Interview: Cal-ISO renewable curtailments reach new record of 318,444 MWh in April

California renewable curtailments spiked to their highest level yet at 318,444 MWh in April, surpassing the record set last May by nearly 43%, according to California Independent System Operator data.

Daily solar curtailments jumped 102% month on month to average 5,053 MW in April, as wind curtailments dropped 9% to average nearly 42 MW, according to S&P Global Platts assessments.

"April and May are typically the months in which curtailments are the highest, because of cool sunny breezy weather, contributing to high generation and lower electricity demand," Cal-ISO spokeswoman Anne Gonzales said. "May's curtailment numbers will be dependent on weather conditions."

Decreased power demand from coronavirus pandemic stay-home orders amplified the problem of insufficient access of inland solar supply to demand centers, leading to increased need to curtail those renewable resources, said Morris Greenberg, senior manager of North American power analytics at S&P Global Platts.

In addition, Pacific Gas & Electric moved to a "summer" or lower transmission rating in April, because hot temperatures can cause transmission line conductors to carry less energy, Gonzales said. The lower rating coupled with transmission line outages leads to localized curtailment of renewables.

CORONAVIRUS IMPACT

California was the first state to implement a stay-home order March 19 to help prevent the spread of the coronavirus. Peakload averaged of 25,138 MW in April, down 9% from the five-year peakload average for the same period, according to ISO data

With demand down, prices weakened. SP15 on-peak day-ahead locational marginal prices plunged 33% month on month in April to average $16.50/MWh, according to ISO data. So far in May, the LMP has averaged $15.94/MWh, pacing 12% below last May's average of $18.11/MWh.

ISO RENEWABLES

While demand for power generation dropped, wind and solar generation increased.

Solar output averaged 84,439 MWh/day in April, up more than 26% month on month, but down 1.5% year on year, while wind output averaged 52,824 MWh/d, nearly 57% higher than March, but down 10% from a year ago, according to ISO data.

Cal-ISO has 23,634 MW of installed renewable resources, with solar accounting for 54.4% and wind 29.1%, according to the monthly key statistics report.

High hydro conditions typically cause curtailments to increase in the spring, Gonzales said.

As warm weather melts the snowpack, hydro reservoirs fill, allowing increased hydro generation.

"A relatively low hydropower supply this year is generally keeping curtailments lower than they could be in a high hydro year," Gonzales said.

Cal-ISO hydro output averaged 43,326 MWh in April, jumping nearly 55% from March, but 57% lower than a year ago. So far in May, hydro has trended up 32% month on month, but is 40% lower year on year.

POSSIBLE SOLUTIONS

Cal-ISO is not recommending any new transmission solutions for policy purposes at this time as the 2019-20 transmission plan did not identify any new needs.

There are two projects currently in development and due for completion in 2021 that may improve access of inland solar projects to loads, Greenberg said.

The West of Devers project will upgrade the existing roughly 48-mile transmission corridor between Devers, El Casco, Vista and San Bernardino Substations, while the El-Dorado-Lugo project is a series capacitor upgrade on the Lugo-Eldorado transmission line and associated terminal equipment upgrades, according to ISO data.

"But it looks like most of the heavy lifting will have to be done by retrofitting storage to existing solar projects," Morris said. "Mitigation steps include adding transmission capacity, adding storage, facilitating trade with other balancing authorities, providing incentives to shift load into curtailment periods."

The Western Energy Imbalance Market is an effective tool to mitigate mid-day oversupply conditions by offloading excess California solar resources, due to the regional collaboration with EIM entities, Gonzales said.

"There are opportunities to develop solutions using price signals for when curtailment may be occurring," Gonzales said of other solutions. "These solutions, including [electric vehicle] charging, can shift the load by incentivizing consumers to use electricity during oversupply conditions."