ECO-SOLAR FACTORY: 40% PLUS ECO-EFFICIENCY GAINS IN THE PHOTOVOLTAIC VALUE CHAIN WITH MINIMISED RESOURCE AND ENERGY CONSUMPTION BY CLOSED LOOP SYSTEMS

M.P. Bellmann1, R. Roligheten2, G.S. Park3, J. Denafas4, F. Buchholz5, R. Einhaus6, I. Lombardi7, B. Ehlen8,

K. Wambach9, P. Romero10, A. Bollar11

1SINTEF Materials and Chemistry, Trondheim, Norway; e-mail: Martin.Bellmann@sintef.no

2Steuler Solar Technology AS, Porsgrunn, Norway 3Norsun AS, Oslo, Norway

4UAB Soli Tek R&D, Vilnius, Lithuania 5International Solar Energy Research Center - ISC Konstanz, Konstanz, Germany

6Apollon Solar, Lyon, France 7Garbo Srl, Cerano, Italy

8Boukje.com Consulting BV, EM Bleiswijk, The Netherlands 9bifa Umweltinstitut, Augsburg, Germany

10Aimen Laser Application Centre, Porrino, Spain 11Ingesea Automation SL, Elgoibar, Spain

ABSTRACT: The European H2020-FOF-13-2015 Eco-Solar project, that started in October 2015 envisions to increase resource and energy efficiency over the entire photovoltaic value chain, while simultaneously maximising recycling and remanufacturing possibilities, by introducing design for recovery, repair and reuse, and collaborating for improvements in waste reduction. Reusing materials and reducing the consumption of raw materials will make solar cell panels both cheaper and greener. When fewer resources, including critical materials are needed, the emissions of greenhouse gases from their production will decrease. Likewise, the energy consumed by these processes will be paid off faster than it is today. All this should improve market penetration for European PV producers. The overarching aim is to strengthen European PV companies who are driven by innovation and who are able to secure Europe’s power supply in a sustainable way. The paper presents the methodology followed by Eco-Solar to reach this ambitious goal. Keywords: crystalline silicon solar cells, remanufacturing, repair, reuse, recycling, eco-efficiency analysis, life cycle assessment, life cycle costing, living lab

1 INTRODUCTION

Eco-Solar is a 3 years project, which involves 11

partners from 7 member states and administers the resources in terms of personnel, knowledge and equipment that are required for success. Details can be found on the project website: http://www.ecosolar.eu.com. It is a medium size focused research project carried out in the HORIZON 2020 EU Framework Programme.

Eco-Solar is an ambitious project. It aims to develop concepts to increase the remanufacturing potential, including repair of PV-modules and cells, while simultaneously improving reuse of resources and components and increasing resource efficiency over the whole value chain. The Eco-Solar project strives towards a PV module that has: • High yield of resources per PV-module produced and per kWh -electricity generated by these modules thanks to a more eco-friendly Bill of Materials (BOM). • High potential for repair: if the module is not properly functioning after manufacturing, or declines function during use, repair of the module is the most sustainable and economic viable solution. This includes a strong argument for implementation of module monitoring systems during operation • High remanufacturing potential, that allows for the extraction of useful components from obsolete, malfunctioning and "end-of-life" modules, to reuse useful

parts and/or materials for new PV-modules or to extend their lifespan. • High potential for reuse of the recovered materials, either within the PV-module value chain or within other markets, including a high material and resource recovery potential during the manufacturing process.

Eco-Solar will focus on further developing remanufacturing, resource efficiency, recovery and reuse aspects over the full value chain. Moreover, a pan-industrial approach to identify by-products, recycled and recovered wastes into the best possible utilisation with respect to the eco-efficiency assessment results and will present solutions for poorly recovered and reused materials. The results for the individual process steps and their impact over the integrated value chain will be assessed with LCA and eco-efficiency analysis methods to provide proof of their success to reduce the environmental footprint. 2 IMPORTANCE OF ECO-MANUFACTURING As a result of global efforts to reduce CO2-emissions and dependence on fossil fuels, the photovoltaic industry is one of the fastest growing economic sectors. The global PV module production capacity has grown with approximately 39 GW (28%) in 2013 [1], and with approximately 62.7 GW in 2014 [2]. The IEA reports that

