Mining Heat

Hot rock technology is either too good to be true, or a perfect, clean energy answer for future electricity generation. By ALAN TITCHALL.

Hot fractured rock (HFR) geothermal energy is a radical step from conventional geothermal energy associated with volcanic activity found in the central North Island. It is based on commercially viable geothermal reservoirs buried under a thick layer (three kilometres) of sedimentary rocks with low thermal conductivity.

The concept is dead simple but hasn’t been possible until deep drilling technology (techniques now used everyday in the mining industry) was able to tap the hot dry rocks some three to five kilometres down where the granite is up to 300 degrees Celsius.

Cold water is pumped at pressure down an injection well where it forms a ‘hydraulic stimulation’ of fractures (a technique derived by the oil and gas industry). Super heated steam returns to the surface via a production well and is then piped into a standard binary geothermal power plant. The cooled water is recycled down the injection well in an endless cycle in a ‘closed-loop’ system, without consuming water or producing emissions.

Research drilling and engineering and scientific testing is an expensive process and projects in the past have been thwarted by a funding.

During the 1970’s oil crisis the US government spent up to $20 million a year at its Los Alamos National Laboratory in New Mexico testing hot rock technology. By the mid 1990s funding had virtually dried up but not before enough technology had been proven to encourage countries such as Japan, France and Germany, who were also involved in the US project, to develop their own HFR research projects. In fact, government funded HFR projects have sprung up around the world and the transition from research to commercialisation of HFR technology is almost complete.

The most advanced project is the Soultz HDR project in Alsace and the closest is in South Australia. According to the Government of South Australia, 22 companies have applied for 205 geothermal exploration licences covering more than 80,000 square kilometres. These licences account for more than 80 percent of all geothermal exploration activity underway or proposed throughout Australia.

HFR geothermal exploration in Australia was given a kick-start by the Government’s Renewable Energy (Electricity) Act 2000. The first applicants for funding under the first round of the Australian Government’s geothermal, ‘hot rocks’ drilling programme received grants of up A$7 million for the cost of drilling deep geothermal wells on a matching funding basis. Another round of funding was granted in the middle of 2009.

The Aussie minister for Resources and Energy, Martin Ferguson, estimates that if just one percent of Australia’s geothermal energy was extracted it would equate to 26,000 times Australia’s total annual energy consumption.

“This extraordinary potential is one of the reasons the Australian Government is making this investment in geothermal energy as part of an A$500 million renewable energy fund.

“In addition to being a low-carbon energy source, geothermal energy also has the potential to add baseload power to the Australian energy grid. This would diversify Australia’s energy supply and add to our overall energy security.”

Looking at the big picture, the Centre for International Economics (CIE) estimates a geothermal station producing 50 megawatts of power could be up and running by 2012, expanding to 500 MW by 2016. By 2030 there could be 4000MW of geothermal energy entering the national grid, accounting for 25 percent of new energy generation.

Geodynamics, a pioneer of HFR in Australia, has the most advanced project at Innamincka near Coober Peddy, the Outback opal mining centre in South Australia. Geodynamics and its shareholders, which include Origin, is the only company in Australia that has actually tested a geothermal flow from hot fractured rock. Back in April 2005 its Habanero 2 production well at Innamincka produced over 10MW of thermal power.

The resource has incredible potential, says the company, and far more (seven times) than originally expected. The 100 square kilometre area is one of the hottest non-volcanic spots on earth with thermal energy within 1000 metres of the hot, 350 million year old granite rocks. Enough to “supply all of Australia’s electricity consumption rates for the next 70 years”, claims the company.

The next step is to gather enough data to prove the economics. Modelling already suggests that a scaled up project could produce electricity for around the same cost as a coal fired thermal plant at A$0.4 a kilowatt hour and another half to one cent a kilowatt hour transmitted to get the power from the remote location to the national grid. High voltage DC transmission lines, like those used in the Basslink Interconnector between Tasmania and the mainland, could transmit power over long distances to cities such as Brisbane, Sydney or Adelaide with minimal loss.

Cost analysis by economic consultancy ACIL Tasman found that, if carbon pricing is introduced to Australia, hot rock electricity will be cheaper than that from advanced coal, clean coal, nuclear, gas and all the other base-load systems.