Why are wind turbines of the tall, horizontal axis type?
In a commentary on a small scale 4 kW wind turbine, Charles Wildman exclaimed that it doesn't make sense to him that currently wind turbines are vertical type, on top of a tall mast.
I think that is is because of the economics involved in generating electricity for sale, as a company. It may very well be that a handy individual with some tools and recycled materials could build vertical wind tturbines for use in low-wind-speeds, and become self-reliant. For a company this doesn't make any sense, due to two facts of physics.
Increase in windspeed increases potential energy exponentially
The energy available in a moving airmass: ½ * Area * Air-density * Wind-speed3. Take optimally built wind-turbine. In slow breeze of 3 m/s, the turbine might give 4 watts of power. Doubling the wind speed to 6 m/s would give 32 W. In a gust of 10 m/s the output would be 150 W, and 15 m/s windspeed 500 W, theoretically.
From economical standpoint, building 10 wind turbines that work well at 6 m/s windspeeds is less profitable than building 1 turbine working at high 15 m/s windspeeds. At least unless the material and construction costs are trivial.
There are no "cheap" electricity production technologies
Producing electricity is costly. A company needs to make profit to make sense. It is next to impossible to generate electricity in a way that, by itself, is economical - or profitable.
Therefore all energy production technologies must be supported by the government or the community. Taxpayer money.
So, in the world of economics, low-wind-speed or small-scale wind-energy isn't on the radar
Thats just how the economics work, and the economics of the scale work - and the economics of scaling. If you build a small wind turbine that powers a tiny house, it might cost 1000 euros. You get no subsidies and it probably won't survive a heavy storm. If you build a 1 MW turbine for 1000 homes, of its 1 million euro cost, you might fund 10-60% with subsidies and tax-deductions.