As people marvel over the total eclipse on Monday, grid operators across North America are braced for a disruption in the intensity of the sun's energy reaching solar-generating stations, forcing them to take measures to ensure continued reliability.
As the moon positions itself in a direct line between the sun and the earth, it will at least partially obscure the sunlight needed to power nearly 2,000 utility-scale solar facilities across North America, including some 2,300-megawatts of capacity in Ontario at peak hours of demand.
For solar-power generators that lie in the path of a total eclipse – which runs west-to-east from Oregon to South Carolina – the sun will be completely obscured for three minutes. The eclipse will last some three hours in North America, from its beginning on the west coast until its end in the east.
However, grid operators say they can handle any impact on photovoltaic (PV) generation by increasing reliance from other sources, especially natural-gas plants which are typically used to meet swings in supply and demand.
"Although Ontario is not on the path of the total eclipse, the eclipse may block up to 70 per cent of the sun across Ontario, which may result in some potential impacts to the power grid," Mary Bernard, spokeswoman for the province's Independent Electricity System Operator (IESO), said in an e-mail.
"Although we are anticipating a decline in the amount of solar power during the eclipse, the system will remain reliable and we expect no issues," she said. "We have been tracking this event for some time and have the benefit of knowing exactly when the eclipse will be happening."
Ontario typically has a surplus of electricity supply. But on hot summer days when air conditioners are running at peak hours, it often imports power from Quebec and other neighbouring jurisdictions. Solar generation can account for as much as 10 per cent of the province's supply on a clear summer day or 2,300-megawatts, and the eclipse could reduce that output by as much as 70 per cent at its height.
As well, demand could spike by as much as 1,500 MW as people turn on lights between 1 p.m. and 2 p.m., due to the loss of sunlight, the IESO said.
The system operator says it has flexible suppliers ready to increase their generation as needed, while it also has demand management programs that it can use to reduce consumption.
In the U.S., the eclipse will obscure sunlight for some 1,900 utility-scale PV facilities, with large concentrations in California and eastern Oregon, as well as North Carolina.
California is most vulnerable to disruption, due to its relatively high dependence on solar power. The state has 10,000 MW of solar capacity which can generate as much as 40 per cent of loan for the Independent System Operator (ISO).
Though California is not in the direct path of the eclipse, it will experience a reduction of 5,565 MW of solar power at the peak of the eclipse, including 4,200 MW from utility-scale photovoltaic generation and 1,365 MW from rooftop panels.
As well, the ISO is preparing for a rapid decrease and then increase in solar generation during the eclipse which can stress the transmission and distribution systems.
Fortunately, the state has had a wet year and has water stored behind its hydroelectric dams that will allow it to compensate for the loss of solar power, said Dave Quinn, a power market analyst at Genscape Inc., a market intelligence firm. If the eclipse had happened two years ago when the state was undergoing a severe drought, the challenges would have been far greater.
"It certainly is going to be an interesting day but it seems like the ISO is prepared for handling it," Mr. Quinn said.