A closer look at our half-scale VAWT impeller model, and an interesting phenomenon that occurs with certain symmetrical Savonius designs.
The estimated wind speed I toss out there is way overstated. When I got down off the roof, the wind speed had been about 5 mph, according to our instrumentation.
Dorje Inc is currently developing other impeller designs for medium to high wind conditions. We feel strongly that the impeller design should match the site conditions for our installations. Our turbines are built so that impellers can be changed easily if needed.
Why do we prefer vertical axis wind turbines (VAWT)? We have many reasons for this choice; some are engineering and performance based, others are ecologically based.
VAWT designs are very tolerant of turbulence, and therefore are suited for rooftop installations or other less ideal conditions. They are also easier to brake and apply maglev technology to (floating magnetic bearings for axial loads). Additionally, the design is inherently omnidirectional. Even abrupt changes in wind direction don't matter at all.
But primarly -- from an engineering standpoint -- VAWT turbines are high-torque, low-RPM systems. Horizontal wind turbines (propeller or fan-blade types) are low-torque and high-RPM systems. With the proper gearing, we can get a lot more power production out of a VAWT system without needing ideal conditions. Horizontals are very finicky about their wind, and an ideal installation places them 30 feet ABOVE the nearest obstruction. That's quite a tower.
Ecologically, VAWT designs also make better sense. Birds and bats sense these machines as solid objects and can easily avoid them. At no time does a working VAWT become a high-speed blur!