Hot rocks may be future power source

By Damon Shorter

ANU geologists plan to use hot rocks buried kilometres below the ground to generate clean, green electricity in Australia.

The small research team has set up a company, Hot Rock Energy Australia, which is seeking corporate sponsors to build a pilot power plant at a site near Muswellbrook in NSW's Hunter Valley.

Dr Wyborn, the geologist who heads the group, says the site - small compared to others in the country - could supply two thirds of NSW's electricity needs for at least 30 years.

"The sheer volume of energy contained in underground rocks is enormous," he says.

A 1994 Federal Government study investigating the feasibility of geothermal electricity production in Australia found there was enough accessible heat stored in Australian rocks to supply the country with power for at least the next 850 years.

Since the early 1970s, scientists in the US, Japan and Europe have spent around $400 million trying to make geothermal electricity production from hot rock viable. However, Dr Wyborn says the geology in those areas makes them unsuitable for economic energy production at present.

To extract the energy, the engineers bore holes up to five kilometres deep and create a network of tiny fissures through the rock using hydraulic pressure. Seismic detectors on the surface track how the fissures form, and a second hole is drilled down to meet the fractured zone. Cold water is then pumped down one hole, percolated through the rock (which can be as hot as 300°C) and comes up the other hole as super-heated steam. The steam is then used to drive traditional electrical turbines.

"All we do is extract heat, so there are no pollutants and no greenhouse gases," Dr Wyborn said.

A crucial factor in the success of the plant is making the rocks fracture the right way.

Ideally, Dr Wyborn said, the rocks must fracture horizontally, making it easy to drill a second hole to intersect the fracture network. But in all other countries where the technique has been tried, the rocks have fractured vertically because of the unstable volcanic geology of these sites.

The rocks in Australia, on the other hand, are thought to be ideal: "We are the only country in the world we know of that has rocks at very high temperatures within easy drilling depths and where there is no volcanic activity," said Dr Prame Chopra, who also works on the project.

The smallest version of the plant planned for the Hunter Valley site would supply power to 8,500 people through the NSW electricity grid and would begin operation within around three years.

The biggest expense would be boring the holes, which cost around $5 million each.

If the pilot phase is successful, Dr Chopra said secondary holes could be drilled and the plant expanded to potentially supply the energy needs for up to two thirds of NSW.

Already, the project has received support from leading mining, research and energy companies, including BHP and Western Mining, the Federal Government through the Energy Research and Development Corporation (ERDC), CSIRO, the ANU and the University of NSW.

"The thing about this technology is that it is available 24 hours a day," Dr Chopra said. "You don't have to wait for the sun to shine or the wind to blow. You can quieten down electricity production in off-peak periods by pumping less water through the system, and ramp it up very quickly when demand picks up."

Dr Wyborn estimates the initial plant would generate electricity at a cost of between five and seven cents per kilowatt hour.

Although this is twice the cost of electricity generated by conventional coal-fired power plants, he says the real costs will fall as the scale increases and the environmental costs of coal-fired power are taken into account.

"Clearly, if there is to be any sort of carbon tax then our technology will become far more lucrative than it currently is," Dr Chopra said. "That is why we are receiving so much interest from industry."