I installed solar at home in 2020. It's asking me for the address of the home where it was installed. Should I use my mailing address or the house's street address?

You must enter the physical address of the home or business where solar panels were installed. Purchasing solar panels which can be installed in your home or business allows you to claim a non-refundable energy credit (Form 5695) which can be used to lower tax liability and can be carryforward to the following year/s until it's exhausted. The cost of installing solar panel is claimed on the year.it was installed. 

The residential energy credit in 2020 is 26% of the cost of installation.