This feasibility study investigates extracting thermal energy from the Bedretto tunnel in the Swiss Alps, which benefits from subsurface heat flux and rock overburden insulation. Using the simulation software COMSOL Multiphysics, we created a numerical model of the tunnel environment to evaluate which medium between rock, air, and water serves as the most effective heat source. Our findings indicate that flowing water is the most effective heat source. Potential applications include distributing the water to nearby villages and storing remaining heat in the subsurface. Estimates indicate that the total extractable thermal energy ranges between 0.8 MWth and 1.5 MWth after reducing the water temperature to 4 °C via a heat pump. The study identifies the most suitable energy sourcing locations based on efficiency and investment costs. Circulating water to individual heat pumps in Bedretto, with the natural elevation difference, enables water transport without a pump. Cost analyses reveal that the investment in piping and heat pumps can be amortized within the equipment’s lifespan with appropriate economic models. With the same initial investments, district heating systems are viable in villages with over 30 connections. The payback periods are 10 years for 60 connections, 4.5 years for 90 connections, and immediate for 200 connections.

Aspects in Mining & Mineral Science No Heat Mining in Utilizing Geothermal Resources Ladislaus Rybach* Institute of Geophysics ETHZ, CH 8092 Zurich, Sonneggstrasse 5, Switzerland *Corresponding author:Ladislaus Rybach, Institute of Geophysics ETHZ, CH 8092 Zurich, Sonneggstrasse 5, Switzerland Submission: April 26, 2024: Published: May 07, 2024 DOI: 10.31031/AMMS.2024.12.000790 ISSN 2578-0255Volume12 Issue3

The flights of the civil (ARM23c) and military (ARM23m) parts of the exercise were performedbetween June 19th and 23rd and between September 11th and September 15th,respectively. The measuring system RLL001 was employed for all measurements. As usual, during the civil exercise the environs of some of the Swiss nuclear power plants were screened, on behalf of the Swiss Nuclear Safety Inspectorate (ENSI). At the site of the nuclear power plant Gösgen (KKG) with its pressurized water reactor, the activation products of the primary coolant loop are kept in the well shielded reactor building, thus generating no elevated readings neither on the premises nor in the vicinity of the power plant. The nuclear power plant of Mühleberg (KKM) is now being decommissioned. During this phase, activated components are temporarily stored and processed on the plant premises. The dose rate produced by these components, easily detected and identified with the Swiss airborne gamma spectrometry system, is nevertheless very modest and closely monitored by the Swiss Nuclear Safety Inspectorate (ENSI). Search exercises for radionuclide sources were performed in both parts of ARM23. The operational software of the RLL systems was able to detect the radionuclide sources placed in military training areas. The Man-Made Gross-Count (MMGC) ratio demonstrated a good sensitivity for the identification of radionuclide sources. Nevertheless, a weak radionuclide source placed in the field of view of the helicopter (300 m x 300 m at a ground clearance of 100 m) together with a much stronger radionuclide source emitting higher energy photons was obscured due to Compton scattered photons and therefore could not be detected. Measurements of two teams using drones equipped with radiation monitors demonstrated that low flying drones (ground clearance below 10 m) can be a valuable and complementary tool to identify sources and to further reduce the target area to be searched with ground teams. An altitude profile over Lake Constance confirmed the already observed influence of airborne radon progeny on the determination of cosmic and background corrections. Background flights were performed over several Swiss regions. Besides attenuation effects of water bodies, variations of natural radionuclide content could be observed. A new flight strategy in alpine topography was tested near the Swiss mountain Chrüz. Following contour lines of the topography reduces the necessity for drastic flight altitude changes compared to the parallel line pattern normally used, but is much more challenging for the pilots.

In an era of accelerating energy transition and growing demand for critical metals essential for clean technologies, the innovative integration of geothermal energy with critical metal extraction stands as a paradigm shift in sustainable resource utilization. This comprehensive review unravels the synergistic potential of coupling geothermal energy systems with critical metal extraction, thereby transforming a dual crisis of energy and resource scarcity into an opportunity for circular economy. Through rigorous analysis of existing geothermal technologies, and extraction methodologies, the study establishes a coherent framework that merges energy production with environmental stewardship. It scrutinizes current extraction techniques, and evaluates their compatibility with geothermal brine characteristics, proposing optimized pathways for maximum yield. Through detailed case studies and empirical data, the paper elucidates the economic and environmental advantages of this multifaceted approach, from reduced carbon footprint to enhanced energy efficiency and resource recovery. It concludes that combined heat and mineral production technology can open new, unexplored resources, increasing the supply of previously untapped resources, while the potential of geothermal energy for sustainable mineral extraction and energy production is in line with Sustainable Development Goal 7, which aims to ensure access to affordable, reliable, sustainable and modern energy for all.

