By Amanda Durish Cook

CARMEL, Ind. — MISO last week laid out a more detailed proposal for how it will determine the capacity accreditation of electric storage resources under FERC Order 841.

The RTO is proposing to determine electric storage resources’ capacity based on two different measurements: the resource’s power output capability and its energy storage capacity as measured by MISO’s generator verification test capacity (GVTC).

Speaking at an Aug. 8 Resource Adequacy Subcommittee meeting, Senior Adviser of Capacity Market Administration Rick Kim said the rule will ensure both a megawatt and megawatt-hour measurement of a storage resource’s capability.

Kim said for storage resources under 10 MW or that have fewer than 12 months of operational data, MISO will apply a 5% default equivalent forced outage rate in its unforced capacity calculation. Other storage resources will be assigned a forced outage rate based on their quarterly data inputs to MISO’s generating availability data system (GADS). GADS reporting is required for storage resources 10 MW and above and optional for those under 10 MW.

Because NERC hasn’t yet addressed unit reporting for storage resources, Kim said resource operators should use the “miscellaneous” unit type option when reporting unit data.

“It’s going to be another year before we see registration of energy storage resources,” he added.

Kim also said storage resources connected to the transmission system will require either network resource interconnection service or firm transmission service with MISO to ensure capacity deliverability. If resources are connected at the distribution level, MISO will ensure deliverability with the distribution provider and transmission owner on a “case-by-case” basis, he said.

MISO has said that when storage resources are connected at the distribution level, market participants “must have sufficient metering or accounting for non-wholesale transactions to prevent double counting of energy.”

The RTO in June said it would accommodate Order 841 by dividing storage bid parameters into four operating modes: discharging, charging, continuous operations and offline. Market participants will be left to choose a mode for individual dispatch intervals and will also be responsible for managing the state of charge of their storage units. (See MISO Weighing Feedback to Storage Proposal.) Storage resources will be able to set prices under MISO’s extended LMP.

MISO and stakeholders will continue to discuss storage capacity accreditation at the September RASC meeting, with draft Tariff language targeted for October. November will be used to finalize the full Order 841 compliance filing before FERC’s early December filing deadline.