SCOTLaND'S onshore wind farms were idle for record periods last year because of unusually calm weather, which industry analysts claimed could lead to higher power bills.  Turbines operated on average for just 21.9 per cent of the time - more than five percentage points less than in 2009, the Renewable Energy Foundation claimed. They are expected to operate at an average output of about 30 per cent of maximum capacity.  The group, which has warned of over-reliance on the power source, said onshore wind farms also produced the least electricity during cold weather, when demand was greatest. It said another factor in the cut in average output was wind farms being developed in less windy places because the windiest spots had been taken.  The foundation's comments followed UK government figures, published on Thursday, which showed UK onshore wind farms generated 7.7 per cent less electricity last year than in 2009, the first drop after years of steady increases. They contributed just over one quarter of the UK's electricity from renewable sources and less than 2 per cent of the total generated.  The figures als