affect crystal quality and lifetime.

Considerable progress in Task activities is noted. In shaped growth and forming techniques, wetting-die ribbon growth up to 50-rnm width at rates up to 7.5 cm/min has been achieved; contact-material studies show silicon nitrides and oxy-nitrides may be promising die coatings; predicted forming-limit diagrams have been done for the hot-forming process, indicating that the deformation sheet process is possible (1300°C).

In substrate-related growth, photodiodes have been successfully fabricated on dip-coated substrates at Honeywell, yielding observed photoconversion efficiency (corrected for resistance loss) of about 8-10%. In'ingot growth, a possible solution to the cracking problem observed in the heat-exchange method has been demonstrated in small-crucible cast ingots, using a spray-on quartz release coating.

Conclusions and comments from the intertask activities are as follows: constitutional supercooling may be significant as it applied to carbon, and

II-3

studies for impact of impurities, on cell efficiencies need to be expanded to include impurities introduced during growth. In the Task 4 area, problem definitions and process technology assessments were incomplete so far as low-cost silicon sheet is concerned.

C. ENCAPSULATION TASK (W. F. Carroll)

Outline of Task Participation

1. Intra-Task Meeting (1:00 - 3:00, 1/17/77)

(a) Discussion of Influence of Encapsulation on Array Efficiency

(b) Rockwell Contract - Progress and Problems

2. Inter-Task Meeting - Tasks 3, 4, 5, Engineering, Operations, LeRC, MIT/LL, and Sandia (3:15 - 5:30, 1/17/77)

(a) Presentation by Battelle (D. C. Carmichael), "Present Status of Encapsulant Materials"

(b) Presentation by Springborn Laboratories (formerly DeBell and Richardson; B. Baum), "Near-term Encapsulants"

(c) Presentation by JPL (H. Maxwell), "Encapsulant Material Costs"

3. Intra-Task Meeting (1:30 - 3:30, 1/18/77), Encapsulation Progress and Problems

(a) Simulation Physics

(b) Battelle Columbus Laboratories

(c) Springborn Laboratories

Assessment of Task Progress

As the Encapsulation Task effort has progressed, significant findings have emerged which are worthy of note. These have become appraent from the results of individual Contractor's efforts, from the results of interactions between JPL and the various contractors, between the contractors, and as the results of Task interactions. The most significant of these findings are described briefly.

It has become appraent that low cost encapsulants that will meet cost and life requirements are not state-of-art. It should be emphasized that materials exist that meet two of the three requirements of cost, life, and appli°cability but not all three. For example, silicone encapsulants might meet life and applicability requirements, but not cost requirements. This does not necessarily mean that whole new polymer systems must be developed. For one thing, there is not sufficient time to develop, such brand new polymer systems. Rather, it is expected that existing materials must be modified to meet the specific requirements of the LSSA program. For interim array requirements, preliminary results

II-4

indicate a wide variety of available encapsulation materials that will meet interim cost goals.

Review of the literature by Battelle has shown a lack of satisfactory life prediction methodology and, in addition, a lack of natural/accelerated/ abbreviated test data that can be used to develop a satisfactory methodology. These life prediction methodology/data must now be developed in an iterative and time consuming process that was not originally expected.

Rockwell has reported results of natural/accelerated/abbreviated testing. The results are interesting but the data does not fit any of the classical degradation mathematical models. Preliminary data three months ago looked like a good fit. (Note that more recent data show fit to a "hazard" function model rather than a classical Weibull model.)

The Springborn Laboratory test results have been encouraging. The test program has done what a good test program should do -- results range from outright failures of some materials to essentially no degradation of specific properties in other materials. The results will be a body of data on a large number of materials for array encapsulation from which manufacturers can select materials for specific array requirements.

Simulation Physics has report~d completion of their new electrostatic bonder. In approximately two weeks of operation they have had the following successes:

1. Made an electrostatic bonded (to 7070 glass) functional cell which had the cell contacts screen printed on the glass.

2. Made a plate with 5 cells bonded in a single three minute bonding cycle.

3. Made an electrically functional five cell assembly (no data received as yet).

Cost/Efficiency and Manufacturing Processing/Cost

Strawman designs were created for "near" term, "intermediate" term, and "long" term designs. Encapsulation costs were then estimated and presented. These costs were incorporated in the "Project Cost Goal Allocations" presented by H. Macomber. Near term materials are oaf-the-shelf, state-of-are products. Intermediate term materials are similar to near term except that minor to major processing modifications might be required. Long term materials do not exist at the present time; it is assumed that these materials will be developed by modifying existing polymeric materials. It is not expected that brand-new polymeric species will be developed specifically for solar arrays because this historically has required from 10 to 20 years and is very expensive.

The costs methodology and cost goal allocations presented at this Project Integration Meeting are considered to be valuable tools for systematically assessing technical progress. It is assumed that the cost allocations will be continually and systematically updated so that everyone will be working toward common cost goals.

II-5

The benefit of increased optical transmission was clearly demonstrated. Transmission efficiency can be improved by using anti-reflective coatings, matching refractive indices, and improving transparent material degradation. Included in optical degradation is loss of adhesion or delamination (since this results in an additional refractive index mismatch).

Another area in which efficiency can be improved by encapsulation design is thermal efficiency. Proper choice of materials and configuration for optimum thermal transmission/emissivity can result in a cooler operating temperature of the cell, with increased cell efficiency.

D. AUTOMATED ARRAY ASSEMBLY (W. A. Hasbach)

The opening presentation on Cost vs. Module Efficiency Tradeoffs given by Project representatives on Monday morning,, January 17, formed. the environment in which all Task 4 inter- and intratask meetings were later held.

This environment was reinforced in the second general session, on Solar Cell Array Manufacturing Processes and Costs. The first part of this session consisted of presentations (see Section III-H, I, J) by the three Technology Assessment contractors of the Array Assembly Task, Texas Instrtm1ents, RCA, and Motorola, completing and updating. the material they presented at the 4th PIM, particularly in the cost area. The second part dealt with the Uniform Costing Methodology being develope~ ~t JPL, the JPL (Task 4) comparative analysis of the three contractors' cost work, and Project cost goals at the task level.

Task 4 participated in an intertask session with Task 2 on Monday, to discuss the relationships between chemical and crystal imperfections in silicon sheet material from low-cost sheet processes and cell fabrication processes. The meeting was chaired by G. Cumming. It included a presentation by G. Schwuttlee of IBM on the nature of defect ~tates in Czochralski, shaped-ribbon, and web-dendritic crystals, based on studies performed at IBM including electronmicroscopy and other measurements. He also mentioned the problem of maintaining crystallinity in rapidly-grown Cz ingots, and the virtures of the web-dendrixic process.

Mobil Tyco and TI pointed out that current fabrication processes, as used on Cz-grown wafers and well understood, may not produce high-efficiency cells when used on crystals from, for example, web or ribbon processes. IBM gave some experiemntal data showing 10%-efficient CAST cells compared to 15-16% Cz cells using the same fabrication processes. Members of both Tasks expressed interest as well in ~ilicon priority requirements for low-cost sheet and cells. The need for joint efforst by the two Tasks to process quantities of, say, web and ribbon crystal under controlled conditions was emphasized, so that the effect on crystal quality and lifetime of impriorities, defects, growth rate, etc., could be understood.

Task 4 also participated in a second intertask session Monday afternoon, with Tasks 3, 5, Engineering, Operations, and the Applications Projects, in which the status of encapsulant materials was discussed by Task 3 contractors and their costs were analyzed by Task 3.

II-6

On Tuesday afternoon, a session was convened for Tasks 2, 4, and 5 to discuss low-cost silicon sheet and cell fabrication interfaces. W. Hasbach, Chairman, opened the meeting by reviewing highlights from the Task 2 and 4 meeting of the previous day. Next, Task 4 Contractors gave individual presentations which represented final Phase I progress reports for them. B. Carbajal (T.I.) and B. Williams (RCA), discussed cell processes, module fabrication requirements and detailed costs related to both. M. Coleman (Motorola) discussed the steps that led to Motorola's choice of a specific process sequence. Costing methodolosy and process cost stmllilaries formed a major part of the Motorola presentation.

Dr. M. Coleman (Motorola) gave a talk on Electrolysis nickel plating technology. Before discussing electrolysis plating, Dr. Coleman discussed metallization as it relates to Task 2 and Task 4 interfaces. He ·indicated that good metallization is characterized by good Ohmic contact, goo~ conductivity~ good adherence, high reliability, and ease of patterning.

According to Dr. Coleman, electrolysis nickel plating, as a metallization technique, has certain advantages. One advantage is that plating is very forgiving to contoured surfaces. Others are that firing and sintering can be readily applied to the formation of a diffused or dispersed metallized alloy layer with silicon.

Cell metallization generally presents a processing problem that evolves from the interaction of the metallization with cell crystal grain boundaries. Grain boundary dislocations cause non-uniform diffusion and absorption of the metallization. Improved boundary and diffused metallization interaction is possible but can result in cell degradation beneath the metallization. A known method of avoiding the unwanted metallization impact on cell structure.is to incorporate a deeper cell junction beneath the metallization so that the alloyed metallization has good adherence but is not electrically distructive. By· implementing this cell configuration modification, a tradeoff will be made for metallization adherence vs. cell performance and complexity of· fabrication processes.

Based on their 12~month study of semiconductor processing technology, all Task 4 Contractors made optimistic projections that the 1986 Project goals could be met. Their general consensus is that a strong application of existing technology must now take place. The goal of low-cost, high-volume module production will most likely be achieved through innovation, not invention. At present, a noteworthy obstacle to goal achievement is the high cost of module materials.

E. LARGE SCALE PROCUREMENT TASK (Ed Sequeira)

The Large Scale Procurement Task conducted intratask sessions during the 5th Project Integration Meeting. During the session, reviews and assessments of the earlier presentations by Motorola, RCA, TI, and by Dr. Ross and Dr. Doane of JPL were discussed.

In addition, the task participated in an intertask session with Task 2, Large Area Sheet, and Task 3, the Encapsulation Task. Individual sessions to discuss current activities were held with Spectrolab, Solarex and Solar Power Corp.

II-7

Review of Presentations

Based on experience, the Task 5 contractors agree with the JPL presentation that the cost of solar array structures is significant, and emphasis should be placed to find ways to reduce this cost. Discussions on solar cell and array efficiency took place, and here there were some opinions that indicated that cell and array efficiency is a must to meet the objective of the program, while others indicated that capability for the cell manufacturer to utilize all the cells he produces is important. The high- and low-efficiency cells are critical to reduce the dollar/watt cost of the solar array.

The presentation by Dr. Ross, providing the formulas and the factors to be considered for calculating cell and array efficiency, were favorably received, and the manufacturers indicated that this would be a useful tool to implement in their own application.

Presentation on the status of standard solar cells and their use for performance measurements of the ~odules was made by Larry Dumas. Evaluation and calibration of solar cells to be used as standards for module measurement is a continuing effort undertaken by Lewis with JPL support. Jim Arnett provided clarification and rationale for the power performance requirements of the 130 kW procurement.

Task Status and Activities

Production of modules has been completed for 15 kW of modules from Solar Power Corporation, the add-on to the 46 kW procurement. Final Reports on the 46 kW buy from the contractors are being distributed through the LSSA Project Office.

The 130 kW buy is in the module qualification phase.

Sensor Technology modules are undergoing tests both at JPL and at Sensor Tech. The completion of the tests is expected June 25, 1977.

Fabrication of prototype modules is in process at Solar Power Corp. Initial delays were encountered due to substrate availability. Prototype modules have been fabricated at Solarex and are currently in qualification testing.

Key events in the Task for the next quarter are:

1. Complete final design reviews

2. Complete Environmental Test on prototype modules, contractor and JPL in-house.

(a) Thermal Cycling

(b) Humidity

(c) Structural Loading

3. Determine temperature coefficients on modules for 60°C operation.

II-8

F. OPERATIONS TASK (L. N. Dumas)

The Operations Task participated in the following intra-linter-task sessions:

Monday, 17 January

Tasks E, O, LeRC, MIT/LL, Sandia, and DOD

Task 5

Tasks 3, 4, 5, E, 0, LeRC, MIT/LL, Sandia, and DOD

Tuesday, 18 January

Tasks E, O, LeRC, MIT/LL, Sandia, and DOD

The prime contractors' meeting on Monday, 17 January, was devoted to a report by Engineering and Operations personnel on the status and results of 130 kW module designs and tests and to brief comments by DOD and LeRC representatives on their respective organizational structures. The meeting adjourned early to permit participants to join the Task 5 meeting.

A status update on performance measurement standards was given at the Task 5 intratask meeting. It was noted that intermediate standard cells (Y-cells) have been delivered to 130 kW manufacturers, and their measurement procedures have been reviewed. It was also observed that the program-wide plan for establishing and maintaining measurement procedures and standards was proceeding as outlined at the last Integration meeting.

1. Assessment of Task Progress versus Plan

Environmental testing in support of Project evaluations of 46 kW and 139 kW block modules is continuing per plan. Exploratory testing of 46 kW modules recently completed includes humidity/freezing and salt fog exposure. Qualification tests of 130 kW prototype modules is under way, as well as experimental determination of temperature coefficients.

Three field test sites are now operational, providing a data base for characterizing module performance under service conditions as well as lifetime statistics. A contract has been awarded for installation of an automated data acquisition system at the Pasadena site, permitting in site evaluation of individual modules.

The module problem/failure reporting and analysis system is now fully operational at JPL, with the rate of P/FR closures approximately equal to the rate of generation. Manufacturers are routinely provided with informa.tion resulting from this activity, and have in some cases participated in the analysis as well as corrective action.

The cooperative JPL/LeRC module performance measurement standards activity has achieved a significant milestone with the delivery of intermediate standard

II-9

cells to 130 kW manufacturers. Comparative assessments of these standards versus those used previously are being carried out at this time. Spectral characterization of the prototype modules delivered to JPL is being performed to insure that the intermediate standards are representative of production modules prior to adoption of official standard cells.

2. Assessment of Interfaces with Other Tasks

Working. relationships with other Project tasks are generally smooth, but there is a continuing need to improve the feedback of information from the Operations Task to the technology development tasks. More timely and informative written reports are needed, as well as closer coordination of problem/failure analysis with technical specialists from these areas. Attention will be given to these needs in the coming months.

Detailed interface arrangements with Test and Applications Projects at Lincoln Laboratory and DOD are in a formative stage, pending completion of planning activities being carried out by these agencies in concert with ERDA. Module shipping schedules and logistics for the 130 kW block must be worked out within the next month or so. Module problem/failure reporting and analysis procedures have been agreed to in general terms, and a review copy of the written plan will be forwarded to LeRC, DOD, and MIT/LL in February to provide a basis for a mo-re detailed agreement.

G. ENGINEERING TASK (Ron Ross)

During the Monday morning general session, Dr. Ross presented the results of current JPL cost versus efficiency trade-offs at the module level. Module efficiency was defined in terms of its component efficiencies. The relationship between project cell efficiency goals and module efficiency requirements was clarified. Methodologies were proposed for.assessing the cost effectiveness of implementing efficiency related improvements in module design or performance. Preliminary examples were given illustrating use of these methods to evaluate system cost benefits accuring from specific efficiency improvements. A more detailed description of the module effieiency optimization presentation appears in Section III.

For the intertask meeting of Task 5, Engineering and Operations on Tuesday afternoon, the Engineering Task presented a review of the 130 kW performance requirements which had been revised as of December 20, 1976. Three important changes to specification 5-342-1 were described in detail. First, the deletion of a minimum voltage requirement at module maximum power point allows the manufacturers to optimize the module performance with respect to the 15.8 Vdc at which modules are rated. Secondly, uniform procedures were introduced for determining the temperature coefficients for correction of performance measurements made at ambient conditions to the 60°C cell temperature at which modules are rated. The third change discussed was the relaxation of the power acceptance requirement. The minimum acceptable output of an individual module is now required to be 86% of the average power. The average power is now equivalent to the 60 watt per sub-array minimum requirement of the previous specification revision.

II-10

The Engineering Task is proceeding with extension of the module efficiency trade-offs described earlier. In addition, in-house programs have been initiated to develop suitable evaluation procedures and engineering requirements in the areas of hail damage, cyclical wind loading and dust accumulation.

II-11

III. PRESENTATION SUMMARIES

A record of each of the detailed presentations given at the Fifth PIM is provided on the following pages by the series of Vugraphs actually used during the proceedings. The illustrations are in the sequence in which they were presented and thus provide both an outline of topics covered and a supplement to the other information obtained in the form of handouts and notes.

A. PROJECT ANALYSIS AND INTEGRATION

Concepts for cost versus efficiency trade-offs were presented by H. L. Macomber. Objectives were to:

1. Initiate a continuing dialogue on cost vs efficiency tradeoffs with an increased systems awareness.

2. Stimulate and enhance interface activities between

{a) Tests and demonstrations

(b) Systems

(c) Tasks

3. Introduce methodology for examining tradeoffs

Certain qualifying conditions exist. It was specified .that there would be:

1. No attempt to select a particular efficiency

2. No attempt to alter the present efficiency goal

An overview of cost versus efficiency showed an area of continuing dialogue and provided spectra of applications, efficiencies, designs, and processes.

Elements to be considered are:

1. System concepts

2. Efficiency definitions

3. Tradeoff potentials

4. Tradeoff methods

A model should be established for tradeoff assessment. On-going studies provide inputs for future tradeoffs.

III-1

B. ECONOMICS AND INDUSTRIALIZATION TASK

ABSTRACT

A presentation was given by J. W. Doane, entitled "Minimum System LifeCycle Cost: A Framework for Design Tradeoff Assessment", that covered details of a standardized methodology for calculating a system life-cycle cost (LCC). Concepts, definitions, equations, and graphs were used to illustrate both capital cost and system cost versus module efficiency. Applications of system concepts for determining system benefits as a function of module efficiency were explained.

It was stated that at current market prices, the dominant element of the photovoltaic power system life-cycle cost is the cost of modules.

The specific method used for calculating system life-cycle cost is available as a standardized ERDA/EPRI methodology.

The discussion was directed, as scheduled, toward the problem of cost versus efficiency tradeoffs within the framework of a power system.

III-2

LOW-COST SILICON SOLAR ARRAY PROJECT

MINIMUM SYSTEM LIFE-CYCLE COST: A FRAMEWORK FOR DESIGN TRADEOFF ASSESSMENT

• SUCCESS OF NATIONAL PV PROGRAM DEFINED AS SIGNIFICANT MARKET PENETRATION FOR PV POWER SYSTEMS

• MARKET PENETRATION IS A FUNCTION OF SYSTEM LIFE-CYCLE COST (LCCI

•THUS ENGINEERING DESIGN TRADEOFFS MUST ULTIMATELY BE EVALUATED IN TH IS CONTEXT

• DUE TO INTERACTIONS AMONG SUBSYSTEMS, IN GENERAL:

L (MIN. SUBSYSTEM COSTSI Z ) MINIMUM SYSTEM LCC 7

/

JWD-1

• A STANDARDIZED ERDAIEPRI METHODOLOGY (PREPARED BY JPU EXISTS. WITH A SPECIFIC METHOD FOR CALCULATING SYSTEM LCC:

LCC • f (TAXES, INTEREST, INSTALLED CAPITAL COST, OPERATING LIFETIME, RECURRENT COSTS, ETC. I

• AT CURRENT MODULE PRICES (:$10/Wpk), lliE DOMINANT ELEMENT OF POWER SYSTEM LCC IS THE COST OF MODULES

• THE RELATIVE IMPORTANCE IN LCC OF COSTS WHICH DEPEND ON THE NUMBER OF MODULES (NOT n-lE PRICE OF MODULES) WI LL INCREASE SIGNIFICANTLY AS MODULE.PRICES DECLINE

•FORA GIVEN SYS1EM POWER LEVEL, THE NUMBER OF MODULES REQUIRED IS AN INVERSE FUNCTION OF MODULE EFFICIENCY

JWD-2

III-3



WHERE: r REFLECTS INCOME TAXES

CRFk. N REFLECTS CAPITAL AMORTIZATION

N REFLECTS SYSTEM OPERATING LIFETIME

'31

+ '1 2 REFLECTS INSURANCE, PROPERTY TAXES

Clpv REFLECTS INSTALLED CAPITAL COST OF SYSTEM I INCLUDING INTEREST DUR I NG CONSTRUCT! ONI

OP + MNT + FL REFLECTS PRESENT VALUES OF RECURRENT pv pv pv COST STREAMS: OPERATIOOS, MAINTENANCE

(INCLUDING PIECE-PART REPLACEMENT, IF ANY), AND FUEL (IF ANY)

JWD-3

FOR PURPOSES OF THIS PRESENTATION:

LCC • COST OF MODULES + COST OF EVERYTHING ELSE

+

ALL MEASURED IN $/KW

CM F. 0. B. PRICE OF MODULES, AND WILL BE ADDRESSED BY RON ROSS

CXM SYSTEM LCC MINUS CM

CMD ·-- + 11M. 1A --MODULE-

DEPENDENT

PE + OM + 0

~

MODULEINDEPENDENT

!DEFINITIONS OF CMD' T7 M' IA. PE, OM FOLLOW)

JWD-4

III-4

10. m



CXM

CMD

11M

IA

PE

OM

0

C CXM • 11 ~O I + PE + OM + 0

M A

SYSTEM LCC MINUS CM ($/KWI

INSTALLED CAPITAL COST Of MODULE-DEPENDENT SYSTEM :~:ri: co~~PCNENTS (EXCL:..:DING CM}

MODULE EFFICIENCY . ( MODULE POWER ) MODULE AREA , !1000 W/M2J

AVERAGE INSOLATION IKWIM21

INSTALLED CAPITAL COST OF MODULE-INDEPENDENT COMPONENTS 1$/KWI

OVERHEAD COSTS IDES I GN. PROJECT MANAGEMENT. ETC. I 1$/KWI

ASSUMED PRESENT VALUE OF RECURRENT COSTS FOR THIS EXAMPL[

JV'(D-5.

CMD 11M. IA IS THE COST COMPONENT IMPACTED BY .d(f1MI

CMD SPIMS/11 LI + ISC + TM

17M · IA= 17M · IA, MS

SP COST OF SITE ACQUISITION AND PREPARATION

MS MODULE SIZE

17 "LAND PACK I NG FACTOR" /. Mz MODULE AREA ) L \ M2 LAND AREA

ISC INSTALLED COST OF SUPPORT STRUCTURES AND CABLING

TM TRANSPORTATION COST OF MODULES

Tl M' I A AS BEFORE

JWD-6

III-5

($/M21

IM2IMODULEI

1$/MODULEI

($/MODULE!

LOW-COST SILICON SOLAR ARRAY PROJECT CAPITAL COST OF SYSTEM

500

(EXCLUDING MODULES) vs MODULE EFFICIENCY

RED LINES REPRESENT "SYSTEM B11

' 200 ', SllE ACQUISITIOO, PREP. AND TRANSPORTATltJ,J ,....._....._ OF MODULES• -1 ($2.5/kWI

..................... __ 7'1M 100 MOfil!.L!j@_E.!2'J![NL Cj!'~Q!.TS-----=-.=:-::::

AND OVERHEAD • $98.8/kW

----------------OS'----6~--"7---"8-----'-9---'-I0--1.._I -..-Jl2

MODULE EFFICIENCY 1'11

JWD-7

LOW-COST SILICON SOLAR ARRAY PROJECT HYPOTHETICAL EXAMPLE OF SYSTEM COST COMPONENTS

vs MODULE EFFICIENCY

C LCC • CM + '1M ~rA + IPE + DM + OI

.'. LCC - MINIMIZING '1M MUST SATISFY:

JWD-8

III-6

C. ENGINEERING TASK

ABSTRACT

A presentation on module efficiency optimization was given by R. Ross. The presentation provided a graph showing optimum module efficiency relationships for the years 1975, 1980, and 1985. Definitions used in module relationships were illustrated by equations and charts. Cost/benefit relationships were pres.ented, together with the criteria used, and typical tradeoffs for $10/W modules were tabulated.

