IS THE AVERAGE PHOTON ENERGY (APE) A SUITABLE MEASURE TO DESCRIBE THE UNIQUENESS OF SOLAR SPECTRA?

摘要

The average photon energy (APE) is often used to characterize solar spectra. Being a single value, that energetically averages a solar spectrum to a mean value, it is easier to use in scientific research in the field of photovoltaics than a whole array of values for a full spectrum. In this study we analyze the APE in two ways. First, the uniqueness of spectra with equal APE is investigated. We show that for individual spectra the APE is not a suitable measure to describe the uniqueness of solar spectra. In a second analysis we focus on the dependencies of electrical parameters of solar cells on the APE, based on high resolution outdoor measurements of a grid connected PV system. These results are compared with analogous calculations with a spectrally weighed factor (SWF) that takes into account both the whole solar spectrum and the external quantum efficiency of the solar cell. We show that the usage of APE leads to reasonable results for cells of amorphous silicon, but fails for crystalline silicon. The usage of the SWF leads to results of higher quality both for amorphous and crystalline silicon.