Solar power and solar eclipses are a bad mix and Monday while a total eclipse of the sun worked its way across the county, researchers at the National Renewable Energy Laboratory set about measuring just how bad it was.
From Texas through the Midwest to the Mid-Atlantic states to New England, NREL engineers in Golden logged the impact of the blackening skies on electricity grids in five-minute intervals.
Since the next total eclipse in the U.S. isn’t for another 20 years, it would seem that this isn’t a pressing issue, but Rui Yang, a manager in NREL’s Power Systems Engineering Center, said there are broader lessons to be learned by a four-minute plunge into darkness.
“A solar eclipse is highly predictable, so we can observe the change and recovery in the grid,” Yang said. “It can give us some idea of how we can operate in similar events, like extreme weather or wildfire.”
It will also give grid operators some insight into how best to manage their systems and which other generating resources fill in most efficiently. “We want to know what types of generation helped the most,” said Seong Lok Choi, lead engineer at the power systems center.
Solar power is the fastest growing energy source in the U.S. and projected, along with battery storage, to make up 81% of new generating capacity in 2024, according to the U.S. Energy Information Administration.
The EIA estimated that the total eclipse passed over about 6.5 gigawatts, GW, of solar generation facilities from Texas to Maine and the partial eclipse covered another 84.8 GW of installations.
☀️ READ MORE
NREL worked with the country’s biggest regional grid operators, including the California Independent System Operator, or ISO, the Midcontinent ISO, which serves the Midwest, the Southwest Power Pool, which covers Oklahoma north into North Dakota, the PJM Interconnection, whose territory includes parts of the Midwest and Eastern Seaboard and the New York and New England ISOs.
NREL collected data on electricity demand, solar output, output from other generation units — such as wind, natural gas, biogas, hydropower — as well as storage and transmission data.
First up on the solar eclipse path was Texas and the Electricity Reliability Council of Texas, or ERCOT, grid and it was the biggest test of the day.
Texas is building solar installations at a faster pace than any other state in the country.
Since 2021, Texas has installed more than 15 GW of solar capacity, according to the Solar Energy Industries Association, a trade group. That is equivalent to about five of Colorado’s Comanche 3 coal-fired power plants.
California still has the most installed solar capacity at 44 GW to Texas’ 23 GW, but in the next 10 years Texas will add another 100 GW of solar, outpacing the next closest state by a 2-to-1 margin, according to the solar association’s projections. Colorado has about 4.1 GW of solar.
So, what happened when the eclipse hit Texas?
Between 12:15 p.m. and 1:25 p.m. Central time, solar generation in Texas plummeted from 13.5 GW megawatt-hours to 1.3 GW. Solar did not slip to zero as there were always some parts of Texas not in “totality” or complete darkness.
Initially, the drop in solar was filled in by battery storage — about 2.5 GW. Texas had 5.6 GW of battery capacity in 2023 and is projected to add another 6.4 GW in 2024, according to the EIA.
Then natural gas-fired capacity kicked up to 27 GW from 19 GW. Nuclear and coal-fired output remained largely stable at a little under 11 GW. Wind, hydropower and a few smaller sources made up the remainder.
The transmission lines were humming as power moved around the state to meet the needs of areas in the deepest darkness. NREL could not directly measure loads on transmission lines but followed the price of moving electricity. As there is electricity moving it creates congestion on the grid forcing the price up.
Before the eclipse the tariff was $50 to move a megawatt-hour of electricity. Then in a matter of minutes it shot up to $870 a megawatt-hour before dropping to $500.
As the solar eclipse moved north and east the grid returned to normal operations, with solar output bouncing back to an hourly average 12.1 GW at 4 p.m, according to the ERCOT website.
“This is a chance to look at extreme conditions,” Yang said. “These are low probability, high impact events and we want to know how the power system can work in them.”