The vertical earth heat exchanger (VHE) is a simple device providing a closed circuit for a fluid to take heat from the first tens/hundreds of meters of ground and to feed the cold side (evaporator) of a heat pump. Different types of VHE have evolved using coaxial tubes or U-tubes inserted into the ground in backfilled drill holes. Tube dimensions up to 10 cm diameter and probe lengths up to 100 m are the most common. Space heating and warm-water supply for a single-family dwelling with 12 KW capacity can be provided by two or three VHE's about 50 m in length. Long-term performance characteristics and the perturbations of the natural temperature field of VHE systems must be known for licensing decisions. Based on the results of field and theoretical studies, key performance parameters like fluid circulation velocity and ground thermal conductivity are identified and the necessary distance between VHE installations is discussed. It is concluded that VHE systems offer an interesting alternative energy source especially if coupled with a simple solar recharge unit.O trocador de calor vertical (VHE) é um dispositivo simples que estabelece um circuito fechado para que um fluido retire calor nas primeiras dezenas/centenas de metros de profundidade e alimente o lado frio (evaporador) de uma bomba de calor. Tipos diferentes de VHE foram desenvolvidos utilizando tubos coaxiais ou em forma de U, que são introduzidos em perfurações no terreno as quais são novamente preenchidas. Dimensões do tubo de até 10 cm de diâmetro e comprimento das sondas de até 100 m são as mais comuns. Calefação e fornecimento de água morna, para uma residência familiar com capacidade de 12 KW, podem ser atendidas com dois ou três trocadores de calor com cerca de 50 m de comprimento. As características de funcionamento a longo prazo e as perturbações do campo natural de temperatura dos sistemas de trocadores de calor, devem ser conhecidas para efeitos de licenciamento. Com base nos resultados dos estudos experimentais e teóricos são identificados neste trabalho, alguns parâmetros importantes, tais como velocidade de circulação dos fluidos e condutividade térmica do terreno. A distância necessária entre os trocadores de calor é discutida. Conclui-se que os sistemas VHE oferecem uma interessante fonte de energia alternativa especialmente se acoplados com uma unidade de recarga solar.

Geothermal energy is a weather-independent, permanently available renewable energy source. In addition to producing heat and electricity, geothermal energy can be used to extract critical raw materials dissolved in the heat-carrying fluid. Researchers working on the frontiers of geothermal energy utilisation may be able to transform ultra-deep metallic mineral formations into “orebody-Enhanced Geothermal Systems”. In the planned technology, the metal-containing geological formation would be manipulated in such a way that cogeneration of energy and metals is possible and can be optimised in the future according to market needs. The potential of geothermal energy for sustainable mineral extraction and energy production aligns with Sustainable Development Goal (SDG) 7, which aims to ensure access to affordable, reliable, sustainable, and modern energy for all. This new technology could substantially decrease Europe’s dependency on importing critical metallic minerals (such as lithium and tungsten) and energy; over and above, it has a small environmental footprint, including very low carbon emissions

Since 1963, the International Heat Flow Commission has been fostering the compilation of the Global Heat Flow Database to provide reliable heat-flow data. Over time, techniques and methodologies evolved, calling for a reorganization of the database structure and for a reassessment of stored heat-flow data. Here, we provide the results of a collaborative, community-driven approach to set-up a new, quality-approved global heat-flow database. We present background information on how heat-flow is determined and how this important thermal parameter could be systematically evaluated. The latter requires appropriate documentation of metadata to allow the application of a consistent evaluation scheme. The knowledge of basic data (name and coordinates of the site, depth range of temperature measurements, etc.), details on temperature and thermal-conductivity data and possible perturbing effects need to be given. The proposed heat-flow quality evaluation scheme can discriminate between different quality aspects affecting heat flow: numerical uncertainties, methodological uncertainties, and environmental effects. The resulting quality codes allow the evaluation of every stored heat-flow data entry. If mandatory basic data are missing, the entry is marked accordingly. In cases where more than one heat-flow determination is presented for one specific site, and all of them are considered for the site, the poorest evaluation score is inherited to the site level. The required data and the proposed scheme are presented in this paper. Due to the requirements of the newly developed evaluation scheme, the database structure as presented in 2021 has been updated and is available in the appendix of this paper. The new quality scheme will allow a comprehensible evaluation of the stored heat-flow data for the first time.

