London — Widespread use of Enhanced Geothermal Systems (EGS) would open the way for production in virtually every region, transforming geothermal into a major provider of renewable baseload power, claim Philippe Dumas and Thomas Koelbel.
Challenged by climate change and the need to secure sustainable economic growth, Europe wants 20% of its total energy consumption to come from renewable sources by 2020. This goal can only be accomplished by a balanced energy mix, which captures the respective advantages from each energy source and allows them to complement each other to form a working ensemble.
The grid integration of energy from fluctuating supply will have a severe impact on future power networks. Baseload supply and controllability will become increasingly important and geothermal is one of the few renewable energy sources able to supply consistent 24/7 power production. Generation based on the heat from deep inside the earth is also adjustable and therefore geothermal power appears to be an ideal addition to the prospective energy mix.
Geothermal energy utilization is neither new nor negligible. The first electricity production happened as early as in 1907 in the Italian village Larderello, and today more than 50 GWh is generated per year worldwide. Nevertheless, this figure is still small compared with the enormous theoretical potential. There is no geographical restriction to the exploitation of geothermal energy, as the source is present everywhere. However, some regions benefit from more favourable conditions that allow an earlier development of geothermal resources, under more economical conditions, using currently available technology. As a consequence, the majority of the geothermal power plants in Europe are located in Iceland and Italy, where unusually high temperatures at comparatively limited depth dominate.
In these high enthalpy (heat potential relative to depth) regions, steam-driven power plants are deployed. However, the development of new geothermal power plants with low-temperature turbine circuits allows electricity production from low- and medium-temperature resources (between 90°C and 150°C), as demonstrated in Germany and Austria. When we consider the fact that more than 95% of the European land surface lies in low enthalpy regions, it is clear what kind of opportunities exist for future development.
The technical feasibility of geothermal energy generation in low enthalpy areas has long been proved. Although hydrothermal deposits are currently those mostly utilized, there is common consent within the international geothermal community that Enhanced Geothermal Systems (EGS) – formerly known as Hot Dry Rock – as used by the French geothermal prototype facility in Soultz-sous-Forêts, represent the key technology for worldwide development.
EGS, The Renewable Technology for Baseload
The compelling possibility is that with EGS, geothermal power production is no longer restricted to special geological characteristics like the natural existence of large quantities of hot water in the deep underground. Apart from a gateway to as-yet unexploited geothermal regions, another key advantage is that recent power plant technology used in the low-enthalpy range produces significantly more heat than conventional plants. This heat can make a valuable contribution to the energy supply of industrial processes, and especially for climate control in buildings and residential areas.
EGS is defined as ‘an underground reservoir that is created or improved artificially’. EGS makes use of naturally fractured, hot rocks with insufficient permeability for power production using other geothermal technologies. The pre-existing joints and fractures are widened by injected water under high pressure. This technique, so-called ‘hydraulic stimulation’, is well known in the oil and gas industry, though in this case the creation of an artificial geothermal reservoir happens at greater depth and temperature. Additionally, crystalline rocks with their (compared to gas/oil bearing sedimentary rocks) significantly different geo-mechanical properties are mainly the target.
Although EGS represents the key technology for an economically successful market entrance for geothermal energy under typical European geological conditions, further challenges can be identified. These include improved geophysical exploration, an advanced understanding of fracture propagation and more developed stimulation techniques. However, all the relevant equipment is already available and just needs to be adapted. Given that EGS technology can provide reliable baseload electricity with capacity factors above 90% everywhere in Europe, major efforts to develop EGS should pay off.
Since the validity of the concept has been demonstrated, EGS plant ratings should move from the 3–10 MW seen in the early development stages of the technology towards 25 to 100 MW units produced from multi-well clusters, as is currently practiced in the oil and gas industry.
Europe has pioneered the exploitation of geothermal resources for power generation for over 100 years and the EU still maintains a leading role, not least due to the development of EGS technology.
The R&D effort of European scientists led to the prototype of an EGS power plant in Soultz-sous-Forêts, France. This project integrated all European EGS research activities, with the drilling of three wells to a depth of 5 km. After a successful four month circulation test demonstrated the feasibility of the EGS concept at Soultz, the plant was commissioned in 2008. With a circulation of 35 litres per second, the capacity of the power plant installation is now 1.5 MW, and is planned to rise to 3–5 MW in the future. Among ongoing EGS projects worldwide, the Soultz European pilot site already provides an invaluable database.
In addition, the EU has the first successful commercially-funded EGS project in Landau in southwestern Germany (with a 3 MW electrical output) and further projects are under development in several other EU countries, including the UK, Portugal, Spain and Slovakia.
