Faced with Hurricane Florence’s powerful winds and record rainfall, North Carolina’s solar farms held up with only minimal damage while other parts of the electricity system failed, an outcome that solar advocates hope will help to steer the broader energy debate.

North Carolina has more solar power than any state other than California, much of it built in the two years since Hurricane Matthew hit the region. Before last week, the state hadn’t seen how its growing solar developments—providing about 4.6 percent of the state’s electricity—would fare in the face of a hurricane.

Florence provided a test of how the systems stand up to severe weather as renewable energy use increases, particularly solar, which is growing faster in the Southeast than any other other region.

When Florence made landfall on Sept. 14, it caused power outages across the region. As energy experts point out, the most vulnerable part of the system is not new at all: it’s the power lines and other equipment that transport electricity to customers.

“What we’ve done this week just underscored what we’ve known for decades: generating assets are never the main vulnerability,” said Chris Burgess, projects director for the Rocky Mountain Institute, a research and consulting firm that specializes in clean energy issues.

The most breakable parts are “the wires themselves, the overhead lines,” he said.

Duke Energy said 1.7 million of its 3.4 million customers in North Carolina had power outages at some point during or in the aftermath of the storm. As of Thursday morning, power had been restored to all but about 80,000, and the company expected power to be fully restored next week. 

Duke and Strata Solar, two of North Carolina’s largest owners and operators of solar farms, said they found almost no damage in initial inspections.

Both companies shut down some systems ahead of the storm in anticipation of flooding. Duke said a peak of about 1,000 megawatts out of 3,500 megawatts of solar were offline after the storm in its territory because of those temporary shutdowns or because of grid damage or other external reasons, but there were few reports of damage to solar panels.

“I know sometimes we think, ‘Oh it’s the wind, it’s the panels flying around.’ But we haven’t found that to be the case,” said Randy Wheeless, a spokesman for Duke, the largest electric utility in the state. “Our bigger worry usually is flooding.”

Wheeless found only one example of wind damage: 12 panels at a 60-megawatt solar farm in Monroe were damaged, which is less than 1 percent of the panels there. The company may find additional damage as it does more inspections, he said.

Duke shut down three of its 35 solar farms before the storm arrived because of concerns that floodwaters would inundate substations and other electrical equipment. Those three remained offline as of Thursday morning as the company waited for waters to recede.

Strata Solar, which has more than 100 solar farms in the state, said it was aware of wind damage affecting small parts of two different sites.

“It’s fairly isolated damage,” said Brian O’Hara, senior vice president for strategy and government affairs for Strata, which is based in Chapel Hill. “I think a lot of people were looking at Florence as a good test for solar generation’s resilience, and I think we’ve seen a really fantastic outcome.”

While solar farms are abundant in North Carolina, the state has only one utility-scale wind farm, largely because political and regulatory opposition has hindered development. The project, called Amazon Wind Farm US East because it sells all of its electricity to a nearby data centers run by an Amazon subsidiary, is in the northeast corner of the state, far from the brunt of Florence’s damage. It never stopped operating during the storm, said Paul Copleman, a spokesman for the owner, Avangrid Renewables.

How Did Rooftop Solar Fare?

The lack of damage to the state’s solar farms is largely because companies selected locations that are not likely to flood, and they built electricity equipment on platforms to allow for some rising water.

Most panels and racks are designed to withstand wind pressure up to the 140 mph range, according to Burgess. Some systems have panels that move to track the sun, which can make them more vulnerable to wind, but that also allows them to be shifted to positions where wind will do the least damage. At one of Duke’s sites, the company locked the panels into a fixed position in anticipation of the storm, something it can done remotely from a control room.

Rooftop solar companies, such as Renu Energy Solutions in Charlotte, say there was little damage to their customers’ home solar systems. However, installers in some of the hardest-hit areas, such as Cape Fear, did not respond to messages seeking comment and there is a higher likelihood of damage there.

There were many areas where solar arrays were capable of working but their surrounding grid was offline, installers said.

That’s a recurring issue in natural disasters, as few places have the capability to temporarily separate from the grid to run on their own power, said Eliza Hotchkiss, a technical project lead at the National Renewable Energy Laboratory.

Resilience, Nuclear and Coal

Florence’s test of how solar power stands up to extreme weather comes as the Trump administration tries to boost coal-fired and nuclear power plants with the argument that they’re more reliable because they can store months of fuel on site.

Tyler Norris, an employee at solar operator Cypress Creek Renewables, hinted at this broader discussion when he tweeted a photo of one of his company’s solar farms that was “in solid shape” after the storm. And, because the fuel is the sun, he noted that the project has “on-site fuel supply.”

As the hurricane approached, Duke shut down its nuclear plants that were most likely to be affected by the storm. One of them, Brunswick nuclear plant near Wilmington, later declared a low-level emergency after flooding temporarily cut off access to the site. It was able to restart one of its units on Wednesday.

The larger McGuire Nuclear Station near Charlotte was operating at 50 percent capacity because of maintenance during the storm and its aftermath. The Harris Nuclear Plant near Raleigh and nuclear plants in South Carolina were able to operate normally, according to the U.S. Energy Information Administration.

During the heavy rain, one coal ash landfill near Wilmington partially collapsed and some ash washed into a nearby lake popular for fishing. Another coal site in North Carolina was inundated, and the South Carolina utility Santee Cooper was working Thursday to keep a site near Conway from being inundated by the rising Waccamaw River.

Decentralized Systems Can Increase Resilience

Richard Sedano, president and CEO of the Regulatory Assistance Project, a nonprofit that advises utility regulators, said he thinks severe storms will increase calls for the electricity system to become less centralized so that when one part stops working, others can remain online. The falling costs of rooftop solar and battery storage are expected to soon make that a reality in more places.

A less centralized system would be less vulnerable to mass outages when a power line breaks or when a substation floods, he said.

Moving to a more decentralized system is well-suited to renewable energy, which often is spread out across the grid, said Thad Culley, Southeast regional director for Vote Solar. He expects that the experience of Florence and other weather events will become an increasingly prominent part of how renewable energy advocates make their case to regulators and lawmakers.

Past Storms Helped Improve Design

In a report in June about how solar farms responded to much stronger winds from 2017 hurricanes that hit the Caribbean, Burgess and a co-author described how solar power designs and installations could be improve to make the systems more secure.

When Hurricane Maria struck Puerto Rico one year ago on Sept. 20, it had sustained winds of 155 mph, well above Florence’s wind speeds after landfall, and some solar panel racks came loose.

“From what we investigated on the ground in the Caribbean,” Burgess said, “solar can be designed and can be installed to be extremely resilient to the most extreme storms.”