In general, the presentation covered a proposed methodology for assessing the cost effectiveness of changes in module efficiency. Specifically, the presentation covered:

1. A definition of module efficiency reflecting all important losses.

2. A conceptual framework allowing systematic tradeoff of module efficiency versus system cost.

As reported in the Engineering Summary, the Engineering Task is continuing activities in the areas of analysis and testing of solar array modules in conjunction with developing the array requirements for the 150 kW procurement, and coordinating the 130 kW purchase design reviews and interface definition in support of the Large Scale Procurement Task. Significant progress has been made in the study of array mechanical interface considerations, evaluation of module thermal performance, analysis of module structural design, and a~sessment of environmental requirements.

III-7


OPTIMUM MODULE EFFICIENCY RELATIONSHIPS

LOWEST MODUl.E I 1'---OPTIMUM MODULE PR ICE ___ , / FOR SYSTEM f2

MODUlE EFFICIENCY ( r, M)

OPTIMUM '1 M DEFINED BY:

- d($/kW) BALANCE OF SYSTEM Ai '7 M

RR-1


DEFINITIONS

MODULE PR I CE • PURCHASE PR I CE FOB

MODULE POWER • PEAK POWER AT MODULE TERMINALS

• 100 mW/cm2, AMI INSULATION

• NOM. OPER. CELL T£MP (NOCTI

•BEGINNING OF LIFE (BOU

MODULE POWER MODULE EFFICIENCY • MODULE AREA x 1000 w/m2

MODULE AREA • TOTAL PROJECTED AREA NORMAL TO CELL PLANE

RR-2

III-8


MODULE EFFICIENCY LOW-COST SILICON SOLAR ARRAY PROJECT

BORDER AND BUSS EFFICIENCY MODULEEFFICIENCY • MODULE POWER

MODULE AREA x 1003 watttm2

"EC "P

"M • ["c"M1s ,,.,. "NocTl x ["BR "es 171c 17N]

where "EC • ENCAPSULATED CELL EFFICIENCY

11c • CELL EFFICIENCY AT 28°C, 100 mWlcm2

l'JMIS • CELL MISMATCH EFFICIENCY

"T • OPTICAL TRANSMISSION EFFICIENCY

"NOCT • CELL OPERATING TEMP. EFFICIENCY

"P • PACKl~G EFFICIENCY

"eR • BORDER AREA EFFICIENCY

"es • BUSS AREA EFFICIENCY

· BORDER AREA 11BR • l - MODULE AREA

IJIC • INTERCONNECT AREA EFFICIENCY • BUSS AREA "es l - MOD. AREA - BORDER AREA

"N • CELL NESTING EFFICIENCY

RR-3 RR-4


CELL INTERCONNECT AND NESTING EFFICIENCY.

SCI.AR CELL

CB..l. INTERCONNECT SPACE

CEU NE.STING SPACE

CELL INTERCONNECT EFFICIENCY

RO NO C L .. tr O t (CELLS/MODULE) U EL, "1c l - MOD. AREA - BORDER AREA - BUSS. AREA

. .. 3 D t (CELLS/MODULE) HEXACON CELL, 111c l - MOD. AREA - BORDER AREA - BUSS. AREA

CELL NESTING EFFICIENCY

,, • TOTAL CELL AREA N· MOD. AREA - BORDER AREA - BUSS. AREA - IC.AREA

RR-5

III-9


CELL OPERATING TEMPERATURE EFFICIENCY

46 kW MODULE MANUFACTURER

A

B

C

D

E

n°c CELL TEMPERATURE

MODUt.E POWER

(P) MOOUUA

-20 0 20 40 60

AMBIENT TEMPERATURE, 0c ,------...... ...!f.. CNOCT - 28) Pat NOCT AT

"NOCT • p at2s°C • l- _P_ll...,..2SoC,,.,....--

. where: NOCT • NOMINAL OPERATING au. TEMPERATURE

• CELL TEMPERATURE FOR: . 80 mW/cm INSCLATION zoOc AIR TEMPERATURE 1 M/SEC WIND VELOCITY OPEN BACK SI DE

RR-6


EFFICIENCY EXAMPLES*

"c "MIS "T "NOCT "Ee "BR "ss '11c

.119 • 98 .105 .90 • 77 . 93

.108 .89 .102 .84 . 95 .94

.117 • 91 .106 . 91 • 91 .96

.113 .94 .107 .84 .87 .93

.095 .85 .070 . 74 • 96 . 73

"N

.80

.80

. 78

.80

. 78

*REPRESENTATIVE OF 1975 TECHNOLOGY DESIGNED FOR SYSTEMS WHICH PLACE LllTLE EMPHASIS ON MODULE EFFICIENCY

RR-7

III-10

"P "M

. 52 .061

.60 .058

.62 .066

.55 .058

• 41 .033


ALTERNATE METHODOLOGIES FOR COMPARING MODULE COST /POWER/EFFICIENCY

CONSTANT MWlW WA.

• SYSTEM POWER • CONSTANT

• MODULE AREA • CONSTANT

• NUMBER MODULES « 1 / MODULE 'I

OR

CONSTANT MQWlll ~

• SYSTEM POWER • CONSTANT .

• MODULE POWER • CONST ANT

• NUMBER OF MODULES • CONSTANT

• AREA OF MODULES ct 1 / MODULE r,

RR-8


MODULE OPTIMIZATION LOW-COST SILICON SOLAR ARRAY PROJECT

TOTAL MODULE COST FORMULA

OPTIMUM "M DEFINED BY:

ACM • - ACMD/ "M OR ACM+ dCMD/ "M • 0

Ar,M dr,M dr,M

BENEFICIAL DESIGN TRADE DEFINED BY:

B(CM + CMD I "Ml B(DESIGN PARAMETER)

"Cr • - $ 0

ax WHERE:

CM •· MODULE PRICE ($/kWMI

CMD • SYSTEM COST DIRECTLY PROPORTIONAL TO TOTAL MODULE AREA OR NUMBER OF MODULES, LESS MODULE COST ($/M2 OF MOD. I

c1 • TOTAL MODULE DEPENDENT SYSTEM COST ($/kW)

RR-9

Cy • MODULE COST + OTHER SYSTEM COST PER MODULE

WHERE:

• TOTAL MODULE RELATED COST ($/kWml

• CELL RELATED COST PER MODULE ($IM2 OF CELU

CF • FIXED COST PER MODULE($)

CA • AREA RELATED COST PER MODULE ($/M2 OF MOD)

CMD • OTHER SYSTEM RELATED COST PER MODULE ($IM2 OF MOD)

AM • MODULE AREA (M2)

RR-10

III-11


COST /BENEFIT RELATIONSHIPS

FACTOR

CELL EFFICIENCY

CELL Ml SMATCH

OPTICAL TRANSMISSION

OPERATING TEMPERATURE

CELL SHAPE

BORDER/BUSS AREA


HEXAGONAL CELL EXAMPLE

dC < ~ J_ _f_ II ( C - IIN llp AM + CA+ CMD)

BASELINE PARAMETER CIRCULAR HEXAGONAL UNIT

cc $900 $1084 $/M2

CF lO 10 $/MOD

CA 30 30 $/M2

CMD 35. 5 35.5 $/M2

IIN 0.87 0.95

llp 0. 700 0. 764

dCC • $1()84. • 900 • 0. 205 CC • $l84/M2

dllN/ IIN (CF ) .092 2 _ll_p_ AM + CA + CMD • • 700 175. 51 s:::: $10/M

CONCLUSION:

• WILL BE COST EFFECTIVE WHEN CC DROPS BELOW S50IM2

RR-12

BENEFIT CRITERIA

dCc s .:t'lC ( ) ~ cT "Ec

dCC ~ £1'1MIS ( 11 ) '1MIS Cr EC

dCA ~ .:1:; (tr "M)

dCA ~ 41'1NOCT ( ) 71NOCT Cr "M

.:ice 4qN I ( CF ) < ---;rn- - A+ CA+ CMD "P M

dCF 5 .:i"BR ( ) ~ CF + CAAM + CMDAM

RR-11


TYPICAL TRADEOFFS FOR $10/WATT MODULES

TYPICAL POSSIBLE SYSTEM BENEFIT 1976 IMPROVED FOR INDICATED

EFFICIENCY VALUE VALUE IMPROVEMENT•

CELL 128°C, 100 mWlcm2) 0.135 0.150 $ll7IM2 OF CELL

CELL Ml SMATCH 0.92 0.95 $34IM2 OF CELL

OPTICAL TRANSMISSION 0.92 0. 95 $2llM2 OF MOD.

NOM. OPER. CELL TEMP 0.92 o. 95 $21IM2 OF MOD.

BORDER/BUSS/IC SPACE 0. 75 0.90 $'lOIM2 OF MOD.

CELL NESTING (CIRCULAR) 0.80

CIRCULAR + 112 CELLS 0.90 $16IM2 OF CELL

HEXAGONAL o. 95 $24IM2 OF CELL

HEXAGONAL+ 112 CELLS 0.98 $28IM2 OF CELL

SQUARE CELLS 1. 00 $3IIM2 OF CELL

RR-13

III-12

D. SILICON MATERIAL PRESENTATION

ABSTRACT

A presentation was made in two parts to cover the influence of cost vs efficiency'tradeoffs on basic task activities.

The first part of the presentation, by R. Lutwack, described efficiency-cost values as they pertained to:

1. Semiconductor grade Si process developments

2. Effects of impurities and processing on Si material/cell properties

3. Solar cell grade Si process developments

The second part of the presentation, by D. B. Bickler, described cost versus efficiency effects on encapsulation and automated array assembly tasks. Subjects covered were:

1. Processes under consideration for use with low cost materials

2. Optical efficiency

3. Cell efficiency improvement

III-13

LOW-COST SILICON SOLAR ARRAY PROJECT EFFECTS OF EFFICIENCY-COST VALUES

SILICON MATERIAL TASK

• PART I - SEMICONDUCTOR GRADE Si PROCESS DEVELOPMENTS

PART 111 - SOLAR CELL GRADE Si PROCESS DEVELOPMENTS

• PURIFICATION PROCESSES

• OVERALL PROCESS - MATERIAL/ENERGY BALANCES ANO COSTS

• MATERIALS OF CONSTRUCTION

• SELECTION OF PROCESSES

RL-1

• FEEDBACK FROM TASK I

• PART II - EFFECTS OF IMPURITIES AND PROCESS ING ON Si MATERIAL/CELL PROPERTIES

• IMPURITIES FOR STUDY

•PROCESSING - STEPS FOR STUDY

• SELECTION OF IMPURITIES

RL-2

• INTERNAL TO TASK I - PART II TO PARTS I AND 111

•FROM PART II TO TASKS 11 AND IV

•ANALYSES OF PROPERTIES FOR ECONOMICS OF PRODUCT Si

RL-3

III-14

• EVALUATIONS OF PROCESSES

LOW-COST SILICON SOLAR ARRAY PROJECT EFFECTS OF EFFICIENCY -COST VALUES

LARGE AREA Si SHEET TASK

• INFORMATION FROM TASK I

•REQUIREMENTS FOR SPEC IF IC PROCESSES

• FEEDBACK FROM TASK 11

• REQUIREMENTS TO TASK I

• ANALYSES OF PROCESSES FOR ECONOMICS OF SHEET •SELECTION OF CANDIDATE PROCESSES

RL-4


EFFECTS OF EFFICIENCY-COST VALUES

• EFFECTS ON TASKS I AND 11

• PROGRAM PLANS

• SUBTASK EMPHASIS

• SPECIFIC PROCESSES TO BE INVESTIGATED

RL-5

• SELECTION OF PROCESSES FOR CONTINUED INVESTIGATIONS

RL-6

III-15

COST

1

LOW-COST SOLAR ARRAY PROJECT

MATERIALS x PROCESSING

YIELD x EFFICIE~JCY

DBB-1

YIELD x EFFICIENCY

DBB-2

III-16

LOW-COST SOLAR ARRAY PROJECT

REDUCED EFFICIENCY EQUIVALENT YIELD)

~~ ' PROCESSING

RED~ MATERIAL

DBB-3

AUTOMATED ARRAY 4$SEMBLY TASK

SAME COST

PROCESSES UNDER CONSIDERATION FOR USE WITH LOW COST MATERIALS:

I EPITAXY

I GETTERING

, LOW TEMPERATURE METALLIZATION

LOW TEMPERATURE JUNCTION FORMATION

, SPECIAL SURFACE A/R TREATMENT

DBB-4

III-17

.06

.OS

.04

$IW .03

.02

.01

ENCAPSULATION MATERIAL COST VS. EFFICIENCY

OPTICAL EFFICIENCY t LOW TRAN5'11SSIOH <-90%) - LOW COST t HIGH TRANSMISSION (95 - 991) - HIGH COST 1 TRAN$M1SSION DEGRADATION IMPROVEMENT - HIGH COST t HATCH OF INDICES OF REFRACTION

1 ANTIREFLECTIVE COATINGS - HIGH COST t MATERIALS DEVELOPMENT - HIGH COST

CELL EFFICIENCY IMPROVEMENT

t THERMAL DISSIPATION - LOW COST t MATERIALS SELECTION • DESIGN t THERMAL COATINGS

DBB-5

0. 7

.~3 -------------- a~---------------

I I I

0.6

0.5 -----------

0.4

$/W ~31, _____ _

0.3

0.2

0.1

0 ----'----ill--"-__ ......_ _ ___..-+---a...__..__ ___________ _

0 2 3 .,n2 ' 5 I

6 0 0.1 0.2 0.3 $/n2

0.12S IN. THICK SODA LIME GLASS ($0.171FT2)

DBB-6

0.4 0.5

0.125 IN. THICK ACRYLIC ($0. 42/FT2 >

III-18

0.125 IN. THICK ACRYLIC ($0, 42/FT2)

DBB-7

0.100 IN. THICK SILICONE ($5/FT2l

E. BATTELLE COLUMBUS LABORATORIES

ABSTRACT

A report on progress was presented by Battelle Columbus Laboratories, by P. Browning, for the Fifth PIM. A paper was made available at the meeting entitled "Materials for Encapsulation Systems for Terrestrial Photovoltaic Arrays," by D. C. Carmichael, G. B. Gaines, F. A. Sliemers, and C. W. Kistler.

·The paper is published in the following pages of this report. Note that a summary is presented in the first paragraph. The paper gives the present status of encapsulant materials.

Four studies under the cognizance of Battelle are:

Study 1. Review of World Experience and Properties of Materials for Encapsulation of Terrestrial Photovoltaic Arrays

Study 2. Definition of Encapsulant Service Environments and Test Conditions

Study 3. Evaluation of Test Methods and Properties of Candidate Encapsulation Materials

. Study 4. Development of Accelerated and Abbreviated Testing Methods for Predicting Performance of Encapsulation Materials Over 20-Year Lifetime

III-19

MATERIALS FOR ENCAPSULATION SYSTEMS FOR TERRESTRIAL PHOTOVOLTAIC ARRA VS

D. C'. Carmichael. G. B. Gaines. F. A. Sliemers. and C. W. Kistler

BATTELL.E Columbus Laboratori•

SUMMARY

As part of the l.ow-Cost Silicon Solar Array (LSSA) Project being managed by the Jet Propulsion Laboratory for ERDA's Division of Solar Energy. a review has been conducted of published and unpublished world experience in the area of encapsulation (protection) systems and materials for photovoltaic arrays and related applications. One goal of the I.SSA project is the achievement of lowcost encapsulation systems to protect the arrays with high reliability for a lifetime greater than 20 years in terrestrial em·ironments. The final process for producing the silicon and the engineering design of the array are yet to be evolved; this review and analysis of the performance of protection-system materials has been conducted to make a contribution to the design evolvement and the encapsulation materials/process selection. Recommendations are made of glass and polymeric candidate materials/processes for potential encapsulation systems for low-cost, long-life terrestrial photovoltaic arrays. The candidates were selected based on the following principal criteria: materials properties. including weatherability; availability; ease of automation: and cost. The recommended materials include various borosilicate and soda-lime glasses and numerous polymerics suitable for specific encapsulation-system functions.

INTRODUCTION

This study was conducted in support of the Encapsulation Task of the Low-Cost Silicon Solar Array ( l.SSA) Project ( l ). which is managed by JPL for ERDA-Division of Solar Energy and is part of ERDA's Photovoltaic Conversion Program. The 1985 goals of the LSSA Project are to develop silicon terrestrial photovoltaic arrays with a

• Price less than $500/kW (peak) • Production capacity of over 500.000 kW/yr • Lifetime greater than 20 years with high reliability • Conversion efficiency greater than 10 percent.

The criteria for consideration or the encapsulation systems for lowcost arrays, described later, were based on these goals.

The objectives of this study (2) were the following:

• To review world experience and properties of encapsulationsystem materials for terrestrial photovoltaic arrays and related applications

• To identify available polymeric and glass materials and processes having potential for application in encapsulation (protection) systems for low-cost arrays having a 20-year service life in terrestrial environments.

A specific goal of the study was to recommend candidate encapsulation materials and. processes for investigation in subseqµent studies to develop and evaluate encapsulation systems for low-cost. long-life arrays.

APPROACH

Information input to the world-experience assessment was obtained from the published and unpublished literature. visits to installations at which substantial field testing of module and/or encapsulant materials has been carried out. and from discussions with numerous researchers in the photovoltaic community. Analysis of this

information was carried out to identify problem areas with encapsulation systems, alo.ng with materials which show promise in meeting re-4uired performance criteria. Selection of candidate materials and processes for future low-cost encapsulation systems was based on the various functions to be served within the system and the requirements of each function. A generali1ed design of a hypothetical encapsulation system (figure I) was used in identification of the functions and material requirements.

Acquisition of Information

Because of the large amount of p<ltentially useful information available in the photovoltaic-cell area and from related applications, extensive use was made of available data bases. The following data bases were interrogated:

. • CHEMCON e ~ASA • CIRC • !"Ii ns • DOC • PI.ASTEC • Engineering lndeit • Reliahilitv Analvsis Center e ERDA RECON (Files I. 9. 10) • SSIF . . • INSPE(' • Solar F.ncrgy Index (ASU)

In addition. relevant bibliographic. journal. and conferenceproceeding sources were searched which covered world-wide experience. In excess of 1300 documents were selected and reviewed by researchers representing the pertinent technical areas. Major emphasis was placed on polymeric materials and glasses and on nonconcentrating systems. Metal components. such as substrates, were not included in the scope of the investigation. although effects regarding the cell mctalli,ation. interconnects, and lead wires were considered.

The following organi1ations furnished significant unpublished data for the study:

• Ari1ona State University • Desert Sunshine Exposure Tests. Inc. • I.a Radiotechnique-Complec (RTC). France • Mitre Corporation • NASA Jet Propulsion l.ahoratory • NASA Lewis Research Center • Sandia Laboratories • Sensor Technology. Inc. • Simulation Physics. Inc. • Solar Power. Inc. • Spectrolab. l nc. • U.S. Coast Guard (Groton)

Criteria for Candidate Material Selection

Based on the analysis of the world experience and a review of the properties of polymeric materials and glasses and their fabrication processes. candidate materials were selected that would be expected to serve the functions of various components in potential encapsulation systems. Four general criteria were placed on the selection.

I. Known and Achievable Properties. Since a final module design which will meet l.SSA goals is yet to evolve. the properties required of a material serving a specific encapsulation function cannot yet be quantified. In order to identify materials for the various functional components in potential encapsulation systems, the generalized

III-20

K A

: . ·.

. - ..

-- - · - -- ---- I

A. An1ireOec11ve or abras11111/ 1111p;i,1- G. Adhe"vc for lw11J111g cell to rcsis1an1 coa ting sub,tra 1c

ll. Top cover II. Substrate

C. Adhesive sealant for lead w11e I. Pn11a11 1

D. Lead wire J. lotCf\."llll lle\." l )

E. Bollom cover K. Me1alli1.a11011 . , ullc<tur grid

F. Silicon ,ells L. Me1alhLa 11n11 . bu110111

FIGURE I. SCHEMATIC OF HYPOTHETICAL ARRAY MODULE IDENTIFYING ENCAPSU LATION-SYSTEM COMPONENTS

III-21

encapsulation system shown in Figure I was hypothesized incorporatina essentially all possible functions. Among the various functional components identified are the antirenective (AR) coating. top and bottom cover. cell substrate. pottant. and adhesives (sealants). Optical transmittance. index of refraction. coefficient of thermal expansion. permeability to atmospheric vapors. resistance to UV radiation. and mechanical strength and moduli are obviously some of the important properties~ the criticality of these properties depends on the one or more functions served by a given material.

. 2. A,allablllty. Materials selected should be available either presently er have near-term availability hased on a projected market. Enough material should be available to meet the 1985 LSSA goals of 500 MW/year.

3. Compatlblllty with Automated Fabrication. Since automated fabrication of modules will he re4uired to meet the LSSA goals. the selection of encapsulation materials and processes should he compatible wi1h low-cos& automated produc&ion. Achievement of required materials properties and minimum energy consumption arc requirements on the automated manufacturing method: in addition to the cost and production-rate re4uirements.

4. Costs. Based on the I .SSA price goal for completed modules. as a maximum guideline. the total module assemhly ·and encapsulation system cost certainly cannot exceed SIOO/kW (or about S20/m:. based on 10 percent efficiency and other assumptions). The goal. of course. is to minimi1e the costs of the encapsulation materials/ process. commensurate with the performance re4uirement11.

SERVICE F.XPERIENCE WITH PHOTOVOI.T AIC' ARRA VS

Over SO results or experiences with terrestrial photovoltaic modules (arrays) found from the literature and unpublished sources were tabulated in this study and have been reported (2). Although experiences in space environments were included in the investigation. only the terrestrial experience is summari1ed in this paper owing to space limitations. Details nf these results are in Reference (2)

Experience with Glass Encapsulation Materials

Considering the proprielilry nature of a new technology. and the impact ha1.ards · associated with arrays manufactured to date for remote environments (railroad crossings. off-shore navigational aids. radio transmitters. etc.). it is not surprising &hat very little information has been published on the use of glass as an encapsulation material. The published and unpuhlished information collected (2) on field experience with glass encapsulated arrays is synopsi,ed in Table I.

A French company ( RTC') has used glass as a cover for silicon cells since the early 1960"s (J 5) and the experience (up to 15 years) is recorded in Tahle I. The original design consisted of a glass sheet clamped to an anodi1ed aluminum hox; a ruhhcr gasket was used hetween the glass and the hox to form a seal. A 1965 modification used an epoxy-glass (printed circuit) hack-panel. a transparent silicone resin pottant. a glass cover. and an epo11.y frame to protect the edges of the assembly. Problems encountered with windows cracking from thermal stresses imposed hy the epoxy frame were eliminated in a 1969 design in which a rubber hell replaced the epoxy. Not listed in Table I is a 1975 dual-glass-laminate design (5) on which field data are not yet availahle.

