High Concentration P.V. 100 Wp Module Making Use of Spectrum Splitting and Si-GaAlAs Coupled Cells

Summary

In the present report the activity concerning the design and fabrication of a small size, high concentration module using GaAs and GaAlAs cells is described.

The aim of the work was that of checking the maturity of GaAs technology for solar cells, making experience on very high concentration and demonstrating the feasibility of multi-cell solutions using spectrum splitting optical filters.

In theory, the bandgap combination (1.7 e V - 1,1 e V) corresponding to GaAs and Si solar cells is nearly the optimum, but no high efficiency Si cells specifically designed and optimized for spectrum split applicptions could be supplied by other laboratories. The combination of GaAs (1,4 e V) and GaAlAs (1,7 e V) was therefore chosen and high efficiency cells designed and fabricated in CISE were used.

The module includes six Fresnel lenses, six solar cell couples with spectrum splitting filters, a full tracking structure, an active cooling circuit and a maximum power tracking circuit. All the principal components such as cells and optical elements, have been individually characterized up to 1000 suns concentration ratios.

For Fresnel lenses, the energy distribution as a function of the distance from the lens, have been measured. The transmission curves of the splitting filters have been measured as well.

All the individual cells have been characterized in full spectrum demonstrating an average conversion efficiency at 800 suns AM1.5 of 18% for the GaAs cells and 16.5% for the GaAlAs cells. Due to lack of sun during the winter season in Milan, only a preliminary evaluation of the module performances could be carried on. On the base of the first measurement sets a total peak power of ~ 120 W (at P_sum = 100 mW/cm²) and an overall efficiency of 14.1% resulted for the module working at a~ 800 suns concentration.