Wind data collection began in September 2007 under the direction of UMass Renewable Energy Lab  and concluded on August 31, 2009.  Four anemometers and two wind directional devices were mounted on the U.S. Cellular tower on Stockbridge Hill.  Wind data was measured at heights of 130 and 165  feet  to gauge optimal site locations and measure available wind energy. The Swan’s Island Electric Cooperative is grateful to U.S. Cellular for donating temporary space on their tower for our wind assessment instruments for the duration of the study.

The average annual wind speed on Swan’s Island is approximately 5.8 meters per second, or  about 13 miles per hour.  The wind comes predominantly out of the southwest during the warmer months of the year, but can shift to the northwest during the coldest months.  The chart below illustrates the greater strength of the wind during the fall and winter months as well as how an increase in the tower height of a turbine can magnify the power that can be derived from our wind resource.


Swan's Island wind speed data



Can our wind resource satisfy the Island’s power needs?
From our Wind Study results it is possible to predict the amount of electrical power which can be generated month-to-month and compare that with the Island’s known power demand.  The two charts below summarize the amount of power generated by one  General Electric 1.5 Megawatt turbine (in red) compared to  Swan’s Island’s monthly power usage (in blue).  The wind data is from the 12 calendar months of 2008.  The power demand data is from the monthly usage totals of the past five years where the highest monthly usage totals have been selected for comparison.

The vertical axes on the charts below are calibrated in 100,000 Kilowatt-hour increments.  So, for example, in January, the turbine would produce just over 600,000 kilowatt-hours, while Islands' demand would total 275,000 kilowatt-hours

The charts above demonstrate that a single utility-scale turbine can generate enough power to satisfy the Islands' demand in every month except August.   During all the other months – particularly from mid-fall until mid-spring, Swan’s Island can expect to be a strong net-exporter of clean renewable electric power to the mainland at wholesale prices.   In  August, when wind speeds are low and the island population  swells to its traditional high level, the Islands' electricity demand will be met from power generated from our own turbine and power purchased from the mainland.   Every kilowatt hour produced and consumed on the Islands is a unit of power which does not have to be purchased on the mainland and transmitted under the ocean to our Island grid. These are dollars saved.  Likewise, every kilowatt hour which is produced in excess of the Island’s needs can be transmitted  across our cable to the mainland and sold on the wholesale power market.  These dollars earned in sales, added to the savings realized from the generation of our own power, are the principal means by which the Electric Cooperative can begin to lower and stabilize electric rates.

Every Day – a buyer and a seller of electric power
While the charts above are useful  in comparing the month-by-month differences between power used and power produced, in actuality the Electric Cooperative will be buying and selling power at different times of almost every day.  For example, even in the winter when winds are strong, there are times of the day when it can be quite calm.  On a calm December morning, when lights go on early in the pre-dawn hours and coffee makers begin drawing power and breakfasts are being made, the wind turbine may be still, because it takes about seven miles per hour of wind for the blades to turn and for power to be generated.  During this time the Cooperative will be buying power from the mainland.  By mid-morning, when electrical demand on the Island has eased, and a brisk wind of 15 mph is generating three times the amount of power needed by the Island grid, the excess power will be flowing across our undersea cables to the mainland for resale.  This wind strengthens further in the afternoon, increasing the amount of excess power being sold until perhaps 5 PM when the wind slackens to 10 mph and most islanders are increasing their power demands by preparing supper, taking baths & showers, and washing dishes. During this time the turbine may be producing just enough power to meet demand. By 9 PM the wind is freshening again as islanders go to sleep and as local power demands begin to decline, more and more excess power is transmitted to the mainland throughout the night, until, as the predawn hours approach, the wind subsides again, and the cycle prepares to repeat itself.

This site was made possible by a grant from Island Institute.