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Energy: tapping a long-neglected source

25 February 2011

Mention geothermal energy production, and most of us would have little hesitation in naming Iceland’s geothermal heating infrastructure as a benchmark for the exploitation of an abundant freely available source of hot water. Given this successful model - which has been providing the sparse population of that northerly island state access to very low-cost energy since the early 1950s, and which by 2008 accounted for 62% of its total primary energy consumption - it is surprising that geothermal energy has not been higher up the priority lists of government energy departments around the world.

Of course, Iceland has the geological advantage in that it is volcanically active and the sources of usable heat are very close to the surface. In other parts of the world, where geothermal exploitation is considered viable, companies have had to develop technologies to drill and then artificially propagate fractures in hot rocks at depths of 4 to 5km before they can expect to recover heat economically from such structures.

Nonetheless, there are promising examples outside of Iceland, not least being the Cooper Basin project in Australia where Geodynamics demonstrated proof of concept back in 2009. The central part of the Cooper Basin is underlain by granite at a temperature of 250 Celsius at its top, at depths of less than 4km. These are extremely high temperatures for this depth, and the region is regarded as the hottest known spot on Earth, excluding centres of volcanic activity. This region of South Australia contains a huge source of geothermal energy and Geodynamics believes there is potential to generate thousands of megawatts of electricity.

Meanwhile, here in the UK, Geothermal Engineering was granted planning permission back in August of last year to develop the UK’s first commercial geothermal power plant at a site in Redruth, Cornwall. The project involves drilling to a depth of 4.5km to access granite at a temperature of 200 Celsius; when completed, it will be the deepest on-shore well in the UK. The plant will provide up to 55MW of usable heat for the local community, and 10MW of electricity.

And only last week a team from Newcastle University began drilling a 2km borehole at the site of the planned 24-acre Science Central, on land formerly occupied by Scottish and Newcastle Breweries. This project follows the geothermal energy related research of Newcastle University’s Professor Paul Younger, which revealed the highest permeability ever recorded for a granite anywhere in the world, in the centre of Weardale, County Durham.

Granite is a useful source of geothermal energy as it is often rich in radioactive elements that generate heat as they decay; however, the permeability of a geothermal source is also important and, until recently, granite was believed to be one of the most impermeable of all geological formations. Professor Younger says this discovery, while welcomed by the geothermal community, does have implications for researchers investigating possible sites for nuclear waste storage.

The Newcastle project is expected to last six months and the team hopes to be able to pump out the first hot (80 Celsius) water in early June. Following additional necessary engineering work, this water could eventually be used to heat not only the Science Central site but also part of the city centre, including the Eldon Square Shopping Centre, which houses over 140 retail outlets.

Eldon Square’s general manager, Phil Steele, says his centre spends around £1.7m per annum on energy from fossil-fuel sources. “We can now look forward optimistically to using deep geothermal energy to supply part or all of our future energy needs and we look forward to working with Newcastle University to develop this major scientific enterprise for the city,” he says.

Professor Younger says the aim of his project is to rise to the challenge of putting a novel form of deep geothermal energy at the very heart of city centre regeneration. “If we’re right and we pump up water at such elevated temperatures, it would mean a fully renewable energy supply for a large part of the city centre, massively reducing our reliance on fossil fuels and reinforcing Newcastle’s position as the UK’s most sustainable city. And unlike other renewables, such as wind and solar, geothermal energy is available at all times, independent of the weather.”

Les Hunt

Newsletter reader Alan Metcalfe questions Professor Younger's assertion that "...unlike other renewables, such as wind and solar, geothermal energy is available at all times, independent of the weather..."  During a visit to New Zealand three years ago, Mr Metcalfe visited the town of Rotorura, renowned for its geothermal attractions. The locals, quite naturally, made use of the abundance of the energy in the ground by sinking heat pumps, but in such numbers that they compromised the amount of heat available, which started to affect the very attractions and hence the tourist industry that the local economy depended on. Inevitably they had to ban installing domestic heat pumps. He likens it to the uncontrolled use of pumps to extract water from artesian sources and the adverse effect this can have on water table levels.

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