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PV systems installed by the end of 2013 are generating 160 TWh/yr of clean electricity and thus avoiding about 140 million tonnes of CO2 per year (MtCO2/yr). Annual emissions from the power sector would increase from 13 Gt CO2 in 2011 to about 22 Gt CO2 in 2050 in the ETP 2014 6DS (IEA, 2014b, see Box 3). Solar PV could be responsible for avoiding 4 Gt CO2/yr of emissions, or 19% of the total power sector emission reductions, by 2050, and 20% of cumulative emission reductions over the entire scenario period, according to the hi-Ren Scenario [3]. However, all of these scenarios imply (shown in Fig. 1) that the PV sector will continue growing rapidly in the next decade, which means the industry will grow to 860 -1,721 GWp until 2030 according to IEA Technology Roadmap (2DS Scenario and hi-Ren Scenario respectively) with a market share of Si-based PV modules of about 70%. Frost & Sullivan forecasted a cumulated global installation of 668 GW in 2025 [4].

Figure 1: Market outlook for the next decades: cumulative installed capacity worldwide based on different scenarios. Even though solar power is pollution-free during use, production of PV-modules consumes considerable energy and natural resources. Moreover, recycling is hardly considered during module production, and therefore still cumbersome and inefficient. Considering that, the fast growth of the PV-industry entails similarly fast growth in resource consumption with growing production capacity: currently modest amounts of use can become very high. When projecting the materials consumption in line with the projected PV-growth from Fig. 1, materials reduction (of the targeted materials in Eco-Solar) in 2030 will be as shown in Fig. 2.

Figure 2: Expected material savings by 2030 based on Eco-Solar innovations (in Megatonnes). (Note: worldwide silver resources in 2014 belong to 0.52 Mt.) 3 CONCEPT AND APPROACH 3.1 Recovery & reuse during Si feedstock crystallisation 3.1.1 Reuse of argon purge gas Pure argon gas is used to remove contaminants during ingot crystallization and it is currently being vented into the air. Though perhaps argon is abundantly

available in the earth’s atmosphere (approximately 1% of mass), there are still (ecological and financial) costs involved in the production of pure argon gas. For solar applications, approximately 5% of the wafer costs are attributed to argon gas. Even if in other industries, argon gas recycling has become state of the art, in PV-production this is not yet the case. The recycling processes from the semi-conductor industry are too refined and hence too costly, but they could be modified for PV-requirements. Within Eco-Solar, we will evaluate an existing argon gas recycling system, with respect to its potential for using it within both Cz and DS crystallisation processes aiming at a recycling rate of >95%. SINTEF will determine crucial parameters from the baseline process, and will make modifications to make the system applicable and cost-effective for PV. Once a working prototype has been established at SINTEF, Norsun will install it, and validate the results in an industrial setting. 3.1.2 Reusable crucibles Crucibles are the main containers for the (molten) silicon feedstock. As silicon at high temperature reacts easily with almost everything, there are only a few crucible materials that will meet purity requirements for manufactures. One of the main drawbacks of using silica, as a current standard practice, is the (ecologic and financial) cost due to single use. Silica crucibles contribute up to ~30% of the conversion cost from Si-feedstock to the as-grown ingot. STEULER SOLAR has developed a concept for reusable crucibles based on advanced silicon nitride ceramics, applicable for both crystallization processes, DS and Cz. In Eco-Solar the impact of crucible manufacturing recipes and crystallization process parameters to meet the requirements for Cz and DS ingot production will be determined, aiming at 10 times reuse.

Figure 3: Directional solidification in conventional crucibles (a) and in reusable crucibles (b), Cz-ingot pulled from a reusable crucible (c). 3.2 Recovery & reuse of Si-kerf-loss After crystallisation, side-, top- and bottom-parts are removed before the ingot is cut into blocks and then wafered. A considerable amount of silicon is lost in form of fine powders (kerf-loss) during the mechanical processing of silicon ingots to obtain wafers: up to 50% of the material is lost in air and water used to rinse the wafers. The ability to recycle the Si-kerf-loss for solar ingot production will have beneficial effect in terms of savings of precious poly-silicon consumption and of waste reduction. Therefore, Garbo has patented and implemented a silicon recycling process which removes

