CAISO sets back-to-back solar peak records in April; power spot prices plunge

The California Independent System Operator has set back-to-back solar peak records so far in April, pulling down spot prices into single digit territory.

The record of 17.802 GW was reached at 12:37 pm PT April 11, surpassing the April 10 record by 3.7%, according to CAISO latest Key Statistics report released April 16.

CAISO also set an instantaneous all-time maximum demand served by solar of 86.4% at 12:30 pm April 11, surpassing the record of 82.4% reached a day earlier. Before that the record was from April 2022.

"We typically hit renewable peaks in the spring season because of mild weather reducing air conditioning and heating use, and the higher sun angle accelerating rooftop and grid-scale solar output," CAISO spokeswoman Anne Gonzales said April 17. "We tend to see records on weekends, as loads are even lower."

CAISO peakload was 26.563 GW April 11 and has averaged 24.985 so far this month, 2.4% lower than a year ago.

CAISO solar penetration reached a year-to-date high of 26.03% on April 11, according to the Platts solar penetration index. Solar penetration didn't reach that high in 2023 until December when it peaked at 26.23% for the year.

Solar penetration for the noon hour on April 11 was 40.45%, the highest level so far this year for that hour, according to Platts' hourly penetration index. In comparison, during the same period last year, solar penetration reached as high as 37.41% for the noon hour on Feb. 1, 2023.

Market impacts

Spot power prices have been trending lower year on year on lower natural gas spot prices and more renewable generation supply, including hydropower following years of drought.

The SP15 on-peak day-ahead locational marginal price was $2.21/MWh April 10 and $8.79/MWh April 11, according to CAISO data. However, prices fell as low as minus $26.26/MWh for April 6 as the thermal market share sank to 14.2% of the daily total fuel mix, after averaging 33% of the mix in 2024 up until that date, according to CAISO data. A 5-percentage point day-on-day increase in solar generation share helped fill in the gap.

CAISO system solar curtailments have averaged just under 25 MW so far in April, 96% lower than during the same period a year ago, according to solar curtailment index data from Platts, which is part of S&P Global Commodity Insights. There are two types of curtailments: system curtailments that occur when there is an oversupply and localized curtailments that occur when the amount of power from one transmission point to another is controlled for congestion management.

Solar stats

CAISO has 19.011 GW of installed solar generation capacity, which accounts for the majority of renewable resources on the grid at 62%, according to the Key Statistics report. Solar capacity has increased nearly 15% compared to a year ago and 26% from two years ago.

There are currently 28.6 GW of solar projects in the CAISO generation queue, including 13.8 GW that have executed interconnection agreements and nearly 4.5 GW of those have on-line dates expected listed for 2024. Only two solar projects slated to come online in 2024 do not have batteries connected.

Solar accounts for about 25% of the projects in the CAISO generation queue, behind batteries with 64%. CAISO has 7.626 GW of installed battery capacity as of April 1, a jump of 69% year on year.

California leads the US in utility-scale solar capacity with 19.98 GW by the end of 2023, up 13% year on year, according to the American Clean Power Association's Q4 2023 report. CAISO manages the flow of electricity for about 80% of California and a small part of Nevada.