This article presents a validation of mathematical models against literature experimental data for alkaline and Proton Exchange Membrane (PEM) electrolyzers. The validation concerns also an Aspen HYSYS alkaline model expected for future large-scale application. The validation demonstrated that simulated outputs closely aligned with theoretical values under various operating conditions, confirming the reliability of these models in predicting electrolyzer performance. This successful validation supports their application in the design and optimization of green hydrogen production systems.

Geothermal targets may be found in naturally fractured rocks of meteorite impact craters hosting low temperature resources. We therefore conducted a study with the objective of evaluating the geothermal potential of the 400 million year old Charlevoix impact crater in Quebec (Canada). Finite element simulations of steady state groundwater flow and heat transfer were made based on field characterization that allowed for the evaluation of rock thermohydraulic properties. Simulations provided a definition of the temperature field in cross-sections of the crater up to 10 km depth. Results allowed quantification of the impact of the deep groundwater recharge, the rock thermal conductivity and the Earth heat flow on the temperature distribution at depth. The calculated geothermal gradient inside the Charlevoix crater reaches 31 degrees C km-1 in the most favorable areas. The average temperature at 3 km depth was 70 degrees C inside the crater and was higher compared to outside the crater. This suggests greater potential for low-temperature geothermal direct use in the crater.

At the 28th Conference of Parties (COP28) a commitment to triple renewable energy capacity by 2030 was made. Currently at 16 GW, geothermal accounts for 0.5% of world-wide installed renewable electricity capacity. In this scoping review, Elsevier’s database was used to determine the role reservoir simulation has played and could continue to play in assisting the geothermal industry in achieving COP28's goal. The review includes journal papers published in English from 2020 to 2023. Particular attention was paid to the applications of TOUGH2 and COMSOL, the benefits of Machine Learning (ML) and recent projects that could assist in promoting the geothermal industry. The topics' categories comprised: Enhanced Geothermal Systems (EGS), hydrothermal, laboratory, and technology synergies. Outcomes of a bibliometric analysis elucidate these trends: ML is vital to ensuring the optimisation of geothermal resources; EGS and cross-industry projects are showing growing global interest. The likelihood of meeting the COP28 target for geothermal would be enhanced with increased participation from the South American and African countries. However, the industry’s growth in these continents is restricted by high initial investment costs, technical complexities, unclear regulatory frameworks, social acceptance, and difficulties with electrical grid integration. Suggestions for overcoming these barriers to development are proposed. A brief country case study is also presented. It focuses on the economic, environmental and technical context to understand the unique challenges and opportunities for geothermal. Finally, five areas for research and development opportunities were identified: Thermo-Hydro-Mechanical-Chemical processes, reinjection and induced seismicity, reservoir characterization, cross-industry collaborations, and laboratory studies.

Two hydrogeological numerical models (2D and 3D) for the geothermal area located to the West of the Nevado del Ruiz volcanic complex (Colombia) are presented here. They are built with the software HydroGeoSphere using data collected in the field, as well as hydraulic and thermal properties measured on rock samples in previous laboratory studies. The purpose of this modeling work is to analyze the influence of faults aperture and depth on groundwater flow circulation and heat transfer in the geothermal reservoir. The 2D model illustrates the relation between fault aperture and temperature distribution. The 3D model shows the behavior of a potential production well located in the Botero-Londoño area that withdraws hot water from a depth of 2600 m. The results highlight the usefulness and limitations of this approach, providing guidelines for future numerical models of this site and for the initial modeling work for any fractured geothermal reservoir.

