A study of preheating liquid desiccant and its effect on the performance of a PV/T system

Abstract

When photovoltaic (PV) cells operate, their electrical efficiency decreases due to a rise in temperature. To counteract this, Photovoltaic/thermal (PV/T) systems have been created to maintain PV cell electrical performance and utilize the heat they release to warm fluids. A low temperature is required for liquid desiccant regeneration, which allows for the possibility of using the heat released by PV cells to preheat a unit prior to the main heating unit. This study investigates the use of an aluminum cold plate with a serpentine tube placed behind a PV panel to transfer heat dissipated by PV cells to a desiccant solution. Two desiccant solutions were tested: lithium chloride (LiCl) and potassium formate (KCOOH). Using COMSOL Multiphysics, three-dimensional CFD simulations were conducted to analyze the temperature of both the photovoltaic cells and the solution exiting the cold plate. The simulation results were then used to determine the hybrid system's electrical, thermal, and overall efficiencies. Under nominal operating cell temperature (NOCT) conditions, the total efficiency of the hybrid system was 57.15 % and 55.28 % when using LiCl and KCOOH solutions, respectively, with a cold plate inlet temperature of 25 °C and a mass flow rate of 30 g.s-1. Given the similar efficiency of the system and the lower corrosiveness and cost of KCOOH solution compared to LiCl solution, the study concluded that using KCOOH solution is more appropriate. Simulations were conducted under NOCT conditions to compare the system's performance using desiccant solution and water. As expected, the thermodynamic properties of water resulted in a greater decrease in temperature and increased cell efficiency, but using the desiccant solution directly in the cold plate for cooling eliminated the need for an additional heat exchanger in the system.