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