This research contributes to the knowledge of the geothermal area of the Nevado del Ruiz Volcano (Colombia) by analyzing the secondary permeability and connectivity of fractures at microstructural and macrostructural level. Although the Nevado del Ruiz Volcano (NRV) area has had geothermal exploration studies for power generation since 1968, there is still no exploitation of its geothermal resources. The NRV geothermal reservoir is characterized by a low primary permeability and the presence of several geological faults crossing a tectonically active and complex region. The analysis was performed comparing a zone affected by intense faulting with another one characterized by the same lithology, but with less influence of faulting and located further from the volcano. Fractures were characterized at outcrops with the window sampling method, and petrographic analysis was performed to confirm the mineralogy of samples collected. At the microstructural scale it was found that faulting does not necessarily influence the interconnectivity of fractures, but it does influence their intensity, quantity, and strike. To analyze the influence of fractures on groundwater flow, it is suggested to consider three main aspects: secondary permeability, connectivity, and fracture intensity. The lithology of major geothermal interest in the NVR area (Pes) presented greater connectivity and fracture intensity, which, combined with the high foliation observed in field, increase its effective permeability. The secondary permeability of different lithologies in the NRV area ranged between 1.15 × 10–6 and 10.32 × 10–7 m2. Most of the hot springs were in areas of high macrostructural connectivity, supporting the idea that groundwater flow is dominated by the secondary permeability of rocks. Estimation of the secondary permeability and identification of areas of high fracturing and connectivity, contributes to the understanding of the NRV geothermal area, which is a key aspect when drilling for successful well production. The methodology presented is useful in the initial exploration phase in fractured geothermal reservoirs.

Geothermal energy has been widely recognized as a renewable, clean, cost-effective, source of energy that can be an alternative to fossil fuels. Geothermal Heat Pumps (GHPs) are tools that can extract heat from subsoil, surface water bodies, or groundwater. In Colombia, geothermal energy is one of the least developed and known non-conventional renewable energy sources. To reduce the operating costs associated with the cooling at 3 °C of a flower's preservation room in the municipality of La Ceja, a surface water source heat pump (SWHP) and a horizontal ground-coupled heat pump (GCHP) were evaluated as energy alternatives. The temperatures in a rainwater harvesting pond and soil were monitored to analyze their potential as a heat sink for the proposed geothermal installations. The water temperature varied with outdoor conditions due to the shallowness of the pond. In contrast, the soil temperature was characterized by an almost constant value. Based on the data collected, it is determined that only during a portion of the day of 4 h (9:00–13:00) suggesting the efficiency of a SWSHP system is higher than the traditional refrigeration system currently used. This result indicates that a single SWSHP is not sufficient to provide the required cooling load. Therefore, a horizontal GCHP is suggested as an alternative installation to be used. This work promotes the use of geothermal resources in Colombia and is also a valuable contribution for the entire Caribbean and Latin America region, where GHPs are not commonly used.

This article presents a study of the electricity generation potential using ORC systems of the most important geothermal sites in northeastern Algeria, combining geological, thermodynamic and economic analysis. The results highlight that geothermal electricity is technically feasible with the selected indirect heat ORC geothermal plant. Such production can present an interesting economic profitability when considering the international electricity price. The best economic performance was obtained for the geothermal site of Meskhoutine leading to a depreciated payback period of 10.8 years. The electricity production cost was evaluated at 0.21$/kWh for an electricity production capacity of 498 kW. Such performance is completely breakdown when considering Algerian subsidised electricity prices. These subsidies must be revised. Otherwise, it will harm the profitability of renewable energy systems, limit their development, and constrain seriously the Algerian energy transition road map. In addition, this study highlights that the selected indirect ORC configuration presents an important internal auxiliary consumption, especially for the Air Condenser (AC) unit, and was not suitable for geothermal temperatures below 117 degrees C. Other configurations, especially hybridisation and combined heating and power production are prioritized for future investigation.

