Power unit, 1 GW (Gigawatt) equals 1 million kilowatts (KW). In Western Europe, a Gigawatt corresponds more or less to the electricity needs of a million people. It is also the power supplied by a standard nuclear PWR reactor. The electric power of 1 GW can make shine 10 million light bulbs of 100 watts at the same time.
The installed electric power should not be confused with the thermal or electric energy supplied. The familiar kWh (kilowatt-hour) being too small a unit to expresses the energy supplied by a reactor, engineers express that energy in TWh (terawatt-hours or billion kWh). The thermal energy produced by the nuclear fuel in a reactor usually is expressed in “gigawattday (a billion watts for one day) equivalent to 24 million kWh.