Experimental investigation of spectral effects on amorphous silicon solar cells in outdoor operation

The effect of varying spectrum on PV output is often underestimated in the case of amorphous silicon photovoltaic devices. This paper gives an indication of the order of magnitude of the seasonal variation of the useful irradiance in a maritime climate and also shows that this will involve a direct change in efficiency. This can be expected to be in the range of 15 percent around the annual average, thus explaining the seasonal performance. The spectral effects are investigated by distinguishing between a primary and a secondary effect. The primary effect is dependent on the availability of useful spectral irradiance while the secondary effect depends also on the spectral composition of the light in the useful range. It is shown that the secondary effect is especially significant for double junction devices.