(230b) Thermodynamic Characterization of a Novel Compressed-Air Energy Storage Technology: Flooded-Mineshaft Compressed Air Energy Storage (FM-CAES)

With renewable energy sources representing a rapidly growing share of the global energy mix, their intermittent nature has led to growing interest in mechanisms of storing energy during periods of high availability for use during times of high demand. Several different types of compressed-air energy storage have been considered, including the conventional constant-volume approaches such as a salt dome or artificial vessel storage and, more recently, newer constant-pressure approaches such as submerged cavern storage. This manuscript proposes a novel approach where abandoned, flooded mineshafts are pressurized with air, displacing water downward in the shaft but upward in other hydraulically-linked shafts in the same geological complex. This approach is thermodynamically distinct from the existing compressed air energy storage methods because neither volume nor pressure are constant. A thermodynamic characterization of this storage method is presented, showing a relationship between depth and energy density, which is unique to this storage method. It is found that, in cases where shaft depth is sufficient, this approach offers energy density higher than an equivalent pressure constant volume scenario, albeit less than a constant-pressure scenario. In certain locations, geography may dictate that of all these various scenarios, the flooded-mineshaft approach may be the most readily achievable, and therefore, the technology merits further development