Monday’s solar eclipse will be a field day for the country’s astronomy buffs as the moon completely blocks the sun in a swath stretching from Oregon to South Carolina. For utility grid operators, the event will be much more than a good show — it will be a chance to see how well they’re prepared for power fluctuations in a solar energy future.
The eclipse starts just after 9:00 a.m. in Oregon, according to a NASA website devoted to the event, with the sun completely obscured during a roughly 2-minute window beginning at about 10:20 a.m.
Columbia, South Carolina, will see the eclipse about four hours later. Those on either side of this narrow “path of totality” will see lesser amounts of the sun covered by the moon.
Grid operators, who are responsible for making sure there’s enough online capacity to meet demand, will be wondering how well they’re prepared for this brief but in some cases significant loss of electrical output from utility solar farms and residential rooftop PV.
In California, for example, more than 5,600 megawatts of solar capacity is expected to disappear, The New York Times reports. That’s nearly one-third of the state’s total solar capacity, which provides about 10% of the state’s power.
“As the eclipse carves a long shadow over California on Monday morning, it is expected to knock offline … a big chunk of the 19,000 megawatts of solar power that currently provide one-tenth of the state’s electricity,” the New York Times reports. “The California I.S.O. [Independent System Operator] plans to fill the void by ramping up natural gas and hydroelectric power plants. Then, a few minutes later, when the eclipse passes, all those solar panels will come roaring back to life, and grid operators will have to quickly make room for the sharp rise in generation by scaling back gas and hydropower.”
In North Carolina, Duke Energy’s Randy Wheeless says output will drop from 2,500 megawatts to about 200 on Monday afternoon.
Solar energy now provides less than 1% of the country’s total electricity, so Monday’s brief outages should be manageable. But as solar steadily becomes a more important part of the country’s energy mix, grid operators will have to get adept at balancing fluctuations in output, and Monday will give them a chance to see how well they are prepared.
Making up the difference with other sources
“An eclipse is obviously not something we see every day, but this is going to be a good exercise for us,” Wheeless told The Times. “There’s no doubt more solar power is going to come onto the grid in the future, and that does increase the challenge of balancing the grid even on days when there’s not an eclipse.”
As solar output declines, grid operators turn to other sources of power to meet demand. That often means turning on gas turbines, or other “peakers,” which gets expensive. California also has agreements with neighboring states to send in small amounts of energy to balance out these losses, what’s called an “energy imbalance market.” The state also uses pumped hydro storage in which excess electricity generated during times of low demand is used to pump water uphill. It can be released later in the day to generate power in a turbine when demand is higher.
These alternate source of energy, and the systems needed to distribute it, will become more important as California and other states add even more solar capacity to their grids. Monday’s eclipse will be a chance to “dip our toes in the water and see what that looks like,” says Eric Schmitt of the California Independent System Operator.
An eclipse in Europe in 2015 gave grid operators there a chance to see what happens with a loss of solar energy, and U.S. operators watched with interest. Another solar eclipse will affect the eastern U.S. in 2024.
“We would anticipate to have a lot more solar generation at that time, so our hope is to use this as a pilot for the 2024 event, which is only seven years off,” Ken Seiler of PJM Interconnection Inc. told the website Philly.com.
If you plan on watching Monday’s eclipse, be sure to follow NASA’s safety recommendations so you don’t damage your eyes.
Get building science and energy efficiency advice, plus special offers, in your inbox.