Cal-ISO curtailments spiking on increased renewables, less demand from coronavirus order

California Independent System Operator systemwide daily renewable curtailments have spiked above 13,000 MW, the highest level since S&P Global Platts started assessing the product in December, due to seasonal generation patterns and ordered public building closures amid the coronavirus pandemic.

Combined systemwide solar and wind curtailments climbed to 13,303.14 MW on Sunday after reaching around 12,000 MW Thursday and Friday, according to S&P Global Platts data. Previously, the highest level was 7,261.14 MW reached on February 29.

Month-to-date ISO daily curtailments have averaged 3,355 MW, an increase of 29% since February and 82% higher than the January average, according to Platts data.

CORONAVIRUS IMPACT

"We also anticipated that the load changes resulting from COVID-19 stay-at-home rules would have an impact on solar curtailments," said Morris Greenberg with S&P Global Platts Analytics.

The California State Public Health Office issued a stay home order March 19 for all residents to stay home except for essential needs.

"Loads seem to be most-affected during [hours ending] 8-17," Greenberg said. "Lower loads make it difficult to absorb all of the energy that could be produced."

After the statewide stay-home order was issued, Cal-ISO peakload fell to an average of 24,670 MW March 18-30, down 8% from the beginning of the month, according to ISO data. In comparison, the five-year peakload average for March is 27,333 MW, 5% higher than the month-to-date peakload average this year, according to ISO data.

Hourly solar and wind curtailments for hours ending 8-17 have averaged about 480 MW for the second half of March, well above the average of around 170 MW for the first half of the month, according to Platts data.

SPRING RAMP

In addition to the impacts from less generation needed due to less power demand on the system, the situation is also seasonal, Greenberg said.

"As suns elevation rises through mid-June, output will tend to increase," Greenberg said. While solar generation increases with more daylight house, demand is lower during the shoulder season due to mild weather.

Cal-ISO curtailments have been increasing since the start of the year, following the annual trend seen by Cal-ISO data going back to 2014. Curtailment ramp up in spring due to lower load, higher wind and solar generation, and increasing hydro generation that typically happens between winter and spring. This shoulder season is also when transmission maintenance may limit delivery of energy from the inland areas, Greenberg said.

Solar and wind generation output has averaged 53,981 MWh/day for the second half of March so far, an increase of 17% from the first half of the month, according to ISO data.

Likewise, combined solar and wind curtailments averaged more than 4,975 MW for the second half of March, more than double the 1,725 MW average for the first half of the month, according to Platts data.

ISO curtailment averaged 147,530 MWh for January and February, well above the 2019 average of 47,687 MWh for the same timeframe, according to ISO data.