The Wind at Otis

What to do with the Wind over Otis?

By Chris Stimpson

With the announcement that the Massachusetts Military Reservation (MMR) may be selected for closure by the Pentagon, the question of whether the proposed Nantucket Sound Wind Farm should be relocated to the MMR site has inevitably resurfaced.

Certainly a deactivated MMR could support a number of wind turbines. And these turbines could produce some clean energy for community use. But it is simplistic to conclude that the value promised to Cape Codders by the Nantucket Sound Wind Farm could be realized by moving it ashore.

That action would take the offshore wind farm out of the realm of a viable commercial project with Cape-wide benefits into one where significantly less renewable energy would be produced, and in which Cape Codders would barely notice the benefit.

The fundamental issue is one of wind resources.  The average wind speed over Horseshoe Shoal is 19MPH, compared to 15MPH at the MMR (1).  This may sound a trivial difference, but the physical laws that govern power output from wind turbines (i.e., proportional to the cube of the wind speed) tell us that a turbine at the MMR would produce about half the electrical power of one in the Sound.  It’s hard to finance a project when your saleable product is reduced by 50%, particularly when Cape Wind Associates must, like any other producer, sell their power into the grid at a competitive wholesale rate or no supplier will buy it.

Land-based wind turbines are, nonetheless, valuable and important.  In Orleans, which has a wind resource comparable to the MMR’s, the expected annual ‘capacity factor’ (ratio of actual power produced divided by the rated capacity of the turbine) for the town’s planned wind facility is 23.6% (2).  This is considerably less than the projected Nantucket Sound capacity factor of 41.2% (3). 

Half as much power

In layman’s terms, this means that land-based wind in a 15 MPH resource area is only about half as productive as properly sited offshore wind.  But Orleans is not trying to sell its power into the grid;  the goal of this community wind project is only to beat the price from the local utility (about 15 cents/KWh) to power the town’s water processing plant.  As the price difference increases, so does the economic benefit for the community.

As a wholesale electric provider, however, Cape Wind must match the wholesale clearing price (between 3.8 cents/KWh and 6.5 cents/KWh at this time of year) to put their power on the grid.  It is clear that a wind farm supplying power to local residents through the grid has a much tougher cost goal to meet than a community project, and must therefore be sited in optimum wind locations. 

The bottom line, then, is this:  if the Cape Wind project were to be relocated to a much less productive land site, robbing the Cape and Islands of the large-scale benefits promised by the offshore wind farm, it would not be economically viable.  How much better it will be for all of us if the wind farm is built in the most productive location, so that it can produce maximum power for the most customers.

1. Wind speed from the Wind Energy Resource Map of Southern New England created by True Wind Solutions funded in part by the MTC Renewable Energy Trust.
2. “Town of Orleans Wind Energy Feasibility Study,” Appendix B-1
3. “Natural Gas in the New England Region: Implication for Offshore Wind Generation and Fuel Diversity,” US Department of Energy White Paper, June 6, 2004. Cape Wind Generation in Exhibit III is stated as 1,691,261 MWh for the yearly period of Apr. 03 to Mar. of 04 based on the meteorological test tower in Nantucket Sound. The maximum yearly full capacity output is 468 MW times 8,762 hours per year which is 4,100,616 MWh. The ratio is the capacity factor with the result of 0.412.