Not to belabor the point, but VAWTs are not efficient enough to actually bother building and deploying.

Vertical turbine technology, even after many years of effort to improve their performance and cost problems, still are approximately 33% less efficient at converting wind into electrical energy. Added to this is the fact that the wind resource in the urban and built environment as a whole is not conducive to the use of wind energy conversion devices – primarily because of the turbulence and lack of steady laminar flow.

Most, if not all, manufacturers of VAWTs rely on the ignorance of the public concerning wind energy to sell their products. There are no (as in Zero) commercially viable large arrays of VAWTs anywhere in the world now, and virtually none of the past commercial installations are still in use. When I say “viable”, I mean those that produce energy at a low enough cost per kWh to make them anything other than an interesting artifact.

I have installed large individual and multiples of Darrieus turbines that have all been taken down for scrap because they just do NOT work well enough to keep in service. Savonius designs are self-defeating and nothing but yard art. A well designed and built up-wind, three bladed, HAWT is the best, most efficient format for generating electrical energy from wind. Period.