Home solar gets most of the attention from people seeking to generate their own clean power, but home wind turbines (usually called micro-turbines) are an up-and-coming power source. Design improvements have reduced the noise and vibration problems with rooftop turbines, and now engineers at the University of Alberta have come up with hardware that could make micro-turbines functionally useful at lower wind speeds.

Traditional micro-turbines provide essentially no power at wind speeds below 18 kilometers/hour. The new controller design from U of A allows the turbines to generate power at speeds as low as 10 km/hr -- and it's cheaper than current controllers, too. Dr. Andy Knight, who headed up the project, had this on-target observation:

"My work is something that can make a small change, and it's probably a bunch of small changes here and there that will add up and one day have a big impact."

Improvements in mechanical efficiency are great, but there needs to be a wind resource in the first place. Wind power falls dramatically as wind velocity decreases. A formula for wind-power turbines:

P = 0.5 * rho * A * Cp * V^3 * Ng * Nb

where:

P = power (watts)
rho = air density (1.225 kg/m^3± at sea level, decreases with elevation)
A = rotor area (m^2)
Cp: coefficient of performance, currently about .35 for a good turbine, with a theoretical "Betz Limit" of .59
V^3: wind speed (meters/second) raised to the 3rd power
Ng: generator efficiency (typically 80% for the best units)
Nb: gearbox efficiency (varies, can be about 90% in best designs)

The big variable is wind speed. Double the wind speed and increase power 8 times; halve the wind speed and reduce power to one eighth. Turbine improvements are great, but they won't make power magically appear where there isn't much now.

Assume a rotor area of 3.142 m^2 at sea level (2 m dia. blade). Compare two wind speeds: 18 km/hr and 10 km/hr. Assume rotor improvements make the term Cp 0.50; Ng = 0.8 and Nb = 0.9.

18 km/hr = 5 m/s; power = 173 watts
10 km/hr = 2.78 m/s; power = 30 watts

This isn't meant to disparage this admirable work, but let's keep it in perspective. We'll need LED lights and LEED buildings first; then the PV's and wind power.

Posted by: David Foley on July 20, 2005 12:29 PM

I would like more detailed information on what equipment is available for a single homeowner. We have plenty of wind being in the country on top of a hill.

Posted by: Morris Gamble on July 21, 2005 1:11 PM