WIND farms are much less efficient than the industry claims, according to new research.  a report produced for the conservation charity the John Muir Trust (JMT) says turbines are producing below 10 per cent of capacity for more than a third of the time.  It claims that for extended periods, all the wind turbines in Scotland linked to the National Grid produce less than 20MW of energy - just enough power for 6,667 households to boil their kettles.  Helen McDade, JMT's head of policy, said: "This report is a real eye-opener for anyone who's been wondering how much power Scotland is getting from the fleet of wind turbines that have taken over many of our most beautiful hillsides. The answer appears to be, much less than is routinely claimed."  The research was carried out by Caithness-based Stuart Young Consulting, on electricity generated from UK wind farms between November 2008 and December 2010.  The wind industry and government have regularly said turbines will generate on average 30 per cent of their rate capacity over a year.  The study concludes there is an urgent need to re-evaluate the implications of reliance on wind for any significant proportion of our energy requirement.  Scottish Renewables policy director Jenny Hogan said it had no confidence in the figures.  "Yet again the John Muir Trust has commissioned an anti-wind farm campaigner to produce a report about UK onshore wind energy capacity output."