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This paper proposes the configuration of an Organic Rankine Cycle (ORC) coupled to a solar domestic hot water system (SDHWS) with the purpose of analyzing the cogeneration capacity of the system. A simulation of the SDHWS was conducted at different temperatures, observing its performance to determine the amounts of useable heat generated by the solar collector; thus, from an energy balance point of view, the amount of heat that may be used by the ORC could be determined. The working fluid that would be suitable for the temperatures and pressures in the system was selected. The best fluid for the given conditions of superheated vapor at 120 °C and 604 kPa and a condensation temperature of 60 °C and 115 kPa was acetone. The main parameters for the expander thermodynamic design that may be used by the ORC were obtained, with the possibility of generating 443 kWh of annual electric energy with 6.65% global efficiency of solar to electric power, or an overall efficiency of the cogeneration system of 56.35% with a solar collector of 2.84 m2.

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This paper analyzes the direct solar vapor generation of acetone by solar radiation falling on the heat pipes of an evacuated tube collector (ETC) that can activate a domestic scale Organic Rankine Cycle (ORC). The irradiance from the sun determines the mass flow of acetone along the horizontal manifold of the ETC to produce vapor at the collector outlet. A Scilab code is developed to simulate the flow of acetone inside the manifold where subcooled acetone undergoes heating and evaporation process. Simulation is run from 60 °C to a saturation temperature of 120 °C at a pressure of 604 kPa, vapor qualities from 1 - 100 percent and solar radiation from 300 to 1100 W/m2. The Kattan-Thome-Favrat flow boiling model is used to obtain the two-phase local heat transfer coefficients along the horizontal manifold and it is validated with the numerical and experimental values of ammonia. The ORC system can generate 218 kWh/year of electrical energy, a thermal power capacity of 1616 kWh/year and achieve an ORC efficiency of 84.4%. The solar-ORC has a thermal efficiency of 3.25% and an exergy efficiency of 21.3% with a solar collector of 2.84 m2.