Matt, thank you for contributing.
I have looked at other possibilities for helping the Darrieus start turning in lower winds. Some use a separate motor to start the turbine, and some use the turbine's alternator and electronics to start the rotation. Those solutions work at a cost. They are using electricity to generate electricity, therefore reducing the efficiency of the system. I also found a patent by Windspire that talks about using magnetic levitation and special low friction bearings to reduce frictional drag.
All those solutions add extra components, complexity and additional cost to the system.
I am aiming at simplicity and low cost, that is why I continue to look at the possibility of using some type of drag device to help start the Darrieus.
Adriaan has been very graceful doing calculations and with his input. I think that it is a matter of finding the right combination of size and placement of the drag device.
After seeing that small Darrieus-Savonius Hybrid from Hi-VAWT spinning and producing power, I know that we are on the right track.
That turbine's rotor is 1.24 meters in diameter and 1.06 meters high and weights 25 Kgs. It turns at 835 RPM at full power to produce 300 watts. It uses two sets of modified 2-cup Savonius rotors in the center, turned at 90 degrees from each other.
Over the years, there have been improvements made to the original Savonius design that makes it more efficient.
The Benesh was an improvement over the original Savonius, and then the Ugrinsky, and more recently, the computer enhanced Benesh by California State University, Long Beach. That design using CFD was built and tested at the Boeing/CSULB low speed wind tunnel and to quote from the report,
“Wind tunnel tests confirmed a 40% increase in peak power coefficients over prior artâ€
I don't know about you guys but I think that is very exciting.
Here are the Ugrinsky and the computer enhanced Benesh.
Ed