Optimization of three and four junction solar cell CPV systems using ray tracing and SPICE modeling

Concentrating optics generally produce spatially and spectrally non-uniform optical profiles across the multijunction solar cells typically used in a concentrator photovoltaic (CPV) systems, degrading fill factors and thereby reducing module efficiencies. These effects maybe more pronounced if the primary-to-secondary distance is sub-optimal and if the system does not track the sun accurately. We integrate ray tracing with a distributed equivalent circuit model to simulate the performance of a three and four junction solar cells under a Fresnel-lens-based CPV system of 1250X geometric concentration. The impact on system efficiency of varying the primary-to-secondary distance is evaluated. Our results indicate a relative enhancement of 11.5 % for the triple junction lattice matched, 9.2% for the triple junction inverted metamorphic design and 8% for the four junction lattice matched design when we optimize the primary-to-secondary distance based on an integrated systems approach using the full optical distribution as an input to a 2-D distributed equivalent circuit model of the MJSC, as opposed to a uniform profile 1-D treatment.