Considering that the rest of the world is moving towards geothermal energy at an accelerated pace (the US Department of Energy will spend several hundred millions of dollars on EGS technology over the next three years), these efforts need to be maintained and expanded ambitiously in order to keep this leadership, both for research and commercial development.
Cost Reductions Possible for EGS
In terms of cost, a dry steam power plant today produces electricity at around €50/MWh (US$61/MWh) and a flash steam power plant at €80/MWh ($97). In low enthalpy regions, where binary cycle systems are used, the production costs are in a range between €100–€300/MWh ($122–$366/MWh). The estimated current cost of EGS electricity generation from the first-generation prototype plants is in the order of €200–€300/MWh. A continued reduction in cost through innovative developments, learning curve effects and co-generation of heat and power should lead to an electricity cost of around €50/MWh.
The keys to minimizing the production costs lie in improved drilling technologies and further developed stimulation techniques and power plant equipment, for example pumps. Especially promising is an upscaling to 25–50 MW of the next generation power plants by using clusters of wells.
This possibility of an integrated exploitation of electricity and heat through a cascade approach is a key element for a further drawdown of production costs. Cascade increases the overall utilization of geothermal energy from the same infrastructure of wells, resulting in a better total efficiency and important economic benefits. However, it should be noted that, depending on the source temperature of the geothermal reservoir, electricity generation may not be possible in any particular scheme, even if the heat content of the fluid is exploited in steps.
By 2030 EGS should be a mature technology capable of providing a reliable, sustainable and competitive source of energy in all areas. The challenge will be implementation across Europe replacing the ageing existing power production infrastructures. At present, one of the bottlenecks for geothermal development is the low number of drilling rigs and therefore the high cost of drilling.
To reach an objective of 20% of Europe’s primary energy supply by 2050 (100 GW), an average of an additional 25 drilling rigs dedicated to geothermal should be brought to the European market every year between now and 2050, resulting in more than 1000 drilling rigs dedicated to geothermal development by that date.
This is a very large number when compared with the five to 10 rigs currently involved in geothermal activity in Europe, but broadly comparable with the 3500 rigs operating worldwide in the oil and gas industry. Manufacturing of rigs and development of all associated services represents not only a big challenge for recruitment and training, but also a major opportunity for job creation.
European Geothermal: Challenges & Opportunities
Being still in a pre-commercial stage and with high capital costs, EGS projects still require financial support like that provided by feed-in tariffs in some regions. Moreover, the risk associated with exploration and first drilling can be mitigated by insurance, as in Germany, France and the Netherlands. Concepts and solutions are already in place and have just to be spread over the EU countries.
Above: A line shaft pump at the Soultz-sous-forêts EGS in France
All the essential equipment and techniques for EGS projects are already available. Concerning subsurface activity, the model is analogous to – and therefore adaptable from – the gas and oil industry. But geothermal power production using EGS has to deal with higher temperatures, and highly saline and corrosive fluids. As a consequence, a further research effort has to be made.
A critical aspect of EGS technology addresses the seismic hazards induced by the hydraulic fracturing process during both stimulation and production. Further R&D, followed by a better understanding of all relevant geo-mechanical processes, will lead to more advanced stimulation with less microseismicity. After some microseismic events in Basel (2006) and Landau (2009), the need for social acceptance of geothermal power production also became evident. New stimulation strategies and advanced reservoir management are the technical solution to this over-stated risk.
Power plant technology is available for steam and non steam geothermal reservoirs. In accordance with Carnot, a certain coefficient of efficiency cannot be exceeded, but there is still room for improvement with new concepts and optimizations.
All these subjects can be managed by further research and development. The European Community is in the lead role for geothermal power production employing low enthalpy resources lately. But the funding for EGS technology for instance in the US, exceeds that inside Europe by several orders of magnitude. In order to minimize this gap, and apart from the R&D related issues already mentioned, EGS has to be tested in other member states of the EU under different geological settings.
Each of the recent two EGS power plants identified consist of two or three wells and provide a limited installed capacity of less than 5 MW. An upscaling can be performed by clusters of wells per site similar to current fossil fuel installations. And, assuming that the capacity per well is say 2 MW, a cluster of 10 production wells can be combined in one power plant of up to 20 MW.
The main advantages of EGS power plant technology are its high load factor baseload performance and its effective independence from geological settings. Therefore, EGS power plants can be constructed close to the end client – an invaluable advantage concerning heat supply – and EGS can consequently contribute significantly to the future energy mix, if the required research effort is realised.