By Kean W. Stimm
The giant three-blade windmills have done a great disservice to the renewable energy industry. They are windmills, not turbines, only the first of many misleading facts and misnomers.
Their claims of power output are unsupported by facts. Advocates would have you believe they capture 100 percent of the energy in the air mass presented to the face of the windmill. The truth is more likely 4 percent of the air mass, since 96 percent of the wind passes directly through and around the three skinny blades and is not used.
Why not use more blades? Because the turbulence around each blade interferes with the adjacent blades, breaking up the partial vacuum that pulls the blade around. More blades bring the blades closer and the interference is greater, hence lower power. This is why they use three blades.
Even with three blades, the turbulence between blades reduces the efficiency so that only about 30 percent of the energy in the wind (that they use) is converted to shaft horsepower.
Thus, 30 percent of 4 percent is 1.2 percent of the wind’s energy. This shaft horsepower then goes through a gear box and 10 percent of the power is lost. It then goes to an alternator, a rectifier and finally an electronic inverter to get 60 cycle alternating current. The output is now less than 1 percent. No wonder they need to be so huge.
These windmills also need to tower at least 150 feet above ground to escape ground turbulence in the wind as it goes over trees and buildings. Hence, the larger the windmill, the higher it must go. Also, these windmills interfere with each other and need to be at least a quarter mile apart. Thus they require square miles of land.
The enormous claims of power generated by three-blade windmills need to be carefully documented. The truth is they are a totally obsolete technology. If they, indeed, generated the amount of power they claim, they would need no government grants, subsidies or tax favors.
New technology for wind turbines, published worldwide in 2011 by the U.S. Patent Office, suggests a conversion rate of over 40 percent of the energy in the wind to useful electrical power so that turbines can be one-eighth the size and one-twentieth the cost for the same output as the three-blade windmill.
The turbines, using the new technology, make no audible sound and do not kill birds. They mount on short sturdy stands under 65 feet in height and connect directly to the power company grid, camouflaged just above the tree tops, no transmission lines required.
The three-blade windmill is a dinosaur. The next big problem is what to do with the carcass. Why is our government subsidizing these monsters no one wants?
Kean W. Stimm is CEO and chief scientist/engineer at Kean Wind Turbines Inc. of Williamsville.