Low-temperature geothermal reserves in New Zealand

Low temperature geothermal resources are ubiquitous throughout onshore New Zealand where heat energy can be harnessed directly from the rock or transported by aqueous solutions in thermal springs and abandoned underground mines and hydrocarbon wells. Inferred subsurface temperatures in low temperature thermal springs are up to 250 °C. However, even in regions deemed geothermally cold outside thermal spring areas, the solute geothermometry of aqueous solutions from abandoned mines and wells indicate the circulation at depth of fluids with median temperatures of 30-155 °C (range: 15-195 °C). An initial estimate of recoverable heat energy from aqueous solutions in low temperature geothermal resources is at least 870 × 103 MW h/a (3.1 PJ/a) with 94% derived from temperatures >20 °C. However this value is but a small fraction of heat energy that can be harnessed conductively from the rock.