California ISO: Board adopts market tools to help integrate new battery storage resources

California ISO COO Mark Rothleder noted that throughout the West, it is expected that energy storage, paired with wind and solar resources, will be pursued to accommodate the retirement of natural gas- and coal-fired generation

The California ISO on Nov. 19 said that its Board of Governors has adopted market tools that will help integrate new battery storage resources, as well as improve overall reliability for fall 2021.

The ISO said that the board’s approval of Hybrid Resources Phase 2 was expedited to accommodate more than 1,500 MW of storage capacity expected to connect to the grid by the end of next year. The storage capacity is part of the state’s procurement goal of 3,300 MW of battery resources by 2023 to help replace retiring fossil fuel generation, the ISO said.

As noted in a Nov. 11 memorandum from ISO Senior Vice President and COO Mark Rothleder to the board, interest in energy storage continues to grow as state and federal policy makers and regulators promote energy storage development to help decarbonize the grid. Throughout the West, Rothleder said, it is expected that energy storage, paired with wind and solar resources, will be pursued to accommodate the retirement of natural gas- and coal-fired generation.

Rothleder said that under the hybrid resources initiative, ISO management has developed two market models for generation with different technology types located behind the same interconnection. The first option is the “co-located” resources model, which the board approved in July, Rothleder said, adding that under that model, the resources behind the interconnection have separate resource IDs and are separately dispatched through the ISO market, even though they may have a shared commercial interest.

The second option, which the board adopted on Nov. 18, is a model for “hybrid” resources, where the generation resources are modeled under a single resource ID, Rothleder said, noting that the hybrid model allows for the underlying resources to be managed by the resource operator as opposed to the ISO.

Rothleder said that management proposes new provisions for managing hybrid resources to allow them to provide energy and ancillary services, with the proposal including a dynamic limit tool that will enable the resource operators to communicate their maximum and minimum operating limits to the ISO in real time.

Rothleder also said that management proposes additional functionality to enable co-located resources to provide ancillary services in addition to energy. He noted that management’s proposal includes a new requirement for telemetered data, called the high sustainable limit, from hybrid and co-located resources that have a variable resource component. That information, Rothleder said, will help the ISO forecast the variable components of the hybrid and co-located resources.

Further discussing the dynamic limit tool, for instance, Rothleder said that while a hybrid resource is modeled and operated as a single resource, it can have multiple underlying generating types supporting it and operating at a single point of interconnection. A hybrid resource that has variable energy and storage components will have operational challenges given the different limitations of the underlying technology types, Rothleder said, adding that management does not propose to extend the same functionality offered to independent variable energy resources to hybrid resources.

For example, unless given a curtailment instruction from the ISO, variable energy resources are allowed to produce as capable to account for variability in output, and the market software optimizes state of charge for storage resources, Rothleder said. A hybrid resource will have neither market function, and will have requirements to submit bids to, and follow all dispatch instructions from, the ISO, Rothleder said, adding that hybrid resources will be managed by their operator like other resources available for dispatch to fulfill market awards and commitments.

To account for the variable nature of hybrid resources, management proposes to develop a new tool for hybrid resources to communicate their generating potential to the ISO — the dynamic limit tool — Rothleder said, adding that that information will support feasible dispatch instructions in real time. The dynamic limit tool will be available to hybrid resources to specify the upper and lower operational limits for the resource for each five minute interval, going out three hours into the future, Rothleder said.

The ISO said in its statement that FERC on Nov. 19 approved the Hybrid Resources Phase 1 tariff.

As noted in FERC’s filing accepting the tariff revisions — effective Dec. 1 — the ISO in September submitted, under section 205 of the Federal Power Act, proposed revisions to the ISO’s Open Access Transmission Tariff (OATT) regarding modeling separate resources that are co-located at a single generating facility, and data requirements for hybrid resources that include a wind or solar generation component.

FERC noted that the ISO proposes to establish market rules for using an aggregate capability constraint in its market model for co-located resources at a single generating facility. FERC said that according to the ISO, its current market rules can result in stranded capacity because they restrict the sum of the maximum operating levels for the resources at a generating facility that can be registered in the ISO’s master file so that the sum does not exceed the generating facility’s interconnection service capacity.

FERC noted that according to the ISO, using the aggregate capability constraint will promote market efficiency by allowing co-located resources to manage the sum of their maximum operating level without the need for additional interconnection upgrades. The ISO notes that while that could allow co-located resources’ combined maximum capability to exceed the generating facility’s interconnection service capacity, the ISO will limit any awards or self-schedules for energy in the day-ahead and real-time markets to the generating facility’s interconnection service capacity, and require the generating facility to install generator limiter controls so that the combined output of the co-located resources does not exceed the generating facility’s interconnection service capacity, FERC said.

Among other things, the ISO said in its statement that implementation of Phase 1 is scheduled for this fall.




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About Corina Rivera-Linares 3286 Articles
Corina Rivera-Linares was TransmissionHub’s chief editor until August 2021, as well as part of the team that established TransmissionHub in 2011. Before joining TransmissionHub, Corina covered renewable energy and environmental issues, as well as transmission, generation, regulation, legislation and ISO/RTO matters at SNL Financial from 2005 to 2011. She has also covered such topics as health, politics, and education for weekly newspapers and national magazines.