Thanks to snap for putting me onto 'quietrevolution' in the uk. These guys are making a commercial turbine designed for urban areas, where wind speeds are lower and tend to change direction more frequently. Apparently the helix design significantly reduces vibration and noise, which would certainly make them easier to live next to.

There's no doubt this one is elegant as well. And as you can see in the image below - has significantly less visual impact than a traditional wind turbine, and less problems with shadows too I'd imagine.

Still it's 5m tall plus mast, and not cheap - you wont get much change from $90 000, and that doesn't include footings (foundations), although I imagine it does take into account all the sparky work.

Not sure what the payoff period would be for one - of course that would depend on the amount of energy it could generate, which in turn would depend on the specific wind conditions of your site.

I'm not sure how windy our neighbourhood is. Alexander Parade would probably be our best bet for picking up a few gusts, but I imagine we would have to measure the specific location we wanted to use for a period of time before we'd have useful figures on productivity.

The quietrevolution mob are working on smaller and cheaper turbine for residential use - but it's not due to be released until 2009.