How geothermal energy works

NARRATOR: Hot, fractured rock (or HFR) geothermal energy is a renewable form of energy harnessed from the Earth itself. Hot granites buried deep below the Earth’s surface contain a huge amount of energy, and the Cooper Basin contains the hottest granites on Earth at reasonable drilling depth. This is a known resource with an energy potential comparable with Australia’s coal reserves.

The Cooper Basin hot rock resource is within reach of conventional oil-drilling rigs and is known to cover 1,500 square kilometres at a depth of approximately 3.5–4 kilometres. Fractured granite found at this level is heated naturally by radiogenic decay from elements within it. This heat is insulated by thousands of metres of sedimentary rocks, and slowly builds up over millions of years. Injecting water under pressure into the granite, in the same way as oil and gas industry, can widen the fractures. This hydraulic injection triggers tiny microseismic events that enhance the permeability of joints a significant distance away from the injection well, creating a geothermal reservoir. Low-temperature water flows through the reservoir, increasing to approximately 280 degrees Celsius at 5,000 metres below the surface. Geodynamics uses a closed pipe circuit to bring the naturally hot pressurised fluid to the surface before running it through a heat exchanger that extracts the thermal energy. The cooled, pressurised fluid is injected back into the reservoir. The closed loop system means the pressurised fluid is never exposed to air or light, and does not diminish at all during the process, meaning zero water loss from the system. The superheated steam from the heat exchanger is used to drive a binary steam turbine in an adjacent power plant, thereby producing emission-free baseload electricity for supply to the national grid.