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contaminations and brings silicon to "six nines" (or 6N), i.e. 99,9999% purity. Then purified silicon is compacted through another patented technology in order to obtain a mechanically stable, pelletized material, which can be used in the standard production of solar ingots and cells, or as fine powder for manufacturing lithium ion batteries and silicon nitride crucibles. SINTEF will carry out crystallization experiments of the recycled compacted silicon powder in order to assess the melting properties of the compacted silicon powder and final ingot properties. The potential of manufacturing lithium ion batteries and silicon nitride ceramics from fine powders will be investigated as well. 3.3 Remanufacturing, resource efficiency & reuse in solar cell processing Wafers are being processed into solar cells, causing waste like etching chemicals, broken wafers and broken solar cells. By reducing and avoiding certain chemicals or metals (e.g. HF, Pb, Ag, Al) and using less pure or recycled chemicals, waste can be reduced and the ecologic footprint of solar cells and panels can be improved. Moreover, as it is extremely costly to undo the processing steps and recover the chemicals and metals as separate elements after solar cell processing, solar cells represent a very valuable half-product. Thus, repair of solar cells can provide significant environmental benefit, while reducing the outcast of solar cells can provide a cost benefit simultaneously. 3.3.1 Solar cell repair In order to capitalise on the value of a solar cell, repair of defect solar cells within the solar cell process can represent a significant financial and ecological impact. AIMEN coordinated the EU-funded project REPTILE, in which ISC and INGESEA participated as beneficiaries. The project resulted in a fully functional prototype system, able to select and cut or isolate non-defective areas automatically in defective cells and wafers, a so-called Cell-Doctor (see Fig. 4). Within the Eco-Solar project, ISC will evaluate the rejected solar cells with an automated system for defects recognition. AIMEN and INGESEA will further develop the accuracy of the Cell-Doctor prototype, aiming to avoid 50% scrapped cells.

Figure 4: Integrated laser processing, machine vision and cell handling equipment used for cell repair. 3.3.2 Reducing silver consumption Silver is used in most solar cells (>98%) currently produced, providing the metal contact that “collects” and “drains” the current from the solar cell. It is of great importance to establish good electrical contact between the metal grid and the emitter surface with a low contact resistance, while having narrow, well conducting, fingers to minimise shadowing losses to produce higher efficiency solar cells. Today’s silver consumption for PV is 3.5 – 15% of the total silver market and is expected to

grow further assuming a market share of crystalline Si PV of approx. 70% in 2030. ISC will experiment with different solar cell architectures, to minimise the use of Ag. In addition, an innovative interconnection scheme enabled by Apollon Solar’s module design, will avoid soldering of the contact tape onto the rear side Ag pads and the front side busbars. Only the small contact fingers on the front side are needed. The full rear contact area is realized by aluminium. In the Eco-Solar project, experiments will be carried out that will test: different solar cell architectures, the novel interconnection scheme from Apollon Solar and metallisation pastes that contain less Ag than current standard, aiming to save at least 66% of Ag.

Figure 5: Current solar cell design with the silver rear-side pads, front side busbars and contact fingers indicated. 3.3.3 Reducing chemicals consumption through resource efficiency and chemicals recovery |In crystalline solar cell manufacturing, several wet chemical etching and cleaning steps are implemented, which have a negative impact on the environmental footprint. ISC, together with SoliTek, will develop an alkaline method for saw damage removal, texturisation and cleaning, that will replace the current state of art concentrated HF:HNO3. Moreover, ISC and SoliTek will investigate advanced processes for emitter formation that will enable higher throughput, resource efficiency and avoid the needs for chemical phosphorous glass layer removal (PSGremoval). The separation of front and rear of the solar cells is normally carried out with wet chemistry. AIMEN will further develop advanced laser treatment, in order to minimize the cut-off area at the wafer edges to a negligible fraction of the whole wafer area. This will be possible due to the small volume of laser-ablated silicon on the real wafer edges (and not on the front surface), using high speed scanning strategies. 3.3.4 Recycling water Tap water is being de-ionised by the solar cell producers (and by solar cell research institutes), resulting in very clean water. This de-ionised water is mainly used for several cleaning steps in the solar cell process: after each chemical processing step, the wafers are flushed with this ultraclean water. The water that goes into the drain, is mainly of higher quality than the water contracted from the tap. As an example, solar cell processing at SoliTek, with a production capacity of 80 MW, consumes about 54.000 m3 de-ionised water/year. The protection of water resources, of fresh and salt-water ecosystems and of the water we drink and bathe in is one of the cornerstones of environmental targets in Europe. ISC will look into industrial viability of recycling

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systems for the waste water. 3.4 Module design for remanufacturing After completion of the cells, they are electrically series connected and assembled into a solar module. Moreover, a junction box is attached that will ensure suitable power output. Within current solar modules, the biggest eco-challenge is that they cannot be disassembled into their components and the only potential for recycling is through destructive processes (see Fig 6.). Current PV modules also contain a vast amount of organic materials (EVA for encapsulation, PVF in backsheets)

