The August 21 solar eclipse will cast a shadow over a United States electrical grid that’s significantly different from the one existing in 1979, during the last total solar eclipse to cross the country. Writes Maggie Koerth-Baker at FiveThirtyEight, “Back then, very little connected the natural sources of light and the electric ones. Solar-generated electricity existed, but it was a niche product.”

Today, however, solar power is common. Writes Koerth-Baker, “And when the sun vanishes for 2 minutes and 43 seconds, the electricity it produces will vanish with it, potentially destabilizing any part of the grid that relies on much solar power.” She adds, “When the sun comes back, there will quickly be a lot of supply added. It’s crucial to make sure those changes don’t upset the balance between supply and demand.”

She notes that few major solar facilities are in the path of total eclipse, but most of California, the state with the largest installed solar capacity, will see 60% or more of the sun obscured. Also of note is North Carolina, with the second highest solar capacity at more than 3,200 MW. “Most of North Carolina isn’t directly in the path of the total eclipse, but, like California, it will see a reduction in sunlight,” she writes. “And, unlike California, North Carolina will get that reduction somewhere around 2:45 in the afternoon—a time of day (and time of year) when electricity demand is usually near its peak, solar supply also peaks, and energy companies tend to rely on solar resources most heavily.”

Koerth-Baker emphasizes that experts aren’t anticipating eclipse-related blackouts this year. However, the U.S. Energy Information Administration estimates that utility-scale solar plants make up about 2% of all utility-scale electric generating capacity and 0.9% of utility-scale generation. In addition, utility-scale solar installations—including both photovoltaic (PV) and thermal—grew at an average rate of 72% per year between 2010 and 2016, faster than any other generating technologies.

Should that growth rate continue, when the next eclipse crosses the country seven years from now, the risks to an increasingly solar-powered grid could be more significant, according to Koerth-Baker. “What we learn from this eclipse will help us better understand how the grid will have to change to make that new influx of solar electricity work…. So while millions of Americans will be staring at the sky on August 21, grid operators will be checking their numbers, watching supply and demand, and making sure our electric system gets a passing score,” she concludes.

See related article “Trimark T1-S SCADA to support grid stability during solar eclipse.”

Home Rick's Blog Eclipse could constitute a three-minute experiment in solar-energy resilience
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Rick Nelson
Rick became Executive Editor for EE in 2011. Previously he served on several publications, including EDN and Vision Systems Design, and has received awards for signed editorials from the American Society of Business Publication Editors. He began as a design engineer at General Electric and Litton Industries and earned a BSEE degree from Penn State.

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