Today's Institute for Public Policy Research report enthuses that in 2011 15.5 TW-hr of fluctuating wind energy displaced 5.5 million tonnes of carbon dioxide. At Renewable Obligation Certificate (ROC) costs of order £50 per MW-hr wind is therefore extracting of order £780M from the UK economy. This translates to a cost of order £140 per tonne of carbon dioxide displaced, based on ROC costs alone - compared to the likely UK carbon floor price of £30 per tonne in 2020.
The report demonstrates that large-scale wind is an expensive and awkward means of displacing carbon - it cuts into gas rather than coal. Displacing coal in an acceptable way will require more nuclear and gas - the long historical trend of increasing energy density and falling carbon intensity.