• 5 min read

What the Total Eclipse Means for Solar Energy

Blog Main

You’ve probably heard that the nation’s first total solar eclipse in 38 years is coming up this Monday, August 21, 2017. This rare celestial event is causing a lot of buzz—and as a solar enthusiast, you might be wondering what this means for solar power across the country.

We’ve got you covered with some key things to know about the impacts of the eclipse on solar energy production in the U.S.

impact of eclipse on utility-scale solar across the United States Figure 1: The percentage of sunlight that will be obscured in different parts of the U.S. during the eclipse, and the impacts of this on utility-scale solar plants. Source: U.S. Energy Information Administration and National Aeronautics and Space Administration (NASA).

Lots of Solar Energy Will Go Offline—But Don’t Expect Service Outages

While America has experienced other total solar eclipses, we have more solar energy installed today than ever before. This presents unprecedented challenges for managing the electric grid. Even outside of the “path of totality,” where the sun’s light will be totally blocked, solar energy production will drop off dramatically during the eclipse.

Before you get concerned that this will wreak havoc on the grid, rest assured that grid operators have been carefully planning and service disruptions are not anticipated. But this will require a delicate balancing act.

There are 45 gigawatts of installed solar capacity in America today—equivalent to the horsepower of 58,500,000 horses!1 At the peak of the eclipse’s impact, solar production across the country will fall by 50%  .

Bloomberg has estimated a loss of 9,000 megawatts of solar power during the eclipse, comparable to taking nine nuclear reactors offline.

how much utility-scale solar will be obscured during eclipse Figure 2: Proportion of utility-scale solar capacity at different levels of obscuration during the eclipse. Source: U.S. EIA and NASA.

So how will this be managed on the grid? Grid operators, who are responsible for making sure the amount of energy being supplied to the grid perfectly matches the amount being consumed, will rely on other sources of energy—such as hydroelectric and natural gas plants—to make up for the drop in solar.

California and North Carolina Will See the Biggest Impacts on Solar Production

While the eclipse will be at least partially visible in all states, its solar energy impacts will be greater in some states than others. This depends on how much solar energy a state has, as well as how complete the eclipse will be in a given area.

Impacts of the eclipse on utility-scale solar capacity by U.S. state. Figure 3: Impacts of the eclipse on utility-scale solar capacity by state. Source: U.S. EIA and NASA.

California, which has more solar than any other state (with 40% of the nation’s solar capacity ), will have the greatest overall drop in solar production—despite the fact that the eclipse will not be total in any part of the state. The state’s energy output from solar will be reduced by half, according to the California Independent System Operator (CAISO) . This translates to an estimated loss of 6,000 megawatts, or enough power to run about 6 million homes.

California’s energy output from solar will be reduced by half, translating to an estimated loss of 6,000 megawatts, or enough power to run about 6 million homes.

North Carolina is another state that will feel the impact of the eclipse on solar energy acutely. 4,000 megawatts of solar power will go offline there during the eclipse. According to the EIA, North Carolina has the greatest amount of solar capacity in the path where sunlight will be at least 90% obscured. Plus, because the eclipse will occur between 1 pm and 3 pm Eastern Time, it coincides with a time of peak solar production.

Many other states will be dealing with these issues on a smaller scale. States in the path of totality include Georgia, Tennessee, Missouri, Idaho, and Oregon; all have increased their solar capacity in recent years.

Loss of Solar Energy Won’t Be the Biggest Challenge for Grid Operators

As mentioned, grid operators will rely on other sources of energy to make up for solar power that disappears during the eclipse. The biggest challenge they’ll face in maintaining grid reliability will be perfectly matching the rate at which these energy sources are activated to the rate that solar energy is dropping off. This is because, to avoid blackouts, the amount of electricity flowing onto the grid from power sources must perfectly match the amount of energy that consumers are using.

While solar energy normally varies throughout the day due to weather changes, these fluctuations are much less rapid than what will take place during the eclipse. In California, for instance, energy from large solar farms is expected to nose-dive by 70 megawatts per minute, and then, as the sun reappears, flood back at 90 megawatts a minute.

“While solar is ramping down, we have to ramp up the other generation. But once the eclipse is over and the sun starts coming back, we have to ramp down the other generation in order to keep supply balanced with demand,” explains Steven Greenlee , a CAISO spokesperson.

Grid operators have been planning for months to make sure this process goes smoothly. Preparations have included seeking advice from Germany, which gets 40% of its energy from solar faced a similar challenge last year when an eclipse blocked 80% of its sunlight.

For those curious to see the changing levels of solar production and energy demand in real time during the eclipse, CAISO has created a webpage for just that purpose .

Grid Managers May Be Keeping the Lights On, But You Can Do Your Part by Turning Them Off

Although disruptions are not expected, reducing your energy use during the eclipse—especially if you live in a state with a lot of solar—will be helpful for grid managers and the environment.

The California Public Utilities Commission (CPUC) is encouraging Californians to cut their energy consumption because it will mean that fewer polluting sources of energy are needed to maintain service. Says CPUC presided Michael Picker , “If millions of Californians turn off appliances and power strips to unplug from the grid during the eclipse… we don’t have to rely on expensive and inefficient natural gas peaking power plants, we can have cleaner air, we can keep our system reliable….”

With such a rare spectacle coming up, give your appliances a break and head outside to check it out (but not without taking precautions to protect your eyesight !).

Now that you know what to expect in terms of the eclipse’s impacts on the grid, here are a few more resources you might find helpful: