Experimental Evaluation of Direct‐Burial Subterranean Battery Energy Storage System

ABSTRACT Battery energy storage systems have become an integral part of the electricity system as an increased quantity of variable renewable energy generation such as solar photovoltaics (PVs) and wind turbines is deployed. Siting and placement of the battery system is important for thermal management, safety, and use of space. Literature on this topic has only considered above‐ground installations. Direct‐burial subterranean installations can address the siting topics by providing access to relatively consistent ground temperatures, encasement of the battery in nonflammable soil, and permitting other uses of the ground surface above (e.g., athletic field). However, batteries generate heat during operation, and although in direct contact with the soil, the soil has poor thermal conductivity, potentially restricting operations to low‐power applications. This research designs, builds, instruments, and demonstrates the operation of a direct‐burial subterranean battery while exploring the thermal dynamics of the battery (NCA lithium ion) versus the surrounding backfill soil (thermal sand, k = 2.8 W/mK), with attention to peak temperatures and heat dissipation timelines. The results identify limitations of a residential behind‐the‐meter battery operation for either PV self‐consumption or load following (LF) application signals. The PV self‐consumption signal, which completes less than 1 cycle per day, results in a 4°C increase in the battery temperature, given the condition of the soil used during battery operation, and returning to original temperatures during the lengthy overnight rest period. The more aggressive LF signal, completing more than 2 cycles per day, elevated the temperature by 16°C within a single day, given the conditions of the soil employed in this experiment. Continued operations of the LF signal would cause overheating and so need to be completed only once every several days. The experimental findings will be used to design and calibrate a new subterranean battery energy storage system numerical models to predict performance for unique battery shapes, installation depths, climates, and arrays of batteries. In this fashion, this new battery technology may be deployed to meet specific applications throughout varied environments.