In a historic first, renewable energy may have generated more electricity than coal in the entire U.S. for the month of April. Coal has long been the backbone of the U.S. electric grid. In the 2000s, coal accounted for more than half of electricity generation. But while King Coal was not dethroned overnight, its demise has been years in the making. According to the EIA’s latest Short-Term Energy Outlook, coal-fired power plants only accounted for 20 percent of total U.S. electricity generation in April, while renewables made up 24 percent.…