http://www.eere.energy.gov/
http://images.google.com/imgres?imgurl=h...
Other Answers (2)
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Aren%26#039;t power companies required to pay for any unused power from people using solar panels on their homes? If so, in the US you might be able to get a rough estimate from the power companies if they track the number of those homes that have been selling back their power and are willing to give it to you.
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Do google and yahoo search, also contact PG%26amp;E
