Grid operators in the U.S. recently detailed the impact of the April 8 solar eclipse on their respective grids.
“The bulk electric system across New York was operated reliability during the solar eclipse on April 8,” said Andrew Gregory, Manager, External Communications, for the New York ISO.
“Prior to the start of the eclipse, behind-the-meter and front-of-meter solar resources collectively generated just over 3,000 megawatts,” he said.
As the eclipse crossed New York, solar generation declined to just under 600 MW by 3:30 pm. Thermal generation and hydro power were dispatched to make up for reduced solar generation during that period. By 4 p.m., solar generation ramped back up to just under 1,200 megawatts before declining again during the early evening hours.
The Southwest Power Pool recorded a loss of approximately 200 megawatts of solar across its 14-state balancing authority area in the eastern interconnection.
“We also have some behind-the-meter solar in our territory that would have also been affected, but we aren’t able to measure the eclipse’s impact on that,” said Derek Wingfield, spokesperson for SPP.
“In the region served by our western energy imbalance service market in the western interconnection, we saw losses of approximately 1100 MW. Again, this doesn’t capture the entire picture of solar generation loss during the event, but it’s as accurate as we can estimate at this time.”
The April 8 solar eclipse led to a steep and significant decrease in solar energy production, but due to extensive planning by ISO New England operators, the event caused no disruptions to the power system, ISO-NE said.
Portions of Vermont, New Hampshire, and Maine were in the eclipse’s path of totality, while the rest of New England saw at least 80% of the sun blocked during the event’s peak. These conditions led regional solar production to drop by an estimated 4,000 MW over the course of two hours.
“Our preparations paid dividends,” said Steven Gould, the ISO’s director of Operations. “The work done ahead of time to understand how the eclipse would impact the regional power system was crucial to a smooth operating day.”
ISO New England system operators accounted for the sudden drop-off of solar resources by dispatching other generators, namely natural gas and hydroelectric resources. The ISO’s market software determined which resources to dispatch, based on the results of the region’s Day-Ahead and Real-Time energy markets.
Small-scale, distributed photovoltaic panels connected directly to distribution systems accounted for most of the reductions -- an estimated 3,300 to 3,500 MW. These systems, which are not connected to the regional power system operated by the ISO, make up the vast majority of solar resources in New England and, when the sun is shining, reduce the amount of energy demand on the grid.
Grid-connected solar systems dropped production by about 650 MW during the eclipse’s peak.
As the eclipse concluded in the late afternoon, approximately 1,350 MW of combined behind-the-meter and grid-connected solar production returned to the system, ISO-NE said.
Meanwhile, Texas was especially affected because of how much solar capacity was in the path of totality, the Energy Information Administration reported.
According to EIA’s Hourly Electric Grid Monitor, the Electric Reliability Council of Texas (ERCOT), which is the primary balancing authority in the state, lost approximately 8.9 gigawatts of solar capacity during the eclipse.
The ERCOT five-minute generation data show solar generation fell starting at 12:20 p.m. central time (CT). The eclipse ended in Texas at 3:07 p.m. CT.
Like the rest of the country, natural gas-fired generation largely offset the lost solar generation in ERCOT, replacing approximately 80% of the lost solar on April 8, EIA said.
According to EIA’s Hourly Electric Grid Monitor, which measures the grid response over a broader time interval than the data pulled directly from ERCOT, natural gas-fired power plants generated an additional 6.2 GW on April 8 between 1 p.m. CT and 2 p.m. CT, the hour when totality took place, to replace the lost solar generation.
Coal and other sources -- mostly battery storage -- each produced an additional 0.8 GW to offset the loss.
In Texas, solar generation is often the second-leading energy source in ERCOT during the time of day the eclipse crossed the state behind natural gas, according to EIA.
In ERCOT, throughout the day, Texas saw less solar generation on April 8 than on April 7, with cloud cover that persisted through April 9.
