How Demand Response Can Keep the Lights On During a Solar Eclipse

On August 21, a total solar eclipse will sweep across the US for the first time in nearly a century. Amid the excitement of such a rare natural wonder right in our own backyard, this event has been a cause for concern in areas where the electricity grid has become increasingly reliant on solar power.

The solar eclipse will affect a 70-mile wide swath following the path of totality between the hours of 11:35 am through 2:30 pm ET. As the moon crosses over the sun, solar power on the grid is expected to diminish at a rate of 70 MW per minute, compared to a downward ramp rate of 29 MW/minute on a typical day. In all, over the three-hour eclipse, more than 6,000 MW (enough to power over 6 million homes) will need to be replaced by other energy resources in order to sustain grid reliability. For states that rely on solar power (California, we’re looking at you), this event has the potential to cause significant disruption.

California’s Independent System Operator (CAISO) has been preparing for the eclipse since 2016, and has asked grid operators to secure additional supply from alternative sources, including both clean generation like nuclear and hydro-power and traditional fossil-fueled sources like coal and natural gas to mitigate any disruptions during or after the eclipse. Similarly, the North American Electric Reliability Corporation (NERC), a not-for-profit regulatory authority tasked with maintaining reliability and security of the US power grid, recommended that solar-heavy states prepare for the eclipse by securing power generated from non-photovoltaic resources.

However, both recognize that generating more supply is not the only answer.  Demand response has been listed among the measures that CAISO can take to protect the grid during the total solar eclipse, if needed. And it’s also a potential alternative to ramping up fossil-fueled generation to accommodate spikes in demand on the grid.

Demand response incentivizes organizations to curtail their energy use when the grid is constrained to keep supply and demand in balance. Instead of firing up an expensive and inefficient peaking power plant, a vast network of participants get paid to reduce their usage in response to grid signals, thereby keeping the grid stable and the lights on. Demand response is fast and sustainable, and could help the grid adjust to the short-term dip in available solar power, as well as help stabilize the grid during ramping—both at the onset of the eclipse when solar power rapidly decreases, and also as it comes back online. 

Over the years, California has focused on building its renewable grid. According to the US Energy Information Administration (EIA), 10% of California’s electricity mix is now sourced from solar (up from 0.4% five years ago), and the state now encompasses nearly half of the nation’s solar generation capacity.

In anticipation of the solar eclipse, California public officials are embracing energy reduction strategies like demand response. In May, California Public Utilities Commission President Michael Picker suggested that energy curtailment can help maintain grid stability during the eclipse without ramping up traditional generation.

"We don't have to rely on expensive and inefficient natural gas peaking plants," Picker said, according to Bloomberg.

The solar eclipse is just one example of the kinds of challenges the grid will face as the generation mix continues to evolve. Demand response has long been critical to protecting the grid, and will play an increasingly valuable role in addressing the challenges of tomorrow.

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Authored By Jacquelyn Cleary

Jacquelyn is a Demand Response Marketing Intern at Enel X.

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