California Independent System Operator wind and solar generation curtailments increased 47% month on month in December as 1.077 GW of installed renewable capacity was added to the grid during the same time.
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Curtailments increased 13.1% year on year to 63.495 GWh in December, according to ISO data. Curtailments reached an all-time record of 341.959 GWh curtailments in March.
"It doesn't look like there is an easy explanation for the increase in curtailments," said Morris Greenberg, senior manager of North American Power for S&P Global Platts Analytics.
While nuclear output rose 95% year on year in December, but so did loads.
For all of 2021, curtailments averaged 125.403 GWh, a decrease of 5.2% from 2020, according to CAISO data.
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 about 91% of the renewable generation curtailed in December and have made up 81.8% of curtailments for all of 2021, according to ISO data. In comparison, localized curtailments accounted for nearly 73% of the wind and solar generation curtailed in 2020.
On-peak wind and solar curtailments averaged 334.5 MW in December, up 31% month on month, according to the S&P Global Platts systemwide renewable generation curtailment index. There were no off-peak curtailments, according to the Platts data.
Wind generation output climbed 51.5% year on year to average 2.070 GW in December, but solar generation output fell 4% to average 2.079 GW due to seasonality, according to CAISO data. Wind and solar generation accounted for 16.1% of the total fuel mix for December, up from 14.6% a year ago.
CAISO-installed renewable capacity increased 8% year on year in December to 26.414 GW, up 1.94 GW from year-ago levels, with solar accounting for 56.9% and wind making up 30.2%, according to CAISO's December Key Statistics report. The remaining 12.8% comes from geothermal, small hydro and biofuels.
So far this month, wind and solar curtailments have totaled 27.8 GWh through Jan. 19, down 28.5% from the same period a year ago, according to ISO data. SP15 on-peak balance-of-the-month was valued in the mid-$40s/MWh on the Intercontinental Exchange Jan. 21, within $1 of the day-ahead package value on ICE.
The six- to 10-day outlook indicates a greater probability for above-normal temperatures across southern California and near normal in northern California, while the three-month outlook shows a greater chance for below-normal temperatures in northern California and equal chances for above- and below-normal temperatures in central and southern California, according to the US National Weather Service.
The SP15 on-peak January package averaged $73.64/MWh in its last month, 74.2% higher than the 2021 package average a year ago following higher gas forwards, according to S&P Global Platts data. On-peak February is currently in the mid-$50s/MWh, 62% above its 2021 counterpart a year ago, while the March package is in the upper $30s/MWh, 36% higher.