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Curtailment

Curtailment is electricity a plant could have produced but did not, because it was told to or chose to cut output. It usually happens when the grid has more supply than it can use or move.

Also called economic curtailment

Formula

Curtailed MWh = available MWh − delivered MWh

Curtailment share = curtailed ÷ (generated + curtailed)

Available
What the plant could have produced, from dispatch records or a model
Delivered
What the meter recorded

With real numbersCAISO 2025: 3.66 TWh ÷ (79.12 TWh generated + 3.66 TWh curtailed) = 4.4%

In the data

3.66 TWhof wind and solar output curtailed in CAISO in 2025, 4.4% of what was available

CAISO curtailed 20 times as much in 2025 as in 2015. The share of available wind and solar output it lost rose from 0.7% to 4.4%.

Reported curtailment in CAISO, TWh per year
0.2'15'16'17'18'19'20'21'22'23'243.7'25

CAISO monthly renewables reports, economic and self-scheduled curtailment, 2015 to 2025. Latest: CAISO December 2025 Monthly Renewables Report. Market-wide, not allocated to plants.On the map

Built from InfraMap's 2025 data with the same tools the analyst uses.

Common mistakes

  1. Counting every zero-output or negative-price hour as curtailment. Calm wind, cloud, outages and maintenance also cut output.
  2. Calling clipping curtailment. A solar inverter capping output at its rating is a design choice, not an instruction.
  3. Reading a shortfall against a weather model as proof. It is a lead to check, not a measured loss.

How the InfraMap analyst defines it

Reduced output relative to a defined available-output or dispatch counterfactual. Zero output, negative price or output below a weather model is not proof of curtailment.

Reviewed October 1, 2026 against the references below. The analyst and the MCP server answer with this definition.

Primary references

See it for any US plant

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