Explainer: The surprising boom in geothermal energy

Australia is seeing a resurgence in geothermal energy, but not for power generation. Our rocks are too deep, too cool, and too far from power grids, and earlier attempts have all ended in failure.

So what’s booming? Direct use of the county’s cooler geothermal water. That, says Professor Graeme Beardsmore of Melbourne University, should be Australia’s current focus, and the way ahead.  

Australia currently uses coal, oil and gas for 90% of its power needs, with remainder from wind, solar, biofuels and hydro, reports the International Energy Agency (IEA).

“No-one’s generating geothermal electricity in Australia at the moment,” says engineer, Professor Rosiland Archer, Dean of Science at Griffith University. 

In contrast, geothermal energy powers 18% of Aoteoroa,with coal oil and gas providing 55% and hydro, wind and solar and biofuels making up the balance.

NZ, sitting astride the boundary of the Australian and Pacific tectonic plates, is ideally situated for geothermal energy, earthquakes and volcanoes notwithstanding.

The earth’s crust, its surface layer, is a jigsaw of rigid interlocking tectonic plates. These move around like skin on a custard, mobilised by convection currents in the underlying mantle made molten by radioactive heat from the earth’s interior.

These upper mantle convection currents cause the plates to continually grind against each other —forming mountains and generating volcanoes and earthquakes. New Zealand is one of the ‘Pacific Ring of Fire’ countries, joining other Pacific islands, the Philippines, Indonesia, Japan, and the east coast of North and South America.

Under New Zealand’s North Island the Pacific Plate is moving towards, and going under the Australian Plate. Underneath South Island’s Fiordland, the two plates are colliding, but the Australian Plate is being subducted under that of the Pacific. All of this means volcanism, earthquakes  and “shallow, trapped pockets of steam or superheated water, which is the easy geothermal energy to find,” says Beardsmore, Senior Fellow in Crustal Heat Flow, at the University of Melbourne. 

“In New Zealand, you might drill to 1500 metres and get 275^oC hot water rushing to the surface under its own pressure.”

Australia sits on its own tectonic plate, far away from the plate boundaries that spice-up life for our trans-Tasman cousins.

“The deepest we’ve drilled for geothermal energy as a nation, is between 4.5 and 5km deep in Central Australia, into hard granite rock, and got to between 250 and 300 degrees. So similar temperature range, to New Zealand [but] three times as deep, and the rocks are very much harder don’t contain much water,” says Beardsmore.

Australia’s challenge is these relatively cool and deep rocks. We simply don’t have hot enough rocks providing large enough water flows within economic reach to drive geothermal power generation, says mechanical engineer, Emeritus Professor Hal Gurgenci of the University of Queensland. 

That said, there were 125 geothermal exploration permits had been granted across Australia as of 2024.  

Many have tried. Wells were dug in the early 2020’s near Innamincka, in the north east of South Australia and Winton in western Queensland. The Winton well delivered above 200^oC from a depth of 3000m to 4000m, and in 2019 a 310kW pilot geothermal power plant was built. Water and money flows were not enough to make this a going concern, says Gurgenci. So, along with Innamincka and others, it folded.

Remoteness was also a killer. “If you generated electricity at five cents per kilowatt hour, then you can argue [the case for] building transmission lines, but if it takes you 20 cents per kilowatt hour, forget it. That’s what Winton did, it took 20 cents per kilowatt hour at that time with the existing platforms, and no one had the appetite for it,” says Gurgenci

Process Heat is the key

But all is not lost. Hot rocks have many uses. Geothermally heated water has many uses, writes Geoscience Australia. Swimming pool heating (40^oC), building heating (80^oC), alumina production (150^oC) or digestion in paper pulp (180^oC).

“There’s a whole second half of geothermal energy globally, which is purely to produce renewable, clean heat so you don’t have to burn natural gas to produce industrial heat, process heat, or even domestic heat,” says Beardsmore.

“50% or more of Australia’s natural gas is used for temperature processes needing less than 250^oC, and in those processes geothermal actually shows some promise to offset natural gas consumption.”

An aquifer flowing below Gippsland in Victoria at a constant and useful, but geothermally modest, 60-70^oC, caught the attention of the La Trobe Regional Council which is using it to heat its public pool.

Gippsland Regional Aquatic Centre (GRAC), two hours east of Melbourne was, until recently, heated with gas, although the warm aquifer was a relatively shallow 600-700m below the pool. Its water exactly matched the temperature used to heat the pool water, Beardsmore told Cosmos.  

“City councils aren’t known for their for their bravery, generally, but, but La Trobe did go ahead and build a geothermal heating system, which is saving them about $700,000 a year, because they don’t have to burn natural gas at $40 a gigajoule.”

“Electricity to pump the aquifer water through their heat exchanger still costs La Trobe council $50,000 a year but the water is free.”

Other Gippsland councils and industries are now looking to tap this resource.

And at Robe in South Australia, barramundi growers, Robarra, fill their tanks with 29^oC geothermal water pumped directly from a 335m bore. Mainstream Aquaculture at Werribee in Victoria grows barramundi fingerlings in 28°C geothermal water, and Midfield Meats in Warrnambool uses geothermal water to wash down and sterilise its industrial meat processing facility.

Process heat and replacing natural gas, in my mind, makes far more sense economically and technically than trying to produce power, Beardsmore says.

Unfortunately, 97% of the geothermal energy can be also lost using lower temperature water to generate electricity, says Archer “The higher temperatures found in New Zealand’s geothermal resource — 200^oC at the surface — mean efficiencies are much higher,” she adds.

Beardsmore adds: “when using the heat alone you’re basically using 100% of what you produce. You’re getting 10 times more of the actual energy, even though it’s heat rather than electricity, for the same cost.”

“Economically, it just seems to make a lot more sense.”  Others have echoed this sentiment. Back in 2014, Professor Ian Johnston the Chair of Geotechnical Engineering at University of Melbourne said: “Introduction of direct geothermal heating and cooling to Australia on even a moderate scale would have a significant impact on power requirements with enormous economic and environmental benefits,”

Australia’s geothermal progress, to date, has all been in coming up with clever ways to use direct heat, often replacing or reducing consumption of natural gas, a major contributor to global heating. Even if those permitted companies don’t find the right rocks at the right temperature and in the right places, regular Australian companies and councils are still contributing to much needed decarbonisation.  

Although the geothermal energy sector in Australia is still in its infancy, Geoscience Australia says the development of geothermal energy for utility-scale electricity generation has recently experienced a resurgence of interest as evidenced by a substantial increase in permit applications across the country.

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