USA Eligibility for solar property credit

[RNY]

Hello. I live with my fiancée in a house that is co-owned by her and her father. The house is both of ours primary residence. We are considering the purchase of a qualified solar system, but had questions regarding the eligibility of the solar tax credit. My fiancée has over the past several years had a federal tax liability of $0. Last year my federal tax liability was appx $18K. Am I eligible to purchase the solar system and take the federal tax credit? I am not the homeowner, but from everything I could find in the code, the credit applies to the purchaser of the solar system installed on the taxpayer’s primary residence. We can find no stipulation in the code that says the credit can only apply to a homeowner. Has anyone encountered this? Thank you