How much power would a wind turbine produce?
A turbine in a good location in Southern England would have a capacity factor of around 10%, meaning a 5kW turbine would produce 5kW 10% of the time. So a 5kWp turbine would produce around 5 x 24 x 365 x 0.10 = 4400kWh / year. These figures are conservative and the south east has a low average wind speed compared to other areas of the UK, so in a good location you should produce significantly more. Roof mounted turbines can be ruled out since anything large enough to produce a meaningful amount of power would not be fixable to an existing structure without major structural work.