“Once upon a time there was light in my life, but now there’s only love in the dark” - Bonnie Tyler
A Plunge Into Darkness
In days of old, the solar eclipse was seen as a harbinger of doom. Nowadays we understand it as a natural celestial phenomenon, occurring on those rare occasions when the moon passes between earth and sun. In modern times, the eclipse is more associated with a chance for experience junkies to chase an awe-inspiring high than with any real sense of calamity. Yet, our increasing reliance on solar energy renders our civilization more vulnerable to the vagaries of astronomical cycles — an experiment with the grid that has yet to be fully tested under the influence of a total eclipse.
During the eclipse on April 8, the path of totality will cross from the southwestern to northeastern United States, traveling directly through Texas, Oklahoma, Missouri, Illinois, Indiana, Kentucky, Ohio, Pennsylvania, New York, Vermont, New Hampshire and Maine. Most other states will experience a partial eclipse.
Although the length of total darkness will not exceed four minutes in any one locale, the impact on grid generation will still be dramatic. Enough so that every major grid operator in the nation has prepared detailed plans to mitigate the potential for power failure. As Barry Mather, a chief engineer at the National Renewable Energy Laboratory recently told CNET, “the impacts on solar generation are actually quite significant.” The good news is that with advanced prediction systems, we are well equipped with fine-grained data to understand the effects of the eclipse on local and grid level power generation. Let’s take a peek at what the regional grid operators have to say.
California
California lies outside the “zone of totality,” and thus will not witness the full brunt of the eclipse. The California Independent System Operator (CAISO) and Western Energy Imbalance Market (WEIM) state that the overall impact on solar generation and grid stabilization will be less severe than the annular eclipse of October 2023, which passed directly over the West Coast states. As of April 2024, there are approximately 18,500 MW of grid-scale solar capacity installed in the CAISO region, and 15,770 MW of behind-the-meter rooftop solar generation. According to CAISO’s eclipse forecast, the change in solar generation will be greatest on the eclipse return, meaning that the main challenge will be in balancing the sudden increase of solar energy added to the grid during the waning phases. The effect will be especially acute in the desert southwest of the state, which will be geographically closer to the path of totality, and therefore require greater ramp-up of baseload power plants (mainly natural gas and hydroelectric) during the descent into darkness (a load increase of 19.4%). Overall, “Grid-scale solar generation will decrease by 6,349 MW from the start of the eclipse to maximum impact and increase by 6,718 MW on the eclipse return.”
CAISO’s grid-scale solar projects will employ special procedures to ensure reliability and correct resource balancing. This effort will depend on Dispatch Operating Target metrics calculated through the day-ahead market forecast. The ISO will also procure additional baseload reserves to ensure continual coverage during the period of diminished solar output, and to “offset potential cloud cover.”
In the CAISO region, the eclipse will affect grid solar and load beginning at 10:00 a.m PDT, reaching a maximum impact at 11:15 a.m., and returning to normal conditions at 12:30 p.m.
Texas
As a state with some of the fastest-growing grid-scale solar generation sites in the country, and lying within the zone of totality, Texas could experience some of the most severe impacts of the coming eclipse on the grid. An outlier among grid operators, the Electric Reliability Council of Texas (ERCOT) is responsible for the maintenance and service of the independent Texas grid, which does not receive interconnections from other states. Despite these potential vulnerabilities, experts seem confident that ERCOT is well prepared to provide smooth coverage throughout the eclipse. According to Dr. Thomas Overbye, director of the Smart Grid Center at Texas A&M University, the Texas grid has plenty of baseload reserve power resources available to step in and fill the void during the eclipse timeframe, when solar farms (mostly in the eastern part of the state near Houston) will drop to near zero productivity at the nadir. “The grid will definitely be impacted, but we’re not expecting any problems,” said Overbye.
ERCOT says it is “working with solar forecast vendors to ensure the forecasting models account for the impact of the eclipse,” and that it will “use Ancillary Services for additional balancing needs.” Like California, ERCOT will rely on data from the day-ahead market to inform the required reserve and ancillary services.
The eclipse in Texas will occur between 12:10 p.m. CDT in the southwest until approximately 3:10 p.m., when the path will exit the northeast part of the state.
Midwest
The midwestern states are served by two grid operators: the Midcontinent Independent System Operator (MISO), roughly operating in the western portion of the region including the Great Plains states, and the PJM Interconnection, serving the eastern portion of the Midwest and the Mid-Atlantic states.