The approach of some U.S.S.R. researchers was to use tubular envelopes to encapsulate various types of photovoltaic solar cells

(6 -9). Fluorescent-lamp-glass tubes were used up to 5.4-cm diameter. above which acrylic tubes were used because glass tubing of the proper sile is not available. Information on the sealing lechniques used by these researchers was not found: il was indicaled that dry gases with high thermal conductivities were used to purge the envelopes before sealing.

In the United States. JPI .. the Coast Guard. and Mitre Corporation have all found more reliahle performance (Table I) with glasscovered modules of the 1ype made hy C'entralah (OCU) than with the other module designs which used polymers for the cover material ( 10 14). The Coast Guard experience appears to have been the most extensive in terms of the numher of units evaluated and length of exposure time. They have ohserved i1ome quality-control problems and leakage at the lead seali1 with the glass-covered modules. but no suhstantive degradation in cell output after 2 years of service. The module construction used. however. ii. inherently high in cost. Spectrolab has recently in&roduccd a design using annealed window glass as a top (additional) co\·cr over a con\·entional silicon pottant. and a design in which the cells arc laminated hctwccn two sheets of glass using a polymer laminating layer. such as PVR which is used in windshield manufacture.

CdS/C'u!S thin-film cells. also heing developed for terrestrial applications. require cffectin~ protel1inn to insure cell stability. Glass has heen the primary enc.apsulant material considered for these systems. Solar F.ner~y Systems (Sf:S) has announced plans to produce modules with a tempered glass CO\'Cr early in 1977; a ttlass/metal seal is used to .ioin the cmer to the suhstrate ( I.S). The University of Delaware ffohlc I) has used CdS/Cu:S cells in a comhined thermal-photmoltaic 1.'Xfh:riment.al collector system ( 16). Because the edt?e seal of thdr 11.it-t?lass. t!ilh ani,cd-steel collector wai permeahle to moisture in an eiirly life lest of experimental cells. a dr~· em·ironmcnt was maintained hy ii ,·onlinuous dry nitrogen pur1e in suhsc4uen1 tests ( 17). l"h"· 1-'rench i1re also Je,dopint? ('dS/Cu:S ccU!I for terrestri;1I applications. ('on, cntion.11 cells co\cred \\'ith glass panels ha\e hecn exposed for a yi:;1r in the P~renees: n:1:ent efforb ha\e hcen directed to di:,elopint! h;1drnall cells deposited directly on SnO·-coated tlat-l!la,s ,uh,trnte/c,ners ( IX). l'he Baldwin ('ompan~ is also Je\clnping a hack\\.111 \.'di ha,eJ on this concert !>ince it niters potential for mass prodm:tion al lo\\ \.0 0!>l ( l'J.:!O).

Thu!> . .although the 4u,1nti1y ol infornrntinn puhlished on the use of ~lass il'i a h:rrcslrial solar encilJ1M1lirnt is not lar~c. the c.,pericncc reported ;ind the unpuhlished dat.i "·ollccted h,m: indicated t?enerall~ satisfactory perform,incc. Pruhli:ms encountered hil\e heen related to lcad-\\ire seal rcliahility and mcchankal failure of the cm·er. When moisture renetration ha!> heen rre, ented. module!I ha, e apparent I~ functioned s;uisl'actoril~ for mer 4 ~e.1rs: under rather detailed testing. no arpreciahle cell degrnd;1t inn has hccn encountered a her 2 rears of exposure. The the of glass to prm ide ii dual CO\er/structure function is e, idcnt in some dc,igns. ;inJ i, .1n ;1pproach \\'hich should reduce costs of glass-,:nl·.1r,ulated modules. \,fonufocturing technology \\ hich hm, he"·n d"'' dop1..·J tor producing im,ul,lling t?lass and lamin.ued windshields ,hnuld he immedi;1tcly useful in th1..· produclion of hi:rml.'lkall~ ,i:alc:d !!la"-enearsul.iti:d module,.

Experience with Polymeric Encapsul1tlon Materlak

Table 2 lists rerrcscnrntiw solar-cell encapsulation experience with polymeric materials in terrestrial en\'ironments. A number of polymers. particularly certi1in acrylics, silicones. and fluorocarbons have shown linle deJradation for moderately long periods in the field. A Plexiglas has shown little degradation in an IK-year materials test in an arid environment.

Failures with polymeric encapsulation components have been due primarily to delamination of components and to moisture permeation. Delaminatinn has heen prominent particularly in encapsulation structures with multiple layers having different expansion

III-22

TABLE I. SYNOPSIS OF WORLD EXPERIENCE WITH TERRESTRIAL PHOTOVOLTAIC MODULES USING GLASS AS A COMPONENT OF THE ENCAPSULATION SYSTEM (2)

Agency /Company

RTC (La RadiotechniqueComplec, France)

Design A

Design B

Design C

SAT/CNES/University of Paris ( F ranee)

U.S.S.R.

JPL

JPL

JPL

JPL

U.S. Coast Guard

Universily or Deleware

Mitre Corporc1tion

Encapsulant Materials Adhesives and

Transparenl Cover Other Components

Glass sheet

Glass top cover over silicone pottant

Glass top cover over silicone pottant

Glass sheet

Cells sealed inside tubular glass modules 3.8 & S.4 cm in diameter

Pyrex. 0.138 cm thick (JPL·fabricated module)

Borosilicate glass (Centralab module)

Coming Microsheet over cell only)

Coming Microsheet ( over cell only)

Borosilicate glass (Centralab modules)

Glass plute(s) with dry nitrosen purse lhrough panel

Borosilicate slass (Cenlralab modules)

Rubber sheet seal; crimped-on Al belt: anodized Al substrate

Injection-molded epoxy belt around assembly; epoxyglass printed circuit board

Neoprene bell around assembly

Direct deposition of C'dS/Cu,S on 1dass substnu;

Method of scalinl! tubes unknown

Adhesive: RTV 602 silicone

Cells bonded with silicone: rubber 11asket between cowr and substrate

Unspecified

Cells bonded with silicone: nabber ttasket between cover and Al substrate/frame

Tenon strins and GE silicone rubber

Service Time and Localion

IS yr. Chile

11 yr. Africa and France

S yr, Africa and

I yr. France

Several yr. U.S.S.R. Calli of 197~)

3 yr ( I ll73-l 'J7(l) Point Vincente, CA

3 yr t 1973-197(,),

Point Vincente. CA

3 mo ( 1968). Pasadena. CA

I yr Cl%H-1969), Barstow. CA

~ yr C 1974-1&.JU,l.

Groton. CT

9 mo C8/7.!-5/7l). Ncwurk. DE

.! yr C 1974-1976), Mclean. VA

Service Experience

No 1noblems reported after initial 1uoblems with fra1ility of system resolved

Cracked !!lass and crJcked belt but no electrical detzradution

No dcllfadation reported

No problems reported

No 11roble111s reported

Source of lnformalionC a)

{3-5)

cJ-5)

~3-Sl

(18)

Adhesive debondinJ and Cl 0-11) clouding: interconnect conosion. Repaired.

No problems reported (10-1 ll

In lcrcon ncct corrosion . (I 0-1 .! )

No rroblcms rcriorted c I 0-1.!)

Ciood pcrfonnance except ( 14) for tcm,inal Ucad-in seal leakage in 4 of JS modules.

Moisture condenSAtion. (IM acid from 110t1ant

No chan,:c in till factor after .! yrs

(I))

NOTE: Additional slass encapsulation systtms on which field experience has not yet been reported are discussed in the text. (a) Numben ref er to references at end or paper.

III-23

coefficients and mechanical moduli. Moisture permeation has resulted in corrosion of the metali1.ations and le~ds. Degradation in propenics owing to UV exposure has not been as major a problem as might have anticipated. but exposure times to date have been limited. The world experience. by polymer materials class. is summarized below.

specimens were noticeably clearer than other materials being tested (Table 2). In earlier work by Hamihon Standard. United Aircraft Corporation. for the U.S. Army Electronics Research and Development Laboratory (23). it was concluded that a Plexiglas II UVA/ RTV-602 composite was the best cover design for protection of solar-cell arrays. This conclusion was based on light-transmission quality. retention of transmission under ultraviolet exposure. and resistance to thermal and mechanical shock.

Acrylics are mentioned frequently in the literature for use in terrestrial applications such as covers for photocells. solar (thermal collectors. and photovoltaic arrays. Sandia Laboratories investigators projected a useful life of 20 years for Plexiglas II UVA on the basis or its performance in a desert exposure of about 18 years (21.22).

A series of experiments by Jet Propulsion Laboratory ( 10.11) included cell arrays coated with acrylic resin and a Plexiglas II UVA sheet specimen. After a year of exposure the acrylic material

A nat-plate module manufactured by Sharp (Japan) is hermetically sealed in acrylic:. and. in studies by the U.S. Coast Guard at Groton. Connecticut. is performing well { 14). Both sides of an evacuated. nat collector from Solar Systems. Inc. have thermoformed. curved Plexi(!las co\"ers (24). Sunstream Division of Grumman Houston Corporalion also uses arched acrylic covers for its flat-plate collectors. The curved acrylic surfaces shed snow easily. ~nd are easily cleaned.

TABLE 2. SELECTIONS FROM THE WORLD EXPERIENCE COLLECTED ON POLYMERIC ENCAPSULATION MATERIALS IN TERRESTRIAL ENVIRONMENTS t2t

Materials

S-2:?4 Acrylic Resin

Plexiglas and RTV 602 silicone

Plexiglas SS Sheet

Acrylic

Stycast I :?66/Epoxy

FEP Type A ( film

FEP Type A (film lamination)

Tedlar ( I-mil)

Lcxan and RTV 602

Lcxan (Type 103)

Lcxan (tube)

Kapton (H-film)

Lcxan (UV stabilized); Sylgard 184 pottant: GR-cpo"y substrate

Sylgard RTV-182 silicone pottant

Agency or Company Service Time/Localion

JPL 4:? mo/Pointe Vincente. C'A

JPL 6 mo/Buoy system in San Diego Harbor

Sandia Labs. 18 years/ AlbuquertJlu:. New Mexico (, 1,·.;t-rt area)

U.S. Coast Guard 14 mo/Groton, CT (Sharp Corp. module)

JPL .m yr/Pointe Vincente. CA

LeRC

LeRC'

JPL

JPL

JPL

U.S. Coast Guard (Spectrolab module)

JPL

Solar Power

Mitre Corporation

!8mo/Sterlintt, VA

.?S mo/Buoy system in Boston Harbor

~ l ~o/Pointe Vincente. C' A

7-8mo/Pointc Vincente. C' A

J8 mo/Pointe Vincente. C' A

:? yr/Groton, CT

8 mo/Pointe Vincente. C'A

36-4:? mo/Africa: Gulf of Mexico

:? yr/Mclean. VA

NOTE: Additional experience and materials arc discussed in text and in Reference(:?). (a} References are at end of paper.

III-24

Experience ReferencesCa•

Only I'~ l'lectrical del!radation (10-1 :!) after 4~ months

Severe 1uoblcm with ocean C 10-1 :!) crustacean

Solar transmission 86-90'~ (:!I-~~) afll'r ex1,osure

Very good condition ( 14}

Fpoxy yl'llowed. Reaction f 10-1 ~) with solderlcss ct.•11 contacts. Oeprndt.•tl 40".f after 31

·~ yrs.

Mcctinl! dcctrkal rc,1uire- C3ll.S~) ments. No marked dc1,tradation

Pcrforminll well (36,5:!)

No chani?c in uppearan,c or ( I 0-11) transmis.\ion

Oe.Jmination after 5 mo (10-1:?)

Specimen durkened f I().. I ~) (ob~rv.1hh: at I year)

Thermal stn-ss l'ati11uc failures C 14) of interconnects. No discolora-tion of Lexan

f.mbrittled after 8 mo (I 0-1 :?)

GR-epoxy substrate dis- (53) colored. but rated cell out1n1t maintained

Open circuits (6 of JS mod- C 13) ules). Some dctnadation cor-rosion of metallization.

Acrylics also have been used as complexly sh;aped thermoformed or extruded components in concentration-1ype colleclors. One of the latest commen:ializa1ions is a curved Fresnel lens that was introduced early this year by Northrup. Inc. (24). Sandia is also employina acrylic lenses in concentrator system research (22). The maximum temperature noted by Sandia with a closed Fresnel system has been about 82 C. In open systems. temperature can be maintained within 10 to 15 degrees of ambient. However. cosls of air filtration and general maintenance ao u·p appreciably.

lposln have been explored in considerable depth as adhesives for solar-cell encapsulation. NASA-LeRC (25) has evaluated epoxies as adhesives for "TeOon" FEP cell covers and found transmission losses in the 10 to 26 percent range after exposures of SIO ESH (equivalent sun houn) compared with a 2 percent loss with FEP alone. NASA-Langley (26) and Goddard Space Center (27) observed relatively high failure rates with epoxies subjected to thermal and vibrational shock.

Epoxies also have been studied as total encapsulants for photovoltaics in marine environment ( 10). However. the materials showed sisns of yellowing ~nd degradation of electrical properties within a few months of exposure. In cover applications. it was shown that the epoxies are less affected than silicones by salt-containing atmospheres. althoush they do not hold up as well as the latter under severe temperature-humidity applications (28). Generally. it appears that appropriate modifications to reduce brittleness and UV sensitivity might make the clear epoxies viable candidates for use in solar-cell encapsulation systems as adhesives. coatings. etc .• particularly in view of cost and processins considerations.

Glass-reinforced epoxies have been used, panicularly by Solar Power and Solarex Corporations. in certain designs as substrate sheets. These materials apparently have performed well under the high-stress conditions that occur in unprotected areas where wind.s much in excess of 44.7 m/sec (100 mph) frequently are encountered. They have been found to weather poorly (discolor and fray) by Mitre Corporation. but strength was not markedly affected ( 13).

Fluorocarbons "Teflon .. FEP has been evaluated as a cover. as an adhesive for glass covers. and as a total encapsulant. Lockheed and NASA Lewis Research Center (LeRC) have published information (29-31) covering the use of this material and patents have been issued.

FEP has relatively good ultraviolet-radiation stability (in terms of terrestrial environments). Researchers at NASA-LeRC have reponed a decrease in short-circuit current of only 3 percent after • 3600 ESH (32) and a 10 percent decrease in 1>ptical transmission after 9500 ESH (29). Their preliminary findings indicated that FEPcovered solar--cell modules showed no degradation in two-year rooftop exposures at the Cleveland site. and reported that the manufacturer states that FEP should withstand Florida sunshine for at least 7 years (30).

FEP has a low refractive index. 1.338. making first-surface reflection losses low (33). Since FEP has a definite melting point. it has been evaluated as a cover and as an adhesive (hot melt). Work by NASA-LeRC indicates that FEP has satisfactory physical properties for use in lightweight. flexible solar-cell arrays (34) and exhibits compatibility with cells coated with Si01. TazO~. TiO!, and ShN. (35).

Heat-laminated sheets of FEP are under active investigation for space usage with the indication that systems with FEP applied to both sides of the modules have better survivability. Lockheed has developed solvents for FEP and has applied 25.4 to 254 ,-im ( I to 10 mils) of FEP by spraying. brushing. or dipping. Evidently. FEP has been judged not suitable for general space use. however. due to radiation damage.

NASA·LeRC indicated that above about 80 C cross-linking is the predominant asing mode exhibited by FEP and is accompanied by embrittlement ()6). This transition is discussed in some depth in related literature (37).

A NASA Tech Brief (38) describes the use of polyvinylidene fluoride (PVDF) to protect solar cells on the surface of Mars from radiation and dust. Transmission characteristics of PVDF are excellent and the polymer was not affected by a solar radiation exposure. Samples have not discolored and still retain 50 percent of their initial tensile strength after 10 years of exposure in a semitropical oceanic environment.

E-TFE has the ability to perform satisfactorily over prolonged periods of UV exposure. The changes produced in physical properties follow the classical pattern in that tensile strength is largely unchanged. eloflgation at room temperature is diminished (stiffness is increased. especially at elevated temperature). and electrical losses are increased.

Tedlar (PVF) has a solar transmission of 92 to 94 percent and. according to DuPont. retains some 95 percent of this transmission after Florida exposure for S years (24). CTFE, on the other hand. is reported to be adversely affected hy ultraviolet radiation (29.39.40).

Polycarbonates have been used as a protective cover for solar arrays in studies conducted hy JPI. ( 10) and NASA-leRC (41 ). In both studies unmodified sheet darkened on terrestrial exposures. However, in work with UV-stahili1ed polycarhonate. the material has weathered well. Both Solar Power Corporation and Spectrolab. Incorporated, have employed stahili,cd grades or polycarbonate in commercial arrays.

Although two to five times as costly as acrylic and various glasses. polycarhonate has an impact strength advantage that may be sufficient to off set this difference in applications involving arrays in which high impact · ,esistance is required. Another advantage of polycarhonate o\'Cr acrylics is its greater thermal stability. However. it has poor abrasion resistance and its optical properties are inferior to those of the acrylics.

Polyesters. PET film ( Mylar) has been evaluated in a number of studies for use in terrestrial solar cell encapsulation. In one study. 127-µm (5-mil) weatherahlc Mylar was life tested along with a number of other materials under conditions simulating those of solarstill environments (laut memhranes exposed to the sun with saturated water vapor condensing on the reverse side). Only two fluorocarbon films and Mylar withstood 1he environment for more than 4 years (42.43).

Specimens of 25-µm ( I-mil) weathcr-durahle Mylar film held up well during UV radiation in \'acuum for more than 500 hours. The light intensity for the experiment was between 0.67 and 1.0 times the integrated solar intensity helow JOO nm (3000 A) al I astronomical unit. The film darkened somewhat during exposure. Elongation decreased from 120 to 69 percent and tensile slrength increased slight· ly. The weatherable film contains an ultraviolet ahsorber and is completely absorbing below 350 nm (JSOO A) (44).

Polyimides. Polyimide film { Kapton) has excellent stability to UV (243). To date. the use of polyimidc film in terrestrial array encapsulation has been limited. possibly because ii has somewhat poorer ·(-80 percent) initial light-lransmission properties than most film candidates. Further. it has heen shown that Kapton may not be suitable for exposure to ocean environments unless covered with a protective layer (23). Howe\·er. it is excellent in terms of UV resistance. mechanical strength. and thermal properties. and. in certain applications. the trade-off may he warranted. Pyre M. l. fdu

III-25

Pont) coatings have been tested extensively in microcircui& applications (45).

Polyxylylenes. The parylenes have heen used in several studies as barrier coatings for microcircuits (46) and semiconductors (47,48). It has been shown that they provide adequate moisture barriers for semiconductor devices under normal humidity conditions and prevent bimetallic corrosion of certain very active metal combinations. However. the availability of these materials is restricted (exclusive under licensing by Union Carbide) and at present no practical method of reworking them is available. Since the materials are vacuum deposited, the integrity of the films and the cost of application need additional study. No optical properties have been described. although the film is transparent. These materials may find use as thin barrier coatings applied directly to the solar cell before assembly into arrays.

Silicones have been investigated widely fnr use as adhesives. pottants. and sealants for solar cells. At least 40 srecific compounds varying in composition and rhysical prnrertics have been studied. In general. they are relatively Ouihle. an mh·antage in counteracting the difference in thermal-exransions hctwecn cell materials and polymeric components of the array. The clear silicones also have good optical-transmission properties. :arc st.thle to ultraviolet radiation. and are useful O\Cr a wide tempernlllrc range.

Studies at J Pl. (49.50) co\'Cring stress :analysis of solar-cell arrays indicated that the methyl rhenyl types of RTV adhesives are superior to dimethyl types for solar-array :applications.

A large amount of information nn the weathering resistance or various silicone materials is a\ailahlc. A recent puhlication (51) cites 13 different silicones that were exposed in hostile environments for extended periods of time with. for the most part. only small changes in optical or strength properties. l>ata also have hecn reported for the lJV resistance of silicones used .is adhesi\'es for protccti\·c izlass and polymeric covers.

Solar Power Corporation. Snlarcx Cnrpnrntion. Spcctmlah and Sensor Technolol?Y International ha\·c hccn using silicones in some form as pottants for solar cells. A hard silicone co.atin~ has hecn used on an clastomeric silicone rott:ant in one design. hut some dcl:amin:a· tion has heen encountered. The use nf rndiufn:4uency-acti\atcd gas treatment to imprO\e the hondahility nl" silicones has hcen described (45).

POTENTIAL ENCAPSULATION·S'\'STEM D~SIGNS

Costs. suitability for low-cost automated processing. performance. and the form of the silicon cells (di!k:s/ sheet/ ribbon) will be controlling factors in the selection of the ultimate encapsulation system(s) for low-cost. long-life arrays. It is expected that application requirements. such as wind loads. replacement of units. concentrators (if any). and whether or not there is an existing structure present. will govern specific types of module designs and encapsulation systems which will evolve.

Systems with Glass Components

The collected experience to date on the use of glass-encapsulant materials for terrestrial applications has revealed an interest in glass for hermetic qualities. but a reluctance to use it because of concern for breakage and a lack of low-cost module designs incorporating glass. It is recommended. however. that glass systems should be given serious consideration for low-cost. long-life arrays to meet long-term goals. and certainly should be more widely used in the immediate future. Glass sheet and shapes offer the potential for achieving moisture and environmental protection. structural characteristics. and

optical transparency with one material. and will therefore be lliply competitive.

Some conceptual encapsulation-system designs arc propolld in Figure 2.

Polymeric Materials Systems

Figure J illustrates several encapsulation concepts utilizing polymeric materials. In these designs. the polymerics serve a number of different functions. i.e.. as adhesives. coatin1s. films. pottants. sealants. and sheet materials. In most runctions. optical transparency is required in the polymcrics. although filled materials can be utilized in certain applications such as substrates and edge sealants.

CANDIDATE ENC APSUI.ATION MATERIALS

As indicated. one of the ohjec1ives of this study was to recom· mend a list or materials which had potential for satisfyina the lowcost. long-life. high-performance automated-production goals of the LSSA Project. The glass and polymeric materials identified below were selected using the criteria described earlier and based on the analyses of the collected information on experience and properties or materials for arrays and related applications.

Gius Candidate Materials

Glass candidates for encapsulation systems are listed in Table 3. Because glass is normally prdormed to the final product Configuration by manufacturers which specialile in a panicular type of product. the candidates are identified for various encapsulation concepts which might be used. The list is not meant to be exhaustive. but to show the availability of glasses which might be used for each en· capsulation .c~ncept.

Of the three types or slass listed in Table 3. conventional sodalime glasses will be the most dcsirahle hecause of low cost and proven outdoor performance of most products. Whether or not low-cost module designs with silicon honded to this relatively high expansion coefficient material (about 3 times that of silicon) will survive temperature cycles and other long-time environmental stresses remains to be seen. The second type of glass which appean to have promise is a low-expansion horosilicate with an expansion coefficient close to that of silicon. With these types of glasses. integral sealing of cells to the glass (such as by electrostatic bonding) could eliminate the need for an organic adhesive and associated UV stability concerns. The last category is a combination of .. special and developmental" glasses which have less potential than materials in the other categories. Some property data have heen compiled for these glasses (2).

