Predicting energy production for multijunction photovoltaics: Effects of spectral variation and cumulative irradiance

Variation of the incident spectrum under real-world illumination conditions can degrade the performance of series connected multijunction solar cells that are optimized for performance under the AM1.5D standard spectrum. Current approaches to correct for this factor and estimate energy production for deployed systems require large amounts of field data and are not useful for evaluating prospective designs. We present a set of 20 spectra that capture the average spectral composition for direct normal irradiance at different cumulative irradiance levels. Combined with the NSRDB information on the frequency of cumulative irradiance levels at locations across the United States, these 20 spectra allow us to predict the energy production of spectrum splitting photovoltaic systems with minimal computation required.