By Rich Heidorn Jr.

FERC on Wednesday accepted MISO’s compliance filing spelling out rules for its new energy storage category, rejecting a protest and rehearing request by Indianapolis Power & Light (ER17-1376-002, ER17-1376-003).

MISO was responding to FERC’s March 23 ruling approving the creation of a Stored Energy Resource Type II that ordered the RTO to flesh out the concept further. MISO proposed the new storage category last year following IPL’s complaint against the RTO’s existing storage participation rules. (See FERC OKs MISO Plan to Expand Storage.)

In its compliance filing, MISO revised the definition of SER-Type II resources to clarify that they are eligible for up/down ramp capability if technically capable.

It also said that SER-Type II resources will be subject to the same must-offer obligation that applies to other capacity resources. MISO said it would be expensive and time-consuming to redesign its day-ahead market software to exclude such resources from the must-offer obligation. However, MISO also revised its Tariff to allow the storage facilities to derate their capacity to limit their supply to four hours.

The filing also revised the definition of station power to exclude the energy used to charge an SER-Type II resource.

In Wednesday’s ruling, FERC said MISO’s filing was largely responsive to the March order, although it agreed with IPL that Tariff changes regarding up/down ramp capability are incomplete and ordered the RTO to add additional Tariff language.

The commission rejected IPL’s protest of MISO’s proposal to apply the must-offer rules to SER–Type II resources that provide capacity. But it noted that Order 841 required each RTO/ISO to demonstrate that its existing market rules allow storage resources to provide capacity in a way that acknowledges their limitations.

“Therefore, while we accept MISO’s clarification that its must-offer rules apply to SER–Type II resources, we note that MISO still has a compliance obligation under Order No. 841 to demonstrate how its capacity market acknowledges the energy limitations of electric storage resources,” the commission said.

The commission also rejected IPL’s request for rehearing, saying it had addressed the company’s arguments in both the March 2018 order and a February 2017 ruling. “Indianapolis Power does not raise any issues in its rehearing request challenging the commission’s conditional acceptance of MISO’s compliance filing that are new to this proceeding or that Indianapolis Power had not raised earlier,” FERC said.