​Solar storms make for a good disaster movie plot: An enormous flare on the sun’s surface, followed by a coronal mass ejection, sends a blast of plasma and a powerful magnetic field hurtling through space and into Earth’s atmosphere, knocking out the power grid and sending civilization into chaos.

Fortunately, the reality is a lot less exciting than a Hollywood screenwriter’s fantasy.

Great River Energy (GRE), a G&T based in Maple Grove, Minnesota, operates in the part of the United States considered most susceptible to a geomagnetic disturbance (GMD) caused by a solar storm. To meet North American Electric Reliability Corporation (NERC) standards, the co-op commissioned a study in 2017 to assess their system’s GMD resiliency.

“There was so much concern about the apocalypse that was going to happen from this kind of event,” remembers Mike Steckelberg, GRE’s principal transmission planning engineer, about publicity in the media and concern in Congress around 2012–2013, as NERC was developing its standards.

But the impact study, which looked at the ability of transformers and other components to handle the direct current flows caused by a GMD, found the Great River system was essentially equipped to handle a solar storm.

Some transformers in Northern Minnesota and North Dakota, the part of Great River’s system with geology that makes it most susceptible to ground currents generated by solar storms, were flagged for attention in the case of an event. But none was of sufficient concern to require the G&T to take the next step in the NERC standards and conduct a thermal assessment to check for potential hotspots.

“The only thing that really affected us was that one of our newer substations, not yet in service, was flagged as being relatively high current,” Steckelberg says.

The co-op dealt with it by installing geomagnetically induced current-monitoring devices in the neutral transformer.

Minnesota is highly interconnected, and Steckelberg notes that other utilities in the area did have some transformers identified for thermal assessments, and further steps could be necessary. But, in general, he believes the region and Great River Energy in particular are prepared for the sun to rage: “What we expect will happen is that we will be able to operate around these events once we get notice that they’re coming.”

Notable disruptions

The impact studies mandated by NERC may provide reassuring results, but that doesn’t mean the concern is unwarranted. Solar flares and the ejections of coronal mass, essentially highly magnetized plasma that erupts from the sun’s surface and reaches the earth, have caused notable disruptions to communications and power service in the past.

The most famous occurrence, the Carrington Event in 1859, knocked out telegraph lines around the world. Some operators were knocked unconscious by current coming down the lines and poles, and even papers on desks burst into flames. One 2016 study estimated that a similar event today could cause $2 trillion in damages, although other analysts believe those fears are overstated.

More recently, in March 1989, a powerful coronal mass ejection released a plasma cloud 35 times the size of the earth that caused a province-wide blackout in Quebec, Canada, after it hit the atmosphere. The storm was powerful enough to create an aurora, or “northern lights,” visible as far south as Florida. The powerful magnetic disturbance also induced current in the ground across much of North America. In Quebec, it made its way into the grid, tripping capacitors and knocking the system off-line up to 12 hours.

Parts of Canada and the Upper Midwest are most vulnerable to the effects of geomagnetic activity because their geology includes a layer of igneous rock that “encourages geomagnetically induced currents (GICs) to flow in the power transmission lines situated above the rock,” NASA states in an online article.

Great River Energy’s territory includes that geology, but, Steckelberg says, “the Quebec event happened because they had some relays that were very sensitive to those ground currents. … GRE has had a change in the standards about how you design your relay systems for 15 years or more, so we’re not susceptible to that loss from inadvertent tripping.”

Mitigation options

The power industry across North America learned from Quebec.

Patti Metro, NRECA's senior grid operations and reliability director, says solar events since Quebec have not led to similar outages.

"We have not had an event since the event in 1989 that created those grid issues," she says. "We've been able to manage potential issues through redispatching assets or taking some pieces of equipment briefly out of service."

Preparations have been spurred by regulatory requirements. In 2013, the Federal Energy Regulatory Commission reacted to concern about potential grid damage from a geomagnetic disruption by directing NERC to develop GMD reliability standards.

Those standards require utilities to assess the resilience of their systems to a "benchmark" solar event roughly based on the 1989 Quebec outage. An updated benchmark is making its way through NERC, but Steckelberg say he expects it to be largely "fine-tuning" the standards to make sure they provide adequate safeguards, possibly for slightly higher current levels in some circumstances.

Mitigation options are available for utilities with systems at greater risk from a GMD event. NERC notes that capacitor banks that absorb excess energy are one option, as are neutral connection blocking devices. Faraday cages, enclosures of conductive material that can block electromagnetic fields, could also provide protection for particularly sensitive or vulnerable equipment.

But experts say proper grid management provides some of the most effective protection. The NERC-mandated impact studies have increased awareness of potential weak spots and helped utilities clarify procedures to deal with a GMD.

"In most cases, because of the redundancies of the grid, the chance of customers being out of service is pretty unlikely," Metro says.

It's also unlikely that a solar storm would catch the power industry by surprise. The U.S. National Oceanic and Atmospheric Administration (NOAA) operates a Space Weather Prediction Center that uses satellites and ground observation centers to monitor solar activity. An alert system is in place to notify utilities and grid operators of an oncoming event.

"Having these systems in place to notify people when these events are occurring, I think that's invaluable to us," Steckelberg says. "Understanding what happens and getting the notification of events, that's the key."

Paul McCurley, NRECA's chief engineer, believes that the occasional hype about solar storms overstates their likelihood and impact.

"The variables that are involved in a solar storm are just astronomical," he says.

If you look at how far away the sun is, the prevalence of solar flares, and the fact that the earth is moving in its orbit, McCurley continues, "the likelihood that a powerful coronal mass ejection will hit the right spot at the right time is really, really small."

But when another solar storm does arrive, McCurley and other experts believe U.S utilities are putting the plans and tools in place that should allow them to cope.