When the total solar eclipse hits on clip khieu damAug. 21, it's going to be quite the party. The problem? Solar panels need the sun to generate electricity.

With the sun dimmed, solar energy sources will be affected. More than 100 million solar panels are expected to be affected, which will drop output by 20 percent -- or the equivalent of all the energy the city of San Francisco uses in a week.

SEE ALSO: 20 questions you're too embarrassed to ask about the solar eclipse

Previous eclipses like the one that blotted out Europe in 2015 can give us a heads up on how much solar power will plummet. In Germany, which leads the world in solar power usage, output dropped from 14 gigawatts (GW) to 7 gigawatts, according to Gizmodo. Here in the states, utility-scale solar production is about 21.25 GW. It helps that the eclipse won't totally black out the sun over California and other states where the most solar energy is generated, so it won't disrupt the power grid. But it'll still mess things up.

More than 1 percent of all energy used in the U.S. comes from solar, a figure that is increasing rapidly as the cost of solar panels plunge. A North American Electric Reliability Corporation (NERC) white paper found that the eclipse is unlikely to cause any real issues with the power system, in part because the path of totality does not cut across the biggest solar generating states.

More likely it will show us how to prepare and plan for power disruptions, now and in the future. It's really California, and North Carolina to some extent, that will be the most impacted. California is the top solar generating state in the country, home to about 40 percent of the country's installed solar generating capacity, according to the Energy Information Administration.

The California Independent System Operator (CAISO), which supplies energy for the state electrical grid, estimates that the eclipse will push the grid to find up to 6,000 megawatts (MW) from alternative sources -- keep in mind one MW powers about 1,000 homes.

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But along with state energy agencies and utilities, the ISO has been prepping for the eclipse and the loss of solar power for more than a year. In a release about the solar event, CAISO wrote, "While the ISO has enough energy supply to make up for lost solar production during the eclipse, consumers should always use energy wisely."

That's where programmable thermostats like Nest are gearing up to help take on the energy disruption. In an effort to keep our power grid from resorting to "dirty" energy from coal, nuclear, natural gas and fossil fuels, the Google-owned company is asking its customers to cut back on its energy usage during the eclipse.

Project Eclipse will offer an opt-in campaign. Ben Bixby, general manager of energy and safety, is realistic about the relatively small loss of solar energy from the eclipse. "There’s no real danger of apocalypse," he said in an interview.

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Bixby anticipates Nest users' reduced energy use will "make a meaningful difference on the grid on this particular day."

For eclipse day, Nest users can voluntarily join the energy-saving effort, similar to the company's ongoing Rush Hour Rewards program that launched in 2013 that pays customers for cutting back on energy at peak times. On the device, an eclipse image will appear and ask if users want to participate in the special solar eclipse rush hour. Energy savers won't be paid this time, however.

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The entire California Public Utilities Commission is collecting pledges from residents to "do your thing for the sun." That means finding ways to reduce electricity usage the day of the eclipse. The state utility, like Nest, wants to burn fewer fossil fuels while the state's solar energy production dips.

Some suggestions include replacing lightbulbs with LEDs, turning off lights, unplugging electronics and appliances, and turning up the thermostat 2 to 5 degrees. Easy stuff, but not always obvious.

A state resolution calls for lower energy use during the eclipse -- especially during the West Coast portion starting around 9 a.m. PT.

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The last eclipse to cross the entire U.S. was in 1918, so our energy demands and technology look a bit different these days. We don't have a lot of experience with the sun out of commission for a few hours in the middle of the day with our current power grids and supply systems.

Phil Mihlmester, an energy expert and executive vice president of the global energy consulting group ICF, called the upcoming eclipse "a test case" to see how power suppliers handle the change in resources.

Based on a model looking at the electrical grid, ICF found the solar energy reduction might also be costly, especially in solar-heavy states like California.

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The ICF analysis found the average energy price for ratepayers just on eclipse day might go up 7 percent in the Golden State. At the eclipse's peak, that cost could go up as much as 18 percent. The average homeowner won't notice the small blip in cost for one day, but the energy industry will.

"It’s not so much the total loss and needing to make up for lost solar power," Mihlmester explained. It's more ramping up gas energy supplies to compensate for solar energy going down. In California alone gas turbines will need to be fired up to release up to 70 to 90 MW per minute to make up the difference.

So unplugging everything could really do something to offset that gas need. "It's always helpful," Mihlmester said. "Energy efficiency and steps taken by consumers clearly have an effect."

With all this energy saving and practice, we should be more than set for the next eclipse in 2024.

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