Monday, July 28, 2008

Who needs coal when you can mine Earth's deep heat?

SURROUNDED on all sides by desert, over 1000 kilometres from the nearest city, lies the tiny town of Innamincka, South Australia.

Innamincka has a permanent population of just 12, but each year up to 50,000 tourists swell their numbers, keen to experience the Australian outback, if not its lack of creature comforts. To keep these visitors cool, the tiny town runs up diesel bills of roughly $250,000 each year.

Come next January, however, the town could be powered for free, with electricity generated from heat mined from subterranean "hot rocks".

Conventional geothermal power taps hot water rising naturally to the surface from shallow beds of volcanic rock. By contrast, hot rock, or engineered geothermal systems, depend on heating water by circulating it through rock as far down as 5 kilometres, that has been shattered to make it porous. Neither type of geothermal power emits much in the way of greenhouse gases, but while volcanic rocks are rare, EGS can harvest heat from common types of hot subterranean rock, raising the possibility of a continuous, affordable, green power supply anywhere on Earth.

"There is an enormous amount of energy in the Earth's upper crust," says Ingvar Fridleifsson, director of the United Nations University Geothermal Training Programme in Reykjavik, Iceland, and author of a 2008 report on geothermal energy for a meeting of the Intergovernmental Panel on Climate Change. "If EGS can be proved economical on a commercial scale, its development potential will be limitless in many countries." A recent study led by the Massachusetts Institute of Technology suggested that for a government investment of $1 billion dollars EGS could provide more than 100 gigawatts of affordable electricity in the US by 2050 - 6 per cent of its current needs.

"There is an enormous amount of energy stored in the Earth's upper crust"

After decades of development, heat mining is now at a pivotal point. The first 1.5-megawatt power station at Europe's experimental EGS plant in Soultz, France, will soon begin operating continuously, and a second 3-MW EGS power station in Landau, Germany, is already selling electricity, albeit heavily subsidised. Meanwhile, the US Department of Energy has announced plans to fund research geared towards commercialising EGS, raising hopes that the US will again become a major player in hot-rock technology after first proving the concept in the 1970s at Fenton Hill, New Mexico.

However, while these plants have proved the technology works, they have yet to show that it is cost-effective, and this is where Innamincka comes in. The town sits on a 1000-square-kilometre slab of granite that reaches a depth of 10 kilometres. This slab is heated by naturally occurring radioactive elements, and covered by four kilometres of insulating sediment - the gas-rich Cooper Basin - on top of which sits the town. It is the biggest, shallowest, and at up to 290 °C, the hottest, non-volcanic rock formation in the world. This makes it an ideal place to try producing electricity from EGS, as the heat reserve in the granite is large enough to allow developers to rapidly build up to commercial-scale operation.

Also in the site's favour is Australia's pro-mining mindset. Government and private investors are ploughing money into EGS, comfortable with the high upfront costs for exploration and development, and the idea that wealth can be dug out of the ground. A total of 33 companies are exploring EGS in every state in Australia. One of these, Brisbane-based Geodynamics, has sole exploration rights to the granite beneath Innamincka.

"We are predicting a resource potential of 5 to 10 GW in this one slab of granite - 20 per cent of Australia's electricity requirements - based on its geology, temperature, and our estimates of how efficiently we can extract the heat," says Doone Wyborn, Geodynamics's chief scientist and executive director.

The only drawback is that the slab is 500 kilometres from the national electricity grid. Building the power line to the grid will add to initial start-up costs, but Geodynamics is happy to provide Innamincka with free electricity to prove the technology works.

Since 2003 Geodynamics engineers have drilled two 4-kilometre-deep wells, dubbed the Habanero wells after a particularly hot chilli. They have also forced water at high pressure down the injection well and through the rock to expand natural fractures, converting it into a porous, underground heat-exchanger. Earlier this year, they ran tests which showed that water could be circulated down the injection well, through the rock and up the production well at speeds that would make it possible to extract enough heat at the surface to run a power station. This is crucial, as if the flow is too slow it risks becoming uneconomic; too fast and it becomes unsustainable, with heat being extracted more rapidly than it can be replenished by conduction from adjacent rocks.

This week Geodynamics plans to inject a dye into the system and then monitor its concentration at the production well for two months. The dye will "smear out" as the water passes through the cracks, telling engineers the size of the underground network. This data will be used with temperature recordings to calculate how much heat can be mined from the two wells. If all goes to plan, Geodynamics will be able to "declare the reserve", meaning the company will release an audited statement of how much energy it can reasonably expect to extract from its wells. The company hopes to declare up to 10 MW, or enough electricity for a town of 10,000.

By January 2009, it plans to have a 1-MW demonstration plant in place to power Innamincka. Three years after that, Geodynamics hopes to go commercial, initially with nine wells and a 50-MW power plant at the site, expanding tenfold by 2016. "The whole world is waiting to see what happens. They are very brave to go in on such a scale," says Fridleifsson.

Whatever the outcome, experts agree that it will take more than one successful demonstration of commercial-scale EGS for the technology to go mainstream. "To bring the risk down so that banks will invest, we're going to need three to five demonstrations, at different locations, running for at least five years," says MIT's Jefferson Tester.

Those sites will inevitably be less favourable than the Cooper Basin area, requiring heat to be mined from rocks that are cooler, deeper and liable to fracture less favourably. But Tester, Wyborn and others are confident it can be done, with a little help from spiralling oil and gas costs. Besides making alternative energy sources like EGS appear cheaper in comparison, the ever-more desperate search for fossil fuels is spurring the development of faster, cheaper ways to drill very deep wells into very hot rocks, just the sort of technology that is needed to ensure that EGS becomes economically viable.

Australian exploration companies are taking a gamble on that happening. According to government figures, they forecast spending $800 million dollars between 2002 and 2013 on geothermal exploration.

As for Innamincka, it won't be getting free power in perpetuity. Ten or so years after its installation, the demonstration plant will be shut down, and the town's electricity meters will start spinning.

Energy and Fuels - Learn more about the looming energy crisis in our comprehensive special report.

From issue 2665 of New Scientist magazine, 17 July 2008, page 24-25

Pump up the heating

Of all the ways to harness the Earth's heat, growth in only one is exponential: geothermal heat-pump systems. Rather than produce electricity for heating and cooling, these systems simply exchange heat between the ground and a building, taking advantage of the Earth's capacity to store huge amounts of heat.

Heat-pump systems have been installed in over 33 countries, with capacity greatest in the US and Sweden. China is catching up fast, however. The amount of space it heats with pumps almost quadrupled between 2004 and 2007 to 30 million square kilometres, according to a report at a renewable energy meeting in L├╝beck, Germany, in January. The units typically comprise two loops of plastic piping. One loop circulates water through the building, while the other circulates water through the ground, allowing it to reach ambient ground temperatures of 5 to 30 °C.

The pump, which replaces the building's furnace or boiler, transfers heat from the ground loop to the building loop, raising its temperature to the 38 °C or more needed for heating. The cooled water then goes back to the ground to pick up more heat. In the summer the process is reversed for cooling.

For every unit of electricity put in to circulate the fluids and operate the heat pump, you get three to four units of heating or cooling from nature for free. Greenhouse gas emissions are 30 to 50 per cent lower than fossil-fuel-fired heating systems.

No comments: