Abstract: In a power plant comprising an evaporator for transferring heat to the working fluid from a heat source whose temperature is subject to variation, thereby evaporating a working fluid, and a turbine driven by the evaporated working fluid, the temperature of the heat source is detected, an optimum physical value relating to the evaporation at the evaporator is caluculated in accordance with the detected temperature, and evaporation of the working fluid at the evaporator is controlled in accordance with the calculated optimum value.

Abstract: A combination power plant including an ocean thermal energy conversion power plant and a steam generation power plant. Water discharged from a condenser in the ocean thermal energy conversion power plant is mixed with water discharged from an evaporator in the ocean thermal energy conversion power plant. The mixed water is used as cooling water for a condenser in the steam generation power plant. Part of the water discharged from the condenser in the steam generation power plant is used as heating water for the evaporator in the ocean thermal energy conversion power plant.