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ECN publication
Novel views on the extraction of energy from wind : heat generation and terrain concentration
Published by: Publication date:
ECN Wind Energy 1-9-2001
ECN report number: Document type:
ECN-RX--01-054 Conference Paper
Number of pages: Full text:
5 Download PDF  

Presented at: European Wind Energy Conference and Exhibition, Copenhagen, Denmark, 2-6 juli 2001.

First it will be shown that an actuator disk operating in wind turbine mode extracts more energy from the fluid than can be transferred into useful energy. At the Lanchester-Betz limit the decrease of the kinetic energy in the wind isconverted by 2/3 into useful power and by 1/3 into heat. Behind the wind turbine the outer flow and the flow that has passed the actuator disk will mix. In this process momentum is conserved but part of the kinetic energy will dissipate in heat via viscous shear. Second we will explain that the classic site calibration in complex terrain has no physical basis. The concentration will depend on the wind direction and this implies that a turbine (pitch- or stall regulated) is expected to have multiple power levels depending on the wind direction under such circumstances. These multiple power levels are expected in particular below rated wind speed. This analysis is put forward in appendix A.

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