Currently the Federal Investment Tax Credit (ITC) provides a credit of 30% of the amount of investment in solar property. Both the residential and commercial ITC are equal to 30 percent of the basis that is invested in eligible property, which commence construction through 2019. The ITC then steps down to 26 percent in 2020 and 22 percent in 2021. After 2023, the residential credit will drop to zero while the commercial and utility credit will drop to a permanent 10 percent. Commercial and utility projects, which have commenced construction before December 31, 2021, may still qualify for the 30, 26 or 22 percent ITC if they are placed in service before December 31, 2023. The Treasury and IRS are currently drafting guidance, which will inform solar developers of which percentage of ITC they will qualify for depending on when they started their project. (Source)
Please consult a tax professional for more information before making any purchasing decisions.