For US Grid Markets, an Eclipse Day Is Like Any Other Day for Managing Solar Power
The solar eclipse that crossed the United States on Monday may have cast its shadow over large swaths of solar PV from California to South Carolina. But with an effect that’s even more predictable than the weather, grid operators across the country were able to manage their way through multi-gigawatt dips in solar generation without any worries about keeping the grid itself stable. That doesn’t mean that the price for megawatts on the energy markets run by grid operators remained stable through the event, though. In California, solar production fell off a cliff, dropping about 3,500 megawatts from 9 a.m. to 10:30 a.m. -- and the price of energy spiked from about $25 to more than $50 per megawatt-hour. Then, as the eclipse passed and solar power returned, the surge of energy coming onto the grid pushed prices down past their starting point, and then into negative territory -- forcing generators to pay the market to take their excess power, and driving those that have some flexibility to curtail output, bringing supply and demand back into balance. Here's a chart from Blake Shaffer, a former energy trader and economics doctoral candidate at the University of Calgary, showing the 5-minute shifts in prices per megawatt-hour during the day of the eclipse.
But this kind of day-by-day swing in solar -- and wind, and hydro -- isn’t unusual for CAISO. To be sure, the continent-wide scope of the eclipse's shadowing effect is unusual. But California can see similar swings in solar from the burn-off of coastal fog in mid- to late morning, or from the wind and clouds coming in from the Pacific.
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