Curtailment Tracker: Cal-ISO wind, solar curtailments in July higher year on year

California Independent System Operator wind and solar generation curtailments increased 10.4% year on year in July on less hydropower generation and lower imports, according to grid operator data.

ISO curtailments sank 63% month on month to 34,086 MWh in July as ISO peakload increased 13% from June to average 37.985 GW, according to ISO data. Curtailments reached an all-time record of 341.959 GWh in March.

Localized curtailments accounted for about 92% of the renewable generation curtailed in June and made up 78.6% of curtailments from January through July, according to ISO data. In comparison, localized curtailments accounted for 68% of the 1,285.193 GWh curtailed from January through July 2020, according to ISO 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.

Generation changes

Imported generation decreased 13% year on year to average 130.361 GWh/d in July, as hydropower generation output sank 39% year on year to average 36.467 GWh/d. Solar generation output slipped 4.2% to average 114.471 GWh/d in July as wind generation output eased 8.3% to 53.348 GWh/d, according to ISO data.

Meanwhile, thermal generation output climbed 41.1% year on year to account for 43.2% of the total fuel mix in July, despite SoCal city-gate spot gas prices climbing 230% year on year to average $6.289/MMBtu for the month, according to S&P Global Platts pricing data.

As curtailments drop, wholesale power prices rise. SP15 on-peak day-ahead locational marginal prices jumped 147% year on year to average $75.33/MWh in July.

Cal-ISO installed renewable capacity increased 3.2% year on year in July to 24.783 GW with solar accounting for 57.6% and wind making up 28.6%, according to the ISO's June Key Statistics report. The remaining 13.8%, or 3.421 GW, came from geothermal, small hydropower and biofuels.

Outlook

So far this month, wind and solar curtailments have totaled 17,745 MWh through Aug. 14, 97% higher than the same period in August 2020, according to ISO data.

SP15 on-peak balance-of-the-month was valued in the mid-$80s/MWh on the Intercontinental Exchange Aug. 16, nearly 23% above where the daily traded. The SP15 on-peak August package averaged $164.31/MWh in its last month, 410% higher than the 2020 package average a year ago due to summer supply concerns with a weak hydropower outlook, continued drought and above-normal temperatures, according to Platts data. On-peak September is currently in the mid-$80s/MWh with October in the low $50s/MWh, 153% and 70% higher than their 2020 counterparts a year ago.

There is a greater probability for above-normal temperatures across California in the three-month temperature forecast, according to the US National Weather Service.