@88MPH
If you are asking about solar panels, the credit is available to a person who uses the "dwelling unit" as a "residence". It does not have to be the taxpayer's only residence or main residence, just "a residence." The taxpayer does not have to own the home. (Although, for many reasons, I would suggest caution when installing permanent equipment on a house you don't own.)
Likewise, the statute says nothing about ownership, so the property owner is not eligible if they live someplace else.
That means the credit can't be claimed by the property owner for a house they use as a rental but don't personally live in. And the credit is not available for property that is not a "dwelling unit." Although "dwelling unit" is not defined in section 25D, in other parts of the tax code, a dwelling unit must be a place where people can live and must have at a minimum, a bathroom and a place to sleep. So the credit is not available for an office building, parking garage, duck blind, or backyard workshop. (However, if the solar panels are installed on the backyard workshop because it has better light, but they power the house-dwelling unit, that's probably ok.) (Also note, there are separate credits available for business and rental property even if the section 25D credit is only allowed for a dwelling unit used as a residence.)
People get confused because different credits have different requirements, but the laws themselves are quite clear in each case.
https://www.law.cornell.edu/uscode/text/26/25D
