The solar eclipse is a critical test for the US power grid

As the moon passes in front of the sun on April 8, its shadow will knock down solar power production in a sweeping band across the United States from Texas to Maine, home to more than 31 million people.

The United States currently has more than 139 gigawatts of solar electricity generation capacity. That’s more than two and a half times the amount of solar that was on the grid during the last total eclipse in 2017. The upcoming eclipse will also shade a path twice as wide as the last one. Though much of the country will see some decline in solar power production, the biggest decrease will be directly under the moon’s shadow.

For the most part, power grid operators aren’t too worried about outages or major problems during the eclipse. In fact, unlike disruptions like clouds, the moon passing between the Earth and the sun is easily predictable up to 1,000 years in advance. But behind the scenes, it will require a carefully choreographed series of energy transactions to precisely ramp up electricity from a handful of generators and route it across hundreds of miles of transmission lines to millions of customers to precisely match the needs of every monitor, air conditioner, and light bulb the instant they turn on.

So grid operators are preparing for the totality, and the lessons they learn will prove useful as even more intermittent power sources connect to the grid and as power generators and transmission systems face even more severe stresses from rising energy demand and threats like wildfires, drought, and storms, many worsened by climate change.

Texas is a case in point. It has the second-largest solar capacity in the US and the path of totality cuts straight through it. According to the National Renewable Energy Laboratory, the US will see a nearly 60 gigawatt drop in solar power production when the moon blocks out the lone star in the sky above the Lone Star State.

The Texas grid operator, the Electric Reliability Council of Texas (ERCOT), has been running simulations and modeling how the eclipse will affect the state’s power network, which, unlike the rest of the continental US, has few connections to other states. That means it can’t easily buy or sell electricity across state lines if it has too much or too little power. Hail storms last month also caused major damage to some solar installations in the state. For power grids like ERCOT’s, the biggest challenge is how quickly solar power will fall off and bounce back up. The eclipse will cause solar power generation to fall and rise at a faster rate than a typical sunset and sunrise.

“ERCOT has analyzed the ramping challenges posed by the eclipse and will continue to monitor this aspect of the eclipse as updated weather forecasts are received,” said a spokesperson for ERCOT in an email.

Farther north, the Midcontinent Independent System Operator (MISO), which runs power transmission across much of the Midwest, is also bracing for a sudden drop and spike in solar energy production, which could cause congestion, a situation in which more electricity is available than can be delivered.

Operators also anticipate that temperatures will drop somewhat during the eclipse, which could lower cooling demand but increase the need for lighting. In response, operators are bringing more reserve power online and coordinating electricity deliveries with neighboring grids.

MISO

Why is it so tricky to keep the lights on when it gets dark during the day?

The main issue is that electricity generation has to closely match demand for it. If there’s too little power, that can lead to brownouts and blackouts. If there’s more electricity than anyone can easily use, it means the utility is wasting money. Excess power can also lead to equipment failures or destabilize the network.

“If there’s a change on either side — the generation or on the load side — some control actions are needed to balance it, and it has to be done quite quickly,” said Adam Birchfield, an assistant professor of electrical and computer engineering at Texas A&M University who studies the power grid. “Typically, that is some kind of traditional generator, whether it’s natural gas, coal, or hydro, that can adjust its output slightly to make up for that difference.”

One way to do this is with “spinning reserve.” That’s where a power generator is already spinning and synchronized with the power grid, but not connected until it is needed. Another way is with dedicated power plants that spool up to meet demand spikes. These are called peaking power plants and they are usually powered by natural gas. Energy storage with pumped hydropower or grid batteries can also kick in, but there aren’t that many of these storage systems right now, certainly not on the scales needed to balance the entire power grid.

Like airline tickets, the longer you wait to book your electricity, the more expensive it gets. And if you’re too late, there may not be enough power to go around. Grid operators and utilities thus try to buy power as far ahead as possible to get the best rates and carefully match it to electricity demand.

A particular concern with solar power on the grid is that it’s not just large utility-scale fields of photovoltaic (PV) panels that feed power into the grid; there’s also solar power generated on rooftops. “A lot of utilities don’t have accurate data for how much PV has been installed on their grid,” said Jin Tan, a principal engineer at the National Renewable Energy Laboratory, during a webinar. That makes it harder to anticipate power spikes and drops.

Still, for ordinary power users, it’s unlikely that they’ll notice anything about their electricity during the eclipse. Some utilities might have to scramble to secure extra power but that won’t manifest at the outlet.

The bigger worry for everyone counting on keeping their phones, computers, and electric cars charged up is what’s over the horizon. Last year, the US set an electricity demand record under intense heat that stressed power production. The grid largely avoided blackouts, due to a combination of planning to have extra power as well as luck that demand didn’t get any higher. Grid operators also issued emergency conservation alerts to their customers, and fortunately, enough power users complied to keep the lights on.

But overall energy demand in the US is growing. The amount of electricity devoured by data centers alone is poised to double by 2026, driven by digital industries like artificial intelligence and cryptocurrencies. Meanwhile, intermittent renewable energy sources like wind and solar power are already providing the most new capacity additions to the grid and are projected to grow further in the coming years. And the US’s aging power lines and transformers are vulnerable to extreme weather and in some cases, can trigger their own disasters. Power lines likely ignited the largest wildfire in Texas history earlier this year.

So, the US’s growing appetite for energy will be fed with a larger portion of some of the most capricious generators across a fragile delivery system, leaving grid operators to walk an even thinner, higher wire as they balance the power they have with the people who need it. It will take careful preparation now to ensure the grid stays balanced in the light and does not tumble into darkness.