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August 2004 Issue
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Could Australia be powered by hot rocks?

Hot rocks deep beneath the earth's surface may be the key to a clean, "green" source of energy for Australia.

That's the view of University of Adelaide scientists who are working to help tap into this unused and highly valuable resource - one that could potentially revolutionise Australia's power industry as we know it.

"South Australia has uniquely hot rocks. In fact, this State has some of the hottest rocks in the world," said University of Adelaide geoscientist Professor Richard Hillis.

Based in the Australian School of Petroleum, Professor Hillis is one of several scientists from the university working on this project.

He is also a non-executive director of the company behind the proposal, Petratherm, which has successfully raised $4 million in a float and was listed on the Australian Stock Exchange last month.

Rocks at hundreds of degrees Celsius can be found just a few kilometres beneath the earth's surface. Large granite bodies found in and around the Flinders Ranges are up to 25 times hotter than "normal" granites, and subsurface temperatures are unusally high in the area.

"The deeper you go down into the earth, the hotter it gets. On average the temperature increases by about 30 degrees Celsius per kilometre," Professor Hillis said, "but because of our hot rocks, in some areas in South Australia we're looking at increases of more than double that average value."

But how can we use those rocks to create electricity?

"There's really three stages to the whole process: 1) discover hot rocks, 2) circulate water through them, and 3) use that recovered hot water to generate electricity," he said.

Geological models are being used to determine exactly where the hottest rocks might be, in much the same way that science can predict the best locations for major mineral deposits, such as Olympic Dam.

The most likely place for hot rock exploration is in and around the northern Flinders Ranges, which is where Petratherm has taken a number of exploration licences. The company will begin drilling a series of shallow wells - again, the same as drilling for minerals - down to about 750 metres.

"At about 750 metres it will start to warm up significantly. You don't have to go all the way down to know you're on the right track," Professor Hillis said. "We will deepen the most promising of these shallow wells to a depth of about 3.5kms to find the hottest temperatures."

The second stage requires pumping cold water down the well, sending it through the super-heated rocks under the earth, and then recovering the now hot water from another well nearby. The hot water is then used to heat a fluid that boils at low temperatures, which vaporises and drives the turbines at a power plant to generate electricity.

After a while, the hot rocks being used will start to cool down. But the solution is simple: just relocate to a different set of wells, start all over again, and keep moving from one location to the next. Within a few years, the previous locations will heat up again and be ready for use.

There have been several government-sponsored tests in Japan, Germany and the United States, but so far no-one has successfully commercialised the hot rock approach to electricity generation. South Australia is now the world focus for attempts to commercially exploit hot rock technology.

"There has been a rush of recent geothermal exploration licence applications in South Australia," Professor Hillis said. "Petratherm is the second company floated to investigate this opportunity, with Geodynamics having drilled a deep well in the Cooper Basin of the State's far north and now commencing drilling of the recovery well.

"It's a high-risk, high-return venture, but it's a simple concept and simple concepts are good concepts," he said.

"One of the big factors in all of this is that we're looking for green, non-CO2 producing, renewable energy. That's philosophically important to us.

"If it's successful it could be an enormous revolution. There's enough heat stored in South Australia's hot rocks that you could potentially produce all of Australia's electricity from this source alone. That's still a long way off, but there is a vast amount of energy resource there that we will try to turn into electricity."

Story by David Ellis

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Interest in hot rocks is being focused on the Flinders Ranges
Photo by John Tonkin

Interest in hot rocks is being focused on the Flinders Ranges
Photo by John Tonkin

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