Telescopic Wind Turbines to Capture Energy at Low Wind Speeds

The reduction in cost of energy of wind turbines requires many technical contributions from all areas of the Wind Energy Conversion System. The variations in the wind (e.g. Diurnal, Monthly, Seasonal and Long term) as normally shown on probability density distributions directly affect the wind turbine performance. The turbine power output is also dependent upon a number of other variables, and a lot of research has been carried out to increase the power coefficient that has an upper limit of 0.593 called the Betz Limit. A possible way for improving the power output of a turbine is to control the swept area by controlling the diameter of the rotor. Ideally the wind turbine designer will use the long term mean wind speed to design and establish the rated power output of the wind energy conversion system. The stochastic nature of wind will fluctuate the power output of the turbine. Therefore to maintain the design rated power of the turbine, the telescopic wind turbine concept can be used. When the wind speed drops, the telescopic blades extend in order to maintain the power output, and when the wind speed increases, the telescopic blades retract in order to reduce the loads on the system. By telescoping the blades, the capacity factor of the wind energy conversion system is thus enhanced. The wind energy characteristic of a region in New Zealand was studied and the results show an 18% increase in annual energy production of a 10 kW wind turbine with telescopic blades.