Date: July 31, 2017

Largest Grid Operator Says Potential Loss of 2,500 MW Solar Power during Eclipse Is Manageable


(Valley Forge, Pa. – July 31, 2017) – The operator of North America’s largest power grid is prepared  to ensure reliable electricity supplies during a total solar eclipse next month when solar power resources will fall temporarily.

Although the eclipse will reduce solar power generation, PJM Interconnection expects no power grid reliability issues in its footprint, which includes 13 states and the District of Columbia and 65 million people.

“Certainly, this is an unusual solar event, but as far as potential impacts to the grid, PJM and its members are prepared,” said PJM President and CEO Andrew L. Ott. “While this is an anticipated event, we routinely plan and prepare for unpredictable events or things that can’t be forecast far in advance, such as severe storms and heat waves,” he noted. 

When the moon blocks the sun on the afternoon of Aug. 21, solar power generators will lose their fuel source in varying degrees from 1:30-3:40 p.m. (EDT). PJM expects a temporary reduction in solar power of up to 2,500 megawatts.  It will use its sufficient reserves for replacement generation.

The exact amount of solar power affected by the eclipse will depend on how sunny or cloudy it is that afternoon.

Certain states will experience a greater impact, including North Carolina, which will experience a complete solar eclipse, and New Jersey, which has more photovoltaic solar generation than most other the states served by PJM.

PJM will ensure sufficient resources are ready to replace any solar generation loss and will refine its analysis prior to the eclipse to factor in the latest weather forecasts.

PJM’s established planning, operations and markets functions have produced a reliable, diverse resource mix that includes natural gas, coal, nuclear, renewables and demand response.

About 500 MW of solar generation is connected to the grid. Another 2,000 MW is generated by rooftop solar panels that serve individual consumers. A reduction in power from the rooftop panels results in an increase in electric demand on the grid.  Although growing in the region, solar generation comprises less than 1 percent of PJM’s 185,000 MW of generation capacity.

For context, 1 MW can power up to 1,000 homes.

Because rooftop solar is not wholesale power and, therefore, not monitored by PJM, post-eclipse analysis will provide valuable information for future planning.

PJM will integrate lessons learned from the Aug. 21 event into preparing for the next solar eclipse, predicted to occur in 2024, when the grid is expected to have more solar generation.

Europe experienced a total eclipse in 2015 with no impact on electric reliability because of coordinated planning for the ramping up and down of electricity on the grid.

The last total solar eclipse to occur in the continental United States was in 1979, before the rise of solar power. It was viewable only from the Pacific Northwest.

August’s planetary event will be the first total eclipse since the year 1257 to begin and end exclusively over the territory that now makes up the United States, according to NASA.


PJM Interconnection, founded in 1927, ensures the reliability of the high-voltage electric power system serving 65 million people in all or parts of Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and the District of Columbia. PJM coordinates and directs the operation of the region’s transmission grid, which includes over 82,000 miles of transmission lines; administers a competitive wholesale electricity market; and plans regional transmission expansion improvements to maintain grid reliability and relieve congestion. PJM’s regional grid and market operations produce annual savings of $2.8 billion to $3.1 billion. For the latest news about PJM, visit PJM Inside Lines at insidelines.pjm.com.