Open Access
Experimental development of a novel thermoelectric generator without moving parts to harness shallow hot dry rock fields
(2021) Alegría Cía, Patricia; Rodríguez García, Antonio; Catalán Ros, Leyre; Astrain Ulibarrena, David; Araiz Vega, Miguel; Ingeniería; Institute of Smart Cities - ISC; Ingeniaritza
Nowadays, geothermal energy in shallow hot dry rocks is not exploited enough due to the high economic and environmental impact as well as the lack of scalability of the existing technologies. Here, thermoelectricity has a great future potential due to its robustness, absence of moving parts and modularity. With this research, the feasibility of a novel and robust geothermal thermoelectric generator whose working principle is phase change has been experimentally demonstrated, as well as the importance of compactness to maximize its efficiency and thus, power generation.
Open Access
400 W facility of geothermal thermoelectric generators from hot dry rocks on the Canary Islands
(Elsevier, 2025-06-01) Alegría Cía, Patricia; Pascual Lezaun, Nerea; Catalán Ros, Leyre; Araiz Vega, Miguel; Astrain Ulibarrena, David; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Geothermal energy has a great potential to be harnessed and requires a boost in technologies to enhance its use. The Canary Islands have a great dependence on fossil fuels, and Lanzarote has important geothermal anomalies currently unexploited due to the absence of water in the soil, what hinders the use of vapour turbines. This work presents the development of the first facility of geothermal thermoelectric generators operating in the world. This novel generators are producing 400 W of power in Timanfaya National Park. It has three geothermal thermoelectric generators, each with 4 thermosyphons per borehole and 40 thermoelectric modules that directly transform heat into electricity. This facility, with the advantages of geothermal energy such as continuity and independence on the weather, requires low maintenance because it does not require moving parts nor water consumption. That makes feasible for the first time to harness the geothermal potential in Lanzarote, producing an electric energy of 9.4 kWh per day, which means 3.42 MWh per year. The field installation of this novel technology has enabled to accurately calculate the Levelized Cost of Energy, which is 0.22 €/kWh. Although a 29% decrease in the power generated by thermoelectric module was detected when installing a GTEG with 40 modules with respect to a GTEG with 10 modules, this decrease is compensated by the fact that by installing more modules, the electrical production per borehole is optimized, reducing the LCOE. The developed facility will avoid the emission of 2.3 tons of CO2 and is totally respectful with the environment if compared to conventional geothermal power plants.
Open Access
Simulation of thermoelectric heat pumps in nearly zero energy buildings: why do all models seem to be right?
(Elsevier, 2021) Martínez Echeverri, Álvaro; Díaz de Garