Hot rocks can help to cool the warming Earth

Geothermal hot springs in the mountains of Iceland. Image: By Reykjavik Geothermal, via Wikimedia Commons

Energy from hot rocks below the Earth’s crust will help to replace fossil fuels and speed Europe’s path to carbon neutrality.

LONDON, 8 May, 2020 − The Romans were the first people to exploit Europe’s geothermal energy, using underground springs warmed by hot rocks for large-scale public bathing pools and as central heating for their houses.

Two thousand years later, the European Union is using modern technology to renew its efforts to exploit the same resource to make electricity and provide district heating as part of its plan to replace fossil fuels and become carbon-neutral by 2050.

With wind and solar power and biogas already well-developed, expanding rapidly and already competing with fossil fuels, the EU has decided that geothermal energy should also now be exploited as a fourth major renewable resource.

The European Commission’s Green Deal aims to exploit what officials admit has been the neglect of a potentially large renewable energy industry, which they think should be harnessed to reduce carbon emissions. As a result, the Commission is spending €172 million (£151m) on 12 different developments, described in what it calls a Results Pack.

“The cost of harnessing geothermal energy has tumbled in recent years, making it far more competitive with coal and gas. Shallow boreholes using heat pumps have cut the cost of harnessing it by 20-30%”

Some countries in Europe with active volcanoes, notably Italy and Iceland, have been exploiting hot rocks for decades to heat water, produce steam and drive turbines to make electricity. More recently engineers in Iceland, exploring further and drilling down to 4,650 metres (15,250 feet), have reached rocks at 600°C, potentially providing vast quantities of renewable energy.

The EU believes that, with hot rocks found everywhere below the Earth’s crust, it is only a question of boring deep enough. It says the technologies being developed in Europe to exploit this heat can be used anywhere in the world, and have great potential for the international efforts to wean countries off fossil fuels.

Its Results Pack says heating and cooling accounts for about half of all the continent’s energy consumption. Currently about 75% of that is provided by fossil fuels. However, drilling deep enough would mean all Europe’s buildings could be heated and cooled using subterranean energy.

Like wind and solar, the cost of harnessing geothermal energy has tumbled in recent years, making it far more competitive with coal and gas. Shallow boreholes using heat pumps have cut the cost of harnessing it by 20-30%.

Rare metal bonus

One of the most interesting of the 12 examples in the Pack is a way of extracting heat for energy while at the same time obtaining rare and expensive metals from far below the Earth’s crust. This is being developed at the University of Miskolc in Hungary.

Cold water is pumped 4-5 kilometres into a borehole at high pressure. It passes through natural fissures in the hot rock and comes to the surface through another drill hole as hot vapour. This gas is used to produce electricity and for heating.

The rocks with their many cracks form a natural underground heat exchanger, but the scheme offers an added bonus. As the cold water is pumped through the cracks it gradually dissolves the rock, making the cracks larger and the system more efficient, and over time increasing the output of both electricity and heat.

But also important, as a potential resource, is the fact that the return borehole brings up precious metals in the vapour. Using patented gaseous diffusion techniques, the vapour can yield the metals with a near-100% recovery rate. The metals’ market value dramatically improves the return on investment, the paper says. − Climate News Network