The solar tax credit is nonrefundable, which means it cannot result in a refund if the individual's tax credit exceeds their liability. Instead, the leftover amount can be carried over to the following year.
For example, if you owe $1,500 in taxes and your tax credit totals $2,000, then the amount you owe is subtracted from the tax credit and the remaining $500 will be credited to your taxes the following year. This is sometimes called “rolling over.”