Airborne Wind Turbines
The winds higher up are stronger and more consistent than those at ground level. This is why the idea of airborne wind turbines has gained acceptance, since it doesn't face the same cost and intermittent issues of ground-based wind turbines.
Makani Airborne Wind Turbine
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The most well-known design of this type is the Makani Airborne Wind Turbine. It actually combines kite surfing ideas with the purpose of wind turbines. It strives to achieve the same motion as that of a turbine but without the entire structure. This wing shape is tethered and free flying, and thus it is able to float higher in altitude than other airborne turbines.
An airborne wind turbine must utilize less materials than those found in ground based wind turbines. It is estimated that the Makani turbine will be 1/10 the weight of a standard wind turbine and cost half the price to install. It will be rated at the same amount of power. The price per kilowatt-hour would be even lower than coal-fired power at the present time, or about three cents per kilowatt hour.
The rotors on the flying wing of the Makani turbine function as generators and propellers. They use stored or backup power to reach their cruising altitude. When they reach 1,000 feet in altitude, they begin creating resistance to the higher winds and then generate electricity just like electric cars do with their brakes.
Is this turbine affected when there is no wind? The wing structures can use steady breezes to remain aloft, but if the wind goes below nine miles per hour, they would actually use electricity instead of generating it. Plans are to land the wing if there are long periods of forecasted low winds. But it will still be able to generate electricity with double the consistency of wind farms that are in operation today. This is due to the winds at the increased altitude, which may be twice as strong as those on the ground.
The future of the Makani airborne wind turbine looks quite bright. It won Popular Mechanics' Energy Breakthrough Award and got three million dollars in grant money from the Department of Energy. It also received 20 million dollars from Google, for venture capital funding.
In order to be fully successful, the airborne wind turbine must be able to generate a consistent and high rate of power. They are developing a larger turbine system that will float at about 1600 feet in altitude, and this can potentially produce enough power for 600 houses. The prototype of this design should be launched in 2013 and in operation commercially in 2015. The Makani turbine may also be used above deeper offshore water, where even more energy can be produced.
Another model, the Altaerod Airborne Wind Turbine, makes use of an inflatable shell filled with helium, allowing it to gain high altitude. This gives it better access to more consistent and stronger winds, much higher than those turbines mounted on towers. The power uses tethers to reach the ground. Harnessing winds at higher altitudes will allow the turbine to reduce the costs of energy by almost 65%. Since it has a unique design that is easily installed, the start-up time amounts to only days, which means that each shell can be prepared and assembled more readily, for increased energy production.
References
http://theenergycollective.com/energynow/69484/airborne-wind-turbine-could-revolutionize-wind-power
http://www.treehugger.com/wind-technology/future-wind-power-9-cool-innovations.html
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