Sunday Herald: POWER SUPPLIERS are turning back the clock to use coal-fired plants as their main source of electricity in a bid to avert potential shortages this winter. Latest figures from the National Grid show that the fuel accounted for 42.5% of all power generation, overtaking natural gas production for the first time in years. The surge, from a usual level of little more than a third of total output, comes as the major networks seek to fill a gap caused by a slump in nuclear energy …