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Wind Power

This wind turbine is part of Green Mountain Power's 6 megawatt wind power facility near Searsburg, Vermont. Photo credit: Bob Thresher and DOE/NREL

Read related articles on wind power:

• Harvesting Offshore Wind
• The Cape Wind Project

Wind energy has been harnessed for thousands of years to perform useful work for humans. Humans have used wind power for transportation, water pumping, and grinding since the time of the ancient Egyptians. In the late 19th century, the Danes began harnessing wind to generate electricity using wind turbines.

People often use the terms windmill and wind turbine interchangeably. However, windmills harness the wind for mechanical power to grind wheat or pump water, while wind turbines use the wind to generate electricity.

Today, modern wind turbines efficiently convert the force of moving air into electricity using modern design principles and high-tech materials. Wind turbines come in many different sizes from small-scale home systems of 5 kilowatts to 15 kilowatts, to utility scale systems ranging in size from 300 kilowatts to 1,000 kilowatts. To take advantage of higher wind speeds and to allow the blades to rotate without interference, wind turbines are mounted on the top of a tower typically 160 feet high. Although there has been some experimentation with vertical-axis wind turbines, most wind turbines have airfoil-type blades that rotate around a horizontal-axis. The blades are designed like the wing of an airplane creating lift when exposed to the force of the wind, which propels the blades around in a circular motion. The wind turbine rotor typically consists of two or three blades attached to a hub. A rotating shaft from the rotor feeds into a gearbox assembly and then into the generator, which converts the mechanical motion of the shaft into electricity. As the wind changes direction, the yaw system allows the wind turbine to pivot so that the rotor spins in a plane perpendicular to the wind.

Understanding the Wind Resource

Ultimately, wind is a form of solar energy. The sun's rays heat the Earth's surface creating temperature differences between the land, water, and air, given their different propensities to absorb heat. This phenomena, in conjunction with the temperature differences that exist between the equator and the EarthÕs poles, creates wind as hot air rises, expands, becomes less dense, and is then replaced by denser, cooler air. In sum, wind can be thought of as the circulatory system of the planet, distributing energy from warmer areas to cooler areas.

The economic viability of wind-generated electricity in a particular location is tied to the amount of wind available throughout the yearÑthe wind resource. A standardized system has been established for classifying the wind resource based on wind power density, a measure in watts per square meter of how much energy is available at the particular site for conversion by a wind turbine. Seven different wind classes have been established, with higher classes corresponding to higher wind power densities. In general, wind classes 3 and above (wind speeds of 11 miles per hour or more) are necessary for producing electricity from wind. For large, utility-scale applications, wind classes 4 and above are preferred.

Although the Northeast does not have the nation's best wind resources, a number of excellent wind sites exist in the mountainous areas of northern New England and New York. In fact, wind classes 5 and 6 can be found in the mountains of northern Maine, New Hampshire, Vermont, and New York. Some wind classes 3 and 4 can be found elsewhere in the Northeast. To date, only several megawatts of wind power have been developed in the Northeast. Green Mountain Power of Vermont owns and operates the largest wind farm in the region at 6 megawatts. This site provides enough power to serve the needs of over 2,000 households. This site is located in Searsburg, Vermont.

Economics and Future Prospects

Of all the renewable energy technologies, wind power is currently the most cost competitive when compared to traditional, fossil-fuel-based energy production technologies. In fact, wind power is the fastest growing energy source around the world. The United States now has a total of 2,600 megawatts of installed wind capacity. This is equivalent to about three or four large coal-fired power plants.

Utility-scale wind farms produce electricity at about 4.5 ¢/kWh which makes wind power competitive with fossil-fuel-generated electricity. It should be noted that these economics are made possible by a federal production tax credit of 1 ¢/kWh. Even though wind is an intermittent resource, meaning wind speeds vary from day to day and month to month, wind power can be easily integrated into the existing supply mix, making a significant contribution to our nationÕs energy supply. Most analysts agree that technological improvements and economies of scale in wind turbine production will contribute to even further cost reductions in the price of wind-generated electricity.

Environmental Issues

Wind-generated electricity provides a pollution-free source of electricity. None of the harmful emissions associated with fossil fuels occur when the wind is utilized to produce electricity. Increased use of wind power in the Northeast would be a valuable step toward improving the health of the regional environment.

The main concern regarding wind energy development in the Northeast revolves around siting. Given that the best wind sites are located along mountain ridges, wind farms could alter the aesthetic character of pristine wilderness areas in northern New England and New York. On the other hand, we need to remember the serious health and environmental impacts of most other energy sources when compared to pollution-free wind power. There will always be, and should always be, places where wind development will not make sense for aesthetic reasons, but environmentally-minded citizens should seek to identify as many suitable wind sites as possible.

In the past, some people raised serious concerns about the swishing noise made by wind turbines and their impacts on migratory bird species. These concerns have largely been dealt with through technological improvements and proper siting.

For Further Information

Visit the following web sites:

• The Energy Efficiency and Renewable Energy Network of the US Department of Energy (www.eren.doe.gov)
• The American Wind Energy Association (www.awea.org)
• The National Renewable Energy Laboratory (www.nrel.gov)