World - Extraordinary contra-rotating floating wind turbines to begin testing

A wildly innovative turbine that could halve the cost of offshore wind is set to go into testing in Norway. The 19-m (62-ft), 30-kW, contra-rotating vertical-axis turbine is a prototype of a design that could scale to unprecedented size and power.

That's what makes World Wide Wind (WWW)'s contra-rotating VAWT such a fascinating alternative. All the heavy generator business is kept right at the bottom – indeed, under water and below the turbine's floating pontoon. That adds enough weight at the bottom to keep the whole thing from topping into the water, requiring only a set of mooring anchors.

The generator's rotor and stator are then connected to a pair of vertical-axis turbines, each running three blades at 45 degrees from the main tower shaft. The lower turbine is set to rotate in one direction, and the upper one, mounted on a pole that runs up the middle of the lower one, is set to rotate in the other direction.

The blades are simple and fixed, and harvest useful torque from the wind most of the way around, much like sailboats can.

"The only time it will not catch speed is when it's going directly upwind, or directly downwind," WWW CTO Hans Bernhoff told us in an interview last year. "As a vertical axis blade goes around, it more or less gets torque on 300 degrees of the 360."

The generator resistance can be managed by the microsecond to control the speed of the turbine.

Thus, whichever way the wind's blowing, the floating double VAWT passively tilts to an optimal angle, and the two turbines begin turning in opposite directions, effectively doubling the speed at which the "rotor" is turning in the "stator."

"You can think of that as a way to double your power generation, or as a way to reduce your generator cost by half," former WWW CEO Trond Lutdal told us. "So it's lower cost, it's much more scalable, and any maintenance happens at the bottom and not hundreds of feet up in the air."

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