reliability of pv elements: lifetime and long-term ... · reliability of pv elements: lifetime and...

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Eleonora Annigoni 1 , Ana Martins 1 , Xavier Niquille 1 , Joël Sunier 1,2 , Christophe Ballif 1,2 , Fanny Sculati-Meillaud 1 1 École Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and Thin Film Electronics Laboratory, Rue de la Maladière 71b, 2000 Neuchâtel, Switzerland 2 CSEM, PV-center, Jaquet-Droz 1, 2000 Neuchâtel, Switzerland e-mail: [email protected] Reliability of PV elements: lifetime and long-term performance prediction Predicting photovoltaic (PV) modules lifetime is of major importance for standard installations as well as for building integrated photovoltaics (BIPV). A model is being developed to assess long-term performance of PV modules considering the different possible degradation mechanisms. In particular, potential-induced degradation (PID) [1] is an increasingly evident failure mode also in temperate climates. In parallel, research is done on novel materials to design reliable lightweight PV prototypes for enhanced BIPV deployment. Accelerated lifetime tests (ALTs) were performed on commercial modules and 2-cells mini modules at different stress levels. Based on this tests, a model for the degradation mechanism under study (here, PID) can be developed. The impact of encapsulant material on PID is also evaluated by ALTs. Considering lightweight elements, their reliability is also evaluated to (i) improve the design and (ii) gain further inputs on possible failures arising when non-standard module materials are used. [1] Hacke, P. et al., 2015. Accelerated Testing and Modeling of Potential-Induced Degradation as a Function of Temperature and Relative Humidity. IEEE Journal of Photovoltaics, 5(6), pp. 1549-1553 [2] Riedel, N., Pratt, L., Moss, E. & Yamasaki, M., 2015. 600 Hour Potential Induced Degradation (PID) Testing on Silicon, CIGS and HIT Modules (Poster). NREL, Golden (Colorado, US) Acknowledgments The authors of this work wish to thank EOS Holding and the Swiss National Science Foundation (SNSF) for funding. The research on lightweight elements presented here is part of the National Research Program "Energy Turnaround" (NRP 70). Further information on the National Research Program can be found at www.nrp70.ch. Goals and Motivations Approaches Predictive model Accelerated PID tests Example of reliability modeling: PID Influence of materials on PID TPO has higher volume resistivity than EVA, limiting the ion migration. TPO has also higher moisture resistance than EVA. Initial 96 h 2-cells mini-modules were tested for PID at different stress levels. A mathematical model for the power is developed from tests results (as those in Fig.2), based on [1]. Impact of encapsulant material Two types of encapsulants were evaluated in 2-cells mini-modules: Ethylene vinyl acetate (EVA) Thermoplastic polyolefin (TPO) Initial 96 h 192 h Volume resistivity [Ohm*cm] WVTR [g/(m 2 *day)] Water absorption [%] EVA TPO Constraints on weight can be significant for PV implementation in the building skin, particularly in case of renovation, and there is clear lack for lightweight BIPV solutions. 2 cells mini-modules were prepared where the front glass is replaced by a thin polymer sheet and the typical backsheet by a composite sandwich structure as presented in Fig. 4. The prototypes were tested in thermal cycling (TC, -40/85°C) up to 200 cycles. Major observations: Thermal cycling was performed and the prototypes showed only limited power loss after 200 cycles with an average relative loss of 3%, see Fig.5. A glass/backsheet mini-module was also tested as “reference”. No degradation was observed with electroluminescence imaging (Fig. 6). To evaluate the resistance of the modules to survive long-term humidity penetration, mini-modules are now being tested in damp-heat test (DH: 85°C / 85%RH). Accelerated lifetime tests (ALTs) results Initial Final Fig. 6 Electroluminescence images before and after TC Thin polymer skin Encapsulant Solar Cells Composite Backsheet Fig. 4 Prototype design As expected from material characteristics, TPO-based mini- modules demonstrate higher resistance towards PID, even for extended test time the impact of encapsulant is clearly confirmed. EVA TPO Lightweight BIPV solutions: glass free Fig. 5 Electrical performance obtained after TC. Conclusions / Outlook A predictive model for PID is under development that shall next be validated with outdoor data corresponding to different climates. In-house developed lightweight mini-modules demonstrate promising potential in terms of design with good results after first ALTs. Further tests are planned at material level both for design and reliability assessment. PID can occur when modules are exposed to high potential towards ground (e.g. in big installations) leading to ions migrations within the module. The impact on module’s performance can be drastic with a strong decrease of shunt resistance. Commercially available modules were tested for PID according to the standard draft IEC 62804-1. Some modules did not pass the test showing a relative power loss of more than 5% (see Fig.1), confirming the importance of PID (see also [2]). ΔP max =-21.8% Fig. 1 Electroluminescence images before and after PID test for a commercial poly c-Si module PID test: 60°C / 85% RH / -1000 V applied to the module’s leads, for 96h Fig. 2 Power-time evolution during PID test on 2-cells mini-modules Fig. 3 EL images during PID test at 85°C / 85% RH / -1000 V -4.88% ΔP max -41.0% -1.11% -1.23% Encapsulant

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Page 1: Reliability of PV elements: lifetime and long-term ... · Reliability of PV elements: lifetime and long-term performance prediction • Predicting photovoltaic (PV) ... PowerPoint

Eleonora Annigoni1, Ana Martins1, Xavier Niquille1, Joël Sunier1,2, Christophe Ballif1,2, Fanny Sculati-Meillaud1

1 École Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT),

Photovoltaics and Thin Film Electronics Laboratory, Rue de la Maladière 71b, 2000 Neuchâtel, Switzerland2 CSEM, PV-center, Jaquet-Droz 1, 2000 Neuchâtel, Switzerland

e-mail: [email protected]

Reliability of PV elements:

lifetime and long-term performance prediction

• Predicting photovoltaic (PV) modules lifetime is of major

importance for standard installations as well as for building

integrated photovoltaics (BIPV).