MISO
According to MISO, solar generation in the region has increased from only 100 MW during the last eclipse in 2017, to more than 5,000 MW today. This relatively dramatic growth in grid-scale solar will test the ISO’s skill and preparedness in balancing the load during ramp-up and ramp-down periods. MISO will also be directly in the path of totality, with the eclipse passing through its command centers in Carmel, Indiana, and Little Rock, Arkansas.
To prepare, MISO has held several meetings to discuss the regulation of short-term reserves within the eclipse window, and plans to use specialized MISO Communication System messages to coordinate between the various baseload and solar generation sites. “Balancing and congestion management are the most challenging areas,” it stated.
Nevertheless, MISO does not expect any significant reliability issues. The ISO anticipates a 4 GW drop in solar at the lowest point, with a rebound of 3 GW, given sunny conditions.
The path of darkness will roughly last from 1:30 p.m. to 4:25 p.m. EDT.
PJM Interconnection
PJM prepared an analysis modeling various weather scenarios to gain insight into potential impacts of the eclipse on its grid operations. According to Michael Stewart, PJM Senior Engineer for Load Forecasting, “the amount of generation we lose will depend on the weather pattern that day.” In other words, a cloudy day will have less solar in the grid mix to begin with, meaning that less work will be performed to ramp up and down supplemental baseload reserves. However, even with cloud cover, PJM anticipates a loss of 80-85% of the 8,200 MW utility-scale solar and 4,800MW behind-the-meter rooftop solar currently installed throughout the region.
PJM states Ohio and Pennsylvania are on the path of totality, and the region as a whole will on average experience 80%-100% solar obscuration. The operator is:
preparing to dispatch generation as needed to respond to solar power losses, including reserve and regulation resources as required. Reserve resources can provide needed backup generation when called upon, while regulation resources can provide energy to help control voltage and frequency on the system.
The eclipse will last about 90 minutes, beginning around 2:00 p.m. EDT in the Cincinnati area, with the totality occurring from about 3:13 p.m. to 3:15 p.m.
New England
The final leg of the eclipse journey across the U.S. will terminate in New England, before exiting into southeastern Canada. The Independent System Operator of New England (ISO New England) forecasters will rely on expected energy demand predicted hour-by-hour in the day-ahead market. All parts of the operator’s territory will experience at least 80% obscuration, with upstate New York, and the northern parts of Vermont, New Hampshire and Maine set to experience 100% coverage.
ISO New England expects a reduction of 365 MW of utility-scale solar at the eclipse maximum, and a reduction of 3,186 MW of residential and commercial rooftop solar generation. Like other regions of the country, New England is becoming more reliant on solar as part of its grid mix, and as of the end of 2022, the region had about 6,000 MW total capacity of solar power.
The grid operator does not anticipate excessive demand or loss of reserves leading to supply deficits during the eclipse. According to a press release, ISO New England will monitor the return ramp-up of solar after the eclipse begins to subside, and will be prepared to adequately reduce back-up generation from gas plants, etc. to maintain the delicate balance of supply and demand on the grid.
The New England eclipse will last from about 2:15 p.m. to 4:40 p.m. EDT, with totality occurring between 3:26 p.m. and 3:29 p.m.
Let The Sunshine In
A few trends come across through the various regional strategic plans for the coming total eclipse: 1) Solar generation WILL impact grid operations, with areas in clear, sunny conditions experiencing more difficult transitions between solar and reserve power 2) Grid operators will rely on day-ahead market forecasts, and most will procure additional reserves in advance to ensure continued service and reliability 3) All regions appear to be relatively confident in their ability to balance supply and demand throughout the eclipse sequences.
The total eclipse of the grid will most likely pass by, uneventfully. But, if there’s one thing these detailed back-up plans show, it’s that solar energy is a capricious mistress. Relying too heavily on her whims can only end in heartbreak. (And remember kids, never, ever look directly into her eyes).
With that, here’s one for the road:
Electrically yours,
K.T.
We need to gird our grid expeditiously. Global energy sanity requires all parties to be practical and environmental.
Considering that Canada extends from the US border to the North Pole, I’m not sure that I would refer to southern Ontario and Quebec as being the “northeastern” part of Canada. Southeastern, maybe?
Since the path of totality extends through to Newfoundland, you could say that it involves the “eastern” part of the country.