MISO’s proposal to bring solar resources under its umbrella of dispatchable intermittent resources (DIRs) prompted a deficiency letter from FERC on Wednesday.

The commission directed MISO to be more specific about its defined categories of solar generation and exactly when the RTO intends for them to come under dispatch (ER20-595).

FERC said according to MISO’s transmittal letter accompanying the proposal, solar resources already in commercial operation “can, but are not required to” register under its DIR category, while solar resources with a generator interconnection agreement as of March 15, 2020, “are subject to the DIR registration requirement and will have until March 15, 2022, to register as a DIR.” Solar resources without a GIA as of March 15 “must register as a DIR in order to operate,” FERC summarized.

However, the commission noted that MISO’s proposal didn’t similarly mention the three solar categories based on GIA date, only stating that “any generation resource fueled by solar energy not in commercial operation prior to March 15, 2020, may qualify as an intermittent resource but must register as a dispatchable intermittent resource by March 15, 2022.”

The commission asked MISO to clarify what solar resources are meant to adhere to the 2022 deadline. It also asked when solar resources must register as DIRs if they are without GIAs as of March 15, 2020, or if their commercial operation dates are later than March 15, 2022.

In preparing the plan, MISO said it was handling the dispatch expansion much like it did with wind generation in 2011. (See Anticipating Boom, MISO Extending Dispatch to Solar.) RTO staff have said they wouldn’t grandfather certain solar resources as DIRs.

— Amanda Durish Cook