The applicable supplier contracts define the end date of the contract for several different circumstances; please review, for example, Paragraph 2 on page 1 of the AIC REC Master Agreement.  Generally, the expiration of the contract is five years after the date of the first REC delivery by the last system in the portfolio. In your example, if the first REC delivery of this single system occurs on January 1, 2018, the contract expires on December 31, 2022.