A method of maintaining the temperature of steam supplied to a steam turbine of a steam turbine power plant which power plant further comprises a circulating fluidized bed boiler comprising - a furnace and - a fluidized bed superheater adapted to superheat steam supplied to the steam turbine by transferring thermal energy to said steam from fluidized bed material outside the furnace, the method comprising the steps of: - selecting a trigger load (W TR) for the power plant, which trigger load (W TR) is less than the full rated load (W F) of the power plant and greater than the minimum rated viable load (W MV) of the power plant, - determining the load of the power plant, - when the load of the power plant is at or above the trigger load (W TR), - superheating steam with the fluidized bed superheater such that the temperature of the superheated steam entering the steam turbine is at or near its maximum temperature (T F), and - conveying the superheated steam from the fluidized bed superheater to the steam turbine, and - when the load of the power plant is below the trigger load (W TR), - superheating steam with the fluidized bed superheater, - additionally heating the fluidized bed material outside the furnace such that the temperature of the superheated steam entering the steam turbine is at or near its maximum temperature (T F), wherein the additional heating of the fluidized bed material is brought about by combustion of combustible gas, and - conveying the superheated steam from the fluidized bed superheater to the steam turbine. - a furnace and - a fluidized bed superheater adapted to superheat steam supplied to the steam turbine by transferring thermal energy to said steam from fluidized bed material outside the furnace, the method comprising the steps of: - selecting a trigger load (W TR) for the power plant, which trigger load (W TR) is less than the full rated load (W F) of the power plant and greater than the minimum rated viable load (W MV) of the power plant, - determining the load of the power plant, - when the load of the power plant is at or above the trigger load (W TR), - superheating steam with the fluidized bed superheater such that the temperature of the superheated steam entering the steam turbine is at or near its maximum temperature (T F), and - conveying the superheated steam from the fluidized bed superheater to the steam turbine, and - superheating steam with the fluidized bed superheater such that the temperature of the superheated steam entering the steam turbine is at or near its maximum temperature (T F), and - conveying the superheated steam from the fluidized bed superheater to the steam turbine, and - when the load of the power plant is below the trigger load (W TR), - superheating steam with the fluidized bed superheater, - additionally heating the fluidized bed material outside the furnace such that the temperature of the superheated steam entering the steam turbine is at or near its maximum temperature (T F), wherein the additional heating of the fluidized bed material is brought about by combustion of combustible gas, and - conveying the superheated steam from the fluidized bed superheater to the steam turbine. - superheating steam with the fluidized bed superheater, - additionally heating the fluidized bed material outside the furnace such that the temperature of the superheated steam entering the steam turbine is at or near its maximum temperature (T F), wherein the additional heating of the fluidized bed material is brought about by combustion of combustible gas, and - conveying the superheated steam from the fluidized bed superheater to the steam turbine.