The fact that it is currently produced in large quantity and at low-cost for windows makC5 Oat glass highly attractive. Wholesale prices for annealed flat glass of various thickness arc shown in Figure 4 for the time period 1971 to 1976. The gradual decrease in the price of thinner float glass reflects technological improvements in glass manufacturing. especially the increased efficiency and production capacity of large float-glass tanb. The data shown in Figure 3 are not indicative of prices manufacturers pay from distributors for small quantities. but they do represent a lower limit for quantity users. Tempered glass is annealed glass which. after cutting to size. is reheated and quanched with air blasts to make it strong enough to use as safety gla1ing. Because it is a premium product. and non• automotive applications arc relatively new. it is priced 2 to J times higher than annealed glass of equivalent thickness. Based on prices quoted by one manufacturer of nuoresccnt tubes. the price per unit of projected area covered by tubing is ahout the same as that of a single thickness of annealed sheet glass.

III-26

Insulating Gloss Type (G-1)

Gloss sheet top cover

~n~~n~~n;:g~..,fjrr Adhesive · Polymeric sealant(s) Aluminum spacer

'T---t--------+---r"'-1--Pottont or void space Silicon cell Gloss Aluminum frame

(discs, ribbons, (optional) or sheet) bottom

cover Alternative: Metal or polymeric bottom cover Alternative :Gloss-to-metal seal at edge

Laminated Windshield Type (G-2) Gloss sheet top

cover Structural polymer

adhesive ( such as PVB)

Aluminum frame (optional)

Glass Top Cover With Polymeric Bottom Protection (G-3)

~nt,Ufl;,(t~i, .. pr,L~::~:·:,::~,. -··· · ~~ - __ c - -· . · -· ·· ··:.... - conformal coottno, Silicon cell Adhesive or film materal

Glass-to-Gloss Sealed Unit (G-4) ( Electrostotlcally bonded) E Silicon-to-gloss lntegrol (electrostoticl bond

f \!; ... 1 v-,,,.,,i' •,-.,. ....... "If l:!::::~:1 . . . . . (such as electrostattc Silicon cell Boros1hcote gloss bonding) (electrostoticaHy bottom cover bonded to top gloss sheet)

Flattened Fluorescent Tube Type (G-6)

Gloss fluorescent-light tube with f lottened top

Adhesive Metal end

cop Sealant/

(Length of tube+-+) adhesive Silicon ribbon cell

Alternative: Extruded gloss tube , flat top and bottom

Pressed Gloss Lenses or Cover Boxes (G-7)

Gloss disc

Pressed borosllicote gloss disc (auto-

. mobile headlight ~~~ lens) ·· · · ·· ·· · ·· · .... ,.. Adhesive

.. Sealant . Metal sheet perforated S1hcon cell (adhesively with cell-diameter

bonded to gloss lens) holes

FIGURE 2. GLASS ENCAPSULATION SYSTEM DESIGNS

III-27

Conformally Top Coated (P-1) Transparent conformal

. ... ......... .. -~ coating

Potted Cells With Rigid (Picture-From~) Substrate (P-5) I

:: Coaling (optional l ~):;<@;;J A~::;~e\~nl~

:: cells (discs, rlbbo:;t.Rigid substrate or sheet)

riii:: ~5~,~~~~. or pattant

Silicon cells R1g1d substrate( flat

Film Lamination (P-2)

or with pictureframe sides as shown)

~Polymer film material

~ P~~7::~~rheat

Adhesive or heat seal material (or rigid substrate)

Box Type-Cells Attached to Cover (P-6)

l:Z:;riiC::2';;~;;1::-: _:;:;i __ :::::i .. :·r;;·,:.·i:. _:z,::z,:attz::1;;:;;c:.;.::z::.:-;z:-:-·;). :-;:::z:z, ~:;;i .. ;;_. _c:::_ .I!';:; .. :i:. ::z~:;c: .. r .. a,....n::~:igid cove, .__ -=== .... --------···_.·.·-·.·._.··-·.-~Void (or pottont)

Tube Type (P-3)

,r c::J t}::::1:0:::il~d:ube

pottont

Silicon cells (ribbon)

----'i.---S-il-ic_o_n_c-el-ls----~--P-icture- frame substrate

Box Type-Cells Potted or Attached to Substrate (P-7)

sransparent rigid cover

Rigid Transparent Cover (P-4), . ~ransparent rigid

cover

·h-,--~-... ,-:,:,-;,:,:-.;.:-s-·11·1-co-r;;;ln·-:-:-·c.-.:.e:-··,:,-.s.,:--~--... -.... ·-..... -.~---_ ... v~!:: solid)

-----111-----------. ~-P-i:re -frame substrate

~z

1 't 1 1 iir ·c:n~:~:~ coating, Silicon cells pottant .or bonded

film

FIGURE J. POLYMERIC ENCAPSULANT SYSTEM DESIGNS

~-00

4.00

N e ..... ~ 3.00 ;; 0 u

2.00

1· 10 .! Float e 4

t:=dt===:=tt===~s~in;glte Strength Sheet ( :; )

1.00

1971

Source=U S Deportment of Commerce Shipment statistics published ,n Current Industrial Reports, Series MQ-32A

1972 1973 1974

Yeo,-197!)

t I SI half data

1976

.!»O

.40

,20

,10

;; 0 u

FIGURE 4. "SHIPMENT VALUES .. (INDICATIVE Of WHOLESALE PRICES) FOR ANNEALED SODA-LIME FLAT GLASS

III-28

TABLE J. CANDIDATE GLASS MATERIALS AND THEIR AVAILABILITY FOR VARIOUS ENCAPSULATION CONCEPTS

Glam Type -Soda-Lime BorosUicatel& t S ,ecial or Developmenlal

I t 8 f " rl

] ac b1 "" 0 Enaosulation Concept (J < Thin Oat glass cover. adhesively bon.cJed to substrale Flat glass ""Over actina also as substrate

• Adhesively bonded cells A • Integrally bonded cells (electrostatic bonding) • Thin-film cell substrate

Cylindrical glass tube cover/substrate

• Flat cells on shelf A A A

• Cylindrical cells adhesively bonded A A A • Cylindrical cells integrally bonded • Thin-tilm cell substrate A A

Rectangular or flattened glass tube cover/substrate • Adhesively bonded cells B B B • Integrally bonded cells

Pr~sed glass lenses or cover boxes lntcgr:d covers ror discrete cells

• Sputt~ring or evaporation • Powder fncinn

la) Lu•· ..:~pansion boro,ilk:iles 1bHloa1 111.111 ;alsu prudui:i:d bt· LOI'. ford. ASG. liu;ardliln, ;ind n: Gl;a~" 1n 1hr l:. 5 . . h:) Tror.11mcn1 whkh Improves transmission b)' rcdut:lftll sur(ai:e n=nri:titil)'.

Av-.iil;ibilitt· (hdi:: A • Gl:aa availabli: in desir"'li form

....

f I 12 a

! 12 ! .r ~ ~ :I

~ ~ if A

' A A A 8

A

B

B Wide variety

A

u l

~ i ! - .I V\

;:. !: .... < i .... ""' 1 C en ~ V\ 1 ' ~ ,0 .r ~ I ii; lb ,.. s z ~ ·a :111111 ....

"" ~ r:

~-I <! 6 6 "" :! c3 a a "" u Ji (,)

A

A 8 ('

A B 8 8 ·- -- A

A A A A

8 8

8 B ot' manufacturers und products

(' A A A

I • Nol i:ummer"i;ally av11ilablt: in di:siri:d l'urn1. bul o1IU:i,·1h1c 1m11k!r1iei, nr ,un.:i:pt (' • GI.an ur prlX"Css nol fully developed

Polymeric Candidate Encapsulation Materials

The selection of polymeric materials has involved (a) defining those polymeric materials classes that are most appropriate to each end-use application. (b) identifying. within each materials class. specific materials with the potential of meeting the system demands. and (c) selecting amons specific materials on the basis of projected properlies, cost. processability. availability, and the world experience.

In terms of specific properties. transparency in the solar spectrum has been a primary consideration in 1he selection of all materials exclusive of certain of the sealants and the substra1es. Other_ properties/ characteristics that were weighed particularly heavily were weatherability. useful temperature range. and processability. The latter includes handleability, repairability. and ease of low-cosl automation.

Materials costs and availability also were important in the selection process. However. because both processing considerations and the finalized system design(s) are basic to the es&ablishment of total system costs. certain materials having relatively high unit costs (e.g .. cenain silicones. epoxies. and fluorocarbons) have been included. These materials appear to fulfill functions in cenain conceptualized designs for the encapsulation system that may not be obtained with lower cost materials. It is anticipated that design modifications might be made, if required, to minimize the amounts required of certain of these high-cost materials while maintaining their unique system functions. Ultimately, it is anticipated that materi~ls development proarams are likely to provide less expensive replacements for. or modifications of, these materials.

It should be emphasi1ed that the materials candidates &hat have evolved from this study are. in ·many cases. only representative of a large number of viable ones available from a variety of manufacturers and suppliers. The identification and description of all materials of potential interest for each end-use application. of course, is not feasible. It is believed. however. that the materials selected are consistent with the general property requirements of terrestrial solar-cell encapsulation and with the results of the world experience in this area.

The recommended candidate polymeric materials. with representative examples of each. are listl'CI in Table 4 on the basis of the form or (unction to b~ served. Of course . .ill module designs will not involve each function or coms,oncnt listed in the first column of the tabulation. In some cases. a material will h,m: to he chosen on the basis of the best compromise between 1hc rrnpcrties re"luin.-d for the functions and the basic properties of the material.

Candidate materials for suhstrntcs. which arc not included in the table. include metals. glasses. and rolymcrics. In considering the polymer materials. the thermal and mechanical property requirements of a thick-sheet subsarate rule oul the use of unfilled polymerics. Reinforced materials or lumimucd structures arc the more. viable forms. such as the tzlass-fillcd epoxies and polyesters. It should also be noted that grarhite-fiher reinforced polymers. although presen1ly much more expensi,·c than tdnss-rcinforccd materials. can provide a better match of coefficient of thermal expansion with silicon. In considering reinforced sheet materials. it was anticipated that the sheet would likely be fastened to a suitahle supporting structure. However. some final system desitzns will not rc4uirc a substrate. as defined here. For example. the roofing-shingle design (S4) or a roll-out hlanket· type design (film encarsulanl) would he attached directly to a suprorting structure withoul an integral suhstrnte.

III-29

TABLE 4. CANDIDATE POLYMERIC MATERIALS CLASSES FOR VARIOUS ENCAPSULATION FUNCTIONS WITH REPRESENTATIVE EXAMPLE OF CLASS MEMBERS

Encapsulation System Component

Adhnives

Coatings

Films

Pottants

Sealants

Sheet/Tubing

Caaof Polymeric Materials

Acrylic (TP)(a) Acrylic (TS)(a) Epoxy Epoxy Epoxy Auorocarbon Silicone Silicone

Acrylic Fluorocarbon Fluorocarbon . Polyimide Polyxylylene Silicone Silicone

Acrylic Fluorocarbon Fluorocarbon Fluorocarbon Polycarbonate Polyester (TP) Composite

Epoxy Epoxy Silicone Silicone Silicone Silicone

Acrylic Butyl rubber/polyisobutylene Ethylene propylene rubber Poly sulfide

Acrylic Acrylic Modifo:d Acrylic Polycarbonate Polycarbonate GR Polyester

Representative Example

Acryloid 8-7 (Rhom and Haas Company) Cavalon 3100 S. (E. I. du Pont de Nemoun. Inc.) Eccobond 4S LV (Emerson & Cuming. Inc.) Epo-Tek 310 (Epoxy TechnoloSY. Inc.) Scotch-Weld 22168/A (3M Company) "Teflon .. FEP (E. I. du Pont de Nemours. Inc.) RTV-108 (General Electric Company) RTV-118 (General Electric Company)

Eccocoat AC-8 (Emerson & Cuming. Inc.) Kynar 202 CE. I. du Pont de Nemours. Inc.) "Teflon .. FEP (E. I. du Pont de Nemours. Inc.) "Pyre M. L •• (E. · 1. du Pont de Nemours. Inc.) Parylene C (Union Carbide Corporation) DC-3140 (Dow Croning Corporation) Glass Resin Type 650 (Owens-Illinois)

Korad A (Rohm and Haas Company) Kynar (Pennwalt Corporation) Tedlar ( E. I. du Pont de Nemours. Inc.) "Teflon° FEP (E. I. du Pont de Nemours. Inc.) Lexan (UV Stabilized) (General Electric Company) Mylar (Weatherable) (E. I. du Pont de Nemours. Inc. )Cb) Flexigard (3M Company)

Epocast 211/9617 (Furane Plastics Company) Stycast I ~69A (Emerson & Cuming. Inc.) RTV-61 S (General Electric Company) RTV-619 (General Electric Company) RTV-66S (General Electric Company) Sylgard 184 (Dow-Corning Corporation)

MONO (Tremco Manufacturing Company) (M)(b) Tremco 440 (Tremco Manufacturing Company) (T)(c) Vist:ilon 404 (Exxon C11emical Company) (T) ( ·) Lasto-Merk (Tremco Manufacturing Company) (M) c

Plexiglas (Rohm and Haas Comrany) Lucite (F.. I. du Pont de Nemours. Inc.) XT-374 (America! Cyanamid Company) Lexan (General Electric Company) Tuffak (Rohm and Haas Company) Sun-Lite (Premium) (Kalwall Corporation)

(a) TP and TS designate thermoplastic and thermosetting materials. respectively. (b) Martin Processing Company formulates a weatherable grade of Mylar. (c) (M) or (T) indicate, respectively. that the sealant is of the mastic or tape type.

III-30

Tables 5 and 6 provide representative cost information. based on large-quantity procurements. for thin-coverage (adhesives. coatings. and films) and bulk (pouants. sealants. and sheet tubing) polymeric materials applications (SS). Properties or the candidate materials have been compiled (2).

Conclusions Reprdin1 Glau Materials

CONCLUSIONS

The conclusions reached with regard to glass encapsulation materials and related technology are:

• Encapsulation systems which utilize glass as a transparent cover and structural member as well as for hermetic protection appear panicularly promising both for near-term and Ions-term requirements. and should receive increased attention.

• Soda-lime-silica (window) glasses are, and will continue to be. significantly more economical encapsulanls than borosilicate glasses on a unit-weighl basis because raw material and processing costs are lower.

• Borosilicate glasses appear necessary for encapsulation systems in which the glass is integrally bonded to the silicon cells. However. the availability or specific shapes (including sheet) of the glasses with the most attractive propcnies is limited at present.

• Because glass has not been used extensively as a terrestrial photovoltaic encapsulation material. there is considerable room for design innovation. with respect to use in nonconcentration, as well as concentration. systems.

• Compared to polymers. most common glass encapsulants have lower expansion coefficients. lower moisture permeability, and better weatherability (negligible UV degradation). These properties are. of course. important desisn considerations for long-life applications.

• The brittleness and poor impact resistance or ordinary annealed glass arc factors which may make glass undesirable for some applications. However. syslem designs which incorporate thermally tempered sheets or chemically strengthened shapes can minimize these limitations for applications where impact-hazard risk is high and the additional cost is warranted.

• Lowest near-lerm ( 1-S year) costs will be obtained only by adoptina glass products manufactured for existing high-volume markets.

• In this early stage in the development of the industry. slassencapsulation systems in most cases will likely be sealed with polymers. both for case of rabrication and potential for cell refurbishment. Glas..glass (i.e.. electrostatic bonded) or &lassmetal scaled systems are also attractive future approaches. Technology from insulating-glass and windshield manufacturing should be useful in developins and producing glus-encapaulatcd commercial arrays.

Condmlolll RepNll111 Polymeric Matertall

Each of the candidate polymeric classes of materials identified above hu cenain characteristics that make it panicularly auractive for use in photovoltaic encapsulation. but each also has cenain disadvantages. However. 1heae classes appear overall to have more favorable characteristics than the other major polymeric materials claua. in general.

• The acrylics are panicularly attractive from the standpoint of proceuability, optical properties. weather resistance. and price; they have relatively poor impact strensth.

• The epoxies have excellent mechanical strength and hardness. and a wide useful temperature range: they have only marginal resistance to ultraviolet irradiation and moisture.

• The nuorocarbons have excellent resistance to weather. chemicals. and water. and they process well; they are high priced.

• The polycarbonates have optical properties that are nearly as good as those of lhe acrylics and have excellent impact strength; they require stabili,ation against ultraviolet irradiation.

• Polyesters have a wide range or physical forms. both unfilled and reinforced; they have only marginal stability to the ultraviolet.

• The polyimides have excellent ullraviolet and thermal stability and very good mechanical properties: the light transmission of these materials is limited. and their price is high.

• The silicones have very good weathering characterislics. are useiul in a variety of forms over a wide range of temperatures. and have good optical properties: adhesion. moisture permeability. and price are limitations for some component functions.

General Conclusions of the World Experience

Implications of the general results of the experience with terrestrial encapsulation systems are:

• Wntberlal/ Aafn1 Effed!I. The maximum period of terrestrial exposure of photovoltaic arrays where performance has been monitored has been about 4 years. Some glass and polymeric encapsulation systems have 11hown acceptable performance for lhis period, but not with high consistency.

l.onger time experience. up to 15 years, with systems incorporating glass covers (!ice Table I). has apparently been favorable. at least for some modules. but performance has not been monitored and the fraeuency of failures is not known.

Clearly. encapsulation systems a11 ma.nufacturcd in the pa11t cannot meet ahe goal of a 20-year life with high reliability. However. some materials appcur promising from the performance standpoint if lower cmt proce55e5 with good manufacturing quality control are developed.

• Fallurn. Many of the failures in arrays tested in the field have been .. materials sy5tems failures" rather than .. materials degradation failur~s". That is. chan1cs in the bulk properties of materials with exposure have not been at foult so much as mismatch in properties of materials in cnntacl with each other. Delamination of materials at interfaces and moisture permeation inlo the module package have hccn p~ominant failure modes. Corrosion of metalli1ation. contact post•. interconnects. and leads has been the conseq&ence. Moisture per:mealion throu1h polymeric encapsulants in some cases is also of concerl).

Mosl other failures hnc been due 10 a design defect or lack of manufacturina quality control. Excessive back-hias on some cells in aeries has also caused encupi.ulant failureli, hut such failures cannot be attributed directly to the encap1ulation material. Failures due to handling and •"flying .. objects have occurred. but not as often as might tia\·e hccn expected.

With reprd to the prC\·alence uf failures due to factors other than materials a1in1. however. it lihould he noted that some cases of degradation ha\·c been observed in monitored exposures and that these expo11ure times ha\·e been relati\"ely short to date.

• ED•lronmen11.. The e,tpcrience to date encompasses a wide ranse of environments. This circumstance is fortunate because many types of failures that can occur have been revealed. However. environmental condilions have not always been well documented; this. or course. complicates past and future comparisons.

• Hazards. Current array 1tructures and encapsulation designs reflect a wide ran1e in 1he degree of concern about such halanb as roush handlins and malicious damage. The desree of risk to

III-31

TABLES. COMPARATIVE COSTS FIGURES (1974-197S) FOR RAW MATERIALSTHIN COVERAGE APPLICATIONS

Specific Raw Material Colts (SS) Class of Gravity S/mZ at thickness of

Application Materials (Typical) S/kg 25.4 mm ( I mil)

Adhesives Acrylic 1.18 uo 0.0JS Epoxy 1.25 To 6.59 (est.) O.:?O (est.) Fluorocarbon 2.13(a) To 11.45(a) 0.62'3> Silicone 1.07 4.40 to 15.40 To 0.4:?

Coatings Acrylic 1.18 1.20 0.03S Fluorocarbon 2.13 To 11.45 0.62 Polyimide 1.43 To 15.00 (est.) To I.SO (est.) Polyxylylene l.!9 Unavailable o.s3tb> Silicone 1.07 4.40 to 15.40 To 0.4:? Glass resin 1.30 !7.SO To 0.90

Films Acrylic I. I 8 l.:?O 0.035 Fluorocarbon :?.13 To 11.45 0.6:? Polycarbonate t.:?O :?.30 0.069 Polyester (TP) 1.38 :?.OS to :?. 70 0.078

(a) .. Teflon .. FEP. (b) Raw material cost is unavailable. Price listed is for custom coating by Union Carbide

Corporation.

TABLE 6. COMPARATIVE COST FIGURES (1974-197S) FOR RAW MATERIALS-BULK APPLICATIONS

Specifk Class of Gravity

Application Mat~rials (Typicalt

Pottants Epoxy l.!5 Silicone 1.07

Sealants Acrylic 1.18 Butyl 0.95 EPR 0.86 Polysulnde I.!:?

Sheet/Tubing Acrylic 1.18 Modacrylic 1.15 Polycarbonate 1.20

be assumed versu1 cost and other factors needs to be decided fur major types of applications.

• Costs. The encapsulation system design and processing methods employed to date for protection systems for terrestrial arrays are not suitable for the future cost goals. even with production scaleup. Batch processes and material choices which accommqclate such processes have been used. due to the low-volume sales of terrestrial arrays; Some of the present materials which have performed satisfactorily might be u1ed if appropriate array designs to more economically exploit these materials or new processing technology are developed. ·

• Development Efforts. There is valuable experience on which to build. but encapsulation systems to meel future price and perf ormance requirements will require developments in design. materials usage. and procet\scs.

• Materials Choices. The direct and related experience indicales that viable candidates exist in hoth glass and polymeric materials. Amons the materials which have been used and show

Raw Material Costs ( 55) S/kg S/100 cc

To 6.50 fest.) To 0.81 :est.) 4.40 to I 5.40 0.47 to 1.65

l..:?O 0.14 1.00 0.10 1.00 0.09 :?.70 to J.60 0.33 lo 0.44

l.:?O 0.14 1.16 to 1.4:? 0.13 to 0.16 :?.JO 0.:?7

pwmisins weathcrahilit~· and trnn,mi, .... i, ity lnr lrnnl c.·nH:r, arc window 1,dass. horosilicHtc ''""· ilnd ccrrnin m:r~lic,. r,ol~carhnnutcs. silicones. ilnd tluorn<.·arhon,. CtndiJitlc 1tli1,, and pol~·meric matcriuls ha\e h~L·n rcL·omm"·nJed tor cnnMlhmuion for ,·arious cncar,suh1tion-,~,tL·m d"·,,~n, .mJ lunct111n,.

ACK SO\\' u:oc; •:'\I•:~ TS

This work ""s ,ur,por1ed h~ th'-· .h:1 Prnrul,u,n l.ahonttor\·, California Institute nf lcc:hnol,,~,. umkr' \S·\ ('11ntrnc1 '-iAS7-l()O for the U.S. fncr8Y Rewan·h .rnd I kHlormL·nt .\dminilltration. Oi\'ision of Si.liar Encrtt~ .

The authors "ish In ad.1111\\l'-·Jp'-' lhl.' ""''tiinc:c in this studv of R. J1ou. R. Rennell. R. Sh.irr,:. ,uut I llru"·h ul hitllclh:: the sill~ifi-cant contrihution, of W < ·.irroll. ff \1,1\\\cll. ilnd others of JPI.; and the heir of numL·rt11h 111h'-·1 "-'''-',m:h'-·r, m the r,hotm oltaic l'ommunity who rn"id.:d 1111,um.,111,n '"' 1h'-· 111,'-",tlt!ation.

III-32

REFERENCES

( 1) J~t Propulsion Laboratory, "Project Quarterly Report, Low-Cost Silicon Solar Array Project", EllDA/JPL-1012-76/6, Oct. 8 1 1976.

C 2) Carmichael, D. C., et. al., "Review of World Ex .. perience and Properties of Materials for Encapeulation of Terreetrial Photovoltaic Arrays", ERDA/JPL 954328-76/4.

( 3) Salles, Y., "Solar Arrays for Terrestrial Applications and Sounding Balloons", Preaented at the Ninth IEEE Photovoltaic Specialists Conference, May 2-4, 1972, Silver Spring, Maryland.

