Eclipse is gone, Solar’s back on

Totality & the sun's corona Photo Credit: Brooke Durham with Southern Alliance for Clean Energy

Southern Alliance for Clean Energy’s Energy Policy Manager Simon Mahan contributed to this blog post.

As we waited excitedly for the moon’s shadow to cross the Southeast during yesterday’s Great American Eclipse, I didn’t think much about how the solar panels at SACE’s Asheville office – or thousands of other rooftop systems and utility-scale solar power plants across the country – were fairing. At about 2:30 p.m. ET on Monday, August 21, 2017 the only thing I was paying attention to was the quickly-dimming golden ball above our heads.

Now I can see why ancient civilizations viewed solar eclipses with confusion and anxiety: as the moon steadily slid across the sun, it produced an eerie light reminiscent of hurricane weather for about 15 minutes. Then the mountain cove I was sitting in was plunged into almost total darkness at 2:37 p.m. ET. For about two minutes, my family and I got to see the sun’s dazzling corona, a few stars popping out, and the brilliant ‘diamond ring’ effect as the moon began to slide away.

Eclipses are still a bit magical even though scientists and their modeling predicted yesterday’s celestial show down to the minute. In fact, it’s because eclipses are exceptionally predictable that utilities and electric consumers can better prepare for reduced solar output during eclipses than they can on an ‘average’ day with intermittent cloud cover or storms. 

When I got back home a few hours later, curiosity got the better of me so I went online to view our solar panels’ output for the day. Sure enough, there was a dip in production that lined up perfectly with the eclipse as Asheville was in the zone of 99% totality:

But I also found it interesting that if you viewed the entire last week, yesterday’s solar eclipse over our panels here in Asheville doesn’t really stand out from the rest of the week in terms of overall production and reliability:  

And here’s another thing that occurred to me: few people are talking about the other side of the eclipse’s energy equation which was notably reduced energy demand. Thousands – maybe millions – took the day off work and school to spend time outside (away from their electricity-powered devices) to enjoy the celestial show. Meanwhile as the sun dimmed, temperatures dropped – in some places by 10-15 degrees. With lower temperatures, air conditioners ran a little less which lowered overall electricity demand – conveniently right at the same time and pace that solar panels begin producing less power. At least in some cases, the same phenomenon that reduces solar power generation, also reduces the need for power generation.

And you may ask: what happened when solar energy generation plummeted while the moon’s shadow covered part of the country? Other power sources took over and the grid was ‘untroubled’ by the eclipse despite the sudden reduction in solar output. In fact, Florida derives so little of its electricity from solar energy (despite claiming the nickname the Sunshine State) that it was ‘just another day at the office‘ for its largest utility, Florida Power and Light. During future eclipses, wind power, battery systems, hydro power, geothermal and bioenergy resources will all be able to provide flexible power response during unusual phenomenon due to technological advances and geographic diversification which improves grid reliability.

As solar power installations increase over the next six years around the country, grid operators and utilities will undoubtedly have more solar power to manage during the April 2024 eclipse, which astronomers predict will wow people from Texas to Maine. I’m confident that the 2017 eclipse will be seen as a teaching moment, perfectly aligned with the future of solar power, and I’m hopeful that I may find myself along the path of totality once again!

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