It's all about the ROCs.
Without the ROCs noone would bother.
On a more serious note, why are they always talking about offshore wind-farms? They only appear to be better value but in reality it's the taxman getting stiffed. Plus, they change the blades every 12 months so that they don't have to pay the normal tax and NI. This means you never get experienced blades. And you have to tell them exactly when they should be turning because they don't do anything on their own initiative. Of course, when you're looking at using them you see all the best turbines but once you've handed over the cash you get turbines that have only just come out of the factory.