to the combustion chamber or generator 14 the addition of the preheated air reduces the amount of natural gas which is required by the gas combustion chamber however the combined cycle system can still operate without the air preheating for maximum flexibility of operation a bypass pipe 25 with associated valves as is well known is provided around the air heater so that the plant can operate at maximum efficiency during periods when the solar heat is not available the combined system of the instant invention has distinct and important advantages over an exclusively solar system the first advantage is that the central receiver will not have to be built on such a large scale since combined cycle equipment is economic in smaller sizes as compared to steam turbine equipment alone for example a viable stand alone solar system would require almost twenty times as many heliostats as the combined system of the instant invention this would result in considerable construction savings as well as savings as to energy costs per kilowatt hour the system of the instant invention also takes advantage of the relative cheap cost of natural gas while preparing for increased use of solar technology in the event the cost for such gas increases also the system of the instant invention uses inexpensive salts although molten metal can be used the molten salt is a very good heat transfer medium thus permitting the central receiver and air heater to be small in size the salt also has low vapor pressure which minimizes.