Where Wind Turbine Generators Work Best
Wind Power Generation For Homes, Business And Industry
Small wind turbines generating electricity for buildings have great potential for saving energy, but only if they are installed where wind conditions are favorable. The average wind speed must be sufficient. Expert assessment is needed of the wind speed and turbulence close to the roof line for turbines mounted on buildings. Turbulence has been an obstacle in densely-built downtown cores and city centers.
Wind Turbine Power In Open Spaces
Best results are obtained in rural and open spaces from both types of turbine: horizontal axis (HAWT) and vertical axis (VAWT).
Turbines can be used to power cabins, campers, farms, schools, telecommunications transmitters, offshore platforms, water pumps and yachts. In these situations, turbines can power equipment and appliances while charging batteries so that battery power can be used when the wind drops.
For rural use, one manufacturer recommends a turbine be mounted on a pole or tower in an open area of 1 acre (0.4 hectare) to avoid obstructions.
In suburban sites, such as shopping malls or industrial campuses, turbines can be mounted on poles in open areas of parking lots or landscaped parkland. Some can be mounted on existing lighting poles.
Wind Conditions For Electricity Generation
In open-area situations, a primary consideration is the average wind speed, which the British Wind Energy Association (BWEA) says should be at least 5 metres per second (m/s), 11 mph or 18km/hr. Many manufacturers specify the minimum wind speed for the turbine to start generating, typically 3.5m/s (8mph) for a HAWT and 4.5m/s (10mph) for a VAWT.
The American Wind Energy Association (AWEA) points out that, because the energy developed from the wind is a function of the cube of the wind speed, little energy is harvested below 4 m/s (9 mph, 14.4 km/h).
Wind Turbine Performance On Building Roofs
Manufacturers can provide average wind-speed figures for any location. However, these figures can be widely misleading, especially for turbines mounted on or close to buildings in densely built-up areas.
In the U.K., Encraft, an independent consulting engineering firm specialising in microgeneration, studied the performance of turbines from several manufacturers on 26 mostly urban buildings of various types, including houses and tower blocks in widespread locations. The turbines had been purchased based on wind speed estimates from a British government database.
Over the 30-month test period, this Warwick Wind Trials project found only 5 of the turbines were operating in the minimum average wind speed of 5 m/s. The wind speed data were obtained from measurements made at the tops of 10, 25 and 45 m poles, but all the turbines in the Warwick study were 6 to 15 ft (1.8 to 4.6 m) above the roof line, where the wind speed was much less.
With proper roof-level assessments, individual turbines and banks of turbines are being installed on the roofs of commercial buildings.
Wind Power Generation In Dense Urban Areas
In densely built urban locations, tall buildings cause turbulence and the powerful vertical air currents up the faces of buildings produce eddy currents over the roofs. Mechanical stress has caused damage to turbines in the past and has hindered the application of them to downtown buildings.
VAWTs are claimed by their manufacturers to be better able than HAWTs to operate in these turbulent conditions. A VAWT responds to wind from any direction whereas a HAWT, with its propeller-type blades, must swivel with the wind.
Despite these claims, both VAWTs and HAWTs are installed on the roofs of commercial and residential buildings. A type of VAWT known as the triple-helix is in use on residential blocks in London, U.K., and in the London suburb of Croydon, both of which are densely built.
Basic Conditions For Wind Turbines
Wind turbines have shown their potential to save costs by generating electricity for individual buildings. Excess electricity can be fed into a power grid and sold to a utility. Equipment powered by turbines can be protected against surges, sags and interruptions due to wind variation.
For a turbine on a pole in an open area to be fully effective, the average wind speed must be sufficient over the geographic location. But for turbines on rooftops of buildings the wind conditions must be assessed at the actual mounting position of each turbine.
See also: Alternative Green Energy Source From Tidal Power
Triple helix vertical wind turbine
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Horizontal wind turbines on a commercial building
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