Figure 6: Standard PV module recycling versus the Eco-Solar disassembly into components As Apollon Solars NICE-modules are already designed for disassembly (see Fig. 6 and 7), in Eco-Solar Apollon Solar will focus on the following: • Further reduction of the module BOM (Bill of materials) focussing on a frameless version of the PV module • Specifications for automated module disassembly equipment including diagnosis tools for quality screening of module components. • Integration of electronics in the junction box, that can monitor the performance of the individual module and provide warning if performance drops drastically. • Investigating the ageing and degradation aspects of solar modules during installation; and assess the technological viability to capture and recycle components at end of life, while considering environmental and economical aspects as well. Moreover, Apollon Solar will demonstrate that module assembly of the Eco-Solar cells will result in comparable module output as with current non-eco-friendly state of the art module technology.

Figure 7: Manual NICE-module disassembly at Apollon Solar. 4 ENVIRONMENTAL IMPACT

In order to be able to determine the actual environmental impact of the Eco-Solar results, a thorough ecological validation is necessary. Moreover, the only chance for implementing eco-friendly production methods is when they are economically viable as well. Therefore, it is of crucial importance, that all

processes are assessed for their ecological and economical viability and that the recovered waste products find (new) markets, where they can be purposefully introduced as (new) resources.

Thus bifa carries out an eco-efficiency analysis, based on data from the project partners and from published data. One strength of the eco-efficiency analysis is the simultaneous investigation of economical and ecological aspects that can be used to identify the most promising development routes and products. It is also applied to develop recycling processes that allow the highest possible recycling yield and quality that will be feasible from an economic point of view for the individual materials used in production and products.

The eco-efficiency analysis starts with setting the system boundaries and defining the processes. After that the collection of environmental and economical data starts, the life cycle inventory (LCI) is built up and state of the art ecological assessment (LCA - life cycle assessment) and cost consideration (LCC – life cycle costing) are carried out (see Fig. 7).

Figure 7: Typical scheme of an eco-efficiency analysis.

4.1 Input data collection for LCI

A standard EVA laminated module (60 6-inch solar cells, about 270Wp) with front glass and polymer back sheet including aluminium framing was defined as baseline for the comparison with the new products developed in this project. The research of recently published LCI data is finished and data gaps were filled by using expert assumptions. All project partners provided input for the LCI. The results were reviewed by the project team and the PV experts in the consortium.

An example section (ingot production) of the preliminary LCI baseline of the module production is presented in Table I.

Table I: Section of initial data set for ingot production. Parameter Unit sc-Si mc-Si Reference product CZ single crystalline silicon kg 1.00 - Casted multi crystalline silicon kg - 1.00

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Materials Argon (liquid) g 1,000 186 Ceramic tiles g 167 289 Hydrogen fluoride g 10 - Lime (hydrated) g 22 - Nitric acid (50 % in H2O) g 66.8 - Helium (liquid) g - 0.1 Silicon g 781 896 Sodium hydroxide (50 % in H2O) g 41.5 5 Water Deionised water kg 4.01 Cooling water m³ 5.09 1.06 Tap water kg 95.1 Energy/Fuels Electricity kWh 68.2 7.7 Natural gas (burned) MJ 68.2 Waste Inorganic waste g 167 289 Water emissions Biological oxygen demand 5 g 130 Chemical oxygen demand g 130 Dissolved Organic carbon g 40.5 Total Organic carbon g 40.5 Hydroxide g 367 Nitrate g 83.5 Nitrogen oxides g 33.9

Due to the progress made in the PV industry since the writing of the proposal, first improvements were already observed. The initial data sets for the individual life cycle sectors ingot, wafer, cell, module and BOS therefore were updated and the expected material reductions based on Eco-Solar innovations were adjusted (see Fig. 8). The reference process used as a benchmark includes recent developments, the absolute project targets are expected to be achieved.

Figure 8: Reduction of waste and resource consumption per PV-module (60 6-inch solar cells) envisaged in Eco-Solar. 4.2 Preparation of midterm LCA

The next steps are the definition of goal and scope (functional unit, scenarios, system boundaries, geographic and time references, dealing with data lacks and credits/benefits, etc.) as well as selection of impact categories (i.e. climate change, acidification, eutrophication, photochemical ozone formation, resource depletion, toxicity) in close consultation with the whole project team.

