MWth

Megawatt thermal (MWth) is a unit of power used to express the rate of heat transfer or heat generation. It denotes one million watts of thermal power. The suffix th clarifies that the quantity refers to heat energy, not electrical energy. MWth is commonly used in engineering contexts such as nuclear, fossil-fuel, solar thermal, or industrial heat plants to specify the heat output of a reactor, boiler, or heat exchanger. It is not an SI base unit, but a conventional engineering unit widely adopted alongside megawatt-electric (MWe) and megawatt-hour (MWh).

MWth is used to characterize thermal power, while electrical output is usually expressed in MWe. The electrical power produced is typically less than the thermal power due to overall efficiency, so P_electric ≈ η × P_thermal. For a reactor or furnace, the thermal power is the rate at which heat is generated by fuel or combustion and transferred to a working fluid.

Calculation methods: In a water-cooled system, Qdot = m_dot × c_p × ΔT for the coolant, where Qdot is the thermal power. For overall plant descriptions, MWth refers to the heat input to the turbine/steam cycle; the turbine converts part of this heat into electricity. As an energy unit, MWth times time equals MWh of thermal energy.

Usage examples: Nuclear plants often list reactor power in MWth (roughly 2,000–4,000 MWth for large reactors). Solar thermal plants report thermal capacity in MWth for collectors and steam generators. District heating networks may quote peak thermal capacity in MWth.