Closed-Loop Geothermal

A closed loop geothermal system, also called an advanced geothermal system or AGS, is an engineered geothermal technology that circulates a working fluid through deeply buried pipes in a hot rock reservoir without letting that fluid touch the surrounding rock pores or fractures directly. Two main designs exist: a U tube system, in which fluid travels down one vertical pipe, runs horizontally through the hot rock, and returns up a separate pipe, and a tube in tube system, in which fluid descends through an outer pipe and returns through a heated inner pipe. Because the fluid recirculates completely with no loss and the system needs no natural underground water, no hydraulic fracturing and no dependence on how permeable the rock is, it can in principle work anywhere hot rock lies within reach, and companies including Eavor Technologies of Canada, GreenFire Energy of the United States, and a joint Chevron and MOECO project in Japan are building demonstration plants, among them the Eavor-Loop project at Geretsried in Germany, which entered construction in 2024.