The Tennessee Valley Authority's coal-fired Kingston plant in Tennessee generates 10 billion kilowatt-hours a year by burning 13,000 metric tons of coal a day, supplying electricity to almost 700,000 homes. If all of the 7.7 billion metric tons of coal consumed worldwide in 2015 was converted to electricity, it would have produced approximately billion kilowatt-hours of electricity. Assume the same efficiency as the Kingston plant.