According to a new report from the U.S. Energy Information Administration (EIA), grid operators in the areas overseen by the Southwest Power Pool (SPP) and Midcontinent Independent System Operator (MISO) curtailed an hourly average of 800 megawatts (MW) of wind generation in the Midwest in 2023, compared with less than 200 MW in 2019. (Curtailment is when electricity generation is deliberately reduced below its maximum generation potential.).

Wind generation increased by 42 percent between 2019 and 2023 and currently makes up a substantial proportion of the energy mix in the Midwest. According to the EIA report, hourly average Midwest wind curtailments decreased last year from a 2022 record of almost 1,000 MW because of less generation brought on by slower than normal wind speeds. Grid operators also made changes in 2023 to how they planned for congestion and oversupply.

“Curtailments can be necessary for grid operators to balance supply and demand,” said the EIA. “Curtailments occur either when generation exceeds electricity demand (oversupply) or when insufficient transfer capacity is available to transmit electricity over its preferred path to meet demand (congestion).”

The report noted that wind is curtailed before other resources are curtailed in the Midwest because:

– It is cheaper and faster to both shut down and restart wind (and solar) plants than other types of generation.

– On very windy days in particular locations, transmission capacity is often insufficient to receive the large amount of wind power generated.

In 2023, wind generation made up 36 percent of SPP’s total generation and 15 percent of MISO’s total generation. Average hourly wind curtailment increased from 136 MW in 2019 to 1,097 MW in 2023 in SPP and from 242 MW to 508 MW in MISO. Fewer curtailments occurred in 2023 than in 2022, largely due to decreases in wind generation.

The EIA report noted that, in MISO, congestion often occurs during winter storms because of associated high wind speeds and transmission constraints. Curtailments were lower in winter 2023-2024 compared with the past two winters partly because of better resource planning and congestion management strategies during winter storms. Although wind generation within MISO set a record of almost 26 gigawatts (GW) within one hour and averaged 16 GW per hour during Winter Storm Heather in January 2024, MISO curtailed wind generation 12 percent less throughout winter 2023–24 than during winter 2022-2023, and 47 percent less than in the winter of 2021–22.

In the Midwest, according to the report, curtailments are more common because of congestion, when the amount of generation in one part of the grid exceeds the capacity of transmission lines to bring it to areas of greater demand. In MISO, the market monitor found that high wind output caused almost half of MISO’s transmission system congestion in 2022, resulting in average hourly wind curtailments of 726 MW per hour, including curtailments of as much as 5.9 GW in some hours of 2022.