Looking Ahead: Reliability & Resource Adequacy in the West

The Western Assessment is a probabilistic analysis of resource adequacy across the entire Western Interconnection at an hourly level over the next 10 years. WECC developed the assessment based on data collected from Balancing Authorities (BA) describing their demand and resource projections. It evaluates two scenarios: a stand-alone scenario, in which each region must meet its own demand without imports; and an imports scenario, in which regions may use imports to meet demand. For each of the five subregions’ scenarios, WECC developed three variations. The first looking at existing resources; the second adding Tier 1 resources, which are those not available yet but under construction, and then Tier 2 resources, which are under some state of acquisition, but construction has not begun. These scenarios highlight a broad range of future resource possibilities, including known and expected resource retirements as well as known-unknowns of future resource acquisition by omitting Tier 1, or Tier 1 and Tier 2, resources in the scenario variations.

The one-day-in-ten-years (ODITY) threshold is a tolerance level for experiencing a loss of load event once every 10 years. The ODITY threshold translates to a 99.97% probability of being resource adequate over a 10-year period. Under the most optimistic assumptions about future loads, resources, and imports, there are still hours in which the interconnection does not meet the ODITY threshold for all 10 years studied. The Desert Southwest (DSW) and Northwest Power Pool-Central (NWPP-C) subregions, and the southern California portion of the California and Mexico (CAMX) subregion are most at risk of experiencing unserved load.

For example, one of the Western Assessment’s findings under the imports scenario using all existing, Tier 1, and Tier 2 resources (the most optimistic set of assumptions for generation availability) indicates in 2021, there could be one to eight hours in which subregions will not be able to meet the planning reserve margin required to maintain the ODITY threshold. The results get worse as assumptions about resource construction and reliance on imports move to the more realistic end of the spectrum.

Another finding shows historical approaches to resource planning, if unchanged, will result in a significant degradation of resource adequacy. The typical deterministic approach to resource planning finds the peak demand hour, applies a flat, fixed planning reserve margin, and compares this information to the expected generation capacity. This approach assumes when the highest demand hour is resource adequate, all other periods are as well. Previously, this approach has been successful because system variability was low, so entities could rely on consistent resource availability.

Looking ahead, as variability increases, the certainty of generation availability for imports decreases and reliance on imports grows more precarious. Reduced availability of excess generation, coupled with increased demand for imports, can result in several entities relying on the same imported resource to be available.

In the interest of achieving high levels of system reliability, WECC provides recommendations in the Western Assessment. One adaptation for planning entities and their regulatory authorities to consider is moving away from a fixed planning reserve margin to a probabilistically determined margin. As variability grows, a dynamic planning reserve margin will better ensure resource adequacy for all hours.

WECC endorses efforts to coordinate regional resource planning on an interconnection-wide basis each year to avoid overlapping reliance on the same imports and to give transparency to subregions’ assumptions on import availability in the context of the entire interconnection.

The first part of the WECC Western Assessment includes further findings and recommendations. In-depth analysis and results for each sub-region will be released January 29 for the Desert Southwest, February 12 for California-Mexico, and February 26 for the Northwest. WECC is looking forward to working with stakeholders on resource adequacy (such as through the Resource Adequacy Forum) and expanding its engagement to meet the needs of the West’s ever-evolving bulk power system.