Please have a look at this brief report: http://www.skepticalscience.com/print.php?n=639
In summary, “the externalities are sufficient to triple the cost of coal power, if they were reflected in its price. If we include the coal externalities, it increases the levalized costs to approximately 28 cents per kWh, which is more than hydroelectric, wind (onshore and offshore), geothermal, biomass, nuclear, natural gas, solar photovoltaic, and on par with solar thermal (whose costs are falling rapidly). Suddenly coal doesn’t look like such a good deal.” QED.