In a Lump of Coal
Coal was the fuel of the industrial revolution, the energy source most responsible for transforming our economy and enabling our modern way of life. Though coal use is falling in the U.S. in favor of natural gas and electricity from renewable sources, it remains a remarkable, energy-dense mineral.
When combusted, hard black coal such as this releases approximately 30 million joules of heat per kilogram. In an electric power plant, only about one-third of this heat energy is converted to electricity. From there, more energy is lost during electricity transmission and distribution from the power plant to your home, through your home wiring, and through the AC power converter for your phone charger.
Despite more than three-quarters of its original chemical energy being lost before reaching your device, the small (29 gram) piece of coal is enough to recharge an iPhone 7 Plus more than five times.