more vawts, yawn

boingboing picked up on Worldchanging‘s story about Former Soviet Weapon Designers Take On Wind Power, claiming ‘this one is supposed to be quieter and less hazardous to birds’. I just had to comment:

Sigh, yet another vertical axis wind turbine claiming world-changing characteristics. Wind Sail are to be congratulated for keeping their efficiency numbers in the realms of the possible. Many companies have sprung up claiming efficiencies (Cp) of greater that 16/27, the Betz Limit, or theoretical efficiency limit of a wind turbine.

Reducing the tip speed ratio reduces the efficiency of the device, so the Wind Sail’s Cp of 28% at 12m/s is quite a bit lower than a typical horizontal axis machine (like the Lagerwey LW900, which has a Cp of 34% at 12m/s).

This machine is miles ahead of the modified Savonius (drag) turbines that some manufacturers are touting. But still, very few knowledgeable wind engineers would advocate roof-mounting a wind turbine. There are issues with turbulence and vibration, not to mention that built-up areas tend to be quite sheltered.

I also take issue with their claims about fewer bird kills. Any structure kills birds. Buildings and windows kill over 5000x more birds than wind turbines, and cats more than 1000x (source: Bird and bat kills and other effects, AWEA ). It would be a very dizzy raptor that could sit on top of a running vertical axis wind turbine.

Vertical axis machinery is not some magical energy source suppressed by The Great Conspiracy. They were the subject of huge development projects in the 1970s and 1980s. There were problems with fatigue, higher costs, and lower operating efficiencies than horizontal axis machines. I design wind farms for a living, and I don’t know of a single utility-scale vertical axis machine that is operating, let alone available for commercial purchase.

The aerospace industries have had limited success in developing viable wind turbines. NASA, Boeing and MAN all tried developing machines, but could never bring a machine to market. It’s interesting to note that most of the successful companies now manufacturing wind turbines started out in agricultural engineering, not aerospace.

Leave a Reply

Your email address will not be published. Required fields are marked *