( 4) Salles, Y., "Industrial Development of Silicon Solar Celle", Acta Electronics, 18 (4), 339-343 (197S).

( S) RTC La Radiotechnique-Compelec (France), Private Coama.anication (1976).

( 6) Pul 'unov, N. V., and Potapov, v. N., "Solar Batteries in Protective Transparent Covers", Geliotekhnika, 8 (S), 25-28 (1972), UDC 662.997.62.

( 7) Karpenko, I. V., and Tykvenko, ll. N., "Poasibilities of the tbin Solar Battery Applications for the Terrestrial Uee Units", Preaented at International Congreae. "The Sun in the Service of Man", Paris, July 2-6, t973.

( 8) Landsman, A. P., and Pulmanov, N. v., "Low-Powered Photoelectric Generators for the Terrestrial Application", Presented at International Congreea, "tbe Sun in the Service of Han", Parle, July 2-6 I 1973.

( 9) Andrianov, K. A., Dmitriev, v. A., Karpenko, 1. v., Keendzatekaya, Yu. N., and Hakarova, L.1., "Stabilization of the Characteristics of CdS Film Photoconvertere", Geliotekhnika, 11 (2), 3.7 (197S), UDC 621.383.

(10) Yasui, R. K., and Goldsmith, J. v., "Status of JPL Solar Powered Experiments for Terrestrial Applications", Presented at Ninth lntereociety Energy Conversion Engineering Conference, San Francisco, August 26-30, 1974.

(11) Yasui, ll. K., and Patterson, R. E., "Utilization of Space Technology for Terrestrial Solar Power Applications", Conference Recot"d of the Tenth IEEE Photovoltaic Specialists Conference, November 13-lS, 1973, Palo Alto, California (1974).

(12) Jet Propulsion Laboratory, California Institute of Technology, Private CODIDunlcation (1976).

(13) MITRE Corporation, Private C011111unication (1976).

(14) U.S. Coast Guard Station (Groton, Connecticut), Private Comnunication (1976).

(15) DiZio, s. F., "Initial Production of CdS Photovoltaic Products", Sharing the Sun! Solar Technology in the Seventies, Vol. 6, pp 108-112, International Solar Energy Society (1976).

(16) Boer, K. W., Freedman, N., Hadley, H., Nelson,W., and Selcuk, K., "Flat Plate Collectors With CdS Solar Cells and Firat Indications of Feasibility for flleir Large Scale Use", Presented at an International Congress! "The Sun in the Service of Man" Paris, July 2-6, 973.

(17) Windavi, H. H., "Performance and Stability of Cu2S-CdS Solar Cells", The Conference Record of the Eleventh IEEE Photovoltaic Specialists Conference-1975, Hay 6-8, 1975, Palo Alto, Califor-

• nia (197S).

(18) Besson, J., Nguyen Duy, T., Gauthier, A., Palz, w., Hartin, c., and Vedel, J., "Evaluation of CdS Solar Cells as Future Contender for Large Scale Electricity Production", The Conference Record of the Eleventh IEEE Photovoltaic Specialists Conference-1975, Hay 6-8, Scottsdale, Arizona (197S).

(19)\ Jordan, J. F., "Development of Lpw Cost Solar Celle". Workshop Proceedings, Photovoltaic Conversion of Solar Energy for Terrestrial Applications, Cherry Hill, New Jersey, October 23-25, 1973, NSF-RA-N-74-013, pp 182-192.

(20) Jordan, F. J., "Low Cost CdS-Cu2S Solar Cells by the Chemical Spray Method", The Conference Record of the Eleventh IEEE Photovoltaic Specialists Conference-1975, Hay 6-8, 197S, Scottsdale, Arizona (l97S).

(21) Reinhart, L. C., and Schirnnel, W. P., Jr., "Effect of Outdoor Aging on Acrylic Sheet", Presented at International Solar Energy Society Meeting August, 1974, Solar Energy, Vol. 17, pp 259.264.

(22) Sandia Laboratories, Albuquerque, Private COdalunication (1976).

(23) Moriai-ty, W. J., ''Modular Design of Improved Solar Converters", Hamilton Standard, Windsor Locks, Connecticut, Quarterly Progress Report No. 7, December 1, 1962-February 28, 1963. Contract No. DA36 039SC8.7!t6 l •

(24) Modern Plastics (May, 1976).

(25) Anagnostou, E., and Spakowski, A. E., "The Effect of Electrons, Protons and Ultraviolet .Radiation on Plastic Materials", Presented at the Eighth IEEE Photovoltaic Specialists Conference, August, 1970, Seattle, Washington.

(26) Beatty, M. E., Woerner, C. v., and Crouch, R. K., "Thermal and Particulate Radiation Effects on Potting Polymers", Journal of Materials, 5 (4), 972-984 (December, 1970).

(27) Haynos, J. G., "Investigation of Resinous Materials for Use as Solar Cel 1 Cover Class Adhesive", NASA-'IM-X-S5333, X-716-65-369 (September, 196S).

(28) Reich, 8., and Haxim, E. B., "Environmental Factors Governing Field Reliability of Plastic Transistors and Integrated Circuits", 10th Annual Reliability Physics Symposium (1972).

(29) Anagnostou, E., and Spakowski, A, E., "The Effect of Electrons, Protons and Ultraviolet Radiation on Plastic" Materials", Presented at the Eighth IEEE Photovoltaic Specialists Conference, August, 1970, Seattle, Washington.

(30) Bernatowicz, D. T., "The NASA-Lewis Terrestrial Photovoltaic Program", Conference Record of the Tenth IEEE Photovoltaic Specialists Conference, November 13-15, 1973, Palo Alto, California (1974).

III-33

(31) Forestieri, A. F., Greenberg, S. A., Mccargo, M •• and Palmer, W. L., "FEP Covers for Silicon Solar Cells", Intersociety Energy Conversion Engineering Conference Proceedings (1971), pp 881-8.

(32) Forestieri, A. F., and Broder, J. D., "Improvements in Silicon Solar Cell Cover Glass Assembly and Packaging Using FEP Teflon", Presented at the Eighth IEEE Photovoltaic Specialists Conference, August, 1970, Seattle, Washington.

(33) Forestieri, A. F., Greenberg, S. A., HcCargo, M., and Palmer, w. L., "FEP Covers for Silicon Solar Cells", NASA-TH-X-67824 (1971).

(34) Rauschenback, H. W., and Ratajczak, A. F., "FEPTeflon Covered Solar Cell Array Advancements", Conference Record of the Tenth IEEE Photovoltaic Specialists Conference, November 13-15, 1973, Palo Alto, California (1974).

(35) Broder, J. D., and Mazaris, G. A., "The Use of FEP Teflon in Solar Cell Cover Technology", Conference Record of the Tenth IEEE Photovoltaic Specialists Conference, November 13-15, 1'973, Palo Alto, California (1974).

(36) Lewis Research Center, NASA, Private Connunication (1976).

(37) Bowers, G. H., and Lovejoy, E. R., I & EC Products Research and Development, Vol. 1, No. 2 (June, 1962).

(38) Wizenick, R. J. 1 "Sheet Plastic Filters for Solar Cells", NASA Tech Brief B 72-10090, Category 4, NP0-11464 (1972).

(39) Lott, D. R., and Crabtree, W. L., "Properties Criteria for Components and Materials Used in Lighweight Solar Arrays", Presented at Intersociety Energy Conversion Engineering Conference, August 26-30, 1974, pp 100-109.

(40) Fayet, P., Paillous, A., and Sable, C., "Prospects for the Use of Stable and Transparent Plastics as Coatings on Solar Arrays", Photovoltaic Power and Its Application in Space and on Earth, International Congress, "The Sun in the Service of Ma~'. Paris, July 2-6, 1973.

(41) Forestieri, A. F., and Anagnostou I E., "The Effect of Sunshine Testing on Terrestrial Solar Cell System Components", The Conference Record of the Eleventh IEEE Photovoltaic Specialists Conference-1975, May 6-8, 1975, Scottsdale, Arizona (1975)

(42) Bjorks ten Research Laboratories, lnc., "Weathering Tests of Plastics and Design of Suspended Envelope Stills", Office of Saline Water Report No. 30, PB 161095 (September, 1959).

(43) Bloemer, J. w., Irwin, J. R •• and Eibling. J. A., "Final Three Years' Progress on Study and Field Evaluation of Solar Seawater Stills", Battelle Memorial Institute (June, 1965); O.S.W. Report No. 190 (Hay, 1966).

(44) Anagnostou, E., "Effect of Ultraviolet I rradia• tion on Selected Plastic Films in Vacuum", NASATM-X-1124 (July, 1965).

(45) DeLollis, N.J., Rubber Chemistry and Technology, 46 (2), 549 (1973).

(46) Hanley, L. D. • and Hartin, J. H., 11A Test of Parylene as a Protective System for Hicrocircuitry", Proceedings of 13th Annual Reliability Phyaica Symposium (April, 1975), pp 53-57.

(47) Caruso, s. v., Perkins, K. L., and Licari, J. J., "Design Guideline& for Use of Adhesives in Hybrid Microcircuits", NASA TMX-64789 (July, 1973).

(48) Noga, E. A., "Evaluation of Parylene as a Bart'ier Coating for Semiconductors", International Microelectronic Symposium Proceedings (1975).

(49) Salama, A.H., Rowe, w. M., and Yasui, R. K., "Stress Analysis and Design of Silicon Solar Cell Arrays and Related Material Properties", Presental at the Ninth IEEE Photovoltaic Specialists Conference, Hay 2-4, 1972, Silver Spring, Maryland.

(50) Salama, A.H., Rowe, W. M., and Yasui, R. k., "Thermoelastic Analysis of Solar Cell Arraya and Their Material Properties", NASA-JPL Technical Memorandum 33-626 (September l, 1973).

(51) Clark, H. A., "Environmental Resistance Data on Silicone P:.>lymers of Utility in Solar Collectors", Proceedings of the 1975 International Solar Energy Society Conference (1975), pp 188-89.

(52) Forestieri, A. F., and Ratajczak, A. F., "Terrestrial Applications of FEP-Encapsulated.Solar Cell Modules". NASA THX- 71608 (September, 1974).

(53) Solar Power Corporation, Private Comn,uni~at ion (1976).

(54) NASA Technical Brief 875-10289, Lewis Research Center (December, 1975).

(55} "P.dce Hikes Follow Plastics Reversal", ~aterials Engineering, 83 (1), 71-74 (January, 197~1.

III-34

F. SPRINGBORN LABORATORIES/DeBELL & RICHARDSON

ABSTRACT

A progress report on near-tenn encapsulants was presented by DeBelle and Richardson. The program goal toward which they are oriented is to develop the most cost-effective polymer system which will protect the solar cell for twenty years.

1

·Participating in a program to develop and test materials and coating I processes, DeBell & Richardson selected materials for three general properties:

1. Clarity

2. Toughness

3. Weatherability

Aging environments in the test program consist of combinations of heat, humidity, and UV light. Approaches for testing were classified as mechanical, optical, and miscellaneous (water vapor permeability; insulation, fungus, and abrasion resistance).

Cost analysis, selection of primers, enhancement of adhesion, upgrading UV stability and processing-repair studies are included in the program.

III-35

PROGRAM GOAL

DEVELOP THE MOST COST-EFFECTIVE POLY~1ER

SYSTEM WHICH WILL PROTECT THE SOLAR CELL

FOR TWENTY YEARS,

DeB&R-1

PROJECT SUMMARY

Materials selected for this program have been chosen for three general properties: clarity, toughness, and weatherability. The testing program incorporates evaluation of initial properties and subsequent retesting aher exposure to accelerated aging conditions. The aging environments consist of combinations of heat, humidity, and ultraviolet light, with sample testing at three time intervals. The testing program consists of three basic approaches:

Ill Mechanical - tensile strength, modulus, brittleness, impact strength, etc,

(Z,) Optical • total integrated transmittance, haze, absorption versus wavelength, infrared attenuation, etc:,.

(3} Miscellaneous - water vapor permeability, insulation resistance, fungus resistance, abrasion resistance.

The overall program h also structured to include four other technical endeavors: cost analysis, selection of primers and enhancement of ad hes Ion, upgrading UV stability, and proce Sl

ing-repair studies,

The final report will encompas• an overall performance analyllla and will Include recommendation• for several optimized designs for complete solar panels,

DeB&R-3

DISSOCIATION OF A POLYMER MOLECULE LEADS TO:

1, Cleavage into 1maller fragments

z. Elimination of 1mall molecule•

3, Formation of un1aturatlon

4, Depolymerlzatlon

5, Molecular rearrangement

6, Croulinklng

7. Oxidation

8 Hydrolyai1 of amides and eateu

DeB&R-5

III-36

PROGRAM OUTLINE

Material Selection

Screening

Accelerated Aging

UV and Adhesion Upgrading

Systems Analysis and Design

Accelerated Aging of Encapsulated Cell Sy11tem11

Outdoor Aging of Materials and Cell Systems

DeB&R-2

THE DEGRADATION PROCESS

Absorption of UV Energy

Dissociation of a covalent bond into a free radical

Initiation of a free radical chain reaction

Continuation a11 an oxidative chain reaction

Formation of degradation products increase11 the number of group11 which can absorb UV light

DeB&R-4

STABWZA.TlON MECHANISM

Reflection • by plamenta

Alnorptton and conveulon Into harmleu lower eneray levels

~ containlna blah concentration of UV ab•orber

DpactlvaUon • UV •tabillzer lnt•rcbanaee with an excited polymer molecule removing the excitation, Referred to a, ,uenchln1

Free-Radical Inhibition by antioxidant•

Hydroperoxide p9compoHu - organic •ulfl.i.r-• and pho•pbit ..

Synerd•m. each inaredient preventl a different type of dearadatlon reaction

DeB&R-6

PAllAMETRIC TESTING

OVEN AGING •

ss0 c AND 100~

ACCELERATED UV (USING AN RS-4 SUNLAMP)

ss0 c AND 100°c

UV PLUS HUMIDITY •

ssoc AND 90° TO RELATIVE HUMIDITY

WEATHER-0-METER o

THERMAL CYCLING

ENCAPSULATED CELLS ONLY

• AFTER 30, lZO AND Z40 DAYS

DeB&R-7

TABLE II

Io1t• To Be Run

Teat Method Per Teat ASTM No.

IU Annlicablel Clarity

Haze and Luminoua Tranamittance D&R Abraaion D673 or MIL-STD

BlOB • Method 50 Reelatance to Fungua CiZl Salt Spray Bll7

Toughneu Tenaile Impact Tut Dl822 Low-Temperature Brittlene•• D746

Heat Reiatance Temperature Modulua Curve Dl053 Thermal Conductivity Cl77 Coefllcient of Thermal Expanaion D696

Mechanical Proeertlca Tenaile Strength (a) D1708 Ultimate Elongation (a) Dl 708 TenaUe Yield Strength (a) Dl708 Yield Elongation (al 01708 Tenlile Modulua (a) Dl708 Hardneea DZZ40 Elaatlc Llmit JPL

Mia cc llaneoua Flamma bili

0

ty UL94 Inaulation Reaiatance (Run at 900/o) DZS7 Permeability - Water Vapor Only E96

Analytical Viaual And Microacopic Examination D&R Carbonyl/ A TR Electrical Propertiu and Solar Power Corp.

Performance

•Code: l - Teating before and after weathering Z - Teat• after firat expoeure period 3 • After third expoaure period 4 • Teated only on encapaulated eolar cell•

(a) Room temperature ia Sequence 1 ' High temperature ia Sequence Z

TESTS AFTER EXPOSURE •

BY DlrR

TENSILE STRENGTH

ULTIMATE ELONGATION

YIELD STRENGTH

TENSILE MODULUS

COLOR

TRANSMITTANCE

CARBONYL

HARDNESS

JPL WILL DETERMINE

VARIATION OF ELASTIC LIMIT WITH AGING

ESTIMATE FATIGUE ENDURANCE

MAXIMUM USE TEMPERATURE

FLEX CYCLE LIMIT

*AFTER 30, lZO AND Z40 DAYS

DeB&R-9

III-37

DeB&R-8

Tee ting Sequence •

I z

z 4

z z

3 z z

1 1 1 1 l I 3

3 3 3

z 3 4

TABLE 1

Matl!rlals List

Resin Generic Type Manufacturer Intended Use Appx. Coet Form

Kynar 460 Polyvinylidene Pennwalt High Modulus $ 5/lb. Thermoplastic Fluoride Encan,ulant

Halar 500 Ethylene - Chloro- Allied High Modulus $8. SO/lb. Thermoplaetic trifiuroethvlene Encao,ulant

Tefzel 280 Ethylene • Tetra- DuPont High Modulus $ 9/lb. Thermoplastic Ouoroethvlene Encao,ulant

FEP 100 Pe rfluoroethylene DuPont High Modulus $ 6/lb. Thermoplastic Proovlene Encaoaulant

PFA 9705 Pe rnuoroalkoxy DuPont High Modulus $11/lb. Thermoplastic Encao1ulant

Tedlar 20 Polvvinvl Fluoride DuPont Laminatino Film - Thin Film Viton AHtr Hexafluoropropylene DuPont High Modulus $10/lb. Thermoplaatic

Vlnylidene Encapsulant Fluoride

Resin Bl Chlo rotri fluo ro - Minnesota High Modulus $20/lb. Thermoplaetic ethvlene Minit1a L M£11. Encaosulant

KEL-F 800 Chlorotrifiuoro- Minnesota Medium Modulus $20/lb, Thermoplastic ethylene • Mining L Mfg. Encapaulant Vinylidene Fluoride

Sylgard 184 Silicone Dow- Low Modulus $ll/lb. Casting Resin Cornin11 Encansulant

Q)-6527 Silicone Gel Dow- Low Modulus $ 4/lb. Casting Resin Cornin11 Encaosulant

RTV 615 Silicone General Low Modulus $12/lb. Casting Resin Electric Encaosulant

Resin 650 Silicone "Glass" l)wcnll • High Modulus $1S/lb. Casting Resin Resin Ulinois Protective Coatina

DeB&R-10

Table ( (Continued - 2)

Resin Generic Type Manufacturer Intended Use Appx. Cost Form

VDEL 1700 Polyaryl SuUone Union Carbide High Modulus $ 3/lb. Thermoplastic Encansulant

Lexan 123 Polycarbonate General Electric High Modulus $ 2/lb. Thermoplastic -111 Encao1ulant

C-4 Polycarbonate Union Carbide High Modulus - Thermoplastic Encaosulant

Tenite 479 Cellulose Acetate - Eastman High Modulus $. SO/lb. Thermoplastic Butvrate Encansulant

CR-39 Diethylene Glycol PPG High Modulus $ 4/lb. Casting Resin Diallvl Carbonate [ndustries Encanaulant < ~· Plexiglass Methyl Methac rylate Rohm la Haas High Modulus $. 91/lb. Thermoplastic

"-' DR-100 Cooolvmer Encansulant Plexiglau Poly Methyl Rohm la Haas High Modulus $. 78/lb. Thermoplastic

V-811 Methacrvlatc Encaoaulanl

[:

Resin 5446 Neopentyl Glycol Cargill High Modulus $ 2/lb. Casting Resin Polvester -n Encaoaulant

ERL 4221 Cycloaliphati5.-P,:,~'r Union Carbide Low Modulus $ 5/lb. Casting Resin Eooxv c·~ ~'4'1C' Encanaulant

DER 7H Polyclycol .t Dow Low Modulus $ 3/lb. Casting Resin Enoxv Encansulant

Strengthened Cl!ramic Corning Cover Material - Sheet Glau

DeB&R-11

III-38

ELONGATION AT BREAK VS. ACCELERATED AGING

120-Day Exposure - Percent Property Retained

Cfo Property Retained V•. Control

Resin Weather- RS-4 Sunlamp Ometer ss•c 100°c 5,;•r.

Kyner 460 300 260 60 FEP 100 147 129 134 VitOD AHV 123 74 61 Halar 500 135 131 94 Resin 81 130 134 42

RTV 615 130 123 53

Tefzcl 280 122 145 Broken

PFA 9705 100 143 180

Tedlar 20 100 141 Broken

Sylgard 184 89 94 56

C-4 81 32 Broken Pleldglas V-811 60 40 Broken Plexiglas DR 6 lK 5'9 29 Broken

CR-39 39 125 50 Kel-F 800 34 26 Melted

Lezan 123-111 21 16 6

Udel 1700 6 so 25

Tenite 479 Broken Broken Broken

DeB&R-12

ELONGATION AT BREA!< VS. ACCELERATED AGING CONDITIONS

Ezpoaed for 30, 60, and 120 Day•

Control

Ruin (Unaged)

<'-> Kynar 460 50

Halar 500 175

Te!zel 280 200

FEP 100 220

PFA 9705 150

Tedlar 20 120

Viton AHV IC) 2430

Rosin 81 (Kel-F 6060) 130

Kel-F 800 zoo Sylgard 184 106

Q3-6527 (di

RTV 615 123

Udel 1700 16

Lexan 123-111 104

C-4 49

Temte 479 81

CR.-39 4

Plexigla1 DR.-61K 17

Plexiglaa V-811 5

(al Meltod/nowed

(bl Broken • degraded

Property Retained - '!. o( Control Value

W ca ther-Ometer RS-4 Sunlamp

55°c 55-c lOO"C

30 60 120 30 60 120 30 60.

370 340 300 340 340 260 so 60

117 122 135 131 131 131 125 151

131 155 122 120 127 145 12.5 (bl

129 113 147 131 140 129 150 134

153 176 100 180 153 143 183 216

146 145 100 158 150 141 12.5 (bl

>131 121 >123 ... 101 108 74 88 >89

146 123 130 120 134 134 lZf 100

13 40 34 30 30 Z6 (a) (a)

87 89 89 141 80 94 61 47

. - - . - . -123 146 130 154 113 123 81 48

25 ZS 6 56 50 so 37 37

31 11.5 Zl 115 11 16 11.6 6.7

173 16.3 81 82 51 32 z (bl

106 30 (b) 86 Z.4 (bl (a) (a)

100 100 37 100 150 125 50 so 247 117 59 176 47 Z9 47 (bl

40 80 60 40 40 . zo (bl

(cl Valuu are approximate whore indicated: elongation ezceed1 machine capac:ity.

(di Camiot be tested

DeB&R-13

III-39

120

60

94

(b)

134

180

(b)

61

. (a)

56

-53

25

5,7

(b)

Cb)

-(bl

.

