Research progress and prospect of geothermal energy storage technology

Geothermal energy storage technology is a kind of technology using injected and subsurface in-situ fluid as heat carrier and underground porous media as storage space to store energy, and exploiting it to the ground for comprehensive utilization when necessary. The technology has been continuously developed since the 1960s to keep balance between energy consumption and emission of different industries, and thus establish a technical system based on different heat carriers, scales and energy storage methods. In the process of technological innovation, the geothermal energy storage concept has realized the transformation from a single energy storage form of "Earth Battery" to a multi-energy complementary storage/energy supply system of "Earth Charge and Geothermal Storage", and made full use of the characteristics of geothermal energy storage technology "large scale, wide application, cross-season and low cost", with the advantages of large heat storage space, high heat utilization efficiency, safety, green and low carbon, etc. At present, there are a number of projects around the world to test the geothermal storage of industrial waste heat and renewable energy, and which has achieved good results. It shows better technical practicability and broad development space. It has great significance to the stable supply and efficient utilization of energy. The main mechanisms of geothermal energy storage and heat extraction include heat conduction, convective heat transfer, heat dispersion, thermosiphon effect and physicochemical interaction, etc. At the same time, energy is stored, transferred and converted underground through the heat-fluid-solid coupling effect between fluid and rock. Therefore, the effect of geothermal energy storage depends on the fluid-rock interaction and the way of geothermal energy storage. And the more fluid types in the reservoir, the more complicated the mechanism involved. This paper first described the developing history of geothermal energy storage technology at home and abroad, summarized the heat transfer and energy storage mechanism based on fluid-rock interaction in the process of geothermal energy storage, and analyzed the key technical problems and research status in the process of geothermal reservoir location, aquifer depth selection and energy storage carrier selection on the basis of summarizing previous work. At the same time, the overview and operation status of major geothermal energy storage projects around the world were sorted out and summarized. It was concluded that the porosity, permeability, thickness, anisotropy and heterogeneity of the thermal reservoir have a great influence on its thermal storage efficiency and scale, and the properties of thermal reservoir and heat carrier, and the matching degree with the ground heat source should be considered comprehensively in the selection process. On this basis, this paper looked forward to the application prospect of geothermal energy storage technology, and pointed out a series of challenges that the technology may face from the perspective of heat storage mechanism. It was believed that the breakthrough point of geothermal energy storage technology in the future lies in the joint storage and utilization of carbon capture, utilization and storage technology, sustainable energy such as wind, light and electricity, searching for underground space with good thermal insulation performance, development and utilization of high-performance thermal energy carriers and anti-blocking and corrosion technology. As a further efficient use of the existing energy system and beneficial supplement, with its unique advantages in peak cutting and valley filling, energy conservation and emission reduction and comprehensive utilization of energy, geothermal energy storage has huge potential resources and market potential, and is the future direction of low-carbon geological energy development.