Isolated at the very end of the transmission line and subject to outages due to high winds and storms, the island of Ocracoke could benefit from a more diverse mix of resources—including a solar-plus-storage microgrid, said Heidi Jernigan Smith, spokeswoman for Tideland Electric Membership, which supplies electricity to the island.
Isolation and outages aren’t the only woes plaguing the island’s electric co-operative. Crammed with tourists in the summer, the island struggles with high demand charges — as high as 57 cents of every dollar spent on electricity. And exposed power lines along the coast mean salt accumulates on the electric equipment.
To address these issues, the co-op is now experimenting with a solar-plus-storage microgrid, along with a residential peak-shaving experiment. The region’s isolation makes it a great laboratory for studying such programs because it’s easy to identify the effects of the trials, said Smith.
“The environment lends itself to a hands-on lab setting,” she said. “You can isolate information.”
The project is a cooperative venture by the North Carolina Electric Membership Corp. (NCEMC), which owns the island’s 3-MW diesel generator, and Tideland Electric Membership.
Ocracoke is now served by transmission lines that travel down the Outer Banks of North Carolina and across the bridge to Ocracoke. At that point, the co-op picks up ownership of the lines and brings them in 12 miles, to the village of Ocracoke. But for 12 miles — until you get to the village — there’s no electric service.
To help avoid brownouts due to high demand, as well as the high demand charges, NCEMC in 1990 installed a 3-MW diesel generator to serve as a peaking plant. With the generator, power became more affordable during peak hours, said Smith.
The microgrid consists of three components — a 15-kW rooftop solar array located on top of the diesel plant, Tesla batteries with 1 mW storage capacity, and 150 Ecobee smart thermostats that residents will use for peak shaving. The microgrid has a Tesla controller.
Solar-plus-storage microgrid manages resources
“A microgrid creates a localized ability to manage resources,” said Smith.
Managing those assets means figuring out how to best take advantage of the batteries.
“We will experiment with how to utilize those batteries,” Smith said. The co-op can control the rate at which energy is stored in the batteries, she added.
“We are testing various distributions of that stored power; we will look at the rate at which batteries download stored energy,” she said. The co-op is testing ways to use the stored energy and comparing the cost of those options with the cost of the diesel generator plant.
The co-op sees opportunities to run side-by-side experiments using the batteries and the generator. Since a lot of electricity is required to recharge the batteries, the co-op will look at how to lower these costs by changing the time of day storage takes place.
Managing assets also involves using the 150 smart thermostats in homes to help shave peak loads. Under the program, the co-op sets up control events for homeowners. The residents are warned about the time and day of an event in advance, and during the event, the co-op lowers the temperatures of the smart thermostats by up to three degrees for three hours. The homeowners have the option of over-riding the temperature drop.
In addition to testing the components that make up the microgrid, the co-op is looking at the human factor — how people react to the peak shaving events. It is testing whether residents react more favorably to a slightly lower temperature change, for example.
“What if we raise the thermostat only two degrees? Does the occupant’s comfort increase and are we still shedding enough load to see savings?” she said.
The microgrid likely won’t be used to island from the co-op because it’s less expensive to rely on power from the main grid. The main goal of experimenting with the microgrid is to understand how various resources will work best together, said Smith. The over-arching goal is to diversify the co-op’s resources.
“We want to have as many options as possible and not have all our eggs in one basket,” she said. “We want to understand for each component individually what’s the most cost-effective arrangement of assets.”
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