Of Scotland's leading bodies has called on ministers to ditch their "obsession" with wind power amid evidence that turbines produce about a quarter less energy than developers claim.  The John Muir Trust (JMT) said a study of 47 wind farms in Scotland and England over a 13-month period revealed that they ran at 22% of capacity.  The wind farm industry has claimed that, during the course of a year, a turbine operates at an average of 30% efficiency.  Helen McDade, head of policy at JMT, said dozens of controversial wind farms had been approved in Scotland based on "inflated" claims of their output. She called for an urgent review of the government's renewables policy.  "Many wind farms in spectacular, wild areas have been approved on the grounds of inflated claims of wind power's contribution to the country's electricity needs," she said.  "Wind farms are costing huge amounts of money, much of it from consumers' bills, yet it isn't delivering what the industry claims. The economics of this is a scandal and needs to be urgently reviewed."  a spokesman for the Scottish government insisted that it was seeking to generate electricity from a wide range of renewable sources including hydro, wave, tidal and biomass.  Claims branded bluster, page 7