How Ocracoke Island's microgrid kept (most of) the lights on during last month's outage
At the height of the summer season, a construction accident severed the island's power. While backup generation failed, most residents still had power.
Ocracoke Island, off North Carolina, experienced not one but two outages last month. But for the island's residents, the lights remained on.
Ocracoke was aided in part by a recently completed microgrid, with one of the island's electric cooperatives now working to expand the demand response potential of that microgrid.
In late July, at the height of the summer tourist season, Ocracoke abruptly lost power when a construction company severed the island's transmission cable, cutting through the lines that deliver its power. It was a worst-case scenario for residents who make their living catering to tourists visiting the Outer Banks, a series of islands off the state's coast.
Ocracoke gets about 12 weeks a year of high traffic, and losing even one of those is "devastating," said Lee Ragsdale, senior vice president of grid infrastructure and compliance for North Carolina Electric Membership Corp. (EMC), the power supplier for most of the state's member cooperatives. Tourists were evacuated, after it became clear repairs would stretch days — and possibly weeks.
Lights stay on
The outage and its financial impacts were a national news story for the week, but less well-publicized was this nugget: Ocracoke residents had power. The lights stayed on.
North Carolina EMC and Tideland EMC, the island's cooperative, earlier this year completed the development of a microgrid. It has been operating since February, providing backup energy to less than 1,000 year-round residents whose power supply is susceptible to strong storms.
The system includes a 3 MW diesel generator, 500 kW/1 MWh Tesla battery, 15 kW of solar, and connected devices to work as demand response. The island's system has about 175 thermostats and 50 water heaters it can control as needed.
While Ocracoke was able to keep the lights on for residents and businesses, and overall was a successful test of the microgrid, it did not go off without a hitch.
"Unfortunately, pretty quickly into the outage the diesel generator failed," said Ragsdale. "It was a catastrophic forced outage. It was completely unexpected. That unit has been operating for 20 years. It was a freak accident."
Despite that, the microgrid was able to provide a modest amount of energy to homes. The cooperative has a small but flexible system. "We've been putting it through its paces. This is a research project, and we're examining the interoperability of these components," said Ragsdale.
A pair of 2 MW diesel generators were brought in while the 3 MW unit was being repaired.
"We're always looking for ways to improve redundancy. The biggest thing is to be flexible," said Ragsdale. "The components all performed like we wanted them to ... The outage itself was terrible. But there can be good that comes out of it. There were plenty of lessons learned."
While a pair of 2 MW generators have more capacity than the single unit permanently on the island, because of how Ocracoke's grid is laid out, Ragsdale said the utility couldn't operate exactly as it would have liked with the mobile generators.
It comes down to the configuration of the distribution circuits, he explained. The island has three circuits, and the control systems were not coordinated with the backup-backup generation. "From a utility operating perspective, it was a different operating mode," Ragsdale said.
Despite that, no public service was in jeopardy. The fire station acted as a cooling station for residents without air conditioning, local businesses were able to restore power quickly, and the island's water treatment plant continued to operate. The Tesla batteries discharged as expected, and the small solar array contributed as well.
One might think solar would be a larger resource for an island community focused on summertime tourism, but there are several stumbling blocks there. Some residents are wary of mounting systems on their roofs, because of the beach climate and potential for storms. And much of Ocracoke is managed by the park service — its wild beaches are the main attraction — and so developable land is not abundant.
"We've talked about adding more solar, but one of the biggest challenges is real estate," said Ragsdale. "These islands are pretty tightly packed in ... any big solar would have to encroach on national parkland. And on an island like Ocracoke, a lot of the residents there are making do with what they have — meaning a substantial investment in solar may not be in their financial best interest."
The cooperative is trying to expand its demand response potential on the microgrid, rolling out more marketing and "boots on the ground." NCEMC is looking at bringing the island's rental properties into the system, by reaching out to management companies that have multiple homes about connecting those thermostats.
The total economic loss in an event like this is difficult to quantify. Repairs to the generator, and the cost of burning diesel rather than purchasing power on the market. Class action lawsuits have been filed against the construction company that severed the transmission tie. "But to the residents, the main one is that economic impact of losing a week of tourism. It's devastating to them," said Ragsdale.
It is unclear whether the 3 MW generator would have been sufficient to keep tourists on the island, had it not failed. Summer peaks rise to 6 MW on Ocracoke, and so even functioning perfectly, the microgrid may not have been enough. Ultimately, the decision was made by Hyde County, N.C., officials.
"One of the biggest things learned is to be flexible in figuring out how we can return service," said Ragsdale."We're looking at ways to improve redundancy and to have a faster response ... we've already had discussions but they will continue over the next couple of months about how to more effectively respond."
Second microgrid coming
NCEMC is also developing a second microgrid. The cooperative power provider is working with Butler Farms, near Lillington, N.C., in the state's center, to develop a generator and grid focused on turning waste from about 7,500 pigs into energy, alongside solar and battery storage.
"We're going to have a community resiliency idea, where this hog farmer can take generation from his swine waste and use that to power the community," said Ragsdale. The plan is to be able to support 100 homes in the community for at least four to eight hours.
So far, the coop board has been supportive of efforts to "think about the future and test these ideas," he said. "The bottom line is, we want to provide affordable and reliable power to our members. Microgrids, batteries and solar are a part of that solution."
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