Long Term Stability of Solar Modules Made from Compensated SoG-Si or UMG-Si Solar Cells

We discuss the degradation mechanisms of solar modules made from multicrystalline solar cells based on compensated solar grade silicon or upgraded metallurgical silicon (“SoG/umg-Si modules”) as well as Siemens poly silicon (“poly-Si modules”). We show that available observations and theories on module degradation lead to the conclusion that initial (wafer material related) degradation may slightly be influenced by the silicon feedstock used. The long term degradation mechanisms are, however, clearly independent of the silicon feedstock used and only related to module or cell properties. This conclusion is supported by performance data for large, medium and small scale systems made from SOG/umg-Si modules and poly-Si modules over a period of up to three years showing no difference in long term degradation behavior.