Dynamic modeling and analysis of an advanced adsorption-based osmotic heat engines to harvest solar energy

Abstract Osmotic heat engine (OHE) is a promising technology to harvest low-grade heat from renewable energy source. In previous studies of OHEs, the features of actual heat source and application scenarios are usually ignored. Here we present an advanced adsorption-based osmotic heat engine to harvest solar energy and a dynamic model for such energy utilization system is established. Firstly, the dynamic characteristics of the OHE from transient to cyclic-steady state is investigated. There exist an optimal adsorption/desorption time to maximize the electric power and efficiency simultaneously. Higher working concentration elevates the electric power and efficiency. Larger direct solar irradiation intensity upgrades the electric power while hinders the efficiency. Then a practical simulation of a small sized OHE harvesting solar energy to generate electricity during a day is carried out and the effects of some important parameters on the system under transient state are analyzed. The results indicate that there is a best number of cycles the system performs during a day to maximize the average electric power and efficiency. Among the ten selected adsorbents, MIL-101 leads to the largest average electric power of 41.8 W and Zeolite 13X leads to the highest electric efficiency of 1.04% when the number of cycles is set as 60 and 7 mol/kg NaCl is employed as working solution.