Tilting at Windmills

The windmills just visible on the horizon (60+miles away!) belong to the Lincs Wind Farm Development.
When fully operational the combined output of the 75 Turbines will be 270 MW... A medium sized conventional Power Station produces 10 x that amount of power.
At a cost of 1 Billion GBP to build and a projected life of only 40 years ( The Turbines & Electrical Equipment are expected to need replacing after 20 years) I am far from convinced that this is a viable source of energy in the long term.
With output like this we are going to need our entire coast line encircled by windmills as well as every hill top splattered with them. I don't know what the answer is but on these figures it sure as hell ain't wind.