They stand about forty feet high, tall enough to be well over the roof of a three-story home. In other words, it would roughly be twice as high as the roof on a two-story suburban home, for example. These are tall enough that you have to check around for local zoning issues to see whether or not you can put such a structure in place (they’re perfectly fine over almost all of Iowa, for example – I checked).
For a wind turbine to be fully functional, you need to live in an area with wind that averages 10 miles per hour or more; on the Great Plains, this isn’t a problem, as you can see from this wind map of Cedar Rapids, Iowa. You can easily find wind maps for your own state as well.
Given that, a fully functional wind turbine produces 1.8 kW of power in a 20 mile per hour wind. To put that in context, that’s just under 1,300 kilowatt-hours a month. For comparison’s sake, we used approximately 600 kilowatt-hours of electricity last month – and this included a particularly vicious cold period where temperatures sunk below zero for a period.
When you install a home wind turbine, it is hooked up to your power meter directly and power is drawn first from the turbine, then from your normal electricity provider (the electric company). When the wind is very low, almost all of your power comes from them and your power meter works as normal, recording the kilowatt-hours you use from the electric company. As the wind picks up, more and more electricity comes from the turbine and less and less from the electric company, until a point is reached where all power comes from your turbine. If the wind blows faster than that (10 miles per hour or more), then the turbine will produce more energy than your home is consuming. The rest of it goes onto the electrical grid and helps to power your neighbor’s homes. Even better, the electric meter at your home will run in reverse, crediting you for the electricity you supply.