Solar spectral variations and their influence on concentrator solar cell performance

Abstract

A comparative study is performed to quantify the difference in efficiency and spectral sensitivity between a tandem junction and its spectrum splitting parallel junction counterpart. Direct normal solar spectra in a representative sunny site, Tucson, Arizona are calculated using the SPCTRAL2 model at 15-minute intervals throughout a year with real-time meteorological data input. The corresponding efficiencies of the two junctions under 500X concentration at cell temperatures deduced from thermal modeling with real-time ambient temperatures are computed. Both junction structures comprise the same materials, InGaP, GaAs and Ge, and are each optimized to the AM1.5D standard spectrum and cell temperature of 25 ο C, under which the parallel junction achieves a 1.0% absolute (and 2.5% relative) higher efficiency than the tandem junction. The two junctions are compared for their hourly, daily, and yearly average efficiencies. It is found that the yearly average efficiency of the parallel junction is 2.65% absolute (and 7.31% relative) higher than that of the tandem junction.

Diffractive Spectral-Splitting Optical Element Designed by Adjoint-Based Electromagnetic Optimization and Fabricated by Femtosecond 3D Direct Laser Writing

“…The current-matching requirement is of particular importance, as it imposes a strong sensitivity of PV efficiency on the shape of the solar spectrum, which varies with the Sun’s position in the sky and with the chemical composition of the atmosphere, both of which will change with the time of day and time of year. As a result, the annual energy production from tandem devices does not necessarily improve proportionally with their high efficiency under the standard AM1.5 spectrum. − …”