Total solar eclipses have passed over the United States before. The last coast-to-coast one occurred in 1918. In March 1970, a total solar eclipse moved along the southeast coast and nine years later another plunged several northwestern states into darkness. The difference on August 21, when a 70-mile-wide shadow moves from west to east, will be all the solar power affected.
California, the state with the most solar power generation, is expected to lose 4,194 megawatts of large-scale solar electricity production, according to the California Independent System Operator (CAISO). Businesses will see production on their solar PV systems lowered and solar thermal systems will not heat as much water, the ISO cautioned.
North Carolina is another state near the top of the list for solar power capacity. The effect of the eclipse on the state’s grid will be comparable to rapidly shutting down several nuclear reactors at the same time, the News & Observer reported. The North American Electric Reliability Corporation (NERC) projects that, in addition to California and North Carolina, Utah and Nevada may require advanced system coordination.
Fortunately for corporate and industrial customers, utilities have had time to prepare. Grid operators looked closely at what happened in March 2015, when an eclipse cut solar power output in half in Germany, Gizmodo pointed out. Engineers carefully throttled the electricity output to keep power supplies stable, ramping fossil-fueled power plants up and down, according to Deutsche Welle.
CAISO has been advising utilities on how to prepare for the upcoming system stress test. The ISO plans to procure around 200 megawatts of additional reserves from energy sources like natural gas, wind or hydro-electricity, the agency’s manager of short-term forecasting told the San Diego Union-Tribune.
In North Carolina, grid operators plan to temporarily disconnect from solar farms and bring in alternative sources of electricity. “We’re going to simulate the gradual ramp-down of the generation just as it would happen at sunset,” a Duke spokesperson told the News & Observer.
Utilities can tap into the Energy Imbalance Market, where members pool available electricity and then dispatch it where needed, Gizmodo reported. “In regions affected by the eclipse, participating EIM utilities will have about 866 megawatts of solar to work with, and because members will be affected by the eclipse at slightly different times, they have some temporal wiggle when shuttling this surplus energy around.”
Customers shouldn’t notice any interruptions in power. NERC communications coordinator Martin J. Coyne told Gizmodo that he doesn’t expect any blackouts. “The grid has built-in redundancies that include a variety of other fuels such as coal, hydro, natural gas, nuclear, and wind,” he said to the outlet.