Originally Posted by gizmo555
It's rare though, to see any accounting for the embodied energy and CO2 in solar systems, whether PV or hot water, when analysing their nett environmental benefit. Does Retscreen account for this or are there any other reasonable figures publicly available which one could use?
I have often heard it said (and blithely repeated it myself without checking) that it took more energy to produce solar PVs than they give back in their lifteime. In Ireland, it may take more money, but that's a different matter.
Of course, a PV will produce about half the energy in Ireland that it would in parts of Spain, so the energy payback may double. On the flip side, our electricity production is a lot more carbon intensive than it is in other countries. We are at 620g/Kwhr compared to 430g in the UK.
In 2004, the National Renewable Energy Laboratory in the USA produced this document
, suggesting at the time that solar PVs had an energy payback time of just 2 years. In Ireland you could maybe double that, but then again, solar panel production has become a lot more efficient in the meantime.
According to wiki
, the energy payback time was estimated at 8 - 11 years in 2000, but more recent studies reduced this to between 1.5 and 3.5 years, with thin film even lower. I guess you could double all that for Ireland.
I did do a "back of an envelope" estimate for solar water heating some time ago, measuring CO2 production for steel, aluminium, glass, processing etc., and came to the conclusion that it was less than two years. I've seen documents
claiming less than 1 year, but again that depends on local climate.
Also, that would depend on whether the system is displacing electricity, or a modern gas-fired condensing boiler, or even a "zero carbon" wood chips / pellets, but of course unless you cut your firewood with your teeth, nothing is zero carbon.