wrote:

If you look at the old stereotypical "prairie" style windmills,
that's how they are. A disk with pie-shaped blades angled at 45
degrees, facing directly into the wind with the help of a fin.

All that surface area catches a lot of wind, but it also creates
a lot of aerodynamic drag which makes it require higher wind
speeds to turn.

I believe that drag is a function of the surface area of either the
front or rear (or maybe both) trailing edges of the blade.

Which if you look at the ratio of blade area to frontal or trailing edge
area, the conventional long thin blades have a horrible ratio.

The reality is that what makes a good propeller or helicopter
rotor also makes a good windmill blade.

Those blades are operating in a wind-speed regime that far exceeds the
design profile of capturing low-speed terrestrial wind currents. So
again I don't know why airplane propeller blades (or in general the
long, thin blades) are being thought of as the most optimal to capture
energy from 5 to 25 mph wind currents.

Look at the cross-sectional area of a jet turbine. Lots of surface area
there. Ever sit on a jet parked at the gate and watch it's turbine
rotate as it catches the calm breeze wafting by?

I think that in the future your going to see more of these helical-based
turbines:

http://www.caleta2.com/video/spirala...-/4vSD8z4fzNg/

http://www.bnet.com/blog/energy/thre...ind-power/2827

http://www.groovygreen.com/groove/?p=2060

http://www.azocleantech.com/news.aspx?newsID=10611

http://www.mywindpowersystem.com/200...bines-designs/

"Helical structured wind turbines are the future of wind mill
technology. These amazingly unique looking twists and turns
will replace those long and boring blades which represent the
conventional image of a windmill. These new and sleek looking
windmills are designed much like the old ones when it comes to
converting their circular motion in to mechanical work, but it
is the structural design that makes them unique and special.

In fact, they logically should function better than the traditional
windmills as the helical structures seems to not just utilize the
energy of the wind, but maximize it by containing the wind."