The solar tax credit is scheduled to step down over the next few years. In 2020 the tax credit will reduce to 26%. The safe harbor provision allows commercial companies to take advantage of 2019's full 30% solar tax credit, even if their system can't be completed until the following year(s).
How to "Safe Harbor" Your Commercial Solar Project
Commercial businesses are able to "safe harbor" the 30% tax credit by taking a few simple steps. The business must be under contract with a solar provider and have made a non-refundable five percent down payment by December 31. These projects will have four years to be completed to qualify for the safe harbor provision. Which means you'll have until December 31, 2023, to complete the project.
This allows businesses to take advantage of the savings while being able to plan for future construction.