Unlike conventional geo-thermal technologies that derive energy from volcanic or hydrothermal heat via the Earths molten core, enhanced geothermal energy systems exploit latent heat from the radioactive decay of deep rock formations.

Durban - South Africa should give more serious thought to digging deep underground to tap the buried heat of the Earth to generate more electricity.

This is the suggestion from geology and climate change researchers who suggest significant volumes of renewable power can be generated from using the latent heat of rock to produce steam and electricity.

Writing in the latest issue of the SA Journal of Science, researchers Taufeeq Dhansay, Professor Maarten de Wit and Professor Tony Patt say most early measurements of heat flow in South Africa were taken in the Witwatersrand area, which contains some of the world’s oldest and thickest rock structures.

Because these rock crusts are up to 2.5 million years old and up to 300km deep, early measurements showed relatively low heat flow measurements.

However, more recent measurements taken in other parts of the country, where the Earth’s crustal rocks are younger and thinner, suggest that geothermal energy could be viable using a technology called low-enthalpy enhanced geothermal energy.

Unlike conventional geo-thermal technologies that derive energy from volcanic or hydrothermal heat via the Earth’s molten core, enhanced geothermal energy systems exploit latent heat from the radioactive decay of deep rock formations such as granite.

To harness this energy, tunnels and wells up to 6km deep are dug into the earth so that water can be injected under high pressure and pumped back to the surface after absorbing some of the latent heat.

 

Fracking

This heated water then reacts with other fluids with a lower boiling point to generate steam and electricity.

However, the technology is controversial because it requires large volumes of water and can also involve hydraulic fracturing (fracking).

The three authors – from the Council for Geoscience, Nelson Mandela Metropolitan University and the Swiss Federal Institute of Technology – note that some of the early experiments with enhanced geo-thermal systems in Japan led to underground water loss rates of up to 50 percent.

They also caution that fracking has the potential to induce earthquakes.

They noted that some enhanced geothermal projects in Switzerland and Germany were forced to close down because of induced seismic events caused by fracking.

Nevertheless, the researchers argue that there are several regions of the country where the technology could be used to produce viable supplies of renewable electricity – including parts of KwaZulu-Natal, the Eastern Cape, Limpopo, the Northern Cape and North West.

But this form of energy is also more expensive at the moment – almost double the cost of current coal-fired electricity.

They say the greater expense will become less of a factor with the gradual introduction of a new global climate gas treaty due to be finalised in Paris next year.

As global and local laws to reduce carbon dioxide emissions intensify, all nations will face stringent financial penalties for failing to reduce greenhouse gas emissions.

They also note that South Africa is the biggest carbon emitter in Africa, one the biggest emitters in the world on a per capita basis, and is unlikely to meet its current voluntary target to reduce carbon emissions by nearly 40 percent by 2050. - The Mercury