Thermal performance of the aquifer thermal energy storage system considering vertical heat losses through aquitards

The aquifer thermal energy storage (ATES) system is an efficient method to overcome the gap between energy supply and demand over time and space. Heat storage and preservation abilities are key issues of a successful ATES project. However, most of previous studies only focus on heat storage and recovery abilities of the ATES, while the heat preservation ability of aquitards is neglected. Besides, effects of key factors on heat losses into aquitards still remain unclear, which makes appropriately selecting reservoirs for the heat storage challenging. Thus, the heat loss efficiency is defined to represent the heat preservation ability of aquitards, through which ATES thermal performances are comprehensively evaluated. Effects of key factors on thermal performances are analyzed and optimal reservoirs for the heat storage are recommended. Results indicated that key factors had different impacts on heat losses and thermal recovery. The conduction was the major loss mode and was sensitively affected by aquitard parameters. An aquifer with a lower thermal conductivity, a higher porosity and a superior heat capacity was more suitable for the heat storage. The aquitard with lower porosity, thermal conductivity and heat capacity was better. On the premise of sealing, increasing the aquitard permeability was conducive.