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Key advantages of Enhanced Geothermal Systems

What are the advantages of EGS technology?

Conventional geothermal applications, except for geothermal heat pumps, rely on the geological coincidence of water-bearing, hot permeable rocks occurring at economically accessible depths. This is a comparatively uncommon situation, and constrains the usable resource because it is site-specific and distributed unevenly among countries. The Hot Dry Rock (HDR) / Enhanced Geothermal Systems (EGS) concept aims to utilise the vast amount of heat stored in the Earth's crust which is not accessible by conventional geothermal technology. Hot Dry Rock comprises a huge amount of useful heat stored in rocks that are technically accessible but lack the natural permeability necessary for heat extraction. Moreover, such heat stores are much more widely distributed and so offer a geothermal potential to many countries where conventional resources are absent. Even in those areas where good conventional geothermal resources exist, there is usually a much greater volume of heated rock than can be exploited with current techniques. The importance of this ‘potential’ resource can be judged by noting that cooling one cubic kilometre of rock (which is about the scale of a geothermal reservoir) by 1°C will provide the energy equivalent of 70 000 tonnes of coal.

Map of Europe showing rock temperatures at 5 Km depth

What is the future potential of EGS technology?

The U.S. Geological Survey has calculated that the heat energy in the upper 10 kilometers of the earth’s crust in the U.S. is equal to over 600 000 times the country’s annual non-transportation energy consumption. It is likely that no more than a tiny fraction of this energy could ever be extracted economically. However, just one hundredth of 1% of the total is equal to half the country’s current non-transportation energy needs for more than a century, with only a fraction of the pollution from fossil-fuelled energy sources. Experts estimate that up to 6 GWe in the U.S. and 72 GWe world-wide could be produced with current (i.e. conventional geothermal) technology at known hydrothermal sites. With enhanced technology, these estimates increase to 19 GWe and 138 GWe.

What specifically does it offer the EU?

The EU's long-term objective is to ensure a sustainable energy supply based on Renewable Energy Sources (RES). EGS could contribute significantly to total EU energy supply and may be easily integrated into existing electricity infrastructures in most European countries. EGS would offer a clean and secure energy supply:

  • On the basis of the resource estimates quoted above, it is realistic to foresee a situation by (say) 2030-2050 where HDR/EGS technologies could permit significant levels of electricity generation in many countries that are not currently considered as geothermal. In Europe as a whole, for example, one could foresee power generation on a scale comparable to existing nuclear systems. This would represent some 10-20% of total electricity demand. A study by Shell – which now participates in the European HDR research project – suggested that exploitation of the prime sites in Europe could support generation on a scale comparable to that of Europe’s current nuclear programme (40-80 GWe), while the total exploitable resource could be 100 times greater.
  • As electricity production from EGS would extract heat from crystalline basement rocks, the levels of CO2 dissolved in the produced fluids would, in most cases, be substantially lower than those from natural aquifers. In addition, such systems would probably operate in a closed loop with re-injection of spent fluids and gases, so emissions to the atmosphere of greenhouse gases (other than water vapour) would be low. Therefore, by displacing fossil-fired units, development on the scale foreseen could result in avoided CO2 emissions of around 100 million tonnes CO2 per year in Europe, and several times this figure world-wide.


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