If temperatures spike this summer, parts of the United States could face electricity supply shortages as demand for cooling increases, according to analysis by the North American Electric Reliability Corporation (NERC). The latest summer reliability report from NERC warns that two-thirds of North America is at risk of energy shortfalls this summer during periods of extremely high electricity demand.

In summer, electricity demand increases as temperatures rise and homes and businesses turn up the air conditioning to cope. Above-normal summer temperatures further push up demand and can reduce electricity supply if power plant outages or reduced output stem from heat-related issues. In addition, widespread heat waves can limit electricity transfers because the electricity is needed to meet local demand. The combination of higher electricity demand and reduced supply can cause energy shortfalls. NERC releases a comprehensive summer reliability report assessing the North American power system ahead of the summer months each year.

All 20 NERC assessment areas have adequate power resources to meet normal peak summer demand this year, according to NERC. However, certain assessment areas are at elevated risk of electricity supply shortages if confronted with more extreme summer conditions. These areas include the U.S. Western Interconnection, SPP, MISO, ERCOT, SERC-Central, and New England.

U.S. Western Interconnection. Resources in the U.S. Western Interconnection, which covers the western half of the country, are sufficient to support normal peak demand. However, widespread heat waves could put the area at elevated risk of energy supply shortfall because it relies on regional electricity transfers to meet peak demand as well as in the evening hours when solar power drops off. Parts of the Western Interconnection, especially California, host a large and growing share of generation from solar power.

SPP and MISO. SPP and MISO, which cover most of the central United States, are home to a significant amount of wind power. The intermittent nature of wind power (wind turbines only generate electricity if the wind is blowing, and how much electricity they generate depends on how windy it is) present operational challenges for grid operators. Wind output during periods of high electricity demand is a key factor in determining whether the system has sufficient electricity supply to maintain reliability in these areas. Low wind and high demand periods could result in energy emergencies.

ERCOT. Resources are adequate for normal peak summer demand in ERCOT, which covers most of Texas. However, there is a risk that dispatchable generation, such as generation from natural gas- or coal-fired power plants, in ERCOT may not be sufficient to meet electricity demand during an extreme heat wave with unusually low winds. Already in June ERCOT asked residents to voluntarily curb electricity use as a heatwave reached Texas. As in SPP and MISO, wind plays a significant role in ERCOT’s generation mix.

SERC-Central. The NERC assessment expects SERC-Central, an assessment area that includes all of Tennessee and parts of Georgia, Alabama, Missouri, and Kentucky, to have sufficient supply for normal peak summer demand. Utilities may deploy demand-side management—the planning, implementing, and monitoring activities designed to encourage consumers to modify their electricity usage—in cases of above-normal peak summer demand or high generator-outage conditions.

NPCC-New England. Although New England has less available capacity this summer than it had last summer, NERC projects that it still has sufficient capacity to meet normal peak summer demand. During more extreme demand or low resource conditions, operating procedures for obtaining emergency resources and electricity supplies from neighboring areas are likely to be needed.