Thanks to smart planning and the power grid’s ever-growing resilience, Monday’s solar eclipse appears to have gone off without a hitch for grid operators and utilities across the country despite the event’s big impact on solar generation.

For example, the California Independent System Operator (CAISO) typically relies on a significant amount of solar energy, but CAISO spokesperson Steven Greenlee verifies, “We did not have any reliability issues large or small – things went very smoothly.”

“The California grid and the western Energy Imbalance Market that serves customers in eight western states performed as expected,” explains Greenlee. “While the eclipse ramp-off and back-on were very fast, we were able to manage them and fortunate that there were not major transmission or generation outages. We also got lucky that the weather in California was nice (Bay Area had fog) and temperatures were seasonable, so loads were reasonable as well.”

CAISO has “several years of managing solar (and wind) and its variability,” according to Greenlee. “Often, clouds will obscure a portion of the 10,000 MW of our grid-connected solar resources, which we have to replace with other resource types, so we have built up a strong expertise in managing such events.”

Greenlee says CAISO is still reviewing just how much of its typical 9,000+ GW of solar production was affected during Monday’s eclipse, but he notes, “Hydroelectric and natural gas provided most of the generation needed to ride through the eclipse and loss of solar output in California.”

Meanwhile, PJM Interconnection, the operator of North America’s largest power grid, reports it also ensured reliable power supplies throughout Monday’s solar eclipse.

According to a PJM announcement, the grid operator saw a drop of approximately 520 MW of wholesale solar generation connected to the grid from before the eclipse until the peak of the eclipse. In addition, PJM also estimates that electricity from behind-the-meter solar generation (mostly rooftop solar panels that offset load) decreased by approximately 1,700 MW.

In its announcement, PJM notes it had expected a reduction in power from rooftop panels to result in an increase in electric demand on the grid. However, because of a variety of potential factors, including reduced air conditioning, increased cloud cover and changes in human behavior related to the event, PJM saw a net decrease in demand for electricity of about 5,000 MW throughout the eclipse.

PJM says it will continue to study the impact of the solar eclipse on its system and will integrate lessons learned from event into preparing for the next solar eclipse, predicted to occur in 2024, when the grid is expected to have more solar generation.

Utility company Duke Energy, which has 2,500 MW of solar capacity connected to its system in North Carolina, reports that it lost about 1,700 MW of that capacity during the height of the eclipse.

Nonetheless, Sammy Roberts, Duke Energy’s director of system operations, says, “We were able to balance the Duke Energy system to compensate for the loss of solar power over the eclipse period. Our system reacted as planned, and we were able to reliably and efficiently meet the energy demands of our customers in the Carolinas.”

Elsewhere on the East Coast, Georgia Power held a Facebook Live event during the eclipse and showed real- time production analytics from the utility’s solar research and demonstration project at its headquarters.

John Kraft, spokesperson for Georgia Power, says, “We were glad for the opportunity to help educate customers about our advancements in renewable energy and the part it plays in a diversified energy portfolio.”

According to Kraft, “We have almost 900 MW of solar capacity, including company-owned projects, power purchase agreements, etc. We saw a significant drop in solar production at our small demonstration project at our Atlanta headquarters during the eclipse and expect that solar facilities across the state experienced declines in output, depending on local weather conditions and degree of eclipse darkening.”

However, he adds, “We did not expect and did not have customer outages related to power supply because of the diverse generation mix we employ on our system, including solar, nuclear, natural gas, coal, hydro and other sources. The company was well prepared for this event.”

Georgia Power plans to keep adding solar to its grid after the Georgia Public Service Commission last year approved its 2016 Integrated Resource Plan, which includes the addition of up to 1,600 MW of solar and other renewable energy through 2021.

“An eclipse is a rare event, and one that can be planned for, but it did illustrate the intermittent nature of solar that more commonly occurs with passing clouds, rainy days, at night, etc.,” says Kraft. “Like any power source, solar has benefits and limitations, and when incorporated into a diverse generation mix, as we have done in coordination with the Georgia Public Service Commission, it is an important part of our state’s energy resources.”