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California ISO issues heat bulletin in advance of forecast high temperatures

June 14, 2021

by Paul Ciampoli
APPA News Director
June 14, 2021

The California Independent System Operator (ISO) on June 11 issued a heat bulletin in advance of high temperatures forecast for this week.

Although no outages or other power disruptions were expected, triple-digit heat is forecast to start spreading across California and the southwest Tuesday, June 15 through Friday, June 18, and the ISO could take a number of actions to reduce demand and access additional energy.

The National Weather Service on June 14 said that temperatures well into the 110s are forecast for the next few days in the Desert Southwest, and temperatures exceeding 100 as far north as Montana especially June 15 will be 25+ degrees above average. “Dozens (possibly hundreds) of daily record high maximum and minimum temperatures are likely to be set over the next few days in California, Intermountain West, Desert Southwest, Rockies, and High Plains,” the NWS said.

The ISO declared a grid Restricted Maintenance Operation (RMO) for noon to 10 p.m. from Tuesday, June 15, through Friday, June 18, due to forecasted high temperatures and demand. The RMO cautions market participants that all available resources are needed, and to defer scheduled maintenance on generators or transmission lines, if possible.

CAISO last week said it was still too early to know the precise impact that the high temperatures will have on the electric grid. But the ISO “is closely monitoring conditions and the anticipated increase in demand for electricity and will issue additional public notifications as warranted.”

Those notifications could include a series of steps aimed at reducing electricity use, such as a Flex Alert, a voluntary call for consumers to conserve electricity between 4 p.m. and 9 p.m. In extreme hot weather, those are the most difficult hours of the day to balance electricity supply and demand because solar resources are diminishing as more air conditioners and other home appliances are typically being used.

“In the past, Californians responding to calls for conservation has significantly reduced stress on the grid and avoided further emergency actions, including the need to rely on reserve power resources or rotating outages. But as happened during an intense regional heat wave last August that hit much of the Western U.S., rotating power outages could become necessary if weather and stressed grid conditions persist or worsen,” the grid operator said.

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