Telegraph: The first detailed study of onshore wind farms has found that 20 of the sites produce less than 20 per cent of their maximum output with some producing less than 10 per cent. Blyth Harbour in Northumberland is thought to be the least efficient wind farm producing just 7.9 per cent of its maximum capacity while Chelker reservoir in North Yorkshire operates at 8.7 per cent of its capacity. The figures were compiled by lobby group Clowd using data collected by energy regulators …