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What Is Curtailment?

CAISO monthly data through July 2026 (CAISO as-of August 05, 2026) · Updated August 21, 2026

Curtailment is a deliberate reduction of a power plant’s output below what it could have produced, ordered or priced in by the grid operator. In the California ISO, the grid operator with the cleanest public series, 241,073 MWh of wind and solar output was curtailed in July 2026, and 4.79 million MWh in 2026 through July (+53% vs the same months of 2025). Curtailment peaks in spring, March and April on average in this series, when strong midday solar meets mild demand. The word also has a second, different meaning now in the news, load curtailment, covered below.

Why curtailment happens

Two mechanisms account for most of it:

• System oversupply. Generation exceeds what demand plus exports can absorb, so the market price falls until some plants reduce output, or the operator instructs reductions. Midday solar in spring is the classic case: output is high while heating and cooling demand are both low.
• Local congestion. A transmission line or interface cannot carry all the power out of an area, so generation behind the constraint is reduced even when the wider system could use it.

Grid operators also distinguish economic curtailment (the plant reduces output because the local price makes running uneconomic) from operator-instructed reductions, and the exact definitions differ between grid operators. That is one reason this page does not add regions together.

How much: the CAISO series

Source: CAISO, monthly wind and solar curtailment totals, 2014–present, as of August 05, 2026. CAISO discontinued its granular daily curtailment feed on June 1, 2025; the monthly totals series continues and is the citable public record.

Annual sums of the monthly series; first and last years are partial and the month count says by how much. For 2024, EIA's analysis of the same CAISO data reported 3.4 million MWh curtailed, up 29% from 2023, 93% of it solar, and estimated that battery storage growth and the Western Energy Imbalance Market avoided roughly 274,000 MWh of additional curtailment (EIA Today in Energy, May 28, 2025).

Other U.S. grid operators publish no comparably clean curtailment series: ERCOT does not publish one, and figures quoted for it come from secondary analyses. This page therefore stays anchored to CAISO and reports other regions only as dated, attributed statements.

The other meaning: load curtailment

Generation curtailment, everything above, reduces a power plant’s output. Load curtailment reduces customers’ consumption, and it is why the word is in the news for a second reason. On July 27, 2026, PJM’s board directed a FERC filing under which, during capacity shortages, new “Large Loads” (end-use customers with at least 50 MW of peak load at a single site, which covers most hyperscale data centers) that do not bring their own generation by June 1, 2027 and have not otherwise secured supply “will be subject to curtailment prior to deployment of Pre-Emergency Load Management” (PJM). A headline about curtailing data centers and a headline about curtailing solar farms describe opposite sides of the same balance: one trims demand, the other trims supply.

Background on the demand side of that story: how much electricity data centers use and whether data centers are raising electricity prices.

China and the world

Curtailment made world news in August 2026 when the Centre for Research on Energy and Clean Air and Global Energy Monitor published a modeled, weather-adjusted estimate that up to 360 TWh of wind and solar output was curtailed in China in the first half of 2026, up 49% year over year, about 26.1% of wind and solar generation (CREA/GEM, August 2026). China’s National Energy Administration reports much lower official utilization-based figures for the same period: about 8.6% of solar and 9.1% of wind output curtailed. The CREA/GEM number is an estimate from a model and contradicts the official statistics; both are shown here, and this page does not decide between them.

Country figures are not comparable with each other or with the CAISO series: definitions differ (economic vs. instructed reductions, utilization rates, unmetered curtailment behind the inverter), so no ranked country table appears on this page.

Questions people ask

What is curtailment in electricity?

Curtailment is a deliberate reduction of output from a power plant below what it could have produced, ordered or priced in by the grid operator, most often because supply exceeds demand on the wider system or because a local transmission constraint cannot carry the power away. It is an operating tool, not an outage: the plant is available, and the grid instructs or prices it down.

Why is solar power curtailed?

Mostly timing. Solar output peaks midday, and in spring the combination of strong sun and mild demand produces more midday energy than the system can absorb or export. In the California ISO, March and April are the heaviest curtailment months on average across the series, and EIA reported that 93% of the 3.4 million MWh CAISO curtailed in 2024 was solar (EIA, May 28, 2025).

How much wind and solar is curtailed?

In the California ISO, 241,073 MWh of wind and solar output was curtailed in July 2026, and 4.79 million MWh in 2026 through July (+53% vs the same months of 2025). No comparably clean public series exists for the other U.S. grid operators, so this page does not publish a multi-region total.

What is the difference between generation curtailment and load curtailment?

Generation curtailment reduces a power plant's output; load curtailment reduces customers' consumption. Both words appear in the news as just "curtailment." PJM's board directed a FERC filing on July 27, 2026 under which, during capacity shortages, new large loads (50 MW or more at a site) that do not bring their own generation by June 1, 2027 and have not otherwise secured supply would be curtailed before Pre-Emergency Load Management reaches other customers (PJM).

Is curtailment wasted energy?

Curtailed output is energy a plant could have generated and did not, so nothing is physically consumed or lost; what is forgone is low-cost generation that was available. Whether that is a problem is an economic question about transmission, storage and pricing, and grid operators treat some level of curtailment as a normal, least-cost operating outcome. This page reports the measured quantities and leaves the label to the reader.

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