Field‐Test Results of Aquifer Thermal Energy Storage at St. Paul, Minnesota

A field‐test facility (FTF) for aquifer thermal energy storage (ATES) was designed, constructed, and operated to study the feasibility of moderately high‐temperature thermal energy storage in a confined aquifer. The FTF was designed to inject and recover heat at a rate of 5 MW (thermal) using a well doublet spaced at 255 m, operating at a maximum water temperature of 150°C. The wells were completed in the Franconia‐Ironton‐Galesville confined aquifer at a depth of 182–244 m, which has static water levels about 55 m below the ground surface. A series of four short‐term and three long‐term cycles showed the technical feasibility of ATES in a confined aquifer at temperatures above 100°C and clarified the ground‐water chemistry and thermal interactions of the heated water with the aquifer and its confining beds. From 46% to 67% of the energy added to the injected water was recovered during a cycle. A summary of representative results and findings (with particular emphasis on the final cycle) is provided. A bibliography of project reports and papers is also given.