Energy, exergy, and environmental assessment of a small-scale solar organic Rankine cycle using different organic fluids

This article presents an energetic, exergetic, and environmental (3E) analysis of a solar powered simple Rankine Organic Cycle (ORC). The ORC is simulated using three organic working fluids, such as Toluene, Cyclohexane, and Acetone, meanwhile the solar system uses thermal oil Therminol 75. The present study shows the performance of this coupled system using historical solar annual radiation data from four of the highest solar potential locations in Colombia. Data used correspond to data for the cities Rancho Grande, Puerto Bolivar, Manaure, and Nazareth. Simulations were performed using commercial programs as MATLAB® and REFPROP 9.0. Energy production, the energy and exergetic efficiencies of the system, the exergy destruction was calculated based on the input of the global solar radiation. Effects generated by each working fluid in the solar powered ORC system was determined. It was stablished that the heat obtained in the solar collector in combination with a storage tank is incorporated during non-radiation hours guarantees the thermal stability of the working fluid in the ORC. The best performance corresponds to the Rancho Grande city, being the Toluene the corresponding working fluid with the highest energy (14.6%) and exergetic (7.37%) efficiencies, as well as the maximum power generation (5.50 kW) for October month, meanwhile, the highest exergy destruction values correspond in April. A sensitivity analysis of the individual elements of the system was performed. This study revealed the preference of a lower evaporator pinch point temperature, higher turbine thermal efficiency, pump thermal efficiency, and pressure ratio to obtain better energy and exergy efficiency of the solar powered ORC system. Additionally, the potential environmental impact of the system was evaluated through a Life Cycle Analysis, obtaining for the solar system solar collector has the highest environmental impact with 78557850 mPts. Meanwhile for the ORC, the turbine registers the most significant environmental impact with 295516 mPts (7.34%), when Toluene is used as a working fluid and copper as a construction material in the location of Rancho Grande. In conclusion, the potentiality of planning the operation of solar powered ORC was successfully evaluated for four specific locations in Colombia.