[r9etb]

I think the turbine blades are elevated with the generator being on the ground. But then I thought the generator on current windmill types was also on the ground.

I think the generators on the big turbines are just behind the blades, so there must be a design aspect there -- perhaps they don't want to spend energy turning a big drive shaft.

Seems to me that the same design issues would be in play for this system, unless the thing in its entirety is sitting closer to the ground.

[saganite]

There are a couple of pics at the link that are helpful in regards to your questions. You can see by the men standing next to the test model that it's quite small compared to the current windmill type generators. I'm sure the 500 KW version would be substantially larger though. The second pic is taken inside the generator room and it appears the drive shaft is very short and is coupled directly to the bottom of the turbine section.

[Robert A Cook PE]

True: The "horizontal" shaft turbines have the shaft (as implied) halfway up the propeller diameter - so the generator is off the ground (on top of the support tower) in a very large housing.

For large power -> large propeller -> very large tower -> very large foundations. Lots of weight up high = large moment arm for vibration, lots of movement, lots of of trouble lifting the replacement parts (hundreds or thousands of pounds of machinery or replacement bearings, bushings, brushes, magnets, etc. up for maintenance. Propeller "wing" maintenance is difficult (these things are the size of a 737 wing, and just about as complex. (Though flaps are much simpler.)

A vertical shaft machine puts the weight of the generator at the bottom. N moment arm, and the generator room is "wlk-in" and low cost. Generator mass is low down, helping to stabilize the weight of the "pole" as well, so the "pole" to the upper bearing is much less complex = much cheaper.

Simple bearing components at the top of the tower (no elctrical generator!) means much easier, and much less, and much cheaper maintenance for does has to go on top.

As you pint out, the wind turbine is closer to the ground, so apparent efficiency is less. BUT - what you can do is use a (relatively cheap) tripod or post to "raise" the bottom of the pole up. You're NOT raising the generator (just using a longer vertical shaft) and your able to use a wide tripod or 4-post support at the bottom to reduce foundation costs. but you've still raised the average height of the vertical turbine 25 - 35 feet. If need be,, these guys seem to think they don't need that extra height. (I disagree, but I don't have their equations for low speed economies. My opinion, as soon as they start needing to sell in low wind (12-15 mph average) environments, they'll start raising the base a bit. It's still much less than a horizontal prop perched with its generator on a high tower.)

No, you can't really put the horizontal shaft generator on the ground and run gears down to it from the hub up above. They simply have failed in use: too much stress and and too expensive for the complex gears and shafts.