PERCENT YIELD STRENGTH RETAINED PERCENT TENSILE STRENGTH RETAINED AFTER lZO DAYS OF EXPO.SURE AFTER lZO DAYS OF EXPOSURE

Perc:ent of Control Perc:ent of Control Control Retained Control Retained

Resin Value Weather- RS-4 Resin Value Weather- RS-4 .!E!!L ~ ~ 1e!!L ometer 55°c

Kynar 460 4750 llO 126 Kynar 460 6810 108 ll3

Halar 500 6090 lll 104 Halar 500 5030 101 109

Tefzel Z80 5380 llO 127 Tefzel Z80 4270 99 109

FEP 100 2800 107 1oq FEP 100 Zl30 95 106

PFA 9705 2980 89 % PFA q706 2000 93 105

Tedlar 20 2820 524 240 Tedlar ZO 12. 100 215 78

Viton AHV 340 165 191 Viton AHV 39. 5 865 918

Resin 8 (Kel-F 6060) 5680 97 q9 Resin 81 (Kel-F 6060) 5690 101 107

Kel-F 800 1920 66 106 Kel-F 800 1260 162 218

Sylgard 184 (a) Sylgard 184 930 59 71

03-6527 Gel 03-6527 Gel

RTV 615 (a) RTV 615 szo 98 143

Udel 1700 10,000 Udel 1700 7860 44 125

Lexan 123-111 8500 105 llZ Lexan 123-lll 8160 88 9Z

C-4 5320 104 107 C-4 5570 92 90

Tenite 479 3470 Tenite 479 4400

CR-39 (a) CR-39 4940 82 139

Plexiglas DR-61K 5630 101 Plexiglas DR-61K 5380 100 84 Plexiglas V-811 9030 Plexiglas V-811 9030 68 67

(a) no observable yield

DeB&R-14 DeB&R-15

PERCENT MODULUS RETAINED AFTER lZO DAYS OF EXPO.SURE

Perc:ent of Control Control Retained

Resin Value Weather- RS-4 (x 105 p•i) ~ 55°c

Kynar 460 1.99 133 140

Halar 500 Z.Z3 113 106

Tefzel 280 l. 80 105 121

FEP 100 o. 704 127 123

PFA 9705 0.532 132 161

Tedlar ZO Re111ult1 not yet available

Viton AHV 103 zoo 188 (200,. Elong.)

Re1ln 81 ~el-F 6060) 1.n 137 134

Kel-F 800 0.198 1141 737

Sylgard 184 586 107 113 (100'-Elong.)

03-6527 Gel

RTV 615 389 56 98 (100-A, Elong.)

Udel 1700 33.3 16 12

Lexan 123-111 31.4 11 lZ

C-4 1.67 144 151

Tenlte 479 1. 54

CR-39 Z6. 7 12 14

Plexlglaa DR-61K z.20 116 lZl

Plexlglaa V-811 4.18 102 109

DeB&R-16

III-40

MATERIAL RANKING

120-DAY OPTICAL PERFORMANCE

Control Optical - 120 Day•

Ream Value (T '¥1 z 'Vo Control)

T ('Vol Weather- RS-4, Omotcr 55°c

Kynar 460 58 14, S 15, 6

Halar 500 81 57,0 65. 0

Tobol 280 71 44.0 42.0

FEP 100 84 58.0 53. 0

PFA 9705 88 71.0 64.0

Tedlar 20 76 15.0 16. 0

Vtton AHV 85 14. 0 59.0

Rea in 81 (Kel-F 6060) 82 51. 0 58. 0

Kel-F 800 85 49, 0 61.0

Syliard 184 76 10, 0 52.0

Q3-6SZ7 94 - (a)

RTV 615 81 8.0 60.0

tJdel 1700 86 o. 3 18. 0

Lezan 123-111 88 32, 0 60.0

C-4 91 47, 5 65. 0

Tonite 479 92 - (a)

CR.-39 92 90, 0 88.0

Plexiglu DR-61K 90 71. 0 71. 0

Plexigla1 V-811 92 68. 0 76,0

(a) Not yet available

DeB&R-17

Polymer Trade Name

Kynar 460

Tefzel 280

Tedlar ZO

Viton AHV

Kel-F 800

Sylgard 184

RTV 615

Lezan 123-111

Udel 1700

C-4

Tenite 479

CR-39

Plexigla1 DR-61K

Plexigla1 V - 811

POLYMER FAILURE(a) AFTER 60-DAY EXPOSURE UNDER FIVE CONDITIONS

Percent Elongation Retained at Break ancl Percent Optical Transmittance R~tained

Weather-RS-4

Generic Typo Ometer S5°C 100°C

Polyvinylidene nu- (SO)(b) F (SO) F 6o<·c\S8) oride

Ethyle1141 tetraflu-0 F oroethylene

Polyvinyl fluoride (SZ) F (48) F 0 F

Hezafluoropropyl-eno / vin ylidene fluoride Chlorotrifluoro-ethylene/ vinyliden e 40 F 30 F Melted fluoride Silicone . 47

Silicone (51) F 48

Pol year bonate lZ F 11 F 7 F

Polyaryl sullone ZS F so (65) 37

Polycarbonate 16(60)F 51 0 F

Cellulo1e acetate 30 F 2 F Melted butyrate

Diethylene glycol/ 50 diallyl carbonate

PMMA copolymer 0 F

Polymethyl-methacrylate

(a) Criteria of failure:

Ranking Number

16

5

11 7

4

15 12

9

8 14

(al

13

17

10

6

(a)

1

3

z

Air Oven Con1id-~reel

ss0 c 100°c Failed

(55) 60 y (d) ea

Yea

(57) Yo1

66

65 Melted Yee

(59) Ye•

6Z 10 F Yea

Yoo

Yea

68 Yea

ZS

Ye1

80

, Loss of at lea1t 60f, elongation in the Weather-Ometcr or RS-4 at 55°C •. • LOIS of at lea,t 90,., elongation in the RS-4 at 100°C or oven aging at 100°C.

Los, of at le&1t 500!, solar transmission in the Weatber-Ometer or RS-4 at 55°C. (bl Numbers in parenthuea are '¥. solar tran,rnittance retained after 60,day exposure. (c) N'Qlllber, not in parentheses designate percent elongation retained after 60 days. (di Locus of failure designated by "F" in respective colllfflllll,

DeB&R-18

III-41

MATERIALS DROPPED

Resin Reason !or Rejection

Tefzel 280 Low optical tran,mission Poor optical stability UV degradation Poor proceuability

, High cost

Kel-F 800 , Very poor mechanical stability • Low flow temperature

High cost

Udel 1700 Very poor optical stability Very poor mechanical ,tability

CR-39 • Decay of ten11ile atrength Development of fractures Completely unprocessable

DeB&R-19

UPGRADE UV RESISTANCE

1, UV ABSORBER AS ADDITIVES

PLUS POSSIBLE SYNERGISTS

2, THIN COATING CONTAlNING A

UV ABSORBER

DeB&R-21

III-42

UV TRANSMITTANCE BEFORE ACilNO

Control Material, Value

T (Oh)

Kynar 460 3

Halar SOO 36

Te!zel 280 IS

FEP 100 34

PFA 9705 42

Tedlar 20 13

Viton AHV 56

Reain 81 (Kel-F 6060) 24

Kel-F 800 60

Sylgard 184 32

Q3-6527 -RTV 615 65

Ruin 650 -Udel 1700 21

Le::an 123-111 0

C-4 50

Tenite 479 44

CR.-39 83

Pleziglas DR-61K 0

Pleziglas V-811 75

DeB&R-20

MATERIALS FOR UV UPGRADING

Lexan 123-111

Tenite 479

Plexiglas V-811

Plexiglas DR-61K

C-4

DeB&R-22

I

Adhesion Study

Peel Strength Refer- Alter One Week's once Material Primer/Adhuive Lamination Condition Initial

Water Immersion

g/cm lb/in. g/cm lb/in,

1 Sylgard 184 None - control Cast/cured, I00°C/lh 6.Z9 0.035 None

Q36-060 (a) Same (a) 2 Sylgard 184

Dry 2 h/30°C Same 357 1.96 Approx. I.96 lb/in

3 Sylgard 184 Chemlok 607 Same 59 0.13 None Dry 30 min. /30°C

4 FEP C-20 None - control Presa /l 70°C, 100 psi 185 1.03 None (Treated) 30 minutes

5 FEP C-ZO Chemlok 607 Same 768 4.3 542 3.03 (Treated) Orv 30 min. /30°C

6 FEP C-20 Z-6020 Silane (1!,) Same 286 1.6 157 0.88 (Treated) Dry Z h/30°C

7 FEP C-20 Q36-060 (b) (Treated) Dry 2 h/30°C

Press/170'C, 100 psi ,324 1.8 375 2.1 l.S minutes

8 FEP C-20 Chemlok 607 Press/ l 70"C, 100 psi ,0 0 None (Untreated) Dry 30 min, / 30°C 30 minutes

9 FEP C-20 KR-TTS, 1% Titan- Press/150°C/Z5 psi 0 0 None

f----<: (Untreated) ate; Air dry lh /!lfc 15 minutes

FEP C-20 Z-6020 Press/150°C, 50 psi (cl 10 0 0 None

(Untreated) Dry 2 h/30°C 15 minutes

11 FEP C-ZO 036-060 lb) Press/160 C/50 p=ii 582 3.3 629 3.5 (Untreated) Dry 2 h/30°C 1.5 minutes

(a) Bond strength exceeds tensile strength of polymer (bl (Coll) • D-282, t0.3'1'. BPO, 80°C/5 min.; 150°C/8 min. film treatment (c) Solder melted

DeB&R-23

Systems for Polyester/Fiberglas Substrates

Primary Se1:ondary Cover Film Over Primary Encapsulant Encapaulant

Material Cost Needed? Reason Material Rationale for Use

Resin 81 High No -Tenite 479 Low Yes

Mech. Kynar 460

Cive1 max. protection: Deg. absorb• UV,

C4 Med. Yea Mech. Tedlar ZO Has lowest UV trans. of Deg. four best secondary filma.

Halar should be used on at

P~e:wau Mech. least one high-modulus pri-

Low Yes Deg. Halar 500 mary vs. uso on low-modulu• RTV 615.

High-modulus film vs. low-RTV 615 High Yes Soil Halar 500 modulus film on Sylgard

184.

Higher ranking 120-day Sylgard 184 High Ye• Soil PFA 9705 optical, vs. Tedlar 20,

which i• used with Nema cao.

Ple,riglass 1. Rigid sheet needed.

Viton AHV High Yea Soil DR 61K 2. Compare vs. Ple.xiglasa V811 below.

Ple.xiglass I. Rigid sheet needed. Oel Low Yea Soil

V 811 2. Compare vs. DR 61K above.

DeB&R-24

III-43

Systems !or Aluminum and Nema 010 Substrates

Primary Secondary Cover Film Over Primary Encapsulant Encapsulant

Material Cost Needed? Reason Material Rationale for Use

Aluminum

I. Practical system.

Tenile 4i9 Low Mech. FEP 100 z. Over high modulus pri-Yes Deg. mary vs. over low

modulus primary below.

Yes, but l. Need understanding of

Mech. effect of UV on cell

C 4 Med, will not Deg. - properties using unstable primary. This primary used

use. because it is not yet a fully commercial material.

'High

1. Less costly secondary

Viton AHV Yes Soil FEP 100 with expensive primary.

z. Use as thin as possible !handleable) film,

Soda 1. Need rigid material.

Gel Low Yes Soil Lime z. Glass is a significant Glass possibility.

~ Lowest ranking optical of Sylgard 1841 High Yes Soil Tedlar ZO four secondary films.

DeB&R-25

CORRELATION OF HOURS OF RS-4 SUNLAMP AGING VS. YEARS OF OUTDOOR WEATHERING

RS-4 Outdoor Ratio

Stabilizer - PHR Polymer Sunlamp, Weathering, Accelerated Hours to Year, to to Outdoors Failure Failure

None - Polypropylene 170 0,Z5 1/10

Cyasorb 0.3 Polypropylene UV 531

zooo z 1/8

Zinc 10,0 Polypropylene Oidde

4000 4 1/8

DeB&R-27

III-44

OUTDOOR AGING(l l

. Material Study

Purpo1e: Provide correlation with indoor accelerated techniquee

Materials: Eleven - ranging Crom excellent to poor aging 1tability

Ezpo1ure: Direct fixed 45° 1outh, in Florida and in Arizona, (or one year

Tests: Microten11ile, optical transmission, carbonyl by ATR infrared

Encapsulated Cells

Purpo11e: Select best material(s)

• Materials: Eight beet

, Sub1trate11: Polyester/!iberglan, aluminum, NEMA G-10

Ezposure: Direct fixed 45° 11outh plus EMMAQUA; Arizona: 4 and 8 month11

, Testa: Adhesion, cell characterilltic11

(l) Energy measurement in Langleys:

1.

z.

45° South 500 EMMAQUA - 5000

DeB&R-26

D &. R APPROACHES

C=O AND LOSS OF ELONGATION

VERSUS TIME

LOG•LOG PLOTS OF PROPERTY (e.g.,

ELONGATION) VERSUS TIME

3, CALIBRATE RS-4 AND WEATHER-OMETER

USING MATERIALS OF KNOWN DEGRADA

DATlON LINE

DeB&R-28

G. ENCAPSULATION PRESENTATION

ABSTRACT

The influence of encapsulation on array efficiency, and encapsulation progress and problems were addressed by Hugh Maxwell.

Encapsulant material costs were covered in three~time periods:

•Near Term Designs

•Intermediate Term Designs

•Long Term Designs

Present to 1980 '

1980 to 1985

1985 onward

It should be noted that the materials and designs in each of these time periods are completely different, and these appear to be the basic reasons for differences in costs.

Contrasts and characteristics worth noting were:

1. Near term materials were essentially soda lime glass and an aluminum substrate with conformal coatings and suitable pottants and adhesive.

2. Intermediate term designs used borosilicate glass with glass/film backing.

3. Long term designs typically used silicon ribbon and films.

III-45

ENCAPSUlANT MATERIAL COSTS

HUGH MAXWELL

NEAR TERM DESIGNS

INTERMEDIATE TERM DESIGNS

LONG TERM DESIGNS

HM-1

TO 1980

1980 TO 1985

1985--+

STRAWMAN DESIGNS NEAR TE~

§ = = = = = ~POLYVINYL BUTYRAL <•val

SODA Ll"E GLASS SILICON CELL SODA LIHE GLASS OR ALUMINUM

l~===~TTANT SODA LIME GLASS OR ACRYLIC SILICON CELL ADHESIVE

LUMINUM SUBSTRATE

SILICON CELL ----~ DHESIVE ONFORHAL COATING

ALIJIINUN SUOSTRATE

HM-2

STRAWMAN DES I GN COSTS NEAR TERM

SODA LIME GlASS/PVB/SODA LIME GLASS SODA WlE GLASS OR ALUMINUM 0.125 IN. THICK TOP 0.17 0.17

0.125 IN. THICK BOTIOf'I 0.17 ALUMINU", 0.060 IN THICK ($1.00/LB) 0.86 POLYVINYL BUTYRAL

0.030 IN. THICK C2 REQ, > 0.64 0.64

TOTAL 0.98 1.67

SODA LIME GLASS/POTTANT/CELLS BONDED SODA LIME GLASS TO AN ALUMINUM SUBSTRATE 0.125 IN, THICK 0.17

ACRYLIC, 0,125 IN. THICK CS0.55/LB) 0.42 POTTANL 0,100 IN. THICK ($2.00/LB) 1.36 1.36 ADHESIVE, 0.010 IN. THICK C$2.00/LB) 0.09 0.09 ALUMINUM, 0.060 IN. THICK CSI.00/LB) 0.86 0.86

TOTAL 2.l48 2.73

CONFORMAL COATING/CELLS BONDED TO AN CONFORMAL COATING ALUMINUM SUBSTRATE 0.010 IN. THICK CS2.00/LB> 0.14

ADHESIVL 0. 01() IN. THICK C$2 .00/LB> 0.09 ALUMINUM, 0.060 IN. THICK Ul.00/LB) 0.86

TOTAL 1.09

HM-3

III-46

STRAWMN DESIGNS INTERMEDIATE TERM

~BOROSILICATE GLASS} ELECTROSTATIC SILICON CELL BONDED BOROSILICATE GLASS PLASTIC (SMC) SUPPORT

~ :i:~::!:ECELL ~~GLASS FLUORESCENT

DESIGN

ELECTROSTATIC BONDED GLASS

GLASS FLUORESCENT TUBE

LIGHT TL'BE WITH FLATTENED TOP

BOROSILICATE GLASS ADHESIVE SILICON CELL FILM

HM-4

STRAWMAN DESIGN COSTS INTERNEDIATE TERM

MATERIAL BOROSILICATE GLASS

0.010 IN. THICK TOP 0,020 IN. THICK BOTIOP\

SMC SUPPORT

GLASS TUBE

TOTAL

ADHESIVE, 0.010 IN. THICK ($2,00/LB)

· TOTAL

0.30 o.so 0.15 0.95

0.60 (l,09

0.69

BOROSILICATE GLASS/CELLS BONDED TO GLASS/ BOROSILICATE GLASS, 0.125 IN. THICK 0.51 FILM BACKING ADHESIVE, 0.010 IN. THICK ($2,00/LB) 0.09

Ftlfll, 0.001 IN, THICK 0.~2

TOTAL 0,62

HM-5

III-47

STRAWMAN DES I GNS LONG TERM

. FILM (e STAGE) --§§~

SILICON CELL (OR RIBBON) ADHESIVE

SUBSTRATE

DESIGN SUBSTRATE/CELLS BONDED 10 SUBSTRATE/B STAGE FILM

FILM/SILICON RIBBON/FILM

~TOP FJU< (B STAGE) SILICON R 1880N

BOTTON FJU, (a STAGE)

~TRANSPARENT .PLASTIC (a STAGE) SILICON RIBBON PLASTIC (a STAGE)

HM-6

STRAWMAN DESIGN COSTS LONG TERM

MAmIAL SUBSTRATE, 0,060 IN. THICK ADHESIVE, 0.010 IN, THICK B STAGE FILM, 0.002 IN. THICK

TOTAL

B STAGE TOP FILM, 0.002 IN. THICK B STAGE BOTTO"' FILM, 0.002 IN. THICK

TOTAL

COST ($/FT2>

0.15 0.03 0.02

0.20

0.02 0.01

0.03

PLASTIC/SILICON RIBBON/PLASTIC B STAGE TRANSPARENT PLASTIC, 0.030 IN, THICK 0.10 B STAGE PLASTIC, 0.030 IN. THICK 0.08

TOTAL 0.18

HM-7

III-48

H. TEXAS INSTRUMENTS PRESENTATION

ABSTRACT

A presentation was made by B. Carbajal at the general meeting on Tuesday, January 18, representing Texas Instrument, Incorporated. The subject of the presentation was "Low Cost Silicon Solar Cell Processing for 1985 Production". The basic philosophy and design concepts formed the base of the projection (see the following pages). Cell processing and module designs were explained in detail.

The problem of producing low-cost solar-grade silicon is being pursued actively by TI. As reported previous.ly, the extent of effort can be appreciated from the paragraph below, extracted from the most recent quarterly summary.

Summaries of present TI efforts related to the presentation are:

1. Carbon reduction of low impurity silica in a plasma heat source.

2. Computer-aided design analyses of·metal pattern designs.

3. Cost analyses for process steps.

4. Layer feasibility studies using dopant solutions.

5. Screen-printed base metal contacts.

6. Low-cost module substrate material.

7. Test-mo4ule evaluation.

8. Moduie design evaluation.

In the large-area Czochralski silicon task, several trial crystals were pulled, both from recycle silicon and from new polysilicon. Many wafering techniques are being pursued.

III-49

LOW COST S !LICON SOLAR CELL PROCESS ING

FOR 1985 PRODUCTION

PHILOSOPHY

t ALL PROCESS STEPS MUST BE DEMONSTRATED NO

LATER THAN 1982

t HIGH EFFICIENCY IS A MUST

t ALL PROCESS STEPS SHOULD BE ADDITIVE

t ALL PROCESS STEPS THAT ARE IN FEASIBILITY

STAGE MUST HAVE AN ALTERNATE FALL BACK

THAT IS PROCESS COMPATIBl£

t PROCESS SHOULD YIELD TIGHT DISTRIBUTION

Tl-1

DESIGN

1 OPTIMIZED METAL PAmRNS

1 COMPATIBLE Wint MODULE DESIGN

t COMPATIBLE WITH LOW COST PROCESSING

Tl-3

METALLIZATION

• RES I ST IV ITV <4 X 10-) n/0

• FINGER LINE WIDTH

>"100 )(ffl

• ntlCKNESS

~6 )lffl

OPTIONS

I. SCREEN PRINTED BASE METAL WITH SINGLE FIRING OPERATION

2 PAmRNED ELECTROLESS PLATING

3. MASK STENCIL EVAPORATION

Tl-5

III-SO

SILICON SHEET

t S INGl£ CRYSTAL

1 80 -120 cm2 AREA

t P-TYPE

N+ Pp+ STRUCTURES

• 0. 5 - I. 5 0-cm MINIMUM SERIES R MAXIMUM LIFETIME

t TEXTURING Will REQUIRE (100)

t NON-SINGl£ CRYSTAL Will BE INCLUDED WHEN HIGH EFFICIENCY PROCESSES ARE DEFINED

Tl-2

JUNCTION FORMAJION

• N+ JUNCTION DEPTH

0.2-0.3)1ffl

• N+ DIFFUSED LAYER RESISTIVITY

50 - 80 0/0

• METAL - N+ CONTACT RESISTIVITY

< 10-2 Ocm2

• p+ CONTACT LA YER ON BACK SIDE

OPTIONS

I. SIMULTANEOUS DIFFUSION OF N+ • p+ Wint DOPED POLYMER SOURCES.

2 ION IMPLANTATION AT N+ AND p+ W 1TH S INGLE THERMAL ACTIVATION.

Tl-4

OPTICAL COATING

1 MINIMIZE REFLECTION

1 PROV IDE SUR FACE PASSIVATION

OPTIONS

I. SPIN-ON HIGH INDEX FILM

2. EVAPORATE HIGH INDEX FILM

3. USE OXIDE GROWnt WITH TEXTURED SURFACE

Tl-6

BASE W~E LOW COST CELL PROCESS

sr,'/ YIELD CUM.

TOTAL

TIXTURE ETCH (NaOHI 98 .0224

CLEAN-ACID 98 .0347

SPIN-ON p+ ANON+ 99 .0729

DIFFUSE 99 .0911

STRIP OXIDE (PLASMA) 99 • 1139

THICK FILM Cu (BACK) 98 .1493

THICK FILM NI (FRONT) 98 .1634

EV A PORA TE AR 99 . 2057

CELL 1EST 85 . 2559

TOTALS .03.96 .0649 .0649 .0359 75. 3 M L 0 D

Tl-7

BASE LINE LO\'/ COST SOLAR CELL PROCESS - ALTERNATE I (JUNCTION)

1t $,\V ..... $/W YIELD CUM.

