Energy payback time and carbon footprint of commercial photovoltaic systems

Energy payback time and carbon footprint of commercial roof-top photovoltaic systems are calculated based on new 2011 manufacturersʹ data; and on 2013 equipment manufacturersʹ estimates of “micromorph” silicon photovoltaic modules. The energy payback times and carbon footprints are 1.96, 1.24, 1.39, 0.92, 0.68, and 1.02 years and 38.1, 27.2, 34.8, 22.8, 15.8, and 21.4 g CO2-eq/kWh for monocrystalline silicon, multicrystalline silicon, amorphous silicon, “micromorph” silicon, cadmium telluride and CIGS roof-top photovoltaic systems, respectively, assuming a poly-silicon production with hydropower; ingot-, wafer-, solar cell and module production with UCTE electricity; an irradiation on an optimized-angle of 1700 kWh/(m2×year); excluding installation, operation and maintenance and end-of-life phase. Shifting production of poly-silicon, ingots, wafers, cells and modules to China results in similar energy payback times but increases the carbon footprint by a factor 1.3–2.1, depending on the electricity intensity of manufacturing.