Deep heat

A technology that could provide the UK with clean, reliable energy is being ignored by the government, despite its commitment to increasing the country’s use of renewable energy, claim supporters.

Man-made geothermal technologies, known as enhanced geothermal systems (EGS), use warmth from rocks buried around 5km under the Earth’s crust to superheat water and drive a turbine that generates electricity.

Its supporters say the energy source is more reliable at delivering electricity than wind or solar power as it does not depend on local weather conditions.

The government’s energy white paper, published in March, pledged that 20 per cent of the UK’s energy should be from renewable sources by 2020.

Geothermal maps show that northern Europe’s most promising site for extracting the energy source lies under Cornwall.

But while the EU is supporting research, and countries such as Australia and Switzerland are funding development of their own geothermal energy plants, funding for research in the UK has dried up, despite the country’s potential.

The technique for EGS was developed by researchers at the US Department of Energy’s Los Alamos National Laboratory in the 1970s. After attracting muchpublicity during the OPEC oil crisis of 1973, countries such as Japan, Germany, Sweden and the UK also carried out research into the scheme, but a commercial EGS plant has yet to be built.

According to Australian statistics, 1km3 of hot granite at 250 degrees C has the stored energy equivalent of 40 million barrels of oil.

Now, Basle in Switzerland is planning to use geothermal heat to provide households with warmth and electricity using deep enhanced geothermal systems, otherwise known as Hot Dry Rock (HDR) or Hot Fractured Rock (HFR) technology. As most of the technology is located underground, the plant is unobtrusive and will be located in the city’s industrial district.

The £33m Swiss project was initiated and is partly funded by Switzerland’s Federal office of energy (OFEN). It has been running since 1996 and is also supported by private companies and public institutions. In 2004 the company Geothermal Explorers will start to create a commercial plant delivering electricity and heat to the city. A second site near Geneva is also being considered.

The Swiss need for an alternative energy source is remarkably similar to the UK’s, where existing fuels are likely to become more expensive in coming years but nuclear power has fallen out of favour – despite the need to lower national carbon emissions.

‘The Swiss government saw problems with increased energy demand but low public acceptance of new nuclear facilities and so put money into this,’ said RobertHopkirk, a partner in the consortium running the Deep Heat Mining Association, which manages the project.

‘Heat from areas that do not have geological anomalies such as Iceland are more difficult to access but have virtually no running costs once the project is set up,’ he said.

Two similar schemes are also under development in Australia’s Hunter Valley, New South Wales, and a site in South Australia.

In the UK, research has been at a standstill since the early 1990s.

In a report concerning the UK’s geothermal resources, commissioned by the former Central Electricity Generating Board in the 1980s, author Dr. John Garnishestimated that geothermal energy could meet at least 10 per cent of the country’s energy needs during the 21st century.

Even by 1990, Baroness Hooper, under secretary of state for Energy, called HDR research a ‘promising technology with a large potential resource in the UK’. But despite having attracted funding of almost £40m from successive governments, four years later support for the scheme was all but abandoned.

‘Originally, geothermal energy was amazingly well supported by both the UK government and Brussels,’ said Dr Tony Batchelor, managing director of Falmouth-based independent applied earth science consultant GeoScience, which carried out government-backed research into the UK’s geothermal potential at Rosemanowes Quarry in Cornwall 20 years ago.

‘Problems came when we were asked whether we could produce energy at 2p per kWh. Setting up the plant is capital intensive and you can’t guarantee future electricity prices at the start.’

Since 1987, EU research has centred on building a working plant at Soultz-sous-Forets in Alsace, where it was thought that access to hot rocks would be easier, supported by industrial partners including Shell. During 2004, the developers plan to install a 6MW power plant to generate electricity commercially for the first time.

‘As it turned out, the original estimates that the optimum heat at Soultz would be found 3km down were wrong and they have had to drill to 5km,’ said Batchelor.

‘However, surveys show Cornwall has the most attractive geological conditions in all of northern Europe – even better than France.’

Batchelor said that while both Cornwall and parts of Devon could sustain sites, Cornwall alone could produce 1,000MW of energy. In anticipation of future demand, GeoScience has identified and purchased a promising site near Truro. As yet they have been unable to fund its development.

‘There are still some questions to be answered over the correct spacing and linking of boreholes, but the French project is answering these. Once that site is producing energy there is no reason why the same technology will not work in Cornwall,’ said Batchelor. ‘But the DTI seems absolutely opposed to geothermal power – despite the fact that it has the potential to make a significant contribution to the UK’s energy needs.’

The DTI was contacted, but at the time of going to press no-one had been able to comment.

How the technology works

Deep enhanced geothermal systems can provide energy throughout the year with no need for the building of energy storage facilities.

Geothermal energy is currently used by around 20 countries across the world. Most geothermal heat generation is associated with geologically active areas such as Iceland, where the Earth’s crust is thin and rock temperatures just below the surface are relatively high, creating natural hot springs or steam fields. However, Hot Dry Rock (HDR) or Hot Fractured Rock (HFR) technology allows other regions to use warmth from the Earth’s molten core.

The technology circulates water between an injection well and a production well along pathways formed by fractures in naturally hot rocks, such as granite, with a temperature of around 200 degrees C. Pressurised water is pumped into the ground 5km below the surface through a borehole drilled using techniques from the oil industry. The water widens existing rock fractures to create a larger surface for heat exchange. It flows through the fractures and is warmed.

Hot water is brought to the surface through a production well and flows through a heat exchanger, vaporising a secondary low-boiling working fluid. This fluid – usually isobutane or ammonia – is then passed through a turbine driving an electric generator, producing electricity. By keeping the water under pressure and preventing it turning to steam, materials dissolved from the underground rock, such as silica or carbonates, are kept in solution for return to the ground. The closed-loop process ensures gas or fluid cannot escape, producing no CO2 emissions. Cooled water is re-injected into the ground.

The system requires very little land and, as in Basle, a plant can be built close to where the electricity or heat is needed.