Although it is easy to say that photovoltaic sources emit much less carbon dioxide than natural gas or coal combustion, careful cradle to grave analyses are difficult and comparisions of - say - wind vs solar - can be difficult. As noted before the National Renewable Energy Laboratory has taken a stab at the problem with an interesting metaanalysis. They "harmonize" data from various sources and, although I'm not a huge fan of harmonization, it may be the best technique for cases like this as there were over 2,000 studies in this meta analysis. They also have some tools to play with lifecycle analysis harmonization yourself.
Their studies have been published in the April issue of the Journal of Industrial Ecology (6 articles) for those of you who really want to dig in. Some high level comments here. With a median of 45 grams/kWh CO2e, olar PV tended to emit about 5% as much as coal which had a 1,001 grams/kWh CO2e median. Wind was a bit better and nuclear was in the same ballpark, although the range was large. Any of these are much better than fossil fuels cradle to grave. Natural gas wasn't studied and there is still a lot of uncertainty about the impact of infrastructure leakage to the atmosphere, but best case it is about half of coal - an improvement, but not close to being a solution worth worrying about ...
392 ppm CO2 and we must get down to 350 ppm.
Posted by: Roger | May 16, 2012 at 16:54
Yup! Sadly it is unlikely we'll start turning things about before passing numbers like 500 or worse - and that assumes we're working at it much harder than now.
I'm happy I don't have kids and grandkids...
Posted by: steve | May 16, 2012 at 17:04