NOVELTY - The system (300) has solar receiver that heats a power cycle working fluid comprises carbon dioxide, krypton, argon, nitrogen and air with concentrated solar flux. A powered cold thermal energy reservoir provides for cooling of a cold thermal energy medium to a temperature which is below a contemporaneous ambient air temperature. A heat exchanger (330) is in thermal communication with the fluid and medium. The system utilizes thermal energy from the fluid to produce mechanical energy and to generate electrical power. The waste heat from the fluid is rejected into the medium.    USE - Concentrated solar power system used for solar energy to heat working fluid for generation of electricity.    ADVANTAGE - The waste heat from the power cycle working fluid is rejected into the cold thermal energy reservoir which is maintained at less than ambient temperature, thus increasing overall system efficiency compared to a similar cycle rejecting heat to ambient temperature. The concentrated solar power system utilizes a phase change material as one or more of the working fluid and cold thermal energy storage medium or a heat storage material to enhance system efficiency. Thermal-to-electric conversion efficiency is increased more by decreasing the cold temperature than by increasing the hot temperature the same amount. The efficiency is improved and the cost of operating the concentrated solar power system is reduced, by rejecting heat from the power cycle at a lower than ambient temperature, thus lowering temperature.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method of operating a concentrated solar power system.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of a concentrated solar power system featuring waste heat rejection at a temperature below the ambient temperature and including cold thermal energy storage.    Concentrated solar power system (300)    Power cycle (318)    Turbine (320)    Cold thermal energy reservoir (327)    Heat exchanger (330)