Exotic energy storage methods will never be economically feasible on a large scale. However, the answer is staring us in the face. Hydroelectric pumped-storage technology is proven, economically attractive, and able to store large quantities of electric energy.There are dozens of such facilities presently installed and operating in the U.S. The largest is almost 2 GW release rate and more than 1 TWH storage capacity. Efficiency is typically 85%.Conventional designs require a fair amount of topographic relief in order to generate sufficient heads. Using an underground lower reservoir eliminates that need. Two projects with underground lower reservoirs are presently under development.