New Opportunities and Applications for Closed-Loop Geothermal Energy Systems

Geothermal energy, the world’s largest continuous heat supply, is available worldwide.Today, renewable geothermal energy systems with near-zero carbon emissions generate continuous, reliable, secure and resilient electric power, largely independent of weather and climate. Despite burgeoning demand for power, geothermal energy growth has been paradoxically low due to the limitations of legacy hydrothermal technology. However, attempts to use enhanced geothermal systems (EGS) to remedy legacy limitations have yet to succeed, due to the complexity of fracturing the subsurface resource to allow adequate flow of heated geo-fluids. In contrast, Closed-Loop Geothermal (CLG) technologies overcome permeability issues by circulating fluid through sealed wells and pipes. CLG systems are defined as commercial scale installations that provide geothermal heat for power generation, energy storage, or industrial applications by an enclosed downhole heat exchanger (DHX) or sealed pipes. CLG systems absorb and transfer subsurface heat into a thermal transport fluid continuously circulating within the sealed wellbore. The versatility of CLG applications is evidenced by the wide variety of different well and pipe configurations that can be evaluated to optimize site-specific costs and performance and by the use of alternative working fluids, such as water and supercritical CO2 (sCO2). This paper first focuses on how CLG expands the range of clean geothermal power generation to include much greater, but previously inaccessible geothermal resources and how CLG enables closed-loop retrofits of unproductive geothermal and oil and gas wells. It then discusses the unique ability of CLG to provide both renewable electric power and precise flows of heat at high pressure to increase the efficiency and reduce the costs of high-value industrial applications, such as lithium extraction from brines and hydrogen production, all while reducing emissions of global greenhouse gases (GHG).