Wind energy is very site specific. You need first to gauge average wind speeds at your site. In our experience, people tend to overestimate how windy their home is, and a turbine that mostly sits unmoving will promote neither renewable energy nor your bank balance. It’s worth checking properly, or you may end up with an expensive wind vane!
A small wind turbine will only work well when sited in an open location, away from turbulence created by trees, buildings and other obstacles. At CAT, our main site is quite sheltered and so not good for small wind turbines. We have mounted turbines on the hillside well above the site, as shown in this photo:
The government funded the development of the 'NOABL' database of wind speeds for the UK - this used a computer model to calculate theoretical windspeeds at certain heights, assuming no obstacles (trees, buildings, etc). The database gives wind speed estimates for a given Ordnance Survey map grid location. However, this is not much use for assessing sites for smaller turbines, as it only gives a modelled wind speed for the kilometre square containing that location and does not take into account the impact of local obstructions. The wind speed you'll actually get on a site will be different to this, and usually much less (the database is quite old now, and was originally intended to give a initial idea of wind speeds for large scale wind power developments).
Several other websites still use the same 'NOABL' wind speed database to give wind speed for a particular postcode. We would not recommend relying on these data as they are not detailed enough for small-scale wind turbine installations. Studies have shown that the figures are often a poor indicator for the actual energy produced by a domestic wind turbine.
Before you spend many thousands on a wind turbine you should seriously consider spending a few hundred on wind measuring equipment, such as a mast and a data logger. See for example the suppliers below - and any decent wind turbine installer should be able to provide (either for sale or hire) or recommend similar measuring equipment.