Of course they don't;

then someone might make an informed decision:

Even shorter on hard facts, however, was Shukman’s report on a monster new wind farm off the coast of Cumbria, where a Swedish firm, Vattenfall, has spent £500 million on building 30 five‑megawatt turbines with a total “capacity” of 150MW. What Shukman did not tell us, because the BBC never does, is that, thanks to the vagaries of the wind, these machines will only produce a fraction of their capacity (30 per cent was the offshore average in the past two years). So their actual output is only likely to average 45MW, or £11 million per MW.

Reporters should really have a better grasp on applied mathematics, because even know what the guy's talking about, but it's written kinda poorly. What he means is that as the output goes down, the cost goes up.

But yeah ... greenies only look at the potential, rather than the actual benefit realized.