PUMPED STORAGE HYDROLECTRIC PLANTS WITH UNDERGROUND LOWER RESERVOIRS

Underground Pumped Hydroelectric Storage (UPHS) is a technique for supplying electric power to meet peak load requirements of electric-utility systems. It will incorporate reversible pump/turbines (or tandem pumps and turbines) and an underground reservoir mined within hard rock. During off-peak periods, low-cost power would be used to pump water stored in the underground reservoir to a surface reservoir, providing a head of 1000 to 2000 m. During the subsequent daytime peak-load periods the surface water would supply hydroelectric power over an 8- to 10-hour period, refilling the lower reservoir after passing through the turbines. The design of a UPHS plant and its equipment, site selection criteria, UPHS economics, and environmental concerns are discussed. Considering the fuel conservation potential of UPHS, the following five efforts are recommended to accelerate UPHS implementation: acquisition of applicable construction and operating experience from surface pumped storage; subsurface stability and design evaluation, especially with respect to penstock and powerhouse; equipment design, development and testing; in-depth economic analysis, and study of influences upon the environment.