Optimization of medium temperature direct steam generation solar plant

The object of this study is the plan of original power systems of reduced size, investigating on the energetic benefits of a solar plant with parabolic trough collectors and steam screw expander. Usually, medium temperature solar systems need to be coupled with organic fluids cycles which allow high specific expansion work at low temperature and pressure, so involving a heat exchange between two fluids with the consequent exergetic degradation of the available thermal energy. This paper focuses on the steam screw expander-based solar thermal electricity system with water as heat transfer and storage fluid, clarifying in which operating conditions this simple plant layout could be convenient in terms of energy saving. A mathematical model on the system part-load behaviour is analysed and the optimum working conditions of this solar system were determined, revealing variations of maximum solar thermal power efficiency with operating pressure ratio and beam solar radiation.