Unsaturated zones are important for geotechnical design, geochemical reactions, and microbial reactions. The numerical analysis of unsaturated seepage is complex because it involves highly nonlinear partial differential equations. The permeability can vary by orders of magnitude over short vertical distances. This article defines and uses H-convergence tests to quantify numerical errors made by uniform meshes with element size (ES) for 1D steady-state conditions. The quantitative H-convergence should not be confused with a qualitative mesh sensitivity study. The difference between numerical and mathematical convergences is stated. A detailed affordable method for an H-convergence test is presented. The true but unknown solution is defined as the asymptote of the numerical solutions for all solution components when ES decreases to zero. The numerical errors versus ES are then assessed with respect to the true solution, and using a log-log plot, which indicates whether a code is correct or incorrect. If a code is correct, its results follow the rules of mathematical convergence in a mathematical convergence domain (MCD) which is smaller than the numerical convergence domain (NCD). If a code is incorrect, it has an NCD but no MCD. Incorrect algorithms of incorrect codes need to be modified and repaired. Existing codes are shown to converge numerically within large NCDs but generate large errors, up to 500%, in the NCDs, a dangerous situation for designers.

This research contributes to the knowledge of the geothermal area of the Nevado del Ruiz Volcano (Colombia) by analyzing the secondary permeability and connectivity of fractures at microstructural and macrostructural level, comparing a zone affected by intense faulting with another one characterized by the same lithology, but with less influence of faulting and located further from the volcano. Fractured were identified and characterized in the field at outcrops with the window sampling method, and petrographic analysis was performed to confirm the mineralogy of rock samples collected. Simulations of groundwater flow and heat transfer in no fractured, low-fractured, and high-fractured are performed to quantify the impact of permeability observed in the field on the physical processes that involve geothermal resources circulation in a fractured reservoir. It was found that the faults do not directly influence the connection of fractures, but they influence the intensity of fractures. To analyze the influence of fractures on fluid flow, it is suggested to consider three main aspects: secondary permeability, connectivity, and fracture intensity. The location of hot springs can be associated with the macrostructural connectivity, to analyze the relation between secondary permeability and geothermal fluid circulation. The presented methodology is useful at the initial exploration stage in fractured geothermal reservoirs.

Groundwater numerical studies do not include H-convergence tests, contrarily to computational fluid dynamics (CFD) studies. In regional groundwater studies with pumping wells, the grids may exceed 106 nodes. The authors examine whether H-convergence tests can help to calculate the numerical errors made by using large grids with element sizes in the 10-500 m range. First, the differences between numerical and mathematical convergences are explained. Then, a method is proposed that most users may easily implement for their groundwater studies to assess the numerical error linked to the element size, ES, and the aspect ratio, AR. A single problem, forming a simple part of a regional groundwater study, was examined and solved by using many uniform grids. The results show that most regional groundwater studies make errors in the 50-500% range, considering their usual values for ES and AR. The numerical convergence domain, NCD, is shown to be larger than the mathematical convergence domain, MCD. This means that the codes can provide a numerical solution for a large range of ES values, even for many values outside the MCD, which is a risky situation for designers who are unaware of the difference between NCD and MCD and ignore the H-convergence tests.

The assessment of the geothermal resources available in a specific area requires a detailed knowledge of the thermal and hydraulic properties of host rock formations. These properties were quantified with rock samples mainly collected at the intersection between Nereidas, Cueva-Pirineos, and La Tosca-El Descanso faults, to the West of the Nevado del Ruiz volcano (Colombia), to improve the characterization of this volcanic geothermal system. The geological formations analyzed in this study are the Cajamarca Complex, PRE-Ruiz lava flows, Andesites unit, and volcanic member of the Quebradagrande Complex. A 3D geological conceptual model for the study area and a geological cross-section are presented. 113 laboratory measurements allowed to quantify thermal conductivity (TC) and diffusivity (TD), heat capacity (HC), porosity, and permeability of the rock samples collected. The Cajamarca Complex is the lithology with the highest TC (2.9 W m-1 K-1), but with the lowest primary permeability (0.038mD) and porosity (3.4%). Regarding extrusive igneous rocks, the Andesites unit present significative porosity (10.7%), and the PRE-Ruiz lava flows show a low TC (1.5 W m-1 K-1). The results of 6 petrographic analyses of thin sections of the PRE-Ruiz lava flows and Cajamarca Complex helped to justify the values of their thermal properties. Quartz-filled veinlets and garnet are identified in the volcanic member of the Quebradagrande Complex. Both minerals indicate that fluids might have circulated at high temperature. It is the first time that garnet is identified in rock samples of this region; since it can be the result of high temperature hydrothermal alteration mineral, its origin must be confirmed, and its identification provides new insights about the geothermal resources in the area. The conceptual model, the thin section results, and the quantification of rock properties are relevant public data for future geothermal development. All data reported in this manuscript are disclosed as supplementary material, providing a significant scientific contribution in the form of an open dataset that can be used as a basis for future hydrothermal modelling of the Nevado del Ruiz geothermal system, where is the most advanced geothermal development project in Colombia, and other similar geothermal systems.

