RESIDENTIAL RENEWABLE ENERGY TAX CREDIT

A taxpayer may claim a credit of 30% of qualified expenditures for a system that serves a dwelling unit located in the United States that is owned and used as a residence by the taxpayer.  
If the federal tax credit exceeds tax liability, the excess amount may be carried forward to the succeeding taxable year.
Solar-electric property:   30% for systems placed in service by 12/31/2019

http://energy.gov/savings/residential-renewable-energy-tax-credit