0

TEXTURE ETCH (NaOH) 98 .0224

LEAN-UP. ACID 98 .0347

IMPLANT p+ 99 .0~10 IMPLANT N+ 99 • 1276

DIFFUSE 99 • 1(54

CLEAN· ACID 98 • 1612

THICK FILM BACK 98 • 1976

THICK FILM FRONT 98 • 2126

EVAPORATE AR 99 .2555

CELL 1EST BS .314'

TOTALS .0614 .cr.20 .0620 .om 73. 8

Tl-8

III-51

BASE Ll!~E Lm'/ COST CEll PROC,SS • Am:r.;:ATE 2 (:,:CTAU

TEXTURE ETCH (NaOH)

CLEAN IAC ID)

SPIN-ON N+ - p+

DIFFUSE

STRIP OXIDE· PLASMA'

P IMDEP - 2 SIDE

EVAPORATE AR

CEll TEST

TOTALS

MODULE REQUIREMENTS

• LOW MATERIAL COST

~/L /o /o···' $/N

I I I I

I I I I

I I I I

I I I I

I I I I

t I I ,0609

I ~ I j H 1---iCJ I I I

I I I

M L 0 D .0292 .~99 .~99 .0540

Tl-9

LOW COST SILICON SOLAR CELL MODULE

FOR 1985 PRODUCTION

I

$f,'I YIELD cu~.t

TOTl\l

93 .0224

98 .0347

99 .0729

99 .0911

99 • 1139

93 . 1784

99 • 2209

85 .ms

76.8

• AUTOMATION FEASIBL£ MODULE ADD-ON COSTS

• 20 YEAR LIFE EXPECTANCY S(W)

M l .Q_

OPTIONS OPTION I .247 .0101 • OIOI

t. GLASS SUPERSTRATE - PORCELAINIZED OPTION 2 .~9 . 0219 .0219 STEEL SUBSTRATE - HERMETIC

2 GLASS SUP~RSTRATE - PORCELAINIZED

S1£EL SUBSTRATE - PLASTIC SEALED

Tl-10 Tl-11

III-52

.Q_Ef: TOTAL

.0048 . 272

.0226 .1354

£¥PLOND VIEW OF P/IOPOSED LSSA MO!JULE

Tl-12

S:OJA!i' t"Etl A.VPAY (N'flM' IJ •:Jo)

. HJCKFRAM£

CIIOSS SECllON OF PROPOSED lSSA A~tJOULE F/J4ME

SllltXW Nt/BB~N SEAL RIM'S (If)

~Bt&a4N

/., .. ··~SSOIARCEU .:::=:.:~~_;,..· .;..;· -;:;,·.;:,-;...·· _.;:;.·~,_-.......;,;~~~. SUBS7RArE ·

~ WITII t:t:w~RJI? ...._ ______ ......,~ ~ff£1i'N

Tl-13

III-53

SOLAR CELL M0DUl£ SUBASSEMBLY

Tl-14

u,oo,,eus••• Ca (Ill Ca 0 .. ''-VAIi

DETAIL OF MODUl£ SUBASSEMBLY ALIGNMENT TECHNIQUE

Tl-15

SOLAR CELL ~·.oouLE YIELDED COST

BASE LINE LOW COST CELL

PROCESS

ALTERNAT[ I

ALTERNAT[ 2

$/W lEXCLUO ING Si SHEET)

HERMETIC MODULE LOW COST MODULE

.5442 . 4076

.6045 .4685

. 5627 .4263

Tl-16

III-54

I. RCA PRESENTATION

ABSTRACT

The RCA presentation on Tuesday, January 18, by B. Williams included designs of solar arrays, descriptions of manufacturing processes, and cost breakdowns.

From the RCA summary for October - December 1976, the following description indicates increased activity in the solar array manufacturing effort.

As part of the presentation background, it is noted that RCA has directed recent effort toward aspects of the inverted Stepanov technique. Experimentation has shown that growth instability is a primary problem. Another problem is the lack of edge definition, i.e., lack of definition of the melt at the die edge. A computer model was used to study the correlation of growth rate with temperature.

Increased activity is taking place in the evaluation of the processes that appear to be most cost effective.

Experiments were conducted with solar cells fabricated by ion implantation and vapor phase epitaxy. Also, measurements of penetration depths of metals from· screen-printed contacts were made, and the formulation of new metallizing ink for screen printing has been explored.

III-55

RCA-1

I I I I I I I

~

RCA-2

III-56

A

t

RCA-3

~ ! II III !! !

Subatrate 1/16 glass sheet 0.19 1/8 glass sheet 0.22 0.005 alum. foil 0.05

Cell Adhesive RTV615/Primer 0.41 0.41 RTV 102 0.10 0.10. 0.10

Window 1/16 glass sheet 0.19 1/8 glass sheet 0.22 0.22 1/4 glass sheet 0.44 1 in. diam. R6 tubing .45 1 in. diam. N51 tubing 2 in. diam. R6 tubing

Assembly Closure Conformal coating + 3-mil metal 0.11 0.11 F.dge seal 0.04 0.06 End caps 0.06

Panel Connector 0.09 0.09 0.18 0.36 0.36

Aluminum Structural 0.10 0.10 0.10 0.15 0.15 Channel

Total 1.15 o. 77 0.94 1.25 1.05

Column Identification:

I - 1/4 glass with conformal coating 4 x 4 ft module II - 1/8 glass window and substrate bonded together 4 x 4 ft module .

III 1-in.-diameter R6 tubing with aluminum for substrate (48 tubes in module) IV - 1/8 glass with conformal coating (4) 2 x 2 ft panels in a 4 x 4 ft module

VI ill

0.05 o.os

0.10 0.10

0.60 1.07

0.06 0.03

0.18 0.13

0.10 0.10

1.09 1.48

V - 1/16 glass window and substrate bonded together into (4) 2 x 2 ft panels in ,1 4 x .'. ft mC\dule VI - 1-in.-diameter NSI tubing with aluminum foll substrate (48 tubes in mod ult•)

VII - 2-in.-diameter R6 tubing with aluminum foil substr:ite (~4 tub1c·~ in ,,,,11,J, l

RCA-4

III-57

RCA-5 RCA-6

RCA-7

III-58

ASSUMPTIONS:

STEP YIELD (S)

99.0

98.0

98.0

4 99.0

98.0

6 98,0

80.0

8 95.0

9 98.0

10 100.0

11 100.0

67.3

ASSUMPTIONS:

STEP YIELD (I)

99.0

2 95,0

3 99.0

4 95.0

5 99.0

6 99.0

7 98.0

8 98.0

9 80,0

10 95,0

11 98.0

12 100.0

13 100.0

62.0

• A w I It A N E It V H E E

A l s L E

0 H N u 0 s u I s N E G

.

SOLAR CELL ASS'Y PRODUCTION AREA

ASS'Y AltEA 161151 } MULTIPLE LINES WAREHOUSE ll DEVELOP£ IN THE INVENTOflY 16 x ll VERTICAL Dlltf;CTION

RCA-8

ION IMPLANTATION

0.717 WATTS PER SOLAR CELL AND $0.00 FOR 7.8 CM (l") DIAKTEA WAFER PROCESS MAT'L. EXP. LABOR INT.+ TOTALS INVEST

+0.H. DEPR.

SYSTEM "Z" WAFER CLEANING (8) 0.0 0.001 0.001 0.000 0.003 0.001

I ON IMPLANTATION :2 S IOES (B) 0.0 0.015 0.020 0.034 0.070 0.150

DIFFUSION (B) 0.0 0.002 0.011 0.004 0.017 0.012

POST DIFFUSION INSPECTION (B) 0.0 0.000 0.007 0.008 0.015 0.033

-:'!'!CK AG folETAL-BACK:AUTO (B) 0.029 0.005 0.010 0.007 0.051 0.030

THICK AG METAL-FRONT :AUTO (B) 0.030 0.012 0.021 0.013 0.077 0.057

TEST (B) 0.0 0.000 0.008 0.010 0.018 0.042

AR COATINGS :SPIN-ON (B) 0.015 0.001 0.019 0.005 0.038 0.018

INTERCONNECT:GAP WELDING (B) 0.002 0.002 0.008 0.005 0.016 0.019

DOUBLE GLASS PANEL ASSEMSL Y (B) 0.081 0.002 0.003 0.003 0.089 0.014

ARRAY MODULE PACKAGING (A) 0.007 0.0 0.001 0.000 0.009 0.000

TOTALS 0.165 0.040 0.109 0.089 0.403 0.376

40.77 10.03 27.24 21.95

RCA-9

0.717 WATTS PER SOLAR CELL AND S0.0 FOR 7 ,8 CM (3"} DIAM(TER WAFER

PROCESS MAT'l. EXP. LABOR INT.+ TOTALS INVEST + 0.H. DEPR.

SYSTEM "Z" WAFER CLEANING (8) 0.0 0.002 0.001 0.000 0.003 0.001

SPIN-ON SOURCE: 1 SIDE (B) 0.007 0.000 0.015 0.005 0.026 0.018

POCl3 DEPOSITION g DIFFUSION (A) o.o 0.029 0.040 0.008 0.076 0.033

EDGE POLISH IB) 0.0 0.021 0.003 0.001 0.025 0.005

GLASS REMOVAL (B) 0.0 0.001 0.003 0.001 0.005 0.005

POST DIFFUSION INSPECTION (B} o.o 0.000 0.007 0.008 0.015 0.033

THICK AG !UAL-FRONT :AUTO (8) 0.031 0.012 0.021 0.013 0.077 0.057

TIUCIC AG HETAL-BACK:AUTO (B) 0.029 0.005 0.010 0.007 0.051 0.030

TEST (B) 0.0 0.000 0.008 0.010 0.018 0.042

AR COATING:SPIN-ON (B) 0.015 0.001 0.019 0.005 0.038 0.018

INTERCONNECT :GAP WELDING (8) 0.002 0.002 0,008 0.005 0.016 0.019

DOUBLE GLASS PANEL ASSEMBLY (8) 0.081 0.002 0.003 0.003 0.089 0.014

ARRAY l«>DULE PACKAGING (A) 0.007 0.0 0.001 0.000 0.009 0.000

TOTALS 0.172 0.075 0.139 0.064 0.449 0.274

' 38.23 16.64 30.89 14 .23

RCA-10

III-59

T 0 It y

ION IMPLANTATION (C)

ASSUHPT !OllS: 0.717 WATTS PER SOLAR CELL AND $0.0 FOR 7.8 CH (3~) DIAMETER WAFER

STEP YIELD PROCESS MAT'L. EXP. LABOR INT.+ TOTALS INVEST (~) +O.H. DEPR,

99 .0 SYSTEM "Z" WAFER CLEANING (B) 0.0 0.001 0.001 0.000 0.003 0.002

2 99.0 ION !MPLANTATIO!i:2 SIDES (CJ 0.0 0.006 o.oos 0.023 0.034 0.098

99.0 OIFF'USION (C) 0.0 0.002 0.004 0.003 0.009 0,010

99.0 l'C'ST 01 FFUS ION INSPECTION lOS ( C) 0.0 0.000 .0.000 0.000 0.001 0.003

99.0 THICK r..:; MU;.;.-6.\CK:AUTO (C) 0.025 0.004 0.004 0.008 0.041 0,037

99 .0 THICK AG METAL-FRONT:AUTO (C) 0,025 0.009 0.010 0.016 0.060 0.069

90,0 TEST (C) 0.0 0.000 0.004 0.008 0.012 0.035

B 98.0 AR COA Tl NGS; SP I tl-ON (C) 0.016 0.001 0.010 0.006 0.033 0.026

98.0 INTERCONNECT :GAP WELDING (BJ 0.002 0.002 0.008 0.005 0.016 0.019

10 100.0 DOUBLE GLASS PANEL ASSEMBLY (B) 0.081 0.002 0.003 0.003 0.089 0.014

11 100.0 ARRAY MODULE PACKAGING I •I 0.007 0.0 0.001 0.000 0.009 0.000

81.4 TOTALS 0.156 0.027 0.052 0.074 0.309 0.313

50,68 8.71 16.67 24.00

RCA-11

SCREEN PRINT 2 SIDES (C)

ASSUMPTIONS: o. 717 WATTS PER SOLAR CELL ANO so.a FOR 7 .8 CM (3") DIAMETER WAFER

STEP YIELD PROCESS MAT'L. EXP. LABOR INT.+ TOTALS INVEST (S) tO.H. OEPR.

99,0 SYSTEM "Z" WAFER CLEANING (B) 0.0 0.001 0.001 0.000 0.003 0.002

2 99.0 SCREEN PRINT SOURCE:2 SIDES (C) 0.011 0.006 0.009 0.010 0.035 0.040

99·.0 DIFFUSION (C) 0.0 0.002 0.004 0.003 0.009 0.010

99.0 GLASS REMOVAL (Bl 0.0 0.001 0.001 0.000 0.003 0.003

99.0 POST DIFFUSION INSPECTION 10: (Cl 0.0 0.000 0.000 0.000 0.001 0.003

6 99.0 THICK AG HETAL-BACK:AUTO (Cl 0.025 0.004 0.004 0.008 0.041 0.037

99.0 TH IC K AG MET AL -FRONT :AUTO (Cl 0.025 0.009 0.010 0.016 0.060 0.069

8 90.0 TEST (C) 0.0 ·o.ooo 0.004 0.008 0.012 0.035

9 98.0 AR COAT ING: SPIil-ON (C) 0.016 0.001 0.010 0.006 0.033 0.026

10 98.0 INTERCONNECT:GAP WELDING (B) 0.002 0.002 0.008 0.005 0.016 0.019

11 100.0 DOUBLE GLASS PANEL ASSEMBLY (B) 0.081 0.002 0.003 0.003 0.089 0.014

12 100.0 ARRAY MODULE PACKAGING (A) 0.007 0.0 0.001 0.000 0.009 0.000

80.6 TOTALS 0.167 0.028 0.057 0.061 0.313 0.258

53.41 8.92 18.12 19.50

RCA-12 ARRAY HOOOLE MHUFACTURING COST

$/WATT 3" WAFERS

ION SPIN-ON + SCREEN PRINT IHPLANT(C) POC13(C) 2 SIDES(C)

JUNCTION FORMATl<Jt 4. 7 8.1 5.1

METALLIZATION 10.1 10.2 10.1

AR COATING 3.3 3.3 3.3

TEST AND SORT 1.2 1.2 1.2

INTERCONNECT• ENCAPSULA Tl ON & PACKAGING ....!l:i ...!L.! ...!Ll..

30 .9 34.3 31.3

RCA-13

III-60

3 ..... ~

20( c,..m) 15

10

200

(µ.m) 170

140

17

0/o 15

13

OPTIMUM FINE GRID THICKNESS

FRACTIONAL #IW

PENALTY (H,d

CENTS

2;,? ~ [ 1.0-------------

0.10

0.05

0

)(

-0.05

0.5 1.0 2.0 ltw

RCA-14

$/W PENALTY DUE TO FRONT CONTACT RELATIVE TO 3

11 (7.6cm) $1/W CELL

X

~x

2 3 4 5 6 7

CELL SIZE (in)

RCA-15

III-61

ARRAY MODULE MANUFACTURING COST lOH lKPLANTATION (C) BEST CASE

MATERIALS & EXPENSE

LABOR OVERHEAD INTEREST DEPREClATlON

3"

0,183

0.126

0,309$/W

RCA-16

s· 0.261

0.045

0.306$/W

III-62

ARRAY KODULE MANUFACTURlflG COST JON IMPLANTATION (C) DETAILED _ESTIMATE

3" WAFERS 5" WAFERS

JUNCTION FORKATlON 0.046 0.039

METALLIZATION 0.101 0.173

AR COATING 0.033 0.025

TEST & SORT 0.012 0.004

INTERCONNECT ENCAPSULATION & PACKAGING _QdJ.! __Q,J9!

0.309$/W 0.349$/W

RCA-17

J. MOTOROLA PRESENTATION

ABSTRACT

Motorola's approach to the topic of "Solar Cell and Array Manufacturing Processes" began by identifying possible processing steps (see following pages). The presentation, by M. Coleman, covered costing methodology in detail, and a complete cost summary was presented.

Conclusions reached:

1. No conceptually new technologies need formulation, but specific process development is needed.

2. Projections are extremely optimistic for goals.

One pertinent aspect of a Motorola low-cost design analysis is shown in the following paragraph from the most recent quarterly report.

Correlations of the presentation with the summaries for October 1, 1976 to December 31, 1976, accent the points that Motorola is performing further technical evaluations of proceses and processing sequences, solar cell fabrication and encapsulation, and analysis of processing costs. Experiments point toward a patterned back metal to increase solar cell efficiency. Plasma processing has been evaluated.

In one study, a unitless parameter called the Purification Figure of Merit was developed. Major progress was made in the following areas:

1. Conical quartz and Mullite flanges with Teflon seals.

2. SiFz polymer transport process.

3. SiFz and SiF4 concentrations at various temperatures and pressures.

4. Spark source mass spectroscopy (SSMS).

A study for Task 2, progress was made in the Ribbon-to-Ribbon (RTR) approach to silicon ribbon growth.

Details of progress in all areas are available in the periodic reports.

111-63

MOTOROLA'S APPROACH

1. IDENTIFY POSSIBLE PROCESSING STEPS

2. EVALUATE TECHNICAL WORTH OF INDIVIDUAL PROCESSl~G STEPS

3. FOLLOW I NG QUALi TA Tl VE COST ANALYSES, SELECT TECHNICALLY DESIRABLE PROCESS SEQUEHCES

4 . PE RF ORM DETAILED COST ANAL VS IS OF INDIVIDUAL PROCESSES AND PROCESS SEQUENCES

5. CHOOSE FINAL PROCESS SEQUENCE

MOT0-1

IECHNICALLY FAVOR~BIE AUXILIARY PROCESSES

U.-PROCESS CLEANING OR ETCHING: WET CHEMICAL TEXTURE-ETCH I NG BRUSHING GAS STREAM DRYING GRAVITY (CENTRIFUGE> DRYING PLASMA

ANNEAL! NG SOURCES: RESISTANCE FURNACE RADIANT HEATING <LOU TEMPERATURE>

MOT0-3

COSTING METHODOLOGY

3, ASSUMPTIONS

A, FACTORY PRODUCES mlE PRODUCT FOR LESS THAN TEN CUSTOMERS AT RATE OF 500 MEGAWATTS/YEAR

B, BASE COATS REFLECT TODAY'S TECHNOLOGY FOR LEVEL OF AUTOMI\TIOIL THROUGHPUT, MATURITY OF PROCESS, ETC.

C. DEF11'4ED OVERHEAD ATTENDANT TO SUPPORT REQUIRED FOR ASSUMED DEDICATED FACTORY

MOT0-5

JECHtllCALLY FAVORABI E

MAJOR PROCESSES

STARTING MATERIAL: SAWED AND ETCHED TEXTURE ETCHED

JUNCTION FORMATION: DIFFUSIOH I ON I MPLA:iT AT ION

iUALLIZATION: PLATING PRINTING SOLDER COA Tl NG

ANTIREFLECTION COATING: VACUUM DEPOSITION CHEM I CAL VAPOR DEPOSIT JON

PATTERNING: PHOTOL I THOGRAPHY ION IMPLMTATIOi~ SHADOW MASKING

I NTE RCONNE CT I ON : SOLDER REFLOW

MOT0-2

COSTING METHODOLOGY

1. CONFORMED TO FORM.'H PRESENTED BY JPL CONSISTHIG OF CATEGORIES FOR:

A. MATERIAL 8. EXPENSE C, LABOR D. OVERHEAD E. INTEREST F. DEPRECIATION

2. REQUIRED DETERMINATION OF EQUIPMENT AND FACILITIES FOR EACH PROCESS •

MOT0-4

CDSJJHG MEJHCDQIPGY

q I GENERAL INPUTS A, SILICON STARTING MATERIAL COSTS II SO 8, AVERAGE CELL EFFICIENCY 11 15% C, LABOR RATES FOR EACH LABOR CATEGORY D, DEPRECIATION IS STRAIGHT LIHE

1,) 7 YEARS FOR EQUIPMENT 2,) 40 YEARS FOR BUILDINGS AND FACILITIES

E, BALANCED LINE OPERATION FOR THREE SHIFTS: 22,5 HOURS/DAY, 240 DAYS/YEAR

F, ELECTRICITY COST= 2.5¢/KWH G. COSTS FOR CHEMICALS, 0.1. WATER, WASTE TREATMENT, FACILITY

CONSTRUCTION, GLASSWARE, CONSUMED PARTS, ETC.

MOT0-6

III-64

COSTING METHODOLOGY

5. ALLOCATIONS:

A. AVERAGE BASE LEVEL OF BUILDIHG ELECTRICAL SERVICES (LIGHTING, HVAC> TO OVERHEAD

B. IDENTIFIABLE ELECTRICAL CONSUMPTION FROi"l PROCESS (EQUIPMENT POWER: HVAC FOR POWER DISSIPATION, EXHAUST AND MAKE-UP, PERSONNEL HEATING: ETC.) TO EXPENSE

C. ALL SUPPORT FUNCTIONS NOT IDENTIFIED AS MATERII\L, EXPENSE, LABOR, INTEREST, OR DEPRECIATION TO OVERHEAD

1. SOME ITEMS CE , G" PURCHASING, MA I NTENANCL QUALi TY ASSURANCE, CAFETERIAS, ETC.) ALLOCATED BY LABOR BASE

2, OTHER ITEMS (E,G,, TAXES. rnsURAHCL JANITORIAL PLANT ENG I NEER I NG, ETC,> ALLOCATED BY FLOOR SPACE

MOT0-7

LEARNING CURVE PROJECTIONS

1. ASSUME CUMULATIVE PRODUCTION TO DATE IS NEAR 800 KW

2, IF 500 MEGAWATT PLANT HI 1985 CERDA GOAU THEN APPROXIMATELY TEN LEARNING CURVE INCREMENTS BY 1985 <DOUBLE PRODUCTION EACH YEAR>

3. A 5% LEARtHNG CURVE REDUCES COSTS TO 60% OF TODAY'S COSTS~

4. A 25% LEARNIHG CURVE <LESS THA~ TOTAL SEMICO;-tQUCTOR limUSTRY TO DATE) REDUCES CJSTS TO 6% OF TODAY'S COSTS

•NOT COMPLETELY APPLICABLE TO COST SUMf'iARIES, SINCE SOME ECONOMY OF SCALE ASSUMED IN THOSE SU~V'1ARIES

MOT0-9

INTANGIBI ES

1. RELIABILITY EFFECTS ON COSTS

2. TODAY'S MATURITY OF PROCESSES

3. UNFORESEEN TECHNOLOGY BREAKTHROUGH

4. EFFECTS OF ARTIFICIALLY ACCELERATED R & D SPENDING < GOVERNMENT SUPPORT>

MOT0-11

LlI11I.lliG COST FACTORS.

1. IF AUTOMATED PROCESS, LABOR COST PER WATT APPROACHES ZERO

2, IF HIGH THROUGHPUT EQUIPMENT. INTEREST AND DEPRECIATIO:~ COSTS PER WATT APPROACH ZERO

3. ULTIMATE LIMITING FACTORS ARE CONSUMED MATERIALS AND EXPENSE ITEMS

MOT0-8

PROCESS AREAS REQUIRING FURTHER DEVEi OPMENJ

1. PLASMA ETCH I NG AND CLEArrn~G

2. ION IMPLANTATIQ;i

3. PRIIITED METALLiZATI011

4. PLATED MET ALLI ZAT ION

5. SPRAY-ON TECHNOLOGY

MOT0-10

e.ROCESS srnurncEs

WILL CONTAIN:

l. BRUSHING 2. CENTRIFUGE DRYING 3. TEXTURE ETCHING 4. ION IMPLANTATION 5. ANTIREFLECTION COATING 6. EITHER PRINTED OR PLATED METALLIZATION 7. SOLDER REFLOW INTERCONNECTION 8. GLASS COVERED ENCAPSULATION <WITH RELIABILITY

DETERMHH NG BACKING REQUIREMENT>

MOT0-12

CONCLUSIONS

1. NO CONCEPTUALLY NEW TECHNOLOGIES NEED FORMULATI 0~ BUT SPECIFIC PROCESS DEVELOPMENT NEEDED

2, PROJECTIONS ARE EXTREMELY OPTIMISTIC FOR GOALS

MOT0-13

III-65

t'lill(t:-:, STEP

1. BRUSHING o.o .0073

2, PLASHA 0.0 .0131 (DI EL~CTRIC

ETCH

3. STANDARD o.o .0041 SOLUTIONS

4, CENTRIFUGE 0.0 .0014 DRYING

5, SILICON 0.0 .0124 pcHING

ONE SIDE)

6. SILICON o.o ,0161 tTCHING

TWO SIDES)

7, TEXTURE 0.0 .0097 ETCH

8, EOOE J 0.0 .0209 GRINDING

9, ~HOTO-RESI 0.0 .0107 APPLY-

EXPOSE-DEV,

PROCESS STEP

10, PHOTO-R,SIST 0.0 .0213 (REMOVE

11, PLASMA) (P,R o.o .0009 REMOVE

12, DIELECTRIC o.o .0044 ETCH (WET)

13, tTCH SJOP 0.0 .0091 APPLY

14, SPIN-ON 0.0 .0154 15, SPRAY-ON 0.0 .0152

16, fRIVE-IN o.o .0099 DIFFUSION)

17, SILICON 0.0 .0173 fOURCE

SOLID)

18. GAS o.o .0174 DEPOSITION AND DIFFUSION

19, yoPE~ OXIDE o.o .0174 CVD

COST Sll'\MARY

TODAY'S TECHNOLOGY

~t-~ o~,..,,~~ .0134 .0066

.0084 .0050

.0061 .0042

.0042 .0035

.0243 .0102

.02113 .0102

.0243 .0102

.0269 .om

.0403 ,0159

MOT0-14

C.OSI S.ltlMAR'i TODAY'S TECHNOLOGY

.0061 .0042

.0084 .0049

.0081 .0047

.0067 .0044

.0067 .0044

.0034 .0032

.0102 .0057

.0407 .0161

.0102 .0057

.0102 .0057

MOT0-15

III-66

,0023

.0064

.0006

.0003

.0012

.0012

.0012

.0046

.0073

.0006

.0004

.0004

.0023

.0023

.0011

.0026

.0053

.0026

.0026

.0031 .0327 99.5

.0096 .0425 99.8

.0005 .0155 99.8

.0002 .0096 99.8

.0012 .0493 99.5

.0012 .0530 99.5

.0011 .0465 99.6

.0061 .0698 ?