From a literature review, various concepts and methodologies useful for the development of the preliminary stages of planning and design of a ground source heat pump were documented. A prototype of a cooling system for a room in the Universidad EIA was proposed. The heat pump selected to supply the demand has a power of 1-9 kW, and the proposed heat exchanger system corresponds to a closed-loop horizontal slinky-type with an approximate pipe length of 1,301 m, which was calculated through Excel spreadsheets and configured in three or six trenches with a total area required for the installation of 911 and 952 m2, respectively. These results provide the initial conditions for the implementation of an air conditioning project at the site, using shallow geothermal energy. Other alternatives for the heat exchanger systems and considerations for future projects are also presented.

The La Miel River watershed is an area of high hydrological interest in Colombia due to its abundant water resources, high annual precipitation, and hydroelectric power generation. This work proposes a sequential modeling framework to quantify the spatially and temporally variable groundwater recharge and to analyze its impact on piezometric fluctuations in the study area, where the groundwater flow is affected by geological faults. Water Modeling Framework (WMF) and HydroGeoSphere (HGS) models have been used to calculate groundwater recharge and distribution of hydraulic heads, respectively. Recharge computed with WMF is used as input to HGS to compare groundwater flow 1) with uniform and spatially variable recharge, 2) with and without discrete fractures, and 3) during dry and wet conditions. The results generate valuable knowledge for water resource management and highlight the importance of groundwater recharge estimation and a proper representation of fractured aquifers.

Tunnels commonly go through fracture zones that used to be analyzed as an equivalent porous medium with homogeneous permeability. However, it is a rough simplification that overlooks the connection triggered by underground works in fractured massifs. This study introduces the use of synthetic discrete fracture networks (DFN) to analyze groundwater inflows through tunnel excavation in a fractured zone considering the daily advance of the drilling front. First, a hypothetical case with six different settings varying the fracture density, the fracture length, and the aperture distribution is analyzed. Each setting has about 100 iterations. DFN hydraulic properties were estimated and compared with previous DFN studies, displaying the same behavior even though the magnitude of the estimated parameters differs. As an application example, structural measurements of the Alaska fault zone in the La Linea massif (Colombia) are used to obtain the statistical parameters of the fracture length and aperture distributions to generate the DFN. Five settings varying the fracture density are built, obtaining measured and simulated groundwater inflows of the same order of magnitude. These results highlight the potential of the synthetic DFN to analyze tunnels’ effects on groundwater flow.

Geochemical surveying is one of the techniques of geothermal exploration that include geothermometry to estimate the temperature of deep reservoirs. This work provides the temperature estimation of geothermal resources, geochemical analysis, and a conceptual model of the geothermal reservoir located to the western flank of the Nevado del Ruiz Volcano (NRV), a mayor geothermal target for energy production in Colombia. Hydrogeochemical data (pH, temperature, electrical conductivity, major, minor, and trace elements) were obtained from water samples collected at several hot springs located to the west of the NRV between 2017 and 2019. The data available from the Colombian Geological Survey database were also included in the analysis to better characterize the hot spring behavior. The hydrogeochemical tools Liquid analysis Powell and Cumming and GQAnalyzer software were used to draw ternary diagrams and to use geothermometers. The results allowed separating the hot springs into two groups, according with their chemical characteristics and spatial location: Nereidas 1, Nereidas 2, Nereidas Pozo, and Chorro Negro hot springs belong to Group 1 (G1), located closer to the NRV; on the other hand, Geysers, El Bosque-La Piscina, Quebrada Negra, and Rio Claro, which are located further from NRV, belong to Group 2 (G2). The latter is made of mature and chloride waters, indicating a water-rock equilibrated interaction with most of ions. The results of this study contribute to the future Colombian geothermal development, and the methodology and analysis can be applied to geothermal systems with similar geological characteristics to infer a conceptual model useful for geothermal exploration.

