By Sharon Adarlo

On Monday, August 21, 2017, the moon will pass between the sun and the Earth, heralding one of the grandest sights in the natural world, a total solar eclipse. People in all of North America and parts of South America, Europe, and Africa will get to see a partial eclipse, while residents in 14 states – stretching from Oregon to South Carolina – will be in the 168-mile wide “path of totality” (the moon’s shadow on Earth) and experience the full eclipse.

Thinking about the prospect of momentary darkness, some in the public have asked whether the event will affect solar-power generation and whether the electrical grid can withstand this loss in power. Photovoltaic installations in the U.S. have doubled from 7,500 megawatts in 2015 to 14,600 megawatts of capacity in 2016, but still represent only about one percent of the nation’s total electricity production.

To answer these questions, we turn to Barry Rand, assistant professor of electrical engineering and the Andlinger Center for Energy and the Environment at Princeton University for the latest Q/A for “The Andlinger Center Speaks.” Rand’s research dives into thin film electronics, such as light-emitting diodes (LEDs) and solar cells, made from semiconductor materials. These semiconductors are deposited as thin films on substrates, such as glass, plastic, or metal foil, for support. Rand explores the physics of these technologies and refines them to be more efficient and lower cost.

Rand is also a co-author on the Andlinger Center’s recent report on solar energy production, “Sunlight to Electricity: Navigating the Field.” This is the center’s latest Energy Technology Distillate, a series of informative reports on emerging energy technologies.

 Will there be any impact on the U.S. electrical grid when the solar eclipse happens?

The grid will be fine. When it comes to any impact on solar-energy conversion, the good thing about the solar eclipse is that it is infinitely predictable and a rare event. We know exactly where and when it is going to happen. The total solar eclipse will last a few minutes while the partial eclipse will last a few hours.

Even if we have more penetration of solar energy – and California has a good amount – it’s predictable. Utilities and power companies can compensate for the decrease in solar power and take action by having power plants burn more fuel during the eclipse.

The other thing – the solar eclipse will happen from mid-morning to the afternoon. You may think this is bad. But with less solar radiation reaching Earth, the air temperature will go down and the need for energy will go down too. For example, you may need less energy for air conditioning.

Also, many energy markets show a peak demand for power after sunset when people come home from work. This is illustrated in a well-known graph called the duck curve, which shows energy demand going up at the end of the business day, just when solar power slopes down and other non-renewable energy sources (i.e., coal and gas power plants) need to rapidly ramp up production to compensate. The graph has a duck-shaped profile.

So, daytime power consumption during the solar eclipse is relatively low compared to peak demand times. This is another reason why the solar eclipse won’t tax the electric grid.

Besides the reduction of energy demand, are there other consequences from the solar eclipse?

The solar eclipse will also reduce wind power, not just solar power.

Basically, the air temperature gradient gets reduced when the sun is obscured. The air becomes calmer. The wind goes down. Wind turbines will produce less power.

For example, during the total solar eclipse on March 20, 2015, researchers in the United Kingdom found that wind power generation went down by 510 megawatt hours while solar power went down approximately twice as much. The impact on overall energy production was small. (In 2015, U.K. wind turbines generated 40,310 gigawatt hours of power while solar produced 7,561.)

But again, because utilities know when this event will occur, they can compensate for this reduction.

If not the total solar eclipse, what is a real problem for renewables?

The problem with renewables is daily unpredictability. When a dark cloud passes over, it cuts the amount of solar radiation and the amount of solar power generated. When the wind dies down, turbines don’t produce as much power. But these problems are not impacting the U.S. electrical grid right now because penetration of renewables is not high at the moment.

(About five percent of electricity is generated by wind while solar accounts for about one percent, according to Warren Powell, professor of operations research and financial engineering, and director of the Program in Engineering and Management Systems. He spoke on wind and solar power penetration in a previous Q/A.)

Does the total solar eclipse speak to the necessity of grid scale energy storage?

No matter what happens with a solar eclipse or daily variabilities, energy storage costs need to go down.

I think the penetration of renewables will need to be higher for there to be an urgent need for grid-scale energy storage. Renewables penetration will need to be 50 percent. We are not there yet. We will only get to that level of penetration when energy use goes way down through energy efficiency.

Could you explain that further?

Within the current cost structure of renewable-energy conversion, such as wind and solar (which cost more than fossil-derived sources), the only way penetration of renewables will get higher, without capital and operating costs coming down considerably, is if our overall energy use is less. That is best enabled by increasing energy efficiency.

If energy efficiency decreases energy demand, we can use less fossil-derived sources, such as gas, naturally increasing the percentage of renewables on the electric grid. Fossil-derived sources can act as back-up or a supplement, but we use less of it if we pursue aggressive energy efficiency standards.

Increasing energy efficiency is the only cost effective energy technology right now. Wind and solar need huge subsidies at the moment. On energy efficiency, it doesn’t mean you have to change your way of life. You can get better insulation, double-pane windows, use a thermostat, and buy and use LEDs.