alex Salmond's vision of a Scotland powered by wind, wave and tidal energy has suffered a major setback with the publication today of a highly critical report warning that the SNP's plans for a renewables revolution will never work.  The report, compiled by the rightleaning think-tank the adam Smith Institute, claimed that renewable energy was too unreliable ever to replace gas, coal and nuclear generation. Researchers insisted that wind energy, on which the First Minister has placed considerable emphasis, would never be economically viable and it concluded that wind turbines were doing little to reduce carbon emissions and fossil fuel consumption.  One of the authors of the report, Martin Livermore, of the Scientific alliance, said that Scotland was in danger of following the course taken by Denmark, which has to sell renewable-generated electricity when it has a surfeit and import electricity when the wind is not blowing.  He said: "If Scotland keeps going on this course, it will have to dump electricity cheaply when there's a glut but import expensive electricity at other times. This is because renewable energy is intermittent."  He added: "The more wind farms you have, the more you need stand-by capacity and the only reliable method of low-carbon energy is nuclear."  The report, Renewable Energy: Vision or Mirage, represents the latest in a series of critical investigations into the drive for renewables, not just in Scotland but throughout the UK.  Last week, audit Scotland warned that the Scottish government had no clear plan to find the ?11 billion it needed to meet its ambitious target of cutting greenhouse gas emissions by 42 per cent in less than a decad