One of wind power’s drawbacks is its variability: sometimes the breeze is weak; other times it is strong. To convert the rotation of wind turbines into electricity efficiently, however, generators require a single turning speed. Faster or slower than this “sweet spot” and efficiency falls off fast. To compensate, engineers design turbine hardware to have adjustable blade angles to shed surplus wind energy or to capture more. Wind turbines often also employ a transmission to gear the shaft speed up or down to the sweet spot. But both mechanisms add weight, complexity and cost.

ExRo Technologies in Vancouver is commercializing what should be a better idea: a generator that operates efficiently over a wide speed range. Retrofitted wind turbines could produce as much as 50 percent more power over time, CEO John McDonald states.

The device works much the same as a traditional generator, except that fast-acting electronic switches can engage individual generator coils as needed to harvest energy effectively at different wind speeds. An intelligent controller turns on only a few coils at low speed and connects more at higher velocities. “This means that the generator has many sweet spots,” says McDonald, who likens the concept to a car engine that saves fuel by shutting down cylinders when the driver demands less power.

ExRo has successfully tested a prototype generator. The company and an industrial partner expect to start side-by-side trials of turbines with and without the new generators soon and plan to commercialize their product by the end of 2009.