Wind
Wind Turbine MechanicsWind turbines convert the kinetic energy of the wind into electricity. Most common are horizontal axis wind turbines, which consist of two or three blades that face the wind and spin around a rotor. The rotor is connected to a low-speed shaft, located in the structure housing the generating components called the nacelle. Gears connect the low-speed shaft to the high-speed shaft, which increases the rotational speed from about 30 to 60 rotations per minute (rpm) to about 1000 to 1800 rpm. The higher rpm is required by most generators to produce electricity. Turbines are mounted on towers to take advantage of faster, less turbulent wind.
Other components include the yaw drive which keeps the rotor of upwind turbines facing into the wind as the wind direction changes. Wind turbines also include a brake used to stop the rotor in emergencies or high winds. Click the image for details on additional components.
Source: DOE/EERE
Turbine Size
The size of a turbine will vary depending on the location and its intended use. Small turbines – defined as 100kW capacity or less – can be used in homes or businesses, telecommunications dishes, or water pumping. Larger, utility-scale wind turbines can be connected to the utility grid, delivering clean power to utility customers.
Photo courtesy of DOE/NREL.
Through interconnection and net metering standards, a home or business can consume electricity generated from both a wind turbine and the local utility. At low wind speeds (less than 7-9 mph), a small turbine would produce little or no energy, requiring the home or business to purchase electricity from their utility. As wind speed increases, turbine output would increase – reducing the amount of power purchased from the utility. If the turbine produces more power than home or business consumes, the excess electricity is sold to the utility and placed on the electric grid. Small wind turbines also can be used in conjunction with diesel generators, batteries, and photovoltaic systems. These hybrid systems are typical in remote locations where connection to the electric grid is difficult.
Measuring Wind Resources
Winds are created by the uneven heating of the atmosphere by the sun, irregularities of the Earth's surface, and the rotation of the Earth. As a result, winds are strongly influenced and modified by local terrain, bodies of water, weather patterns, vegetative cover, and other factors. Wind potential is divided into seven classes with one being the lowest and class seven being the highest. Class 2 areas are often adequate for small wind applications, but Class 4 winds are needed for utility-scale applications.
As evident from the map, North Carolina has ample wind resources in the mountain and coastal regions. However, in the mountains, concern exists over the North Carolina Mountain Protection Act, commonly referred to as the Ridge Law, which prohibits the construction of tall buildings or structures on the ridges of many North Carolina’s mountains.
Photo courtesy of DOE/NREL
(Paul has a larger, pdf of this map)
Wind Turbine Considerations
A major benefit of wind energy is that the system operations do not generate any air or water emissions or hazardous waste. Most notable, wind systems do not release carbon dioxide or other greenhouse gases. Even when turbine production is considered, the wind energy carbon dioxide emissions are about 1% of coal and 2% of natural gas per unit of electricity generated.
Several concerns often arise over wind turbines. One concern, erosion around the turbine site, can be prevented with proper installation and landscaping technique. A second concern, noise, was a common issue with early turbines. This problem has been largely eliminated with improved engineering and careful siting.
Finally, the most common concern over wind turbines is birds and bats colliding with the structures, resulting in death. While some sites may be more problematic than others, the overall impact of the wind industry is minimal compared to other anthropogenic threats. A 2002 study found buildings, vehicles, and cats prove a much greater threat to bird populations than wind turbines.
Source: Erickson, et al., 2002. Summary of Anthropogenic Causes of Bird Mortality.
Additional Resources
American Wind Energy Association
The American Wind Energy Association (AWEA) is a national trade association representing wind power project developers, equipment suppliers, services providers, parts manufacturers, utilities, researchers, and others involved in the wind industry. The website contains a recent market report – Wind Power Outlook 2007 – and an excellent Wind Web Tutorial.
North Carolina Wind Energy
Maintained by Appalachian State University, this site contains upcoming events in North Carolina, reports and research, wind maps for counties in western North Carolina, turbine dealers and installers, and much more.
Small Wind Electric Systems: A North Carolina Consumers Guide
Published by the US Department of Energy – Energy Efficiency and Renewable Energy.
Danish Wind Industry Association
The Danish Wind Industry Association offers an excellent website, providing extensive technical details.
