The present invention relates to an arrangement for the storage of energy in power plants for peak-load coverage where hot water is heated in the feed water preheaters and is stored in a hot water storage tank which is filled and emptied alternately with a tank receiving cold water. 
With a known conventional arrangement of this type, the storage is carried out as follows: Feed water is taken from a feed water tank and is delivered via a separate feed water pump through the feed water preheaters and is supplied via a charging valve to the hot-water storage tank which is constructed as a mixing preheater.  At the same time, enough water is taken from the cold-water tanks that the water level in the feed water tank remains at the same level.  To withdraw from storage, the hot water is delivered as boiling water, at a temperature corresponding to feed water temperature, under stepwise heat emission and expansion in the various feed water preheat stages, and is delivered back to the feed water tank and from there, together with the remaining feed water, to the feed water preheater.  The storage reserve of such a storage system is about 10 minutes and is used where the furnace is sluggish and the storage capacity of the steam generator is low and greater load jumps are required. 
Also it is known how to store hot water in a subterraneous cavern and to withdraw it during peak-load periods.  The hot water storage is shunt-connected to the high-pressure feed water preheaters.  The hot water is fed into the storage tank on top, and the cold water is withdrawn at the bottom.  During the partial-load period, the cold water is passed through the high-pressure feed water preheaters, together with the feed water delivered to the steam generator.  During the peak-load period, the withdrawal openings for the high-pressure preheaters are closed and the boiler is fed directly from the storage tank.  Depending on the load condition, the separating surface between hot and cold water shifts in the hot-water storage tank.  Hence the tank wall is subject to continuously changing expansions. 
It is, therefore, an object of the present invention to simplify the storage of hot water and to keep the number of steam withdrawals to be used for peak-load periods as large as possible. 
Another object of the present invention is to provide an arrangement of the foregoing character which is simple in construction and may be economically fabricated. 
A further object of the present invention is to provide an arrangement, as described, which may be readily maintained in service and has a substantially longer operating life.