Circling kites gather more power
Tom Shelley reports on a novel way of extracting energy from wind and water that saves cost by bending with the flow instead of trying to stand up to it
Rotors constructed in the form of a series of tethered kites are able to extract energy from wind or water flow with high efficiency at low cost. Being light, such rotors work in light winds, are highly efficient and are inherently flexible enough to bend to conform to stresses exerted by more severe conditions.
The assemblages have been given the name "Kenape" rotors by inventor Ken Upton. Their ancestry is in kites and sailing yacht design, both extremely ancient technologies, stemming from Upton's active membership of the Amateur Yacht Research Society. The Society claims to be responsible for the invention of surf boards and a number of other projects.
Upton describes the rotors are being based on flexible spoke wheels without rims. Over the spokes is a cobweb-like net to which the kits are fixed. The kite tethers allow just enough movement to allow the kites to find the correct flight angles. The rotors are supported on inclined tripod bases, which allow the rotors to weathercock and align themselves with wind direction.
Because the rotors trail in the wind, rather than being forced to face it, construction can be exceptionally light and simple. The driven areas are at maximum distances from the rotor hub, making best use of surface area. Because they conform to airflow, the kites also cause less turbulence than conventional wind turbines, working more efficiently and producing less noise. In the event of higher wind speeds, the rotors are to a large extent self regulating. In such circumstances, the spokes bend inwards, reducing effective rotor radius and mechanical advantage.
A series of prototypes, made from scrap and re-used common materials have demonstrated the effectiveness of the principle of the idea over the past three years and the ability of the rotors to survive all weathers. The team is currently assembling a kite assemblage, which has a 12m diameter, 40 sq metre rotor and has plans to extend the idea to harnessing tidal and other sea currents. The idea is protected by patent application.
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