What a bloody laugh.
Just been doing a few calculations on those bloody B & Q wind turbine things, I reckon that by the time they have paid for themselves, the bearings will have gone and the unit will be shafted. So for all your troubles you will end up with a free scrap wind turbine, which ironically will have created roughly the same amount of carbon emissions in its production and subsequent disposal, as it saves by coming into existence. Its enough to make you want to roll about on the bloody floor laughing, you may as well get one of those kiddies windmills from the seaside and stick it on your roof, the effect on your wallet will be pretty much the same.