Those credit percentages changed due to the Tax Law changes in 2018.
You are entitled to a 10% credit for the roof and a 30% credit for the solar installation. I would see if that math works out to be $3600.
The other most common reason this is happening is the
Residential Energy Credit is a non-refundable credit
which means it can only lower your tax liability. It cannot create a
refund. If you already have a $0 tax liability, then you would not
qualify for the credit.
Now, if you are claiming a credit
for the Residential Energy Efficient Property portion of the credit which is
related to solar, geothermal and wind power and fuel cells, then your unused
credit will be carried forward to future year(s) to be applied against your
future tax liability.
