Today we convert stored energy (coal/natural gas) to thermal energy by burning. Then we convert the thermal energy by transfering the heat from that burning to water, which makes steam that expands rapidly creating a force that is used to turn turbines, creating mechanical energy. The mechanical energy is then converted to electricity by passing a series of magnets at the end of the shaft around a coil (an alternator), creating electricity. This article shows the details of the alternator.
