I looked up some small turbines that are designed for boats. One of those that costs £500 will only generate up to 60W. That would not run much, but could keep the light on in a boat. Even in our garden we would not get constant wind due to other buildings.

We can get all our power from solar (apart from car charging) in the summer, so it balances out over the year and will pay for itself. If you live on a hill with constant wind then a turbine may be an option, but you just don't tend to see them on urban homes. In some cases people could have both.