Summary Very low enthalpy geothermal energy is one of the least known NCRES in Colombia, but it has been widely used around the world in particular for space conditioning (heating and/or cooling) for domestic and industrial purposes, due to its great adaptability since all it needs is a GHP to directly exchange heat with subsoil and/or groundwater. This investigation evaluates the possibility of implementing a SWSHP system to cool at 3°C a preservation room for exportation flowers in La Virginia S.A.S located in La Ceja, at 41 km to the southeast of Medellin (Antioquia, Colombia). The temperature of two reservoirs belonging to the flower farm was monitored to analyze their potential as heat sinks for a SWSHP. The traditional and geothermal refrigeration systems were compared using empirical formulas based on the theoretical performance proposed by Carnot. It was found that the water temperature had a very little variation with respect to the ambient air temperature. The feasibility of using a surface water body as a heat sink of a SWSHP was evaluated. The coupling with other geothermal arrangements such as vertical and/or horizontal Ground Source Heat Pumps (GSHP) and even combining aerothermal is suggested.

Summary One of the main uses that is given to shallow geothermal energy corresponds to the implementation of Heating, Ventilation and Air Conditioning (HVAC) systems, using the ground or groundwater as a sink or source of heat. From a bibliographic compilation, various concepts and useful methodologies were documented for the development of the preliminary stages of planning and designing a system with geothermal heat pump. A prototype of a cooling system for a computer room in the EIA University was proposed.

Unconventional geothermal resource development can contribute to increase power generation from renewable energy sources in countries without conventional hydrothermal reservoirs, which are usually associated with magmatic activity and extensional faulting, as well as to expand the generation in those regions where conventional resources are already used. Three recent drilling experiences focused on the characterization of unconventional resources are described and compared: the Campi Flegrei Deep Drilling Project (CFDDP) in Italy, the United Downs Deep Geothermal Power (UDDGP) project in the United Kingdom, and the DEEP Earth Energy Production in Canada. The main aspects of each project are described (geology, drilling, data collection, communication strategies) and compared to discuss challenges encountered at the tree sites considered, including a scientific drilling project (CFDDP) and two industrial ones (UDDGP and DEEP). The first project, at the first stage of pilot hole, although not reaching deep supercritical targets, showed extremely high, very rare thermal gradients even at shallow depths. Although each project has its own history, as well as social and economic context, the lessons learned at each drilling site can be used to further facilitate geothermal energy development.

Advances in new technologies and the desire to achieve a sustainable and safe energy supply, enable communities to transition from conventional to renewable resources, such as geothermal energy. Perception and acceptance amongst different audiences have a high impact on the feasibility of energy projects, which is an important aspect to analyze. For this reason, this study focuses on describing the level of awareness and acceptance of deep geothermal energy within an educated segment of the population in five European and American countries (Canada, Colombia, Chile, Belgium, and France) at different stages of geothermal development. This study was conducted through an online survey, which was targeted to post-secondary students and professionals. Some of the most significant conclusions are: 1) there is a high degree of awareness of geothermal energy among the respondents in Chile and Canada, a medium level in Belgium and France, and a low one in Colombia; 2) there is a favorable acceptance of a geothermal project in each country, even when hydraulic stimulation is considered; 3) environmental aspects and community safety are the most important issues that must be addressed to support a pilot geothermal project.