Professor Hal Gurgenci

Interim Director, Queensland Geothermal Energy Centre of Excellence

Tel: +61 7 336 35607

 

The Queensland Geothermal Energy Centre submission to the Garnaut Review on Climate Change is about the infrastructure and resource implications associated with a yet unproven but very promising technology to be pursued by the Centre in extracting electricity from Hot Dry Rocks.

 

Hot Dry Rocks or Enhanced/Engineered Geothermal Systems (EGS) are defined as underground reservoirs not naturally suitable for geothermal energy extraction but can be made so through economically viable engineering procedures. The requirement for significant engineering work prior to heat extraction distinguishes EGS from conventional geothermal applications. Australia is estimated to have 22000 EJ or 5000 times its annual energy consumption stored in EGS resources[1]. The State Government of Queensland has recently awarded $15m to the University of Queensland to carry out R&D towards electricity generation from such resources.

 

The EGS is already being targeted by a sizeable industry in Australia and, according to an estimate by Electricity Suppliers Association of Australia, may provide up to 5 GW or 10% of present Australian electricity generation 2030[2]. 

 

In the standard EGS concept, a primary fluid, typically brine, is circulated through the geothermal reservoir in a continuous loop. The brine brings the heat to the surface, and transfers it to a secondary fluid, typically isopentane. This secondary fluid is then expanded through a turbine-generator to generate electricity.

 

The Queensland Geothermal Energy Centre of Excellence is pursuing a significant modification of this concept. In this modified approach, CO₂ instead of brine is circulated through the subsurface reservoir at supercritical pressures and then expanded at the surface through a turbo-generator before being sent back to the reservoir.

 

The new approach is expected to significantly increase the cycle efficiency and improve the financial viability of an EGS project. On the downside, the technology needs a steady stream of CO₂ to make up for losses to the EGS reservoir and surrounding subterranean structures. In a future energy regime, however, where carbon emissions are priced, this can be an advantage as it offers CO₂ sequestration while generating electricity.

Download the complete submission here.

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