NERC Releases Summer Reliability Assessment

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NERC Releases Summer Reliability Assessment

May 28, 2021

The summer of 2021 is shaping up to be a challenge for electric system operators in parts of the United States, according to the North American Electric Reliability Corporation (NERC) 2021 Summer Reliability Assessment.

The report, released May 26, looks at the reliability of the North American bulk power system, June through September.

Among the key findings: California and Texas are at elevated risk for energy emergencies.


The Western Electric Coordinating Council (WECC)-California region is at risk of energy emergencies during periods of normal peak summer demand and high risk when above-normal demand is widespread. Studies indicate 10,185 MWh of energy in the area is expected to go unserved this summer.

Last summer, a wide-area heat event caused energy emergencies and rolling outages. Peak demand projections have increased in many parts of the West, noted the report, and overall resource capacity is lower compared to 2020. 

Over 3 gigawatts (GW) of additional resources are expected, most being new solar photovoltaic (PV) generation. These generation plants can provide energy to support peak demand; however, solar PV output falls off rapidly in late afternoon while high demand often remains. 

Some planned generation retirements have been put on hold.

Battery storage systems can supply energy to smooth the system ramping needs associated with high amounts of variable generation; by summer, nearly 600 megawatts (MW) of large-scale battery storage projects will have come on-line in California with an additional 800 MW expected by Aug. 1.

Imports to the area are needed to maintain reliability when demand peaks in the afternoon and to ramp up even further for several hours as solar resources draw down. Reliance on non-firm imports to cover high demand or low resource output conditions heightens the risk that operators will need to use energy emergency alerts and trigger the shedding of firm load in above-normal heat conditions. 

Increasing demand and lower resource capacity across WECC can mean the availability of surplus capacity for transfer into stressed areas is declining.

Also, government agencies warn of the potential for above-normal wildfire risk beginning in July in parts of the West, which can impact operation of the bulk power system.

Electric Reliability Council of Texas (ERCOT)

With forecasted growth in peak demand and new generation resources primarily coming in the form of variable wind and solar generation, notes the report, the risk of shortages that lead to energy emergencies in ERCOT continues for the upcoming summer.

Furthermore, with a significant portion of electricity supply coming from wind generation, operators must have sufficient flexible resources to cover periods of low-wind output.

On-peak Planning Reserve Margins have increased with the addition of 7,858 MW of wind, solar, and battery resources. However, extreme weather can affect both generation and demand and cause energy shortages that lead to emergencies in the region. With a significant portion of electricity supply coming from wind generation, operators must have sufficient flexible resources (this is not defined but appears to mean fossil-fueled dispatchable) to cover periods of low-wind output.

Combinations of high peak demand and extreme low resource output are exceedingly rare; however, they are plausible and provide industry and stakeholders with insights into potential emergency conditions. In challenging conditions, operators would resort to implementing rotating outages as a measure of preserving the bulk power system. 


The report notes that both the Midcontinent Independent System Operator (MISO) and NPCC-New England have sufficient resources for periods of peak demand. However, the above-normal levels of demand in certain forecasts are likely to exceed capacity resources and require additional non-firm transfers from surrounding areas.

In MISO, high resource outages and high demand may require use of load modifying resources (LMRs) and non-firm imports during peak periods. LMRs are an increasingly important segment of the MISO resource portfolio.

Above-normal summer peak load and outage conditions could result in the need to employ operating mitigations (i.e., demand response, transfers, and short-term load interruption).

During the pandemic, MISO load has run 1–2 percent below normal in mild weather and 1–2 percent above normal in hotter weather. During a heatwave, load could trend 1–3 percent above normal due to increased residential demand.

The report also notes that there is remaining uncertainty in demand projections as governments adjust to changing COVID-19 public health guidelines and conditions and as the behavior of society adapts.

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