Comparative analysis between concentration difference energy storage method and super-capacitor energy storage method for absorption air-conditioning system

Abstract

Increasing the proportion of renewable energy in the energy resource structure helps promote energy conservation and emission reduction worldwide. In the field of building energy conservation, the use of solar energy to drive green air-conditioning systems is a hot research topic. One representative is the solar-driven LiBr-H₂O absorption cooling system that exerts no negative influence on environment. Due to the intermittency of solar energy, the solar-driven system cannot operate continuously and stably. The analysis has been made based on two kinds of solar energy driven system that are the traditional absorption cooling system and capacitive deionization (CDI) absorption cooling system. Different energy storage solutions have been proposed for absorption systems and compared in terms of energy storage density (ESD) and efficiency (ESE). The CDI unit in CDI system works similarly to a double-layer capacitor, and the ions adsorbed on the electrodes can be used to concentrate the absorbent solution in the system to obtain the refrigeration potential. Therefore, it is a novel perspective to consider it as a cooling energy storage device. The results show that the main advantage of the supercapacitor energy storage (SCES) method over the concentration difference energy storage (CDES) method are the consumption of only one-tenth of the energy storage solution and high ESD, leading to lower costs. However, the low efficiency of photovoltaic (PV) cells limits its energy storage performance. A combined solar thermal and photovoltaic drive system utilizing waste heat from PV cells is an effective solution. With a coefficient of performance (COP’) between 0.56 and 0.59 on the design day and an ESE of up to 0.586, the system exhibits the strongest solar energy utilization and storage capability.