Why do magnetohydrodynamic generators require very hot electrically conducting gas?

Magnetohydrodynamic (MHD) generators require very hot, electrically conducting gas because their power output is directly proportional to the gas's electrical conductivity. For an MHD generator to operate with competitive performance and reasonable physical dimensions, the plasma must reach temperatures above approximately 1,800 K.1

At these high temperatures, the gas becomes sufficiently ionized to conduct electricity, which is essential for the interaction between the moving fluid and the magnetic field required to generate an electromotive force via Faraday’s law of induction. To achieve the necessary conductivity—typically 10 to 50 siemens per metre—a small amount of a readily ionizable "seed" material, such as cesium, potassium, or sodium, is often added to the gas. Operating at these elevated temperatures also allows for significantly higher thermodynamic efficiency compared to conventional power plants, as the maximum theoretical efficiency of a heat engine increases with the temperature of the heat source.12