I am an activist working to STOP wind turbines from killing birds.
In my search for a better wind energy source,

I can now report a substantial difference in the power output between 3 blades and multiple blades which makes the three bladed design no longer a consideration.
I see that you are interested in wind energy.
I was reading the http://www.urban-wind.org/pdf/CATALOGUE_V2.pdf yesterday and remembered seeing something similar at another site. The other site was for a "low wind speed startup" Wind Powered Generator which has at least 15 wide flat blades instead of 3 aerofoil blades. The web site is at http://www.reasonablepower.com/ .
I checked the difference in the startup power and found it to be significant. Before I was finished reading all of the reasonablepower.com web site I was in agreement that there is a fundamental physics problem with using aerofoil lift for wind turbines.
All of the horizontal axis wind turbines (HAWT), when they showed the calculated power curve, listed in the catalogue_v2.pdf, listed no power output at all below 2 meters per second wind speed. Only two of them showed promise of any power below 3 m/s (0.4W at 2.5m/s for Aircon, and 0.1W at 2m/s for Pitchwind Systems AB). That, for the 3 bladed wind turbine industry, is embarassing.
I looked again at the graph for a Wind Powered Generator on page http://www.reasonablepower.com/ or http://www.reasonablepower.com/nice_to_know/Torque_at_low_wind_speeds.jpg and compared the power outputs. At 1.8 meters per second wind speed their calculated torque on the drive shaft is 65 newton meter. Since 1 newton meter/second = 1 watt, then that is 65 watts at 1.8 m/s. At even slower wind speed, a calculated 36 watt at 1.3 m/s; and 16 watt at 0.9 m/s; and 4 watt at 0.5 m/s. Absoultely radical! The assumed new technology of using aerofoil three bladed wind turbines does not work so well, but the old tried-and-true technology of flat bladed, multi-bladed, windmills still works the best.
It is NOT necessary to use three blades.
MORE BLADES