I added a solar power system to my house in 2017; financing cost over 25 years. Can I get a credit for the full cost on my 2017 return?

[Critter]

The solar credit is limited to only 30% of the total cost of the system installed and you can only use it against federal income taxes and if you cannot use it up in one tax year the unused portion is carried forward.  The fact that you are making payments on the unit over many years has nothing to do with the credit.