Physics / mechanism
Closed-loop geothermal (CLG) — also called Advanced Geothermal Systems (AGS) or deep closed-loop — circulates a working fluid (water, CO₂, or supercritical fluid) through sealed wellbores drilled 3–10 km into hot dry rock. No hydraulic fracturing; no aquifer contact. Heat transfers conductively through the pipe wall from surrounding rock into the fluid, which returns to surface to drive ORC or steam turbines. Key parameters: rock thermal conductivity (~2–3 W/m·K for granite), temperature gradient (~25–35 °C/km typical, >50 °C/km in favourable basins), flow rate, and pipe surface area. Current systems (Eavor, Quaise targeting millimeter-wave drilling) demonstrate 5–20 MWth per well cluster; power density remains the binding constraint vs. open-loop hydrothermal. No seismic risk is the regulatory differentiator.
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