An evaluation on the life cycle of photovoltaic energy system considering production energy of off-grade silicon

Abstract

In this study, single-crystalline silicon (c-Si) photovoltaic (PV) cells and residential PV systems using off-grade silicon supplied from semiconductor industries were evaluated from a life cycle point of view. Energy payback time (EPT) of the residential PV system with the c-Si PV cells made of the off-grade silicon was estimated at 15.5 years and indirect CO 2 emission per unit electrical output was calculated at 91 g-C/kWh even in the worst case. These figures were more than those of the polycrystalline-Si and the amorphous-Si PV cells to be used in the near future, but the EPT was shorter than its lifetime and the indirect CO 2 emissions were less than the recent average CO 2 emissions per kWh from the utilities in Japan. The recycling of the c-Si PV cells should be discussed for the reason of the effective use of energy and silicon material.