September 12, 2017 - Cuttyhunk witnessed New England’s whale oil industry give way to kerosene and incandescent light bulbs. Now the tiny island is deep in another energy revolution — reducing diesel use by way of a solar plus storage microgrid. With a $2.1 million microgrid in operation since the early spring, the fishing mecca offers good argument for pursuing the new energy paradigm. The microgrid is bringing the island price relief and fuel stability.
Sunlight and battery now provide over 50 percent of the island’s electricity. That number will rise to about 80 percent when the last of the season’s tourists (mostly boaters and striped bass fishermen) leave the town for the winter, putting the island on track to reduce its diesel fuel use by 30,000 gallons this year. The project offers guideposts for other islands and far-flung communities looking toward the microgrid-era. But as is often the case for pioneers, getting there wasn’t easy for Cuttyhunk.
Cuttyhunk understands what it means to be isolated and to need energy. Fittingly, the island’s original name was Poocuohhunkkunnah, Wampanoag for “point of departure.” The outermost of the Elizabeth Islands, it is 14 miles away from a mainland port, that being the historic whaling city New Bedford. Cuttyhunk’s sole town, Gosnold, has just 75 residents, making it Massachusetts’ smallest municipality. All of this means that Cuttyhunk is too small to justify the expense of an undersea electric cable connection from the mainland.
Before the solar plus storage microgrid was installed, the island’s 174 electric meters were served via diesel generators. Fuel had to be shipped by barge from the mainland, which was sometimes a logistical ordeal for the island’s sole power and light company. Diesel can be expensive and creates environmental and permitting hassles. And no one on the island knew how to maintain and repair the generators; mechanics had to be imported from ashore.
So Cuttyhunk recognized the value of a microgrid as many as five years ago. But it took time for the island’s small utility to plan and muster resources for the project. First the island’s utility, Cuttyhunk Power & Light, had to figure out how to pay for the facility. Ultimately, most of the funding came from the U.S. Department of Agriculture Rural Energy for America Program (REAP). Because it was one the program’s early solar + storage projects, navigating the application process took more than two years.
1,020-panel solar array and a 1 MW energy storage system delivered over 50% of the electricity this summer for Cuttyhunk Island, Massachusetts
When the funding was finally in place, there were new challenges. For one, it’s not easy to find space for a solar array of 1,020 panels on an island that is only 1.5 miles long and ¾ of a mile wide. The panels needed about three acres, including a setback, with proper orientation toward the sun to gain maximum efficiency.
A nature preserve takes up about half of the island’s land. And no other public property proved ideal for the array. Fortunately, a private landowner agreed to lease land. But then a whole new trial emerged — getting the panels to the spot. A special barge had to carry a 55-foot tractor trailer loaded with solar panels to the island.
“Everything has to be barged over and you have to plan for the tides. The barge has to be large enough for a tractor trailer to be able to drive on and drive off with all of the equipment. You have a crane or other lifting capability to unload on the island, etc., etc.,” he said.
Once on the island, the 55-foot truck was forced to back all the way down a 1.5-mile road that was the width of a driveway — there was no room to turn around at the other end.
This and other logistics “added a whole different level of complexity to the construction process,” said Strong. “And of course, that’s illustrated in the cost, over all.”
Design challenges also emerged because of the big shifts in population on the island from summer to winter, as did the island’s weather extremes — plentiful summer sun followed by cold winter storms. But the tiered nature of the micro-grid’s multiple resources helped overcome this seasonal problem. Of the ‘remote’ variety, Cuttyhunk’s microgrid differs from most in the U.S., which have access to a massive central grid. It is truly on its own, always ‘islanded’ — the term used to describe when a grid-connected microgrid separates from the central grid during a power outage. It achieves reliability by using multiple resources; a 351.9 kW photovoltaic system, 1.25 MWh lithium ion battery and legacy diesel-powered generators. A microgrid controller dispatches the resources for maximum efficiency.
The changing winter and summer population actually creates a sort of symbiotic relationship among the microgrid assets. With the winter’s low population, the battery capacity can carry days of load. In summer, the population — and energy demand — is higher but the solar panels have more sun to harvest and feed into the batteries.
“You’re going to have two weeks of cloudy weather sometime in January and February for at least a few years in the life of the system,” Strong said. “The solar has priority…the batteries carry the solar when the clouds come over or when the sun goes away. When the batteries are depleted and the sun doesn’t return the generators come on automatically.”
The multiple generators are staged, with some larger than others, according to Strong. This helps reduce their maintenance costs, which is important because the island must import it diesel mechanics along with the fuel.
The microgrid conserves diesel by prioritizing use of the solar plus battery assets, then by dispatching the most efficient generator to meet that load requirement at the time. The generators also charge the battery with their excess capacity to get maximum fuel efficiency out of a diesel generator. This means loading them at an optimal point, which is roughly 85-90 percent of the generator’s nameplate capacity.
“Diesel fuel consumption is not linear with load. In other words, if you are running diesel at 50 percent and then you bump it up to 75 percent, and then bump it down to 50 percent, you don’t save that. 50 percent is not half of full operation. 50 percent loading is about 65 percent fuel use,” Strong said.
The microgrid controller is programmed so that if the generators are called upon during a period of modest energy use, usually mid-September to early June, the generator will charge the batteries while it is powering the island. This makes maximum use of the fuel and reduces waste. Other times the solar panels charge the batteries.
“Whenever there is surplus, it is put into the batteries,” he said.
Cuttyhunk powerhouse with battery storage unit on left
Cuttyhunk’s venture into a solar plus microgrid makes sense for other North American islands which tend to see burgeoning summer population. Another project in Maine on the Isle au Haut is being developed. Its microgrid is expected to provide 100 percent of the island’s year-round electricity and eliminate its dependence on a 35-year-old undersea electric cable. Isle au Haut has 140 year-round and seasonal electric customers. By Elisa Wood
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