Keeping geothermal energy on the table

The Swiss government’s Energy Strategy 2050 plans a greater expansion of new renewable energy sources, an increasingly more efficient energy use and the gradual phase-out of nuclear power while striving to meet ambitious climate goals. With its goal of 4 to 5 terawatt hours a year by 2050, geothermal energy is supposed to become a key pillar of Switzerland’s power supply, covering 6 to 8 per cent of the country’s target power demand of around 60 terawatt hours. While the expectations placed on geothermal energy are high, the technology still needs to pass the praxis test in Switzerland. A globally renowned deep geothermal project in the city of Basel failed in 2008 because palpable earthquakes were triggered by the drilling work. And another geothermal project in St. Gallen suffered a similar fate in 2013. Here the idea was to use an existing hot water reservoir deep underground instead of extracting the heat from dry, artificially cracked rock like in Basel. However, the tremors triggered also spelled the end of the endeavour.

The Centre for Technology Assessment TA-Swiss has now presented a study with the aim of assessing the opportunities and risks of deep geothermal energy in Switzerland in a comprehensive, balanced way. The study, which is already considered a reference work, was coordinated by PSI researcher Stefan Hirschberg, Head of the Laboratory for Energy Systems Analysis at PSI. The research consortium comprised thirty-two researchers from PSI, ETH Zurich, Zurich University of Applied Sciences (ZHAW) and the Institut Dialogik at the University of Stuttgart. “We brought together experts from many different disciplines for this study, including geology, economics, engineering, environmental science and law. That alone makes the study globally unique,” says Hirschberg before adding: “Not only did we analyse the past experiences in geothermal energy with this study; we also acquired new knowledge that allows us to define the parameters for the future development of this technology. For instance, we developed a new cost model and coupled to it a model for environmental assessment.” Both models are based on physical parameters, such as the temperature gradient underground, the borehole depth and the water permeability of the rock. Moreover, the study also reveals that the prioritisation of different subjective preferences influences the assessment of geothermal energy. If the earthquake risk is given more weight, geothermal performs worse than other new renewables. If the priorities lie with climate protection goals and with risks other than induced earthquakes like toxicity for humans and metal consumption, however, geothermal comes out top of the class.

The advantages of geothermal energy

The authors of the study see enormous domestic energy resources in deep geothermal with the potential to cover Switzerland’s basic energy needs in an environmentally friendly way and at any time of the day or year. According to estimates, the amount of thermal energy stored in Switzerland’s underground rock is hundreds of thousands of times higher than today’s domestic energy consumption. These immense energy reserves are constantly refilled by geological processes and are thus virtually inexhaustible. However, targeted exploration projects still need to be undertaken in order to clarify exactly how many of these gigantic resources can actually be classiffied as reserves, by which experts mean resources that can be exploited economically and with social acceptance based on the current state of the art. Switzerland’s geothermal reserves, the study authors note, may well be several times smaller than the estimated resources once the technical, political and legal circumstances have been taken into account.

Nonetheless, geothermal remains a valuable energy source compared to other new renewables. Unlike wind and solar power, geothermal energy can be tapped into twenty-four-seven, whatever the season. The life-cycle analyses conducted for this study also reveal that electricity from deep geothermal involves very low CO₂ emissions.

Hurdles and risks

To obtain energy from hot underground water – the St. Gallen concept – several prerequisites need to be satisfied simultaneously. Specifically, there would have to be a sufficiently large, self-replenishing water reservoir with the necessary temperature of at least 100 degrees Celsius at a depth of 3 to 5 kilometres. The study deems it very unlikely that these conditions exist at many locations in Switzerland. The future of the country’s geothermal energy will thus lie more in the enhanced concept, as applied in Basel, for instance. This involves extracting the energy underground from dry rock, the heat of which is transferred to water that has been previously pumped in.

According to the study, the main technical challenge for enhanced deep geothermics remains the creation of the artificial heat exchanger deep underground. The underground rock is rarely cracked enough to let water through. Circulating water, however, is a prerequisite for heat extraction in this concept. In order to optimise the heat transfer, water is forced into the bedrock to crack the rock. Water pumped in through a borehole can then flow through the artificial cracks, heat up and be pumped back up through a second borehole. The hot water that reaches the surface turns into vapour, which is used to power a turbine and subsequently a generator. While installing the heat exchanger underground, however, earthquakes of different magnitudes can be triggered. This risk, as the study authors explain, cannot be ruled out entirely; only limited at most. Consequently, its transparent and comprehensive communication to the population, including the risk management strategies envisaged, is all the more important.

In an economic respect, the drilling costs affect geothermal the most severely. They are also a highly unpredictable factor as it is hard to foresee how many boreholes will be necessary to drill at a location before usable heat can be extracted. The study estimates that a gradual optimisation of the drilling technology harbours the potential to noticeably reduce costs. In the long term, the next dramatic cost reduction could result from a breakthrough in drilling technology. The costs can be significantly reduced by selling the heat, as well the power, that is produced in geothermal plants. This would especially make sense if the plants were constructed in the vicinity of existing district heating grids, i.e. in densely populated urban areas. Here, the economic benefits thus have to be weighed up against the increased risk of damage in the event of an earthquake, the encroachment on the landscape and noise pollution.

Swifter approval procedure

The use of the underground is regulated by the cantons in Switzerland. Every canton uses a different model to examine applications for geothermal projects. In order to render the approval process more efficient, the study recommends that the cantons examine the applications for geothermal projects based on the so-called concentration model, where a single cantonal authority coordinates and simplifies the approval process in consultation with all the other cantonal offices responsible. Any approval would then be issued in a focussed way.

The Swiss federal government does not have any basic competences to regulate geothermal today. However, the study authors regard it as virtually inevitable that a kind of “soft” legislation will be created through consulting and the establishment of a government platform without any legal powers. “The federal government could thus actively support the cantonal governments in realising and enforcing their individual courses of action, regulations and guidelines,” the authors write.

Funding required

The state should provide funding to broaden the geothermal market and encourage interested companies to invest more in research and development. Besides the current funding instruments, such as risk guarantees and feed-in compensation, the exploration and characterisation of heat sources, technological development and demonstration projects should also receive financial support in future.

As far as the considerable uncertainties regarding Switzerland’s potentially usable geothermal reserves are concerned, the researchers propose launching a usage-driven research initiative in combination with a programme of pilot and demonstration projects. The aim of these programmes should be to enable the construction of an enhanced deep geothermal plant on a commercial scale. “If we want to achieve the goals set for geothermal energy, two to three of these demonstration plants need to be launched in the next ten to fifteen years, as elaborated in the roadmap for deep geothermal by the Swiss Competence Centre for Energy Research (SCCER) on Supply of Electricity,” says Hirschberg.

Text: Paul Scherrer Institute/Leonid Leiva