The California Public Utilities Commission on Thursday approved changes to the state’s resource adequacy requirements meant to bolster its ability to withstand extreme weather events like those that led to energy emergencies in recent summers and to account for the replacement of thermal generation with wind, solar and battery storage.
“The goal is a framework that can ensure resource sufficiency for grid reliability in all hours of the day, even as the state’s energy mix evolves and statewide load increases,” CPUC President Alice Reynolds said, referring to the state’s move toward 100% carbon-free resources by 2045 and its efforts to electrify buildings and transportation.
In its decision, the CPUC adopted a proposal by Southern California Edison for a “24-hour slice” that requires each load-serving entity to show it has enough capacity to satisfy its specific gross load profile, including a substantial planning reserve margin, in all 24 hours on CAISO’s “worst day” of each month.
“The worst day would be defined as the day of the month that contains the hour with the highest coincident peak load forecast,” the decision said. “For an LSE that uses energy storage to meet requirements, the LSE must demonstrate it has excess capacity that offsets the storage usage plus efficiency losses. An LSE could combine the capabilities of its resource mix to cover all 24 hours.”
The CPUC decided to revise its 16-year-old RA framework in response to “recent trends and concerns that have arisen, which have led to the commission’s re-examination of the RA program to ensure that the framework can provide grid reliability at all times of the day,” the decision said.
In particular, the commission had relied on a maximum cumulative capacity (MCC) “bucket” structure that it said was no longer adequate.
“The MCC bucket requirements are developed using average monthly summer load duration curves and monthly resource use limitations to prescribe cumulative caps that limit how much LSEs can rely on certain resources in meeting monthly RA requirements,” the decision said.
The MCC buckets largely ensure LSEs bring a mix of resources to meet peak demand, which traditionally occurred on weekdays starting in the late afternoon lasting until nightfall. Recent experiences, however, have shown that to be inadequate. Rolling blackouts and near-blackouts in August and September 2020 occurred on weekends and well after sunset.
An increased mix of weather-dependent variable resources, mainly solar and wind, and four-hour battery storage have shifted the overall reliability picture. So has the retirement of coal and natural gas plants throughout the West.
“With the growing penetration of variable energy and use-limited resources, we observe that the 24-hour slice framework can better address reliability than the current MCC bucket structure,” the decision said.
“We have previously emphasized the concern that the MCC buckets are not binding and do not account for energy storage charging needs,” it said. “The 24-hour framework directly addresses energy sufficiency at an individual LSE level by requiring each LSE to provide sufficient excess energy to charge any storage it shows across the 24-hour slices.”
Commissioner Clifford Rechtschaffen said he supported the changes “given what’s happened on our grid the past few years. The mix of resources that we’re employing is changing rapidly, and this has led to new reliability challenges.”
“Ultimately our hope is that load-serving entities will use this new construct … as an opportunity for them to tailor the mix of resources that they procure for their customers’ energy needs to match … the hourly, daily and seasonal variation in their customer load.”