Cogeneration with a Fresnel thermosolar system coupled to an organic Rankine cycle for rural applications

Abstract

Urban applications of solar thermal energy include electricity generation and process heat. The goal of this work was to carry a thermodynamic evaluation of an Organic Rankine Cycle (ORC) that is coupled to a photo-thermal system of 20 Fresnel Linear Collectors (CLF) with an opening area of 23m2. The system is designed to generate 10 kW of power in a radial turbine at the ORC and, as a by-product, process heat to domestic or urban requirements. Thermodynamic computations were performed in MATLAB, using CoolProp as the thermodynamic database. The CLF thermal load was computed using the Direct Normal Irradiance (DNI) data from Cuentepec (@18.86,-99.33), a rural community in Morelos. The photothermal system uses water pressurized to 7 bar and the thermodynamic evaluation of the following working fluids was carried out at the ORC: R1233zd(E), R245fa, R123, R113 and Novec649. The fluid R1233zd(E) generated the highest net power (11.65kW) in the turbine and the lowest amount of heat (133.70 kW) for alternative processes. With the fluid Novec 649 the lowest power (6.40kW) was obtained but the highest amount of heat (138.95 kW) for other processes. The thermal efficiencies for R1233zd(E) and Novec 649 were 8% and 4%, respectively. The exergetic efficiencies achieved were 4% and 22%. For fluids that presented the higher net power in the turbine, R1233zd(E) and R245fa, its thermodynamic performance was also determined with recovery rates (TR= 0.1, 0.2, 0.35 and 0.5) of the thermal load at the turbine output, achieving an increase in power of 38% for R245fa and 40% for R1233zd(E).