Wind is defined as air in motion. In simple terms, wind is caused by the uneven heating of the Earth's surface by the sun, which causes pockets of warm air to rise, with cold air rushing in to take its place. Wind energy represents an attractive alternative to fossilfuels and nuclear power.
But how can wind be turned into energy? We asked Dennis Scanlin, a professor at Appalachian State University whose research focuses on wind energy measurement and assessment, renewable electricity generation and solar thermal technologies. Questions and answers have been edited.
Q: How can the wind be harnessed?
Wind turbines have blades on their rotor that turn when exposed to sufficient wind velocity. The blades are shaped like airplane wings, and the movement of the wind over the blades causes them to move. The blades are attached to a shaft that turns a generator that then produces electricity. The larger the diameter of the rotor or the longer the blades, the larger the collection area and the greater the potential energy production.
Q: What has to be considered when choosing a location for wind turbines?
Air density is affected by altitude and temperature, with cold and low elevations having the highest density and as a result more potential power. However, the most important variable is wind velocity, and that is why people often measure the wind for some time before installing a wind turbine. The power available in the wind is quite significant, and good wind sites will have between 300 and 2,000 watts per square meter on average.
Western North Carolina has some of the highest land-based wind velocities on Earth and would enable wind turbines to produce a lot of inexpensive electrical energy per square foot of rotor diameter or dollar of investment. The state also has high wind velocities offshore and is investigating the possibility of building wind turbines out in the sounds or offshore in the ocean.
Q: How does the variability of wind affect the practicality of wind energy?
Good sites for wind turbines generally have pretty consistent winds, although there will be daily and seasonal variability. Wind turbines typically work in conjunction with other methods of electricity production. But one could also store excess electricity produced when the wind is blowing hard and/or the demand for electricity is lower than production, so that power will be available when needed during times of lower wind speeds. The effectiveness of a wind turbine, however, is most often based on the performance or energy production over a year's time.
If the value of the electricity produced in a year's time exceeds the costs associated with building the turbine, then it could be economically viable. The value of wind energy is often at a premium because no air pollution or waste is created by the production of the electricity.
Modern wind turbines can produce electricity less expensively than any of the other methods of electricity production.