South Australia has substantial geothermal energy resources with potential to provide sustainable, low emission thermal energy for direct heat use applications and for the generation of reliable, dispatchable electricity. Increased deployment of geothermal technologies particularly in direct use applications could aid in diversifying the energy resource portfolio, increasing the State’s energy efficiency, energy productivity and energy security, while decreasing energy-related greenhouse gas emissions.
Industry activity in South Australia between 2003 and 2012 focused on exploring for deep geothermal energy resources and attempting to engineer reservoirs to produce electricity. Current interest is focused on shallow, lower grade geothermal systems and direct use technologies.
Interest was first expressed about geothermal exploration in South Australia by Ashton Energy in 1996, around the Olympic Dam Mine. Other parties expressed interest in exploring the known ‘hot spots’ in the Cooper Basin around the same time. However, licences could not then be granted because there was no available legislative framework.
During extensive stakeholder consultation for the new Petroleum and Geothermal Energy Act 2000, which commenced in 1996, interested geothermal parties provided input. Because the most prospective geothermal area in the state was perceived to be under the Cooper Basin, and drilling would involve deep holes using petroleum industry technology, it was determined that geothermal exploration licences and activities would be regulated by the new Petroleum Act, rather than the Mining Act 1971 or separate legislation.
Natural decline in petroleum reserves in South Australia, risks of climate change and likelihood of future carbon-constrained economies, plus the recognition of South Australia's vast natural geothermal resources, were drivers to set out a supportive framework to entice investment in exploration and development geothermal energy in the Petroleum Act. The process commenced in South Australia in October 2000 with the release of three geothermal exploration blocks over hot granites underlying the Cooper Basin.
Public domain seismic and drilling data from previous petroleum exploration activity by Delhi Petroleum and the Santos Joint Venture were readily available from the department and helped to high-grade this region. Applications were received for all blocks and the first South Australian geothermal exploration licences (GELs) were granted in October 2001.
Since August 2004 over-the-counter applications for GELs can be accepted over the entire state, except over current GELs or lands excluded for exploration (e.g. certain parks). Because geothermal exploration is not regarded by the Government of South Australia as mining under the Commonwealth Native Title Act 1993, the right to negotiate process is not required. The average turn-around from lodging a GEL application (GELA) with the department to grant of licence is roughly three months, depending on whether parks and/or compatible licences are involved.
At the peak of commercial interest in geothermal electricity generation in 2009, about 248 GELs were held by about 29 companies across South Australia and a number of geothermal electricity generation projects were commenced.
Engineered Geothermal Systems
To date 74 geothermal exploration wells have been drilled in South Australia. The vast majority of these are shallow wells drilled to measure heat flow or other rock and geomechanical parameters. In total 9 deep wells have been drilled to test reservoir conditions at four different project locations, namely; Geodynamics Ltd’s Innamincka Deeps Project targeting an EGS resource in the Cooper Basin (also known as the Habanero project), Geodynamics Ltd’s Innamincka Shallows Project targeting the Great Artesian Basin HSA resource, Petratherm Ltd’s Paralana EGS Project located east of the Mt Painter Inlier, and Panax Ltd’s Limestone Coast HSA Project in the Otway Basin near Penola.
Geodynamics Ltd’s Innamincka Deeps Project is noteworthy as it was the first Australian EGS resource to generate electricity and one of very few to achieve this goal worldwide (e.g. Soultz sous Florets, France). Between 2005 and 2013 Geodynamics constructed an operating production and injection well doublet and successfully stimulated a connected reservoir within the Big Lake Suite granite. Short term closed loop testing of the system achieved many milestones and was able to deliver hot water from the reservoir to surface at up to 38 kg/s and 29MPa at an unequilibrated temperature of 241oC. The well doublet system was connected to a 1MW demonstration plant in April 2013 and generated electricity under trial conditions until shut-down on October 7th 2013.
The technical successes achieved did not build enough confidence to further progress commercial development of these projects however, and the utility-scale commercial potential of geothermal power generation is yet to be fully demonstrated in Australia. At present, the main barriers to large-scale geothermal electricity generation are: the high development and implementation cost; the current poor international investment climate; and the need for more certain policies at international to national levels for low emissions technologies.
Hot Sedimentary Aquifer Systems
There have already been two successful small-scale geothermal electricity production projects which used geothermal energy from the vast Hot Sedimentary Aquifer system in the Great Artesian Basin, in NE South Australia and SW Queensland. The projects operated at Mulka Springs in South Australia in 1986 and at Ergon Energy’s Birdsville plant, which produced both electricity and domestic hot water for the town of Birdsville for 25 years until its decommissioning in 2017. The potential to replicate this approach for locally powering remote communities is viable.
A recent study by the Australian Renewable Energy Agency (ARENA) has verified that Hot Sedimentary Aquifer (HSA) geothermal power can have one of the lowest levelised costs of electricity (LCOE) of any energy type and affirms that it could play a role in South Australia’s low emission electricity framework.
Direct use technologies
Electricity generation is not the only application of geothermal energy. A large range of industrial heating and cooling applications in manufacturing, desalination, agriculture, aquaculture and space heating require low-grade heat between about 50 and 150OC. Geothermal resources at these temperatures usually occur within 3 km of the Earth’s surface. Direct-use systems operate very efficiently since non-geothermal energy input is limited to electricity supplied to the submersible pumps in the geothermal bores and have lower lifecycle costs when compared to conventional technologies, with an added advantage of lowering CO2 emissions. A geothermal fluid may also be used in multi-stage successive steps to maximize benefits. For example, the heat could first be used for process heat and the lower-temperature waste fluid could then be used for space heating. This multi-use approach is called cascading or waste heat use.
The single biggest use of geothermal energy globally is for heating and cooling buildings using Ground Source Heat Pumps (GSHPs). A GSHP system is made up of loops of fluid-filled pipes which are buried to a depth where the ambient temperature is between about 5 and 30OC, so most systems are only a few metres deep. The fluid in the pipes is warmed by the heat from the ground and pumped to surface, where it is used in standard air conditioning systems to heat the air in the building. In summer, the system is reversed; heat from the building is rejected into the fluid in the pipes and dissipates into the ground, cooling the building.
GSHP are a very efficient, passive system using between 25-50% less electricity than air source heat pumps or conventional air conditioning systems and are also less polluting, with between 44% to 72% less greenhouse gas emissions.
Currently in South Australia, there are about 20 geothermal direct use and GSHP installations in operation at both residential and commercial scales. These technologies are generally mature and well understood and so there is significant potential to expand the use of geothermal energy for these applications in the future. Prospective development opportunities could include low temperature dispatchable electricity generation and desalination systems, particularly for remote communities, large direct-use applications for industry, agriculture and aquaculture, and district heating and cooling networks for new green suburbs.
At present, the main barriers to large-scale geothermal electricity generation are:
- the high development and implementation cost;
- the current poor international investment climate; and
- an uncertain national policy environment.
As with most renewable energy sources, continued research and technical advances will result in reduced exploration and development risks and costs for this type of resource. More certain policies at international to national levels relating to low emissions technologies will also assist to progress the industry.
The technical successes achieved to date have proved the concepts of EGS and HSA generation, and identified a number of high quality geothermal resources across South Australia with potential for future development. There are about 20 geothermal direct use projects up and running in South Australia and potential exists for more uptake of these technologies.