The Residential Energy Efficient Property Credit, also known as the Nonbusiness Energy Property Credit, is a tax credit available for homeowners who install eligible energy-efficient improvements in their primary residence. This credit can be claimed for expenses related to qualified solar electric property, solar water heating property, fuel cell property, small wind energy property, and geothermal heat pump property. The credit is calculated as a percentage of the qualified expenditures, and the percentage varies depending on the type of property and the year of installation. For more details, refer to 26 U.S. Code § 25D.