The flights of the civil (ARM22c) and military (ARM22m) parts of the exercise were performed between June 13th and 17th and between September 5th and September 9th, respectively. Both parts of the exercise included the measurement of altitude profiles. Two profiles were measured during ARM22c over Lake Thun and one profile during ARM22m over Lake Neuchâtel with sufficient altitude range to determine the slope of the altitude-dependent cosmic correction. The altitude profile over Lake Neuchâtel showed a clear deviation from the expected profile, suggesting a massive influence of airborne radon progeny on the result. According to the alternating schedule of the annual ARM exercises, the environs of the nuclear power plants Beznau (KKB) and Leibstadt (KKL), the Paul Scherrer Institute (PSI) and the intermediate storage facility (ZWILAG) were surveyed with an extension of the measuring area into German territory, following a request of German authorities. The site of the former Lucens reactor was measured and found unobtrusive in the measured data. Background flights were performed over several Swiss cities, regions and valleys. Besides attenuation effects of water bodies, variations of natural radionuclide content could be observed. Remains of the Chernobyl deposition were detected near the French border and in southern Switzerland.

Geothermal heat pump systems (GHP) are the spearhead of geothermal achievement and development, and one of the fastest growing applications of renewable energy technologies worldwide. When Swiss GHP activities started in the late 1970s, market introduction and penetration needed science-based proof of reliable, stable, long-term GHP operation. A special, extended project, realized in a field-laboratory setting, provided this proof. Detailed measurements, as well as numerical model simulations, proved the sustainable operation of the installed GHP system. The measurement setup, the recording of the various time series, and their interpretation are presented. Furthermore, basic perceptions were elaborated concerning geothermal resources behavior in production and regeneration. The Swiss GHP was developed from nothing. Early GHP installation costs halved within 20 years; GHP growth was nearly exponential from 1980 to 2020 (8.5% annually). Drilled borehole heat exchanger (BHE) meters are today around 300,000 m per year; heat delivery of GHPs in Switzerland amounted to 3280 GWh 2020-over 85% of Swiss geothermal direct uses (among others like thermal spas, district heating). Large installations with hundreds of BHEs are now common, and are also used for heating and cooling. The international ranking of Swiss GHP realizations is excellent in terms of annual energy use (TJ/yr/area), and is number one worldwide. Switzerland is a global GHP leader, and the Swiss success story is well documented.

Tunnel geothermal systems hold the potential to promote decarbonization of the building heating and cooling sector. They can be integrated into existing infrastructure, resulting in low additional costs. In addition, these systems have large contact areas with the ground leading to larger heat fluxes. However, tunnel geothermics is relatively unknown and rarely used. Thus, the objective of this study is to provide an overview of the two primary tunnel geothermal system types as well as their application and potential. Open hydrothermal systems use the tunnel drainage water as a heat source, whereas closed absorber systems harness the heat flux from the subsoil and the warm tunnel interior via heat exchangers. The evaluation of the global application of existing and planned tunnel geothermal systems shows that all open systems are currently located in mountainous regions with a thick rock overburden. In contrast, closed absorber systems are mostly installed in urban tunnel infrastructures. The spatial distribution of geothermal tunnel systems has a focus in central Europe with Switzerland, Germany and Austria being the countries with the highest number of installed systems. Finally, this study also presents a brief summary of existing methods to determine the geothermal potential of tunnels.