• A model is being developed to assess long-term performance of PV

modules considering the different possible degradation

mechanisms. In particular, potential-induced degradation (PID) [1] is

an increasingly evident failure mode also in temperate climates.

• In parallel, research is done on novel materials to design reliable

lightweight PV prototypes for enhanced BIPV deployment.

• Accelerated lifetime tests (ALTs) were performed on commercial

modules and 2-cells mini modules at different stress levels.

• Based on this tests, a model for the degradation mechanism under

study (here, PID) can be developed.

• The impact of encapsulant material on PID is also evaluated by ALTs.

• Considering lightweight elements, their reliability is also evaluated to

(i) improve the design and (ii) gain further inputs on possible failures

arising when non-standard module materials are used.

[1] Hacke, P. et al., 2015. Accelerated Testing and Modeling of Potential-Induced Degradation as a Function of Temperature and

Relative Humidity. IEEE Journal of Photovoltaics, 5(6), pp. 1549-1553

[2] Riedel, N., Pratt, L., Moss, E. & Yamasaki, M., 2015. 600 Hour Potential Induced Degradation (PID) Testing on Silicon, CIGS

and HIT Modules (Poster). NREL, Golden (Colorado, US)

AcknowledgmentsThe authors of this work wish to thank EOS Holding and the Swiss National Science Foundation (SNSF) for funding. The

research on lightweight elements presented here is part of the National Research Program "Energy Turnaround" (NRP 70).

Further information on the National Research Program can be found at www.nrp70.ch.

Goals and Motivations Approaches

Predictive modelAccelerated PID tests

Example of reliability modeling: PID Influence of materials on PID

• TPO has higher volume

resistivity than EVA,

limiting the ion migration.

• TPO has also higher

moisture resistance than

EVA.

Initial 96 h • 2-cells mini-modules were tested for

PID at different stress levels.

• A mathematical model for the power is

developed from tests results (as those

in Fig.2), based on [1].

Impact of encapsulant material

Two types of encapsulants were evaluated in 2-cells mini-modules:

Ethylene vinyl acetate (EVA)

Thermoplastic polyolefin (TPO)

Initial 96 h 192 h

Volume

resistivity

[Ohm*cm]

WVTR

[g/(m2*day)]

Water

absorption

[%]

EVA

TPO

• Constraints on weight can be significant for PV implementation in the building skin, particularly in case of

renovation, and there is clear lack for lightweight BIPV solutions.

• 2 cells mini-modules were prepared where the front glass is replaced by a thin polymer sheet and the typical

backsheet by a composite sandwich structure as presented in Fig. 4.

• The prototypes were tested in thermal cycling (TC, -40/85°C) up to 200 cycles.

Major observations:

• Thermal cycling was performed and the prototypes showed only limited

power loss after 200 cycles with an average relative loss of 3%, see Fig.5.

A glass/backsheet mini-module was also tested as “reference”.

• No degradation was observed with electroluminescence imaging (Fig. 6).

• To evaluate the resistance of the modules to survive long-term humidity

penetration, mini-modules are now being tested in damp-heat test

(DH: 85°C / 85%RH).

Accelerated lifetime tests (ALTs) results

Initial Final

Fig. 6 – Electroluminescence images

before and after TC

Thin polymer skin

Encapsulant

Solar Cells

Composite

Backsheet

Fig. 4 – Prototype design

• As expected from material characteristics, TPO-based mini-

modules demonstrate higher resistance towards PID, even for

extended test time → the impact of encapsulant is clearly

confirmed.

EVA

TPO

Lightweight BIPV solutions: glass free

Fig. 5 – Electrical performance obtained

after TC.

Conclusions / Outlook

• A predictive model for PID is under development that shall next be validated with outdoor data corresponding to different climates.

• In-house developed lightweight mini-modules demonstrate promising potential in terms of design with good results after first ALTs.

• Further tests are planned at material level both for design and reliability assessment.

• PID can occur when modules are exposed to high

potential towards ground (e.g. in big installations)

leading to ions migrations within the module.

• The impact on module’s performance can be

drastic with a strong decrease of shunt resistance.

• Commercially available modules were tested for

PID according to the standard draft IEC 62804-1.

• Some modules did not pass the test showing a

relative power loss of more than 5% (see Fig.1),

confirming the importance of PID (see also [2]).

ΔPmax =-21.8%

Fig. 1 – Electroluminescence images before and after

PID test for a commercial poly c-Si module

PID test:

60°C / 85% RH /

-1000 V applied

to the module’s

leads, for 96h

Fig. 2 – Power-time evolution during

PID test on 2-cells mini-modules

Fig. 3 – EL images during PID test at 85°C / 85% RH / -1000 V

-4.88%ΔPmax -41.0%

-1.11% -1.23%

Encapsulant