As I showed in a recent post, a typical solar cell will generate at least 10 times the electricity used to produce it, and probably substantially more. This Energy Return on Energy Invested (EROEI) calculation didn’t take account of battery storage, which is needed to make solar PV comparable to dispatchable technologies like gas.
For this purpose, I’ll assume that each kilowatt of PV capacity requires 2 kilowatts of battery storage. The reasoning behind this is that we get an average 5kWh/day from the PV system, of which 3kWh is used during the day and 2kWh is stored.
According to this life-cycle assessment, a 26.6 kWh battery has a life-cycle cost of 4.6 tonnes of CO2, which comes out to around 0.4 tonnes for the 2kWh system proposed here. Assuming that the system displaces black coal, which conveniently yields about 1 tonne of CO2 per mWh, we have a cost of 400 kWh, which is only a few months worth of generation from a 1 kW system.
This seems amazingly good, so I may have made an order of magnitude mistake somewhere. If so, I’d be grateful to have it pointed out. If not, I think we can put the EROEI constraint to bed, at least as regards solar PV.