Here Are the U.S. Regions Most Vulnerable to Solar Storms

Grid operators in Minnesota, North Dakota, and Wisconsin should take extra precautions against solar “weather”

4 min read

Margo Anderson is senior associate editor and telecommunications editor at IEEE Spectrum.

Map of the United States of America showing geo electric voltage
This map shows 100-year storm-induced voltages on the national electric power grid.
U.S. Geological Survey/Wiley

A new study about solar-induced power outages in the U.S. electric grid finds that a few key regions—a portion of the Midwest and Eastern Seaboard—appear to be more vulnerable than others. 

The good news is that a few preventative measures could drastically reduce the damage done when a solar storm hits Earth. Those include stockpiling electrical transformers in national strategic reserves.

Jeffrey Love is a research geophysicist at the U.S. Geological Survey (USGS) in Golden, Colo., and coauthor of the new USGS solar geoelectric hazard study. He’s one of many voices in the worldwide geophysical community warning that geoelectric “perfect storms” will happen—it’s not a question of if, but when. Such storms can last between one and three days. 

Love explains that solar flares and other solar-mass ejections that travel through space can slam into Earth’s atmosphere and generate powerful electric and magnetic fields. These magnetic storms can occasionally be intense enough to interfere with the operation of high-voltage electricity lines. 

Depending on the geology of a given region, the currents a geomagnetic storm induces in the power lines can destabilize the power grid’s operation and cause damage to (or even destroy) transformers. 

Fortunately some kinds of rock, such as sedimentary formations, are relatively electrically conductive. Which means they’re more effective at dissipating storm-induced electric fields. And so the regions of the country with more of these conducting-type rocks will be more resilient to a magnetic storm. As it happens, that’s most of the United States. 

Some regions with bad geological luck, however, happen to have more electrically resistive rock (including igneous and metamorphic formations) in the ground. And that means high-voltage electrical wires in those parts of the country will be more subject to geomagnetic disturbances from solar flares. Utilities in those regions need to know that power disturbances and outages—and possibly blown transformers—are more likely in the case of a big solar storm hitting Earth. 

In a worst-case scenario, Love said, portions of the electric grid without enough backup transformers and other equipment could find themselves unable to operate until they can swap in backup systems. Of course, if there are not enough transformers and other devices, many in the hardest-hit regions could be without power for days or weeks until equipment could be delivered or built from scratch.

In March 1989, for instance, a so-called coronal mass ejection from the sun slammed into Earth. Because of how the planet was oriented when it hit, it blew out power grids and transformers primarily in the Canadian province of Quebec. For the next 12 hours, millions of people were thrown back to a world without any electricity, lights, heating, or other necessary services.

“The geomagnetic disturbance was global, but the effect was prominent for Quebec because Quebec has old and geologically resistive rock,” Love said. “Also, power grid systems in Quebec have very long lines, meaning that the integration of electric field along the lines [produced] very high voltage.”

The United States avoided the brunt of the 1989 geomagnetic storm because it happened to be more concentrated above the Canadian province.

How a power grid responds to a powerful solar storm is primarily a function of three factors, Love said.

The first is the intensity and locality of the storm itself; the second is the geological responsiveness of the minerals in any region to electrical activity in the atmosphere.

Love says a 2019 study mapped that second factor across two-thirds of the United States. The survey containing the remaining one-third—comprising the south and southwestern regions of the contiguous 48 states—will be completed within three years.

The third factor has to do with the orientation of high-voltage lines. If the geoelectric field during a solar storm points, say, north-south, it’ll induce the highest voltages in electrical lines traveling north-south. (Love noted that although the geoelectric fields in a storm are at worst only around a modest 25 volts per kilometer, that field is then integrated over the length of the power line. So for long-distance power lines aligned parallel to the geoelectric fields, the induced voltage can be thousands of volts. Which can wreak havoc on a power grid and transformers designed for alternating current.)

The worst-case scenario, the one that keeps grid experts up at night, happened last in 1859. It originated in a solar flare that blasted off the solar surface on 1 September 1859 and was observed by the English amateur astronomers Richard Carrington and Richard Hodgson.

Fortunately, when the “Carrington Event” hit Earth, the world had precious little electric infrastructure to disturb. It was mostly telegraph wires along railway lines that felt any high-voltage surges.

Geoelectric “perfect storms” will happen—it’s only a question of when.

“There’s some expectation that if we were to have a repeat of the 1859 storm, it could have some substantial effects on the electric power grid and other technology that modern society depends upon,” Love said. And because so many of today’s electrical systems are built around computer chips that are not robust to high-voltage surges, the fear is that a modern-day Carrington event could also blow out some portion of our computerized world.

Which, Love said, makes studying and mapping out this phenomenon in advance all the more important. Grid operators in Minnesota, North Dakota, and Wisconsin as well as along a Maine-to-Virginia stretch of eastern states must recognize they could be hit harder than other regions in a geoelectrical “perfect storm.”

Those operators will have options for how to respond, especially if they’re prepared in advance. They can bring on additional generating capacity, can reroute power along less-impacted regions, and can swap in any available transformers from a strategic stockpile. Of course, there would need to be enough transformers in that stockpile to handle the demands that a big geomagnetic storm might place on the grid.

In 2015, eight U.S. electric utilities created a transformer stockpile for emergency use. A March 2019 executive order signed by U.S. President Trump instructed agencies to shore up the grid’s resilience to electromagnetic pulses. The same month, the National Oceanic and Atmospheric Administration released a National Space Weather Strategy and Action Plan [PDF] (which updated a 2015 plan [PDF] that spawned an interagency space-weather working group in 2016). Those are positive steps toward being prepared for any future geoelectrical storms.

“Space weather effects generated over our heads and the geology underneath our feet… affect our technological systems,” Love said. What we do with this knowledge, then, is ultimately up to us.

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