A hard hat lies on top of a coal seam at UK Coal's Cutacre surface mine near Bolton, northern England, in this April 16, 2008 file photo. Coal isn't always the cheapest source of power, with wind and natural gas both cheaper in upfront capital costs in the developed world, according to estimates by the Paris-based International Energy Agency, energy adviser to rich nations. But its future is safe. In the United States about 28 coal plants are being built. Another 20 are poised for build and 66 awaiting permits in interest driven by high gas prices. To match feature CLIMATE-COAL/ REUTERS/Phil Noble/Files (BRITAIN)