The federal solar tax credit is a tax credit that you can receive when filing your annual tax return. There is no limit to the amount you can claim on this credit, you can claim your 30% tax credit on this amount.
If your roof needs to be replaced as part of your solar project it may qualify for the tax credit.
The Office Of Energy Efficiency & Renewable Energy has provided this homeowner’s guide to the Federal tax credit for solar photovoltaics.