Henry says the advantages of the VAWT configuration (like the Quietrevolutionelsewhere in the Wind Power section ) are that the generator and gearbox can be housed on the ground, and even some distance away from that turbine; and that a VAWT is omnidirectional and requires no yaw mechanism.
The disadvantages of typical VAWT systems are that they usually operate near the ground where theres not much wind; they produce wavy (sinusoidal) power pulses to drive mechanism; they dont start themselves in a breeze; and repair of the main bearing usually means having to take the whole machine apart. (The Quietrevolution appears to solve at least the first problem by being mounted on a tower.) Most importantly, the VAWT is typically about 40% less efficient than the HAWT in energy production. According to Henry, you would need a VAWT almost twice the size of a HAWT to get the same amount of juice.
The main advantage of the HAWT is the increased efficiency in power production, and the smooth transfer of that power from the rotor to the gearbox. HAWTs are also generally mounted on taller towers, where they have exposure to higher wind velocities and present smaller footprints on the ground. However, they require tall cranes for set-up; they require a yaw system; and any maintenance required has to be done at the top of a tower. The photo here shows Henry duPonts colleague Kim Granbery at altitude during the installation of a new HAWT above the Western desert.
Reference: altenergyprograms.blogspot.com
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