Solar cell efficiency divergence due to operating spectrum variation

Abstract

A limitation in the performance rating of solar cells and modules is that they are tested using a single value for the solar spectrum. To map the performance expected under the varying spectra found in operating conditions, solar cell efficiencies have been evaluated using solar spectra generated by the National Solar Radiation Database, applied to confirmed record-efficiency cell parameters. Nine solar cell types (single-junction and multijunction) are evaluated using spectra at more than forty locations, spanning 76° of latitude and 150° of longitude, at hourly intervals over a year. Relative to the standard test efficiency, increases in operating efficiency are seen in cadmium telluride and (single-junction) perovskite designs. Silicon exhibits the least variation, while efficiency decreases are observed in two-terminal multijunction structures. This divergence in operating efficiencies indicates that evaluation using a single spectrum is not a sufficient basis for comparison, or prediction of energy yield in operation. Application of additional “operating spectra,” to supplement the standard test spectrum, is proposed.

Impact of measured spectrum variation on solar photovoltaic efficiencies worldwide

“…Cells with a wider spectral response (Figure 2) are more tolerant to the increased spectral variation that arises from sun tracking. In Appendix H, increasing the sun tracking is seen to benefit single-junction cells with a wider spectral response (silicon, CIGS), but is a detriment to cells with a narrower spectral response (cadmium telluride, perovskites), confirming predictions from synthetic spectra 28,48,49 . For cells with more than one junction, the correlation is more complex, as losses due to current mismatch between the junctions trade against the wider spectral response of the overall stack.…”

“…As seen in analyses of synthetic spectra 28,48,49 , increases in the amount of sun tracking increase the degree of spectral variation and therefore tend to be less favorable for cells with a narrower spectral response. As the degree of tracking increases in Figure 12 below, efficiency tends to increase for single-junction cells with a wider spectral response (Si, CIGS) and decreases for the cells with a narrower response (CdTe, PVSK).…”

Impact of measured spectrum variation on solar photovoltaic efficiencies worldwide

“…Cells with a wider spectral response (Figure 2) are more tolerant to the increased spectral variation that arises from sun tracking. In Figure 6 and Appendix F, increasing the sun tracking is seen to benefit single-junction cells with a wider spectral response range (silicon, CIGS), but is a detriment to cells with a narrower spectral response (cadmium telluride, perovskites) 23,39,40 . For cells with more than one junction, the result is more mixed, as losses due to current mismatch between the junctions trade against the wider spectral response of the overall stack.…”

“…As seen in analyses of synthetic spectra 23,39,40 , increases in the amount of sun tracking increase the degree of spectral variation and therefore tend to be unfavorable for cells with a narrower spectral response. As the degree of tracking increases in Figure 13 below, efficiency tends to increase for single-junction cells with a wider spectral response (Si, CIGS) and decreases for the cells with a narrower response (CdTe, PVSK).…”