Aquifer underground pumped hydroelectric energy storage

I. Introduction Pumped hydroelectric energy storage (PHES) is the dominant technology currently deployed for storing large amounts of energy for the generation of electricity. Unfortunately, the feasibility of these systems is heavily dependent on geography, geology, local regulations and water usage policy. To address some of these concerns, underground pumped hydroelectric energy storage (UPHS) has been proposed. UPHS systems need only one surface reservoir (the forebay), with a subterranean reservoir (the afterbay) and power plant. A conceptual diagram of a generic UPHS system is shown in Figure 1. The underground reservoir can be any structure that has the capability to store water without compromising water quality or structural integrity. The authors could find no evidence of an installed, working UPHS system anywhere. The reason for this is likely the cost of building an afterbay deep underground, sealing it, and maintaining structural stability. Evidenced by the literature, a surge in interest in UPHS occurred in the late 1970s and early 1980s, but apparent interest has fallen off since then. While it has been claimed that the economic capacity of a UPHS plant would be in the range of 1000 to 3000 MW [1], there is no evidence of studies of smaller systems in the literature. With the advent of modern renewable energy sources, advanced excavating techniques, and considerable computer modeling capability, it is time to revisit this promising energy storage technology.