Enhanced thermal efficiency organic Rankine cycle for renewable power generation

Abstract

The Organic Rankine Cycle (ORC) technology is recognized to supply electricity from low temperature waste heat and solar energy sources. When the ORC system is heated by solar energy it uses two-fluids and two-loops, producing a relatively low thermal efficiency. To increase the ORC applicability, a solar energy assisted ORC system of single loop is proposed. The aim is to reduce the ORC heat transfer losses, minimize the equipment initial and maintenance cost and enhance the thermal efficiency. This is achieved by using bladder tanks which may improve drastically the ORC technical and economic performance. This method allows the heating to vary in the collector keeping the turbine inlet condition as a constant, impacting on the heat transfer losses and simplifying the configuration. The paper shows that an ORC of a single fluid can keep a constant turbine inlet despite the mass flow rate variations due to the suńs radiation incidence, therefore, reducing the risk of likely faults in the turbine caused by high frequency vibration. An ORC enhanced 10.54% thermal efficiency is obtained with 0.5 kg/s of R1233zd(E) and a pressure ratio = 5, powered by parabolic trough collectors to generate 10 kW during eight hours per day. The ORC competitiveness is dictated by a total generation cost of 54.3 $/MWh and the advantages of a single working-fluid single loop simplicity for overall configuration.