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Yield and Spectral Effects of a-Si Modules
P. Grunow, A. Preiss, S. Koch, S. Krauter
Degradation, Performance, Spectral Response, Energy Rating
Thin Films Solar Cells
Subtopic: Amorphous and Microcrystalline Silicon Solar Cells
Event: 24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany
Session: 3BV.4.36
2846 - 2849
ISBN: 3-936338-25-6
Paper DOI: 10.4229/24thEUPVSEC2009-3BV.4.36
0,00 EUR
Document(s): paper


Aim of this study was to investigate the relevant factors that influence electrical energy yield of photovoltaic modules based on thin film technologies, in particular amorphous silicon (a-Si). Models of different manufacturers have been compared in theory and in the outdoor laboratory of TU-Berlin and PI-Berlin. Amorphous silicon modules show higher energy yields for diffuse light irradiation. This was as well calculated – using the spectral match of the diffuse irradiance (as given in the spectra of CIE 85) and the spectral response for single junction a-Si modules – as confirmed via outdoor field measurements. Highly diffuse skies and high sun elevation angles (AMs) result in the highest increase of short circuit current (and electrical yield) for amorphous based modules relative crystalline silicon (c-Si) modules. For moderate diffuse skies c-Si performs better. Although spectral effects have been successfully separated from other performance factors with the result that their influence can be quite significant for some conditions (e.g., >30% gain in ISC at a-Si for a 90% overcast sky at spectral matching), their overall contribution to the annual energy yield is relatively small: 1.3 % for a tandem μ-morph, and 3.2% for single junction amorphous (a-Si) modules. Therefore, spectral effects alter performance in about the same range as thermal and weak light performance factors. Particular problems for yield evaluation of a-Si modules occur due to degradation of power output. In the outdoor lab the effect of the annealing/degradation process on electrical performance has been investigated: Seasonal degradation and recovery of the a-Si modules resulted in a fluctuation of ±6% of the short-circuit current Isc and of energy yield. Accordingly, the effects of seasonal degradation (resp. recovery) are by a factor of two higher than the spectral effects observed. Future efforts are targeted on the modeling of degradation and recovery of tandem cells.