Curves can make a big difference in wind-energy generation.

That's what Majid Rashidi has figured in his windmill design, a silo-shaped tower with wind turbines hanging on both sides. The tower serves as a deflector that boosts wind speed as it passes through, turning the turbines sooner and faster than a conventional wind equipment setup.

Rashidi, a mechanical engineering professor at the Cleveland State University, believes each turbine in his design can produce four times the energy of a stand-alone one.

Armed with $1.5 million from federal and state funding, Rashidi plans to put his design to test in the coming months by erecting a prototype system on top of the university's plant services building.

The tower will be 25 feet in diameter and topped with a rotating platform from which four turbines will be hung (see diagram below). Each turbine would be six feet in diameter. The platform can swivel to meet the changing wind directions.

The tower is key to the design's success. When the wind hits the curved surface, it kicks up its speed, much like how the curvature on top of a jet's wind can increase wind speed and create lift.

With the curved surface to enhance wind speed, the turbine can start working sooner. Conventional turbines have to wait until the wind reaches a minimum speed to get going.

Mathematician Daniel Bernoulli first discovered the relationship between air speed and curved objects in 1738.

Meanwhile, Rashidi figures that his design can make an energy system not only smaller enough for urban deployment, but perhaps cheaper, too. The tower, for example, can be existing water tanks. The turbines are much smaller than the 80-foot or larger wind turbines in wind farms today.

The professor's windmill will have an 8-kilowatt generation capacity, compared with the 1.5-megawtt to 3.6-megawatt wind turines offered by General Electric Co.

Rashidi has spent the past three years designing his windmill. Some of his earlier designs resembled a corkscrew.

Adding curves to wind energy system isn't a new concept either, though many companies are focusing on new turbine blade designs.

FlexSys Inc. in Ann Arbor, Mich., for example, is developing a flexible flap to be added to a wind turbine blade for increasing wind-energy capture and reducing physical stress to the turbine. The company first developed the technology for military aircrafts (see Hunting for Cash at the Cleantech Forum).

Other companies, such as Knight & Carver Wind Group and Wind Energy Corp., have altered the shapes of the turbine blades to make them capture wind at low speed (see Unfurling Wind Power's Sails and Wind Energy Corp. Raises Cash, Installs First Small-Wind Turbine). Wind Energy's vertical turbine looks like a spinning hourglass with spiral blades.