Form 3468 leads to Form 3800.
See:
https://ttlc.intuit.com/community/state-taxes/discussion/re-can-a-trust-claim-a-solar-tax-credit/01/...
The best guide I've found is:
https://www.thetaxadviser.com/newsletters/2017/oct/credit-residen[product key removed]s.html
https://recsolar.com/blogs/calculate-solar-tax-credit-2020/
"Business credit
While Sec. 25D does not allow a solar tax credit for the cost of installing solar panels for use in residential rental property, Sec. 48 is more favorable. Sec. 48 provides for a solar energy tax credit for the installation of solar panels as part of the general business credit under Sec. 38. Under Sec. 48(a)(5)(D)"
"Sec. 48(a)(3)(A)(i) defines equipment that uses solar energy to generate electricity or to heat or cool a structure as energy property, as long as it is not used to heat a swimming pool."
