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Curtailment Tracker: Solar, wind generation curtailments fall 55% year on year


January curtailments rose slightly month on month

Localized curtailments made up 75% of month's total

Houston — California Independent System Operator wind and solar generation curtailments started the year 55% lower than a year ago as localized curtailments accounted for 75% of the generation curtailed in January, according to grid operator data.

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In comparison, localized curtailments accounted for 92% of the 138.002 GWh curtailed in January 2020, according to ISO data. January wind and solar curtailments across the ISO's footprint totaled 62.330 GWh, up 6.199 GWh from December, but down 54.8% from a year ago, according to Cal-ISO data. In comparison, curtailments last January jumped 99% month on month and spiked 981.3% year on year.

ISO curtailments have been on the rise, climbing 65% year on year in 2020, jumping 108.5% in 2019, up 14.8% in 2018 and an increase of 30.2% in 2017, according to ISO data. Curtailments reached an all-time peak in April 2020 of 318.444 GWh.

There are two types of curtailments. Systemwide curtailments occur when there is an oversupply, and localized curtailments occur when the amount of power from one transmission point to another point is controlled for congestion management. Localized curtailments accounted for nearly 72% of 2020 curtailments, according to ISO data.

Generation & spot prices

Solar-powered generation accounted for 10.3% of the total fuel mix in January, an increase of 2.4 percentage points year on year and up 1.3 percentage points month on month, according to ISO data. Wind-powered generation made up 6.3% of the fuel mix in January, an increase of 1.2 percentage points year on year and up less than 1 percentage point month on month.

Cal-ISO has 24.474 GW of installed renewable capacity across the ISO footprint and solar accounts for 57.5% with 14.066 GW, while wind accounts for 28.3% at 6.933 GW, according to the ISO's latest "Key Statistics" report. The remaining 14.2%, or 3.475 GW, comes from geothermal, small hydro and biofuels.

Cal-ISO peakload averaged 26.869 GW in January, down 4.3% month on month and a decrease of about 1% year on year, according to ISO data. Average temperatures across the ISO footprint were 2% higher than normal, causing heating-degree days to be 13% lower than normal, according to CustomWeather data.

SP15 on-peak day-ahead locational marginal prices average of $32.29/MWh in January, down 19.7% month on month on lower spot gas prices, according to Cal-ISO data.


So far in February, wind and solar curtailments have totaled 162.419 GWh through Feb. 21, 34% lower than the same period in February 2020, according to ISO data.

SP15 on-peak balance-of-the-month traded in the low $30s/MWh on the Intercontinental Exchange Feb. 23.

The on-peak February package averaged $36.28/MWh in its last month, steady with the 2020 package average a year ago, according to S&P Global Platts data.

There is a greater probability for below-normal temperatures across California in the 6-10 day temperature forecast while precipitation is forecast normal to below normal, according to the US National Weather Service.