from:
http://www.irs.gov/newsroom/article/0,,id=154657,00.htmlAdditionally, the new law makes a credit available to those who add qualified solar panels, solar water heating equipment, or a fuel cell power plant to their homes in the United States. In general, a qualified fuel cell power plant converts a fuel into electricity using electrochemical means, has an electricity–only generation efficiency of more than 30 percent and generates at least 0.5 kilowatts of electricity.
Taxpayers are allowed one credit equal to 30 percent of the qualified investment in a solar panel up to a maximum credit of $2,000, and another equivalent credit for investing in a solar water heating system. No part of either system can be used to heat a pool or hot tub.
more details:
http://www.irs.gov/pub/irs-drop/n-06-26.pdf