4. 1 PV Module Design, Manufacture, Performance and Reliability
Summary / Abstract:
Various common crystalline silicon cell technologies were exposed to UVA radiation (1.24 Wm-2 nm-1 at 340 nm peak) on the front and back faces at 45 °C for periods up to 3000 h, representing about 3 y of solar exposure in Phoenix, Arizona, USA. The resulting degradation of the open-circuit voltage and short-circuit current is presented. Of the various cell types examined, significant levels of degradation were seen in all cases. Less degradation was generally found after UV irradiation of cell fronts and older cell types, whereas a bifacial PERC type exposed on the rear showed about 25% degradation in short circuit current, attributable to lack of a diffused surface field. Selected cells were exposed to UV irradiation with the addition of long pass UV filters to replicate UV-absorbers in encapsulants. For most samples, it was found that the degradation rate increased below 360 nm cut-on, near the 3.5 eV binding energy of the Si:H bond. The degradation rate of modules with and without UV absorber was modeled with an emitter recombination current analysis. The LCOE of an example system with modules with sub360 nm UV filtering was calculated to be 3.07 US¢/kWh, while that without any UV filtering was 3.12 US¢/kWh because of the greater module degradation rate. Reduction of UV-induced degradation as with the use of appropriate UV absorbers in the encapsulation is therefore recommended for maximization of energy yield and to minimize the LCOE.