What is the carbon footprint of a photovoltaic cell?

Answer 1

One current estimate is 35 to 58 g CO2e/kWh (this is explained in the last paragraph of this answer). Another estimate at the link cited below says 23.6 g CO2e/kWh for thin film CdTe cells. This compares to 25 to 80 for biomass, 3 to 10 for hydro, and about 5 to 15 for wind. I have often seen huge differences in estimates of the carbon footprint of nuclear power, ranging from 2 to 288 g CO2e/kWh. It seems that the actual number is probably more than 66 g CO2e/kWh, and very possibly more than 90.

PV technology is changing rapidly, both for the actual PV and for the manufacture of PVs. The above estimate is not for thin-film PVs, and these promise to have a much smaller carbon footprint. Also, the estimate given is for PVs that are 5% efficient in producing power, and increases in power output will decrease the carbon footprint. Current PVs are mostly considerably more efficient, and at 7.5% efficiency, the carbon footprint is cut to 23 to 39 g CO2e/kWh. New, gadolinium-based PV technologies are said to be as high as 40% efficient, but I have not seen any estimates of their carbon footprints and could not guess, because I do not know how they are manufactured.

By the way, thermal solar power, such as is used in solar hot water, is about 60 to 65% efficient, and has much lower cost, in terms of global warming gasses, than PVs. It has a carbon footprint that might even be smaller than wind's.

The carbon footprint is calculated in grams of CO2 equivalent per kilowatt hour (g CO2e/kWh). Properly, this includes all phases of manufacture of equipment and fuel, transportation, installation, operation, and disposal. Calculations are often deceptive because steps are left out for some technologies, notably the decommissioning and disposal steps are often left out in calculation of carbon footprints for nuclear power. The "equivalent" part happens because of global warming gasses other than CO2. For example, the nitrogen trifluoried used in manufacture of photovoltaic panels is about 17,000 times as powerful as CO2 for global warming, so an estimate of the amount leaking into the environment from the manufacturing process has to be included.