Much has changed during Maine’s 15-year year journey to launch a full-scale test of offshore wind power, and the destination is still in the distance.
The idea of a test turbine off Monhegan Island is an outgrowth of ambitious goals envisioned in 2008 by Maine’s Ocean Energy Task Force – to build 5,000 megawatts of offshore energy capacity by 2030, codified by the 2010 Ocean Energy Act.
Conventional ocean wind turbines are supported by steel towers, anchored to the seabed in shallow waters. But the next generation of wind farms are expected to be farther offshore, floating in deep water. The University of Maine’s Advanced Structure & Composites Center developed a semisubmersible hull made of concrete, which, unlike steel, could be fabricated more economically in Maine.
The test site off Monhegan Island was selected through a state-run process. The site was picked because it’s 12 miles from the mainland, has steady winds and is plied by only a modest number of fishermen – and because island residents pay extreme electric rates.
The 2009 law that designated the site allowed up to two turbines, a maximum capacity of 25 megawatts and one transmission cable.
But over time, the scope of the project changed. Engineers decided to test a one-eighth scale model of the concrete platform off Castine in 2013, in more protected waters. Its performance in winter storms helped prove the concept of the four-column, semisubmersible concrete hull, a patented design called VolturnUS.
Maine Aqua Ventus, as it was known at the time, also won federal Department of Energy awards for commercial-scale testing, worth $47 million. That led to an upgraded design for two, six-megawatt turbines on full-size platforms off Monhegan, with a cable to the mainland and the island.
The Maine Public Utilities Commission then approved a 20-year power contract in 2014. Now the plan is for a single, larger turbine and platform.
That’s because the wind turbine industry has been developing larger units that can capture more energy. Danish maker Vesta is testing a 15-megawatt turbine for offshore use, a giant that features 379-foot blades and could power 20,000 homes. It’s likely that the Monhegan project, if built, would feature a turbine on that scale.
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