If I have the paperwork dated for 2017 that I plan to go solar but due to scheduling had it installed in 2018, can I claim the federal tax incentive for my 2017 taxes?

I have been working with an agency to put solar panels on my roof and have signed all the loan paperwork for 2017 but due to scheduling I won't get a slot till 2018. Does that make me ineligible for the tax credit? What if I do end up getting a slot and it's installed in 2017 BUT I don't have permission to operate from the city yet?