.0097 .0839 99.4

.0006 .0328 99.7

.0003 .0149 99.9

.0004 .0180 99.6

.0031 .0256 99.8

.0031 .0319

.0014 .0243

.0032 .0316 99.5

.0065 .0859 98.0

.0032 .0391 99.0

.0032 .0391 ~:LO

COST S1R'1MARY. TODAY'S l[.CliMO!-QG.Y

~"' "'~~e, '\;"' ,'I' ' ~"'""'

4.'-'<;

<c,4 ~<c, c,? ,t-~ ~~ ~<c,<f- L<,;

ri-nnss STEP <c,~----() 40 _q _____

?O. ION IMPLANT 0.0 .0097 .0746 .0357 .11106 ,2029 .4635 98.0

21. fON IMPLAr 0.0 .0014 .0022 .0030 .0067 .0101 .0234 99.5 ADVANCED

22. VACUUM .0024 .0490 .0318 ,Qlll6 .0236 .0326 .1540 99.0 MPALAIZAT 10

U, L

23. THICK FILM AG FRONT

.0457 · .0040 .0060 .• 0040 .0011 .0016 .0624 99.8

24. THICK FILM AG BACK

.1988 .0040 .0060 .OOl!O .0011 .0016 .2155 99.8

25. ELECTROLESS .0305 .0256 .0145 .0089 .0011 .0012 .0818 99.6 PLATING

26. ELECTROLYTIC .0305 .0256 .0145 .0089 .OOll .0012 .0818 99.6 PLATING

27, SOLDER .0223 .0002 .OOlll .0025 .0002 .0003 .0269 99.8 COATING

28, SILICON NITRIDE (cvD

0.0 .0098 .0102 .0057 .0026 .0032 .0315 99.8

29, OXIDE 0.0 .00~9 .0051 .0039 .0013 .0016 .0168 99.8 GROWTH

MOT0-16

COST S llfflARY TODAY Is TE.C..liH.llL!lCY

<.r_,'\;~ .i,"\

~c,":. PH0lE$S STEP ~()~

~--30, SPIN-ON o.o .0079 .0067 .0044 .0023 .0031 .0244 97.0 31. EVAPORATE .0019 .0022 .0318 .0146 .0236 .0326 .1067 99.0 32, ADD SOLDER .0014 .0001 .0007 .0022 .0001 .0001 .0046 99.8 33. REFLOW 0.0 .0001 .0170 .0032 .0008 .OOll .0222 99.8

SOLDER

3LI , CONDUC Tl VE .0045 .0002 .0060 .0040 .0011 .0016 .0174 99.5 ADHESIVES

35, GLASS SUPERSTRATE .1817 .0004 .0006 .0027 .0012 .0010 .1876 99.4

36, GLASS WITH .3Ll48 .0004 .0006 .0027 .0013 .0011 .3509 99.0 SUBSTRATE

37. ELECT,ICAL 0.0 .0001 .0085 .OOLl8 .0008 .0012 .0154 99.8 TEST CELLS

38. ELECTRICAL 0.0 .0000 .0003 .0021 .0001 .0001 .0026 99.8 TEST

MODULES)

MOT0-17

III-67

I1f1Tft fl: F·Ei=t[1 FF'Dt1 FILE l'IIISTEO !'11.1.\J 11 X ll'MI II lllllll Sllll:S l'XCl.ltlll'lC: 1·11n:r.•:1•11;

F·F'D :: 111:.:1:F--1r1:u11 11HT E:P L~l: DVF' llll DEF' TOT YIEL[1

1 1-F'U:SHING • 0 1.3 .~ • 3 3. 3 ·:1·;0.'5 2 6 STANDARD S'DLN~. .o .4 .,; .4 ,1 .t 1,5 ·:1·:1.:3 3 14 TEZTLIF'I:E ttA-OH .o 1 .o 2.-1 1. 0 ,I .l 4,,.; ·~~.~ 4 :~ 1:EflTF'IFIJGE ,I) .t .4 .;: .o ,1) I ,(I ·~·~ .:;; s 28 IDII IMP AitVftNC'ED .o .I -~ . ~ 1.0 2.3 ·.4·:-f.45 ,; 2:3 IDII IMP AI•VANCED .o .I . .:: .;: l.O 2.3 ":''1.5

.:;r) Itf;'IVE-IN DIFFIJStl .o 1 ,(I 1.1) ,,; ,3 .3 3,2 ':'':1,5 "' ~:t,:. THICr FILM AG FR 4.6 .4 .o .4 ,I .2 6,2 ':J':1.8 9 .:,, THIC'I< FILM AG BA 19.9 .4 .,; .4 .I .2 21.5 -;.·?.=:c

10 45 -:ILlfDN tll TRIDE .o 1.0 1.0 . .; .3 .3 3. l '?":".!3 11 4;' ~DLDEF' CDATHIG 2.2 .o ,I .z .(1 .o :, ~ ····;:,.:;e 12 t;.1) El.EC • TE·: T CELLS .o .(I .8 .'5 .I .l 1.5 ·~?.:3

I11'1Tft AFTEP HI( TOF'lr!G BY YIELD!.

F'FD :: l•f :,:p lf'T I Ott MAT E>:P Lftl< O'v'F' lltT DEP TOT '1'IEl[1

tP1.1:Hllt1; .o ., I .4 .2 • 3 "·4 .... ;.. .~·. 2 '=' : TAIIDflF'I1 :au1;. .o .-1 .to ,4 .1 .t l.,;, ···=· .:;:

14 TE::TI.IF'IZE ltft-DH .o 1.•) • ~ .'3 1.1 .1 .t .,.·;e ·•·;4.,: . 4 :ae (EIITR I FUGE .o .I .4 .4 .... ,l) l.(1 .,,: .. _:;: s ;:::,al Jail IMF· AD\l~NCED .o .l -~ .:< 1.0 ~:.4 ,·,·~. ~~ 6 23 1011 111P AI•VAttCED .o .l . .:· . ) 1.(1 2.4 -~-~. ';i 7 20 l•F'IVE-111 DIFFLISN .o l,1! I .O ·"' . ~ . ~ ;; .,~ ·l·:..~ • 8 36 THIO FILM AG Ff; 4.6 ,4 .~. .4 ., .2 '=·. ~= ·:a·:•.::: ·:1 3~ Tltl(I F ILl1 A1:; l<A zo.o .4 -~ • t .1 :, 21.i' •:.·:·• .:?

1(1 4:5 :111u111 1111F'111E .o 1.11 ,.,, • $ . ~ -:c •• ~ ·:,·:.. . ::~ 11 4,:, :111.1,r:.i:· t.DHT ltlG i.~· .fl ,I .. -, .1) ·'·' .. ·:···· -·~ 12 t,o EI.E(. IE: 1 CELL$ .(1 .o . ~ ., .l t.:, -~·-~. ::·

TOTAL: -:'~.9 5.4 ~ ~ .. 5.:~ 2.i' '$.:' 5.i.a ·:•.:.;:

·•·:-1 • .; 10.11 l7 .:3 l oJ .·~ 4.':'I 6.:· 1,01,i1

MOT0-18 DATA AS F·EAD FF'OM FILE INTERCONNECT & PACKAC:INC:

PRO u DESCRIPTlCli MAT E>:P LAll DVR ltlT DEP TOT YIELD

1 so H[ID SDLDEP .1 .o ,I .2 .o .o .5 99.8 2 SI i;·EFLOIJ SOLDER .o .o 1.7 .3 .l .l 2.2 ':19,8 3 ":,7 GLASS I.JITH SUBST 34,'5 .o .1 •. 3 ,1 ,1 3'3.1 ":'·~.o 4 61 ELEC TE.ST MODULE .o .o .o ,2 .o .o .3 99.8

DATA AFTER FAr.TDPING BY 'l'IEL!IS

FPO,:: I•E~CRIPTIDN MAT EXP LA[( OVP INT IIEP TOT YIELD

I '50 flDD :OL:DEP .1 .o ., .z .o .o .'5 9·;0,:~ ,: 51 F·EFLDIJ !OLDER .o .c, l .7 .3 ., .t 2,3 -=-~.$ 3 57 GLA~S IJITH SIJBST )4.9 .(1 .1 .3 .I .l 3'5 .'5 ·:1·:1.0 4 61 ELEC TEST MODULE ;o .o • 0 .2 ,Q .o • 3 ·=•-:•.::;

TUIAU J5 ,I) .1 1.·~ I.I) .2 . ,;~ ~:~ .5 ·,:: .4

·:-1.0 ,2 .a.·;"' e.~ • .=.1 .,;, 11111,ll

MOT0-19 DATA AS PEAD FPDl'I FILE 1'1.All'II MEI,\!. II !1'11111Fll 1111111 ~1 111 ~ I ~II 11111 '11' l'\I 1:,v: l'J•:

PRO u !IESCRIPTIDU MAT E>'.P LAB OYR HIT DEP TDT YIELD

BF'IJZHING • I) I .. : .i:! 3. ;: '•I:' • ~~ 2 ,.; ~TAIIDAPD ZDLIF. ,ll ,4 ,'> ... .1 .1 1.'5 ·;,-:. ,::1 3 l .. TE>:TUPIZE f!A-CH .o 1,0 2.-1 1.0 ,1 ,1 4,.; •;,·;,.,.,. ., :3 t:EttTPIFUt-E .o .1 .4 • 3 .o .o 1.(1 ·;,9,.;i 5 45 : ILICOII Ill TF'1I1E .o 1.0 l .u . .; .l • 3 3. l -;i,;..8 I:, 15 F·F' APPLY .o 1.1 4,0 t .6 .7 t. 0 :3,4 ·:1·:1.~

' :-z Dll::LE( ElCU•I.JEf.' .o .4 .a ., .( .u 1.8 ~~.,:. 8 lo:- PF' PEt1DYE .o ~-1 .b .4 .l .I 3.3 ~·~.; ':I .:!8 1Dtt IMF' ADVANCED .o .1 .i! .:3 .7 t.O 2 •. 3 99.'5

10 28 1Dli IMF' ADVANCEIJ .o .1 .i! .·3 1.0 2.'3 ':l':1,'5 11 i!O I.IPI\IE-rn DIFFUHI .o t.0 LO .... .·3 • 3 '3,2 ':1':l,'5 12 40 ELECTPCLESS PLTN :).0 2.6 1.4 .·~ ., .1 ::1.2 n.,.; 13 43 :ULllEP CCATING i!.2 .o .1 .a .o .o 2.7 ,;.·:i.a 14 60 ELEC. ,en CELL~ .o .o .a .'5 .1 .1 1.~ ~·=-.s DATA AFTEP FACTOPING l<Y YIELDS

F'PO u DESCPIFTION MAT EXP LAB OYR INT DEP TOT YIELD

EPIJ:HING , IJ .:3 1.4 .. ,,: • 3 3.4 ":'':4.-S 2 b :TAIIDAPD :DLIF. .o .4 .b .4 .1 .1 I.e. ':'':I ,:3 3 14 TE>:TURIZE IIA-CH • (1 I.ti a.s 1.1 .1 ,1 4.':-1 ·:1·:.,.,, .. 8 1:EIITPIFI.IGE .o • 1 ... .4 .o • (1 I, (1 9·:f.:?, 5 4'5 : ILIC Ott IIITPU•E .o I.CJ I.I .,.; •. 3 • 3 3. ~ -;,·;..:,: ,.; 1'5 pp APPLY .,) I.I 4.i! 1.6 .a 1.0 8.;- :'·~ .~i ( ;92 DIELEC ETCH•i.JET\ .o .5 .e .5 .o . •) l.':1 ~·:' .t; . 8 16 pp f;'El'IDVE .... 2.2 • 6 .4 .1 .1 3 .•t :t·;•,1 ... ':I 28 llltl IMF AJIVANCED .o .1 .2 .3 1.0 2.4 ':l':',5

10 28 IDtl It1F ADVANCED .o .1 .i! . ~: 1.1,1 1? •• 1 ':l':l,"S II ~o 111,· 1 VE- Ill DIFFIJSN .o 1.0 1.11 ··-=· .:: ... ~.2 ·;l·;I.';', 12 -10 ELEC. TF'DI.E! S PLTN 3, I c,.; 1.'5 .·~ .1 ,I :L.a: =-~-~ 13 .. 3 snlflEP COATING 2,2 .o .l .3 .o • 1) 2.7 99.a 14 60 El.EC. TEH CELLS .o .o .9 -~ .1 .1 l ,5 '?'?.8

rainLS 5,3 l l, 0 15,;' e.s 3.4 4 ,t;. 4E: .,~ ....... 1

10.9 22.7 3?..2 17 • .; ;".I ;..~. 1(11).11

MOT0-20

III-68

K. UNIFORM COSTING PRESENTATION

ABSTRACT

The subject of uniform costing methodology for manufacturing processes was discussed by R. Chamberlain in a scheduled presentation Tuesday. The SAMICS concept (Solar Array Manufacturing Industry Costing Star\dards) was reviewed, and components of the costing standards were listed and discussed.

The directed summary of the subject is that "the fundamental input to the uniform costing methodology is a description of the economic characteristics of each manufacturing process". A standard format for expressing that information has been developed. The use of that format is explained and illustrated here.

III-69

UNIFORM COSTING METHODOLOGY FOR MANUFACTURING PROCESSES$

SOLAR ARRAY MANUFACTURING INDUSTRY COSTING STANDARDS

• LSSA IS DEVELOPING A MEfHODOLOGY TO STANDARDIZE

ASSUMPTIONS AND M£fHODS FOR ESTIMATING COSTS I

PRICES

• A PRELIMINARY VERSION OF THIS METHODOLOGY, SAMICS,

IS NOW READY AND WILL BE ITERATED OVER THE NEXT

FEW MONTHS

RC-1

COMPONENTS OF THE COSTING STANDARDS

• STANDARD FORMAT FOR DESCRIBING PROCESSESS

• NOW IN FINAL FORM, BARRING MINOR REVISIONS

• DETAILED EXPLANATION IN HAND OUT AND IN PROCEEDINGS

RC-2

COMPONENTS OF THE COSTING STANDARDS

• STANDARD FORMAT FOR DES CR I BING PROCESSESS

• NOW IN FINAL FORM, BARRING MINOR REVISIONS • STANDARD FORMAT FOR DESCRIBING PROCESSESS

• NOW IN FINAL FORM, BARRING MINOR REVISIONS


• STANDARDIZED DATA

• NOW RUDIMENTARY: AWAITING FEEDBACK

• INDEPENDENT ACTIVITY TO BE CONDUCTED

RC-3


• STANDARDIZED DATA

• NOW RUDIMENTARY: AWAITING FEEDBACK

• INDEPENDENT ACTIVITY TO BE CONDUCTED

• STANDARDIZED ALGORITHMS

• WORKBOOK READY TO BE TRIED

• COMPUTER PROGRAM ( NOT ESSENTIAL TO USE OF METHOD)

- SCHEDULED FOR SEPTEMBER 1977

RC-4

III-70

L. PROJECT PRICE GOAL

ABSTRACT

In a Project cost summary, H. Ma~omer presented the allocations for non-ingot and ingot technologies. Elements of the Project price goal were discussed, and the allocation structure was shown graphically.

In comparing the allocations charts for non-ingot and ingot technology, similarities in improvement exist except for materials; sheet for non-ingot and crystal for ingot.

Dramatic improvements are projected in ingot technology for crystal growth and slicing (Task 2) and for cell fabrication and module assembly (Task 4).

III-71


PROJECT PRICE GOAL

• EXPRESSED IN CONSTANT 1975 DOLLARS (ADJUSTED BY GNP DEFLATOR FROM DEPT. OF COMMERCE) PER PEAK WAIT !UNDER DEFINED CONDITIONS!

• PACKAGED MODULES ON MANUFACTURER'S LOADING DOCK

• AMOUNT THAT WOULD BE PAID BY PURCHASER OF LARGE QUANTITIES

• IF MANUFACTURER'S PROFIT WERE THAT IMPLIED BY A SPECIFIED RATE OF RETURN ON EQUITY

• THUS, PRICE ENCOMPASSES

• .DIRECT EXPENSES (INCL. EQUIPMENT DEPRECIATION, MATERIAL RECYCLING, BYPRODUCT I NCOMEl

• INDIRECT EXPENSES I NEEDED TO OPERATE THE FACI LITIESl

• OVERHEAD EXPENSES I INCL. PROFIT, TAXES, SALES FORCE, MANAGEMENT, FACILITIES DEPRECIATION)

HLM-1 ALLOCATION STRUCTURE

HIGH GRADE POL YS ILICO N: PRICE IN $/KG

CRYSTAL GROWTH AND S VALUE ADDED IN $/M2wA

LI Cl NG:

FER

ENCAPSULATION MATERI PR I CE IN $/M2MODULE

ALS:

CELL FABRICATION & MO (INCLUDING ENCAPSULAT VALUE ADDED IN $/M2MO

DULE ASSEMBLY INGI:

DULE

PROJECT PRICE GOAL IN

HLM-2

III-72

vi 0>--Ju !::::!z >- ~ oU

~ tt ~UJ -, (.!) Oz ~-Cl..~ .. u z< oo.. .:: 0 sz o< ~ >-" -u oZ

i5 :::,-Cl') It Cl') UJ <

-- $/Wpk

- $/Wpk -

- $/Wpk -

- $/Wpk

$/Wpk


ALLOCATIONS - NON-INGOT TECHNOLOGY

1980 1982 1984 1986 TASK 1:

HIGH GRADE POLYSILICON. PRICE IN $/KG 45 25 17 10

TASK 2: SHEET GROWTH AND CUTIING. VALUE ADDED IN $/M2wAFER 130 70 24 10

TASK 3:

ENCA PS ULAT I ~N MATERIALS PRICE IN $/M MODULE 9.1 9.1 9.1 6.0

TASK 4:

CELL FABRICATION & MODULE ASSEMBLY I I NCLUOI NG ENCAPSULATING) VALUE ADDED IN $IM2MODULE 121 69 47 30

PROJECT GOAL IN $/Wpk 4 2 0.5

HLM-3

ALLOCATIONS - INGOT TECHNOLOGY

1976 1978 1980 1982 1984 1986

TASK 1:

HIGH GRADE POLYSILICON PRICE IN $/KG 60 45 25 17 10

TASK 2:

CRYSTAL GROWTH ANf SLICING. VALUE ADDED IN $/M WAFER 260 160 80 35 20

TASK 3:

ENCAPSULATl9N MATERIALS PRICE IN $/M MODULE 9.3 9.3 9.2 9.2 6.0

TASK 4:

CELL FABRICATION & MODULE ASSEMBLY IINCLUOING ENCAPSULATING)

2 VALUE ADDED IN $/M MODULE 259 169 114 61 28

PROJECT GOAL IN $/Wpk 20 7 4 2 0.5

HLM-4

III-73

APPENDIX

AGENDA

LOW-COST SILICON SOLAR ARRAY PROJECT 5TH PROJECT INTEGRATION MEETING

Held at San Diego Hilton Hotel

January 17-18, 1977

Monday, January 17

7:45 am

8: 30 am

8:40 am

10:35 am

1:00 pm

Registration

General Meeting

Introduction

Cost vs. Solar Cell/Array Efficiency Trade-offs Presentations covering the various aspects of system trade-offs

Cost vs Efficiency Presentations & Discussion

Intra-/Inter-Task Sessions

Task 1 (exclude*) Processes to Produce Silicon Cost vs. Efficiency Influences on Task 1

Task 1 (include*) & Task 2** Impurities in Silicon Growth Processes/ Efficiency

Task 2** & Task 4 Influence on Efficiency of Silicon Sheet Characteristics

Task 3 Influence of Encapsulation on Array Efficiency and Encapsulation Progress and Problems

Task 5 Cost vs. Efficiency Comments, Standard Cell Measurements, and 130 kW Performance Requirements

*Contractors for Subtask II, Effects of Impurities **Representative from each Task 2 contractor

A-1

R. Forney

H. Macomber

H. Macomber

R. Lutwack C. Yaws ·

T. Digges A. Yamakawa

G. Cumming

H. Maxwell

E. Sequeira

3: 15 pm

Tasks E & 0, LeRC, MIT/LL, Sandia & DOD Programmatic Interfaces

Tasks 3, 4, 5, E, O, LeRC, MIT/LL, Sandia Present Status of Encapsulant Materials-Battelle Near-Term Encapsulants--Springborn Labs Encapsulant Material Costs

Tuesday, January 18

8: 15 am

8:30 am

8: 4.5 am

9:45 am

10:30 am

11:15 am

11: 55 am

12:05 pm

1:30 pm

General Meeting

Welcome

ERDA Program Status

Solar Cell & Array Manufacturing Processes

Introduction

Texas Instruments

RCA

Motorola

Uniform Costing Methodology for Manufacturing Processes

Project Cost Goal Allocations

Discussion

Intra-/Inter-Task Sessions

Task 1 Review of Contractor Status

Task 2, 4, & 5 Silicon Sheet, Manufacturing Processes, & Influence of Cost/Efficiency

Task 3 Encapsulation Progress & Problems

Tasks E, 0, LeRC, MIT/LL, Sandia & DOD 150 kW Procurement Requirements

A-2

L. Dumas

W. Carroll

H. Maxwell

L. Liebermann

L. Magid

J. Goldsmith

B. Cardajal

B. Williams

M. Coleman

R. Chamberlain D. Bickler

H. Macomber

J. Goldsmith

R. Lutwack

W. Hasbach

H. Maxwell

R. Ross

4:00 pm Highlights and Discussion

Task and Meeting Status Task Managers

5:30 pm ERDA Comments L. Magid

5:40 pm Summary, LSSA Project R. Forney

6:00 pm Meeting Close

A-3 NASA-JPL--caml., LA., Calif.

this work was performed by the jet propulsion laboratory, 5th pim 1... · rca, and ti the...

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