I am not 100% sure it is still this way with the revised Solar credit, but I don't think the credit is calculated on the 1065.  The BASIS of the energy property is passed through to the 1040, and the credit is calculated on the 1040.  At least that is how it has worked in prior years.

See the Instructions for Box 20, Code "E".

https://www.irs.gov/instructions/i1065#en_US_2025_publink1000100862