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Cuttyhunk Island’s Microgrid

The Market at Cuttyhunk, Massachusetts. Photo: John Phelan, Wikimedia Commons

By George Harvey

The Elizabeth Islands form a small chain between mainland Massachusetts and the island of Martha’s Vineyard. The westernmost of these has the small community of Cuttyhunk. Because it has only fifty full-time residents, a submarine cable to supply power from the mainland is economically unworkable. The island’s population swells to about three hundred during the summer including visiting boating enthusiasts who like the shelter of the island’s harbor.

There is no car ferry to the island, and this helps keep Cuttyhunk quiet and clean. Its electricity, however, has always been supplied from diesel generators, a source of noise and air pollution. Depending on diesel oil also made Cuttyhunk’s electric power very expensive, as the fuel had to be delivered by barge to the island. Because the price of diesel oil varies, electricity can cost as much as 75¢ per kilowatt-hour (kWh).

Last year, Solar Design Associates (SDA), of Harvard, Massachusetts, converted Cuttyhunk’s electric system into a much- more-modern “microgrid,” with most of its power coming from renewable resources backed by energy storage. An array of 1,020 photovoltaic (PV) panels supplies a maximum of just over 350 kilowatts of power. On sunny days, surplus solar power is stored in a system of lithium-ion batteries to deliver 1,000kWh of energy to the island grid when solar is not available.

Solar array on Cuttyhunk consisting of 1,020 PV panels supplying a maximum of just over 350 kilowatts of power. Courtesy Solar Design Associates.

The Cuttyhunk microgrid retained the existing diesel generators for backup power, both for when solar is not available and battery storage is depleted and for times of especially high demand. During most of the year, the solar array will provide about 80% of the island’s power, and, even in times where there are large numbers of visitors, it should provide more than half. Consumption of diesel is about 30,000 gallons less than it had been, resulting in significant savings in fuel and maintenance costs as well as reductions in pollution and noise.

Pioneering systems such as the one on Cuttyhunk provide compelling examples of how microgrids can operate in other applications. Islands dependent on diesel fuel for power are places that can benefit immediately from solar PV systems and wind turbines, because the cost of running diesel generators is high, the reliability is relatively low, and fossil fuels have environmental issues. These are places where microgrid technology is being installed and tested, providing the experience needed to field similar systems in a growing range of applications. Solar Design Associates is currently designing another solar-plus-storage microgrid to power an island off the coast of Maine.

Apart from addressing cost and pollution problems, microgrids based on renewable energy and battery storage technologies provide increased energy security. On Cuttyhunk, this is significant because the solar system’s power supply is no longer entirely dependent on oil, which is subject to price and availability fluctuations, and because the diesel system needs regular maintenance by technicians from the mainland. Interruptions in service can also be lengthy, so many such locations rely on multiple generators to keep the lights on.

Even on the grid-tied mainland, production and transmission issues can lead to lengthy power failures. One way to address these problems is to develop renewably-powered microgrids. The sunlight is delivered free, and these systems require very little attention.

The cost of solar electricity has declined to the point where it is competitive with wind power to produce the lowest cost electricity in large parts of the country. Both solar PVs and wind power have reached a point where, coupled with storage, they now are competing with natural gas to become the least expensive source of electricity.

Seven Strong, founder and President of SDA, explained, “While solar plus storage is an especially compelling approach for island communities dependent on high-cost diesel generators or costly-to-maintain cables, we’ve developed solar plus storage solutions for commercial, industrial, educational and utility customers as well. We see enormous potential around the world for this transformational energy technology. Storage is truly the next frontier.’’

The website of Solar Design Associates is http://solardesign.com/.

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