In the meantime the preparation of the material and energy flow model based on the LCI baseline has already started. The first step – the development of the model structure – is already finished (see Fig. 9).

The model structure is designed to facilitate a sectoral evaluation of the results of the LCA. On the one hand it

will make it possible to identify the contributions of the individual life sectors ingot, wafer, cell, module and BOS to the individual impact results. On the other side the model structure enables to use the results to evaluate direct emissions from sources that are owned or controlled by the reporting entity (scope 1 emissions), indirect emissions from consumption of purchased electricity, heat or steam (scope 2 emissions) and all other indirect emissions (scope 3 emissions).

5 REPURPOSING OF WASTE PRODUCTS 5.1 Living Lab – Establishment of Pan Industrial Material Re-use Opportunities

The target is to identify reuse and recovery routes for the main products and the by-products within the solar industry and if this will not be possible in other industries. The major material streams are assessed with respect to reuse, remanufacturing, recyclability and utilization of the output for different applications to optimize the eco-efficiency utilizing the Living Lab Methodology [5]. The use of the output may take place in completely different industrial branches. Potential customers and users will be invited to test the materials and provide feedback on the experience made. This will be done via a living lab, project webpage, trade fairs and conferences.

Living Lab is a kind of research in order to develop and to apply new products, services and systems by involving users to improve the products. A user can be everyone who deals with the object, especially consumers, workers, producers, suppliers, craftsmen or waste treatment companies. The target is to introduce the object successfully in a defined branch in order to save time and money. Living Lab is based on a four-step-cycle-system which includes the steps: co-creation (ranking and filtering of ideas), exploration (preparation of models/prototyping), experimentation (testbeds and observation) and evaluation (discussion of results). In the application for the solar industry it is necessary to determine the waste products/byproducts with the highest environmental impact and to identify possible customers (co-creation). Afterwards, negotiations with identified customers are required (exploration). The next step is to integrate the determined waste products/byproducts in a re-use process (experimentation) followed by an assessment of this process (evaluation). If the implementation of the determined waste products/byproducts in a re-use process is sufficient, the Living Lab process will be finished. If the implementation is not suitable, the four-step-cycle-system will be restarted.

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Raw materialsPre-products

Auxiliaries/SuppliesT Manufacturing

Energy consumption

(external)

Scope 3

Disposal Recycling

T

Equivalence system

IngotBenefits i.e. energy, secondary material

T

Scope 1Scope 2

Raw materialsPre-products

Auxiliaries/SuppliesT Manufacturing

Energy consumption

(external)

Disposal Recycling

T

Equivalence system

WaferBenefits i.e. energy, secondary material

T

Raw materialsPre-products

Auxiliaries/SuppliesT Manufacturing

Energy consumption

(external)

Disposal Recycling

T

Equivalence system

CellBenefits i.e. energy, secondary material

T

Raw materialsPre-products

Auxiliaries/SuppliesT Manufacturing

Energy consumption

(external)

Disposal Recycling

T

Equivalence system

ModulBenefits i.e. energy, secondary material

T

Raw materialsPre-products

Auxiliaries/SuppliesT Manufacturing

Energy consumption

(external)

Disposal Recycling

T

Equivalence system

Plant_BOSBenefits i.e. energy, secondary material

T

= Subsystem T = Transport= Flow

= Potential flow Figure 9: Structure of the flow model. 5 CONCLUSION Europe wants to reduce its needs for raw materials and raise the level of recycling of resources in the solar power industry. Our target is that after the successful completion of this project the greenhouse gas emissions from solar panel manufacturing will be reduced by 25 to 30 per cent and the waste generated will be decreased by 10% minimum. 6 REFERENCES [1] IEA PVPS TRENDS 2014 IN PHOTOVOLTAIC APPLICATIONS. [2] International Technology Roadmap for Photovoltaic

(ITRPV) 2013 Results, Revision 1, 24 March 2014. [3] IEA, Technology Roadmap Solar PV Energy 2014 p.20. [4]http://ww2.frost.com/news/press-eleases/photovoltaic- wind-and-hydro-star-top-renewables-finds-frost- sullivan/, accessed 2015-29-01. [5] S. Vicini, S. Bellini, A. Sanna: The City of the Future Living Lab, International Journal of Automation and

Smart Technology, Vol. 2, No. 3 (2012). 7 ACKNOWLEDGEMENT

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 679692.

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