Western utilities and their state regulators should increase their coordination and adopt dynamic planning reserve margins to help ensure the region’s grid is equipped with adequate resources as it takes on more variable generation, according to a new WECC report.

The recommendations come out of WECC’s first Western Assessment of Resource Adequacy Report, released last week. The report, the regional entity’s signature work for 2020, is the product of an internal effort to repurpose its mission by focusing on the growing challenges of resource adequacy in the Western Interconnection. (See WECC Seeks to ‘Invent’ Future with RA Forum.)

“We are really excited about this work,” Branden Sudduth, WECC vice president of reliability planning and performance analysis, said when staff provided a preview of the study at a meeting of the organization’s Board of Directors on Dec. 9.

The report is intended to supplement NERC’s 2020 Long-Term Reliability Assessment, published Dec. 15. (See NERC: Grid Operations ‘Fundamentally’ Changing.) Some Western stakeholders have complained that last year’s assessment failed to capture the risks that emerged this summer when a record-setting heat wave forced CAISO to initiate rolling blackouts for the first time in two decades while other balancing authorities prepared to take similar measures.

Both WECC and a joint root-cause analysis by California agencies have cited supply shortages as a key factor behind the energy emergencies, although WECC’s effort to address regional RA preceded the heat wave event. (See WECC Says Extreme Events Require Forecast, RA Changes.)

To account for the local and topological factors that contribute to interconnection-wide RA issues, the study divides the Western Interconnection into five subregions that align with the region’s three reserve sharing groups: CAISO, Southwest Reserve Sharing Group (SRSG) and Northwest Power Pool (NWPP).

Because of variations in peak seasons, the NWPP subregion is further divided into Northwest, Northeast and Central subsections. The report refers to CAISO as California-Mexico (CAMX) and the SRSG as the Desert Southwest (DSW).

Scenarios and Variations

WECC’s assessment applied two scenarios to each of the five subregions “to highlight a broad range of future resource possibilities, including known and expected resource retirements.” Scenario 1 assumes each subregion is required to meet its own demand, while Scenario 2 allows for imports.

The RE overlaid each scenario with three variations of resource availability. Variation 1 includes all resources currently in service and expected to run in future forecasts. Variation 2 includes existing resources and those under construction and expected to run in the forecast year (Tier 1 resources). Variation 3 includes existing and Tier 1 resources as well as those currently in licensing or siting phases but not yet under construction (Tier 2).

The reports points out that RA planning has typically relied on a “deterministic” — or static — approach that calculates needs by comparing the amount of available generation capacity, plus a planning reserve margin, to the highest demand of the year. If those resources cover the peak day, they are assumed to be sufficient for all other days of the year.

That planning approach is fraying at the edges with the increased adoption of variable renewables, prompting WECC to adopt a “probabilistic” approach that examines resource needs on an hourly basis over the next 10 years using supply and demand projections provided by Western balancing authorities. WECC ran the data through its Multi-Area Variable Resource Integration Convolution modeling tool, which matches generation to load for each hourly interval to determine if there is enough capacity to meet demand and to calculate a planning reserve margin.

“The model determines whether there are enough resources in the interconnection to meet expected demand while maintaining reserves to account for any variations from the expected forecasts or loss of generation. The results from this analysis are used to determine where resource shortfalls may occur in the system over any given study period,” the report said.

WECC’s analysis found that under Scenario 1, all subregions show some risk of loss of load, even with Tier 1 and 2 resources. All variations of that scenario contain hours with insufficient resources to serve load and maintain planning reserve margins.

The RE also found that most hours of unserved load can be solved under Scenario 2.

Still, the report notes that “under the most optimistic assumptions about future loads, resources and imports, there are still hours in which the interconnection does not meet” the one-day-in-10-years (ODITY) threshold for the 10 years studied. The DSW, NWPP Central and Southern California portion of CAMX were particularly vulnerable to loss of load, WECC found.

In what might be the most pressing finding, the analysis showed that even under the most optimistic assumptions under Variation 3 of Scenario 2, 2021 could see one to eight hours in which some subregions fail to meet the required planning reserve margins of the ODITY standard.

“The results worsen as the assumptions about resource construction and reliance on imports span to the more realistic, less optimistic end of the spectrum,” WECC said.

WECC also found that increased volumes of variable resources on the system compound the RA issues, making resource planning more challenging because more resources are not consistently available to meet demand. Additionally, demand is also becoming increasingly variable because of climate change, behind-the-meter generation and transportation electrification.

The report’s final finding: RA will suffer “significant degradation” if historical approaches to resource planning are left unchanged.

Getting There

WECC’s first recommendation is for resource planners and regulators to transition away from fixed planning reserve margins to dynamic margins aligned with hourly needs.

The second recommendation is for planning entities to not only consider how much additional capacity is needed to mitigate variability but also the expected availability of new resources. “Understanding the differences in resource type availability is crucial to performing resource adequacy studies,” WECC said.

The report’s final recommendation encourages balancing authorities to coordinate their planning activities each year to help prevent them from relying on the same resources. “This coordination will help subregions make assumptions about import availability in the context of the entire interconnection,” WECC said.

“I think we got the train on the track now and can understand how to manage this resource adequacy issue,” WECC Director Gary Leidich said during the Dec. 9 board meeting. “This information has to get in the hands of policymakers so they understand what’s going on.”

Director Richard Woodward said he liked the idea of a dynamic reserve margin but asked, “How do we get there?”

Matt Elkins, WECC manager of performance analysis, said he wants the RE to meet with planning entities to explain the range of resources they will need to meet reliability requirements. “We have to do it together.”

WECC’s Sudduth added that he was encouraged to see multiple states already working together to address RA issues.

Director James Avery said it will be necessary for every state in the West to count RA in the same way. “Otherwise, the work we do is going to be meaningless.”

WECC said it will release a more detailed analysis of subregional RA issues in the first quarter of 2021.