Geothermal heat pump systems (GHP), producing from shallow resources, are the spearhead of geothermal achievement and development. Global heat delivery grew exponentially to 600 PJ in 2020. GHP is the fastest growing segment in geothermal technology and one of the fastest growing application of renewable energy technologies worldwide. Other, various direct-use applications like space heating, bathing and swimming/wellness, industrial, agricultural (especially greenhouses) and aquacultural applications are based on deep, hydrothermal resources. These varieties produced worldwide 420 PJ heat in 2020; the average linear growth was, from 1995 on, about 10 % per year. It can be expected that this trend continues. Power generation, also from deep, hydrothermal resources, develops slowly but steadily, with an average growth-rate of 5 % per year, producing 95.0 TWh in 2020 in 30 countries. When comparing with other renewable power plant technologies (hydro, biomass, solar PV, wind), geothermal falls far behind – both in installed capacity (GWe) and in production (TWh). Only the annual availability of geothermal electricity is the highest among the renewables (60 %). Low geothermal productivity and growth-rate is due to extensive investments for solar PV and wind, which are by orders of magnitude higher than for geothermal power. The technology of Enhanced Geothermal Systems (EGS), based on deep, petrothermal resources, could be a game-changer. Requirements, problems and research goals to find solutions are presented.

AbstractTunnel geothermal systems hold the potential to promote decarbonization of the building heating and cooling sector. They can be integrated into existing infrastructure, resulting in low additional costs. In addition, these systems have large contact areas with the ground leading to larger heat fluxes. However, tunnel geothermics is relatively unknown and rarely used. Thus, the objective of this study is to provide an overview of the two primary tunnel geothermal system types as well as their application and potential. Open hydrothermal systems use the tunnel drainage water as a heat source, whereas closed absorber systems harness the heat flux from the subsoil and the warm tunnel interior via heat exchangers. The evaluation of the global application of existing and planned tunnel geothermal systems shows that all open systems are currently located in mountainous regions with a thick rock overburden. In contrast, closed absorber systems are mostly installed in urban tunnel infrastructures. The spatial distribution of geothermal tunnel systems has a focus in central Europe with Switzerland, Germany and Austria being the countries with the highest number of installed systems. Finally, this study also presents a brief summary of existing methods to determine the geothermal potential of tunnels.

The flights of the civil part (ARM21c) of the exercise were performed between June 28th and July 2nd and the flights of the military part (ARM21m) were performed between August 30th and September 2nd, 2021. Both parts of the exercise included the measurement of an altitude profile over Lake Neuchâtel with sufficient altitude range to determine the slope of the altitude dependent cosmic correction. According to the alternating schedule of the annual ARM exercises, the environs of the nuclear power plants Gösgen (KKG) and Mühleberg (KKM) were surveyed, the former extended with an area to the south-east of the power plant. The measurements showed no artificial radionuclides outside of the plant premises. The series of background measurements over Swiss cities was continued with flights over Frauenfeld, Lugano, Nyon and Wil. As a follow-up of the Caesium deposition in the wake of the Chernobyl accident, measurements were performed over areas in western and southern Switzerland. Residual 137Cs activity can still be detected in the vicinity of Lugano and several other sites tested during ARM21 as a follow-up of the Chernobyl deposition. Comparison to results of ground measurements, maps published in the scientific literature and previous airborne measurements yielded reasonable agreement to the measurement results. Detector RLL001 used in ARM21c continues to operate as specified. Problems with one NaI(Tl) crystal of detector RLL004 used during ARM21m indicates that not all of the crystals with poor quality have been identified in previous exercises.

Heat mining” is, in fact a complete deceptive misnomer. When a mineral deposit (e.g. copper) is mined and the ore has been taken out, it will be gone forever. Not so with geothermal resources: The heat and the fluid are coming back! Namely, the heat and fluid extraction create heat sinks and hydraulic minima; around these, strong temperature and pressure gradients develop. Along the gradients, natural inflow of heat and fluid arises to replenish the deficits. The inflow from the surroundings can be strong: around borehole heat exchangers, heat flow densities of several W/m2 result, whereas terrestrial heat flow amounts only to about 50 – 100 mW/m2. The regeneration of geothermal resources after production, in other words, extraction of fluid and/or heat) is a process that runs over different timescales, depending on the kind and size of the utilization system, the production rate, and the resource characteristics. The resource renewal depends directly on the heat/fluid backflow rate. Heat, respectively fluid production from geothermal resources can be accomplished with different withdrawal rates. Although forced production is more attractive financially (with quick payback), it can nevertheless degrade the resource permanently. The longevity of the resource (and thus the sustainability of production) can be ensured by moderate production rates. The sustainable geothermal production level depends on the utilization technology as well as on the local geologic conditions. The stipulation of the sustainable production level requires specific clarifications, especially by numerical modelling, based on long-term production strategies. In general, resource regeneration proceeds asymptotically: strong at the beginning and slowing down subsequently, reaching the original conditions only after infinite time. However, regeneration to 95 % can be achieved much earlier, e.g. within the lifetime of the extraction/production system. In other words, geothermal resources may under certain circumstances may be considered as having potential regrowth, like biomass. Concerning the requirements for such sustainable production, it is convenient to consider four resource types and utilization schemes. These may be treated by numerical model simulations that consider heat extraction by geothermal heat pumps, hydrothermal aquifer, used by a doublet system for space heating, high enthalpy two-phase reservoir, tapped to generate electricity, and enhanced Geothermal Systems (EGS).

The flights of the civil part ARM19z of the exercise were performed between June 2nd and June 6th, 2019, covering the recurrent measuring areas around the nuclear power plants Gösgen and Mühleberg, a transversal from Chur to Torre (TI) and an altitude profile over lake Neuchâtel. A short report of the measurement results of ARM19z was placed on the NEOC website https://www.naz.ch/ on June 7th, 2019. The flights of the military part of the exercise ARM19m were performed from September 2nd to September 5th. ARM19m contained source search exercises ver the Spiez military training area, measurements over a prospective reference area at the Thun military training area and measurements in the vicinity of the towns Bulle, Köniz and Vevey. The survey of the environs of the Swiss nuclear power plants Gösgen (KKG) and Mühleberg (KKM) showed no artificial radionuclides outside of the plant premises. The measurements over the towns of Bulle, Köniz and Vevey expanded the database of radiation background over Swiss cities. No unusual values of the radiological quantities were observed. An altitude profile over lake Neuchâtel lead to a revision of a model planned to be used for compensating the influence of airborne radon progeny on the measurement. The deterioration of the energy resolution of several NaI(Tl) crystals used in the RLL detectors continues to downgrade system performance. The analysis of cosmic dose rate data measured over the boiling water reactor of KKM indicates a misinterpretation of high energy photons emitted by the radionuclide 16N using the evaluation software developed by the manufacturer of the RLL system (Mirion). Results of training flights over radionuclide sources demonstrated the advantage of the online identification of radionuclides by the Mirion software and the subsequent alert to the operators. Nevertheless, in cases with several sources of different radionuclides, a visual inspection of the associated photon spectra by operators well acquainted with gammaspectrometry is advisable. First estimates of correction factors for 232Th and 40K activity concentrations were determined from results of current and past measurements to align data evaluations with ARM and Mirion software.

The flights of the civil part ARM19z of the exercise were performed between June 2nd and June 6th, 2019, covering the recurrent measuring areas around the nuclear power plants Gösgen and Mühleberg, a transversal from Chur to Torre (TI) and an altitude profile over lake Neuchâtel. A short report of the measurement results of ARM19z was placed on the NEOC website https://www.naz.ch/ on June 7th, 2019. The flights of the military part of the exercise ARM19m were performed from September 2nd to September 5th. ARM19m contained source search exercises ver the Spiez military training area, measurements over a prospective reference area at the Thun military training area and measurements in the vicinity of the towns Bulle, Köniz and Vevey. The survey of the environs of the Swiss nuclear power plants Gösgen (KKG) and Mühleberg (KKM) showed no artificial radionuclides outside of the plant premises. The measurements over the towns of Bulle, Köniz and Vevey expanded the database of radiation background over Swiss cities. No unusual values of the radiological quantities were observed. An altitude profile over lake Neuchâtel lead to a revision of a model planned to be used for compensating the influence of airborne radon progeny on the measurement. The deterioration of the energy resolution of several NaI(Tl) crystals used in the RLL detectors continues to downgrade system performance. The analysis of cosmic dose rate data measured over the boiling water reactor of KKM indicates a misinterpretation of high energy photons emitted by the radionuclide 16N using the evaluation software developed by the manufacturer of the RLL system (Mirion). Results of training flights over radionuclide sources demonstrated the advantage of the online identification of radionuclides by the Mirion software and the subsequent alert to the operators. Nevertheless, in cases with several sources of different radionuclides, a visual inspection of the associated photon spectra by operators well acquainted with gammaspectrometry is advisable. First estimates of correction factors for 232Th and 40K activity concentrations were determined from results of current and past measurements to align data evaluations with ARM and Mirion software.