The solar panel tax credit may be claimed by the person who actually pays for the system to be installed on a home that they live in. It does not have to be their main home, and they do not have to own the home.
However, you must take care in your own accounting of the solar panel system. Normally, if you pay for a permanent improvement to be installed on your home, the cost of that improvement is added to your cost basis, and may reduce the amount of capital gains tax you owe when you sell the home. With the solar tax credit, you have to reduce the cost basis by the amount of the credit. For example, if you paid $30,000 to install a system and received a $9000 tax credit, you would add $21,000 to the cost basis of your home. However, you can only increase your basis by the amount you actually pay, even if the solar system cost more. You can’t increase your basis by the cost of an improvement that somebody else paid for.
