You will be eligible for the Residential Energy Efficient Property Credit on the new home with the solar panels installed.
As stated in the instructions for Form 5695 Residential Energy Credits - https://www.irs.gov/pub/irs-pdf/i5695.pdf
Only the residential energy efficient property credit (Part I) is available for both existing homes and homes being constructed. The nonbusiness energy property credit (Part II) is only available for existing homes.
