NOVELTY - The run-up method involves using a heat exchanger system (5), capable of providing overheated steam (OS) for driving a steam turbine (6) during a subsequent power mode, to produce auxiliary steam (AS). The auxiliary steam is used to generate seal steam (SS) for the steam turbine. Preferably, the auxiliary steam is kept under a given auxiliary steam pressure in the drum type heat exchanger (29) of the heat exchanger system during a standby mode, while flow of heat transfer fluid (100) through the system is controlled so as to maintain the given auxiliary steam pressure.    USE - Run-up method for solar steam power plant (claimed).    ADVANTAGE - The heat exchanger system, instead of the auxiliary steam generator, is used to produce the auxiliary steam, allowing for reduction in terms of production and or installation costs as well as maintenance, service and operation costs of the solar steam power plant. Number of failure sources is reduced, increasing efficiency of the power plant. The flow of heat transfer fluid through the heat exchanger system is controlled in terms of pressure or mass flow to maintain a given auxiliary steam pressure as auxiliary steam is held during the standby mode, permanently supplying the steam turbine with seal steam even during standby mode. Run-up duration of steam power plant is faster, since the auxiliary steam already exists in the heat exchanger system. Plant efficiency is further increased due to use of sunlight or stored heat in molten salt to produce the auxiliary steam. Emergency shutdown of plant may be performed in event of detected leakage of heat transfer fluid, preventing penetration of such fluid into the water steam cycle and causing pollution in the same cycle.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a solar steam power plant; and    (2) a control unit for a solar steam power plant.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of a solar steam power plant.    Heat exchanger system (5)    Steam turbine (6)    Drum type heat exchanger (29)    Heat transfer fluid (100)    Auxiliary steam (AS)    Overheated steam (OS)    Seal steam (SS)