Wind energy is the fastest growing method of generating electricity in the world. It’s also one of the most ancient of energy sources. Sailboats have existed for thousands of years.
Wind exists because the sun heats the earth and its atmosphere unevenly. As warmer air rises, colder air rushes in to take its place.
Hills, valleys, and other irregularities in the earth’s surface, as well as bodies of water, vegetation, man-made structures, and the rotation of the earth all influence wind flow patterns.
Rotors mounted on towers capture the wind and operate a generator, which converts the kinetic energy of the wind to mechanical power, which in turn creates electricity.
Most typically, commercial wind power generation combines multiple turbines in areas known as wind farms.
How wind turbines generate electricity
Although inventors are working on bladeless alternatives, most wind energy comes from turbines that operate by a rotor mounted on a tower.
The tower and foundation must not only carry the weight of the rotors and the generating equipment, but also withstand wind from all directions and at various speeds.
Towers are usually made either from round concrete or steel tubes (not strictly cylindrical) or less frequently from steel lattices. The larger the rotor, the taller the tower must be.
Taller towers are more expensive to build, but they also produce more electricity. The tower and foundation typically account for 15-20% of construction costs.
The rotor must be capable of turning in response to wind direction, so it is mounted on the tower with bearings.
The central part near the hub contains the drive-train components: the rotor shaft and its bearings, the transmission, the generator, the coupling, and the brake.
The structure also has components that
- follow wind direction
- control heating and cooling
- protect the entire structure from lightning
- lift spare parts for maintenance
- can extinguish a fire
The rotor spins at 18-50 rpm. The blades turn slowly in terms of rpm, but the tip of large blades can exceed 140 mph. The generator requires about 1500 rpm. The transmission, therefore, by various means and in multiple steps, matches the slow rotation of the rotor with the fast rotation of the generator.
Whatever the design of the generator, it comes equipped with a variety of electronic sensors and controls. A wind turbine can be understood as the opposite of a fan. Instead of requiring electricity to turn the blades, the turning of the blades produces electricity.
Rotor diameter largely determines the capacity of a turbine. They come in three broad size ranges:
- Residential: rotor diameter of 4-43 feet, hub height of 60-120 feet, and rated capacity less than 30 KW.
- Intermediate: rotor diameter of 43-100 feet, hub height of 115-164 feet, and rated capacity of 30-500 KW
- Commercial: rotor diameter of 100 to more than 325 feet, hub height of 164 to more than 260 feet, and rated capacity between 500 KW and 4.5 MW
Rated capacity measures generation of electricity under ideal conditions, but wind blows intermittently and at varying speeds. The actual capacity depends on the wind speed at hub height.
Transmission and distribution of wind energy uses the same technology as any other electricity.
Some problems with wind turbine power
The amount of wind available varies with geography. Areas are rated in seven different classes, with Class 1 being the lowest. Wind generation is feasible only at Class 3 or higher, or an average annual wind speed of no less than 13 mph.
Calm winds do not turn the rotors to make electricity. Because wind power is intermittent, it requires some kind of storage. So far, there is no cost-effective storage technology available on a commercial scale. Therefore wind must be used with other sources of electricity.
Wind installations cost more to build than conventional fossil fuel plants, but have much lower maintenance costs and no fuel costs. Over their entire life cycle, they are competitive, but they don’t get built without financial incentives.
Let’s keep in mind, though, that fossil fuels receive subsidies from the federal government. Subsidies for emerging technologies are more justified. There seems to be no good reason to rely on market forces alone to develop wind energy.
The military invented and supported the Internet for 20 years and turned it over to the National Science Foundation for 10 more years before it became public. Computers, jet planes, integrated circuits, and satellite communications came first from government programs, not the market.
Wind turbines kill as many as 440,000 birds every year. Compared to the 976 million birds killed when they collide with buildings, that’s a small number, but with the development of more and more wind farms, the problem will only grow. Fortunately, the government is funding projects to minimize the problem.
People care more about birds and bats than insects, but insect debris distorts the shape of the rotors. It can cut turbine power output in half. Rain washes it off, but in the absence of rain, crews with trucks and sprayers must do it, which increases the plant’s operating costs.
Many people consider wind farms an eyesore. Between that and the noise from the rotors, wind energy triggers the “Not In My Back Yard” syndrome more than any other alternative energy source.
In fact, former Senator Ted Kennedy, otherwise an enthusiastic supporter of green energy, fought hard to prevent development of a massive wind farm off the Massachusetts coast.
Offshore wind farms can’t be built in water more than 120 meters deep. Shallower water is close enough to shore that the turbines are still visible from land—including Senator Kennedy’s home.
Researchers and inventors are working to develop new technologies to mitigate these and other problems. Among other things, they have proposed at least a dozen or so wind generators that don’t uses rotors. One or more is bound to become technologically feasible and scalable. Any of them would have lower construction and maintenance costs than rotors on a tower.
Is there a wind farm in your vicinity? What do you and your local public think about it? Please let us know in the comment area.
Wind Energy Guide / Upper Great Plains Wind Energy
Wind Turbine Technology / World Wind Energy Association [link no longer works, May 17, 2017]
Wind Energy Pros and Cons / Mathias Aarre Maehium (Energy Informative)
Wind farm. © Copyright Stephen Craven and licensed for reuse under this Creative Commons Licence
Wind turbine components. Public domain from Wikimedia Commons.
© Copyright Chris Downer and licensed for reuse under this Creative Commons Licence