The running cost of generating wind power is close to zero because unlike your filthy coal, wind is free. This means wind power is able to bid a lower price than coal during periods of high demand, provided the turbines are running. This makes our power cheaper.
You would have a marginal point if the cost of the RET were not being offset by cheaper wholesale prices.
But it is so you don't!
Heres the link from an authoritative, impartial source.
