Breakeven is achieved when the energy from fusion reactions is larger than the energy required to sustain the plasma. So far JET has reached about 60 percent of this level, but in ITER we expect to exceed breakeven by a factor of ten.
In the process of converting the energy created into usable electricity for the grid a percentage of the power is lost. Predictions based on current coal and fission power plants suggest about two thirds of the power is lost. This means that the power plant would need to create about three times as much power as it consumes to break even (termed a “Q” of 3).
Future power plants will probably operate at about a Q of 30, in other words producing 30 times the power they consume. After losses in conversion this will amount to electricity production of about 500 GW, 10 times the plant’s consumption.