A closed Rankine cycle power plant using an organic working fluid includes a solar trough collector for heating an organic working fluid, a flash vaporizer for vaporizing the heated organic working fluid, a turbine receiving and expanding the vaporized organic working fluid for producing power or electricity, a condenser for condensing the expanded organic working fluid and a pump for circulating the condensed organic working fluid to the solar trough collector. Heated organic working fluid in the flash vaporizer that is not vaporized is returned to the solar trough collector.