A critical appraisal of the factors affecting energy production from amorphous silicon photovoltaic arrays in a maritime climate

Contradictory reports exist in the literature regarding the energy production from amorphous silicon photovoltaic arrays. The majority claims high-energy output compared to crystalline silicon arrays of the same power rating (i.e. high kWh/kWp), but some reports point to less favourable comparisons. The reasons for these conflicting reports are investigated using long-term measurements of the I–V characteristics of a number of amorphous silicon devices, in conjunction with in situ measurements of the solar spectrum and other relevant environmental parameters. It is shown that the variation in the performance of devices produced by different manufacturers is so significant that one cannot speak of the performance of amorphous silicon devices in general; one has to investigate each type of amorphous silicon panel separately. The causes of differences in energy production are investigated in detail. The major factor impacting on the seasonal performance in the UK is identified to be variations in the solar spectrum. Single junction devices exhibit some seasonal thermal annealing but multi-junctions do not show this effect at a significant level. Scope for further improvement is identified, largely in the photon absorption. The response to different spectra can be modified to some extent, which would bridge the gap between the best and the worst performers in the field. It is also shown that in the case of multi-junction devices an optimised current matching might bring a 5% increase in energy production for this location. Differences in the magnitude of the fill factor have been identified to be the second most significant cause for performance variation between the different samples in the test, suggesting additional scope for improvement. 2004 Elsevier Ltd. All rights reserved.