California should have enough capacity to get through this summer’s peak demand but dwindling hydropower and limited imports during late-season heat waves could strain supply, CAISO said Friday.

“Projections for summer 2020 show that the CAISO faces a low but somewhat increased risk of encountering operating conditions that could result in operating reserve shortfalls than was projected for 2019,” CAISO’s annual Summer Loads and Resources Assessment concluded.

CAISO’s summer demand is expected to peak at 45,907 MW, a negligible increase from last year’s weather-normalized peak of 45,826 MW. The increased risk this year compared with 2019 comes from lower-than-normal hydro conditions that could be “particularly impactful in late summer” when reservoirs are at their lowest.

California’s snowpack from winter storms is the primary source of water during the state’s dry months from late spring through early fall. The statewide snow-water content in mountainous areas, including the Sierra Nevada, was 63% of average at its peak on April 7, the report said.

The state’s major reservoirs were filled to 101% of average in April, but the snow that gradually melts and refills the reservoirs is far less than last year. On April 11, 2019, the statewide snow-water content was 161% of average.

Pacific Northwest hydropower, a major source of imports for California, is expected to be about the same as last year. For instance, the Northwest River Forecast Center projected the April-to-August reservoir storage at The Dalles Dam on the Columbia River to be 95% of average. It was 94% of average in 2019.

California, however, is competing more with other Western states for a tightening supply of electricity as coal plants retire. (See Western Resource Adequacy Program in the Works.) Moreover, the state’s peak demand has shifted to later in the day, as solar energy diminishes and stops.

CAISO reiterated its concern with the situation last week.

“The CAISO will be at the greatest operational risk of a system capacity shortage later in the summer if hot weather occurs that extends beyond the CAISO footprint and diminishes the availability of surplus energy in neighboring balancing authorities for imports into the CAISO during peak hours when solar production is near or at zero,” it said.

The 2020 summer report didn’t assess risk from transmission outages because of wildfires but acknowledged it “could hinder imports during critical supply conditions.”

Planners didn’t have enough data to factor in the effect of decreased load on summer demand from the COVID-19 crisis and California’s stay-at-home order.

After Gov. Gavin Newsom issued the order in March, weekday loads were down by about 7.5% during peak-demand times and down 5% during off-peak times; weekend load reductions were 3% during peak demand and 1% off-peak, CAISO has said. (See Western EIM Governing Body Hears COVID-19 Updates.)

CAISO and the California Public Utilities Commission have been worried about capacity shortfalls that were projected to start as early as this summer and grow significantly worse beginning in summer 2021.

The CAISO assessment could allay fears about capacity shortfalls this summer, but next year may be another story.

Last September, Mark Rothleder, CAISO vice president for market policy and performance, told the CPUC that the state was facing shortfalls to its capacity needs, including a 15% planning reserve, of 4,400 MW in 2021 and 4,700 MW in 2022. (See CAISO, CPUC Warn of ‘Reliability Emergency’.)

“The issue is not so much at the peak hour,” Rothleder said. “It’s at the near-peak hour as the sun goes down.”

CAISO and the CPUC have been working to address the issue. The commission ordered some older once-through-cooling plants that were scheduled to retire to remain open through 2023. It also ordered all load-serving entities under its oversight to collectively procure 3,300 MW of capacity, on a basis proportional to projected load, by August 2023. (See California PUC Votes to Keep Old Gas Plants Operating.)