Unfortunately, if you don't have to pay any taxes in SC, then you won't get any benefit from the solar tax credit. Both the SC and Federal solar credit are non-refundable tax credits, which means it can only bring your taxes owed down. This could bring your taxes down to $0 in the case of Federal tax, so if you got money back it was probably a refund of taxes withheld. The SC solar tax credit is even more limited, since it can be no more than $3500 or 50% of your tax bill, whichever is lowest (in your case, 50% of $0 is $0). Both of these can be carried forward to subsequent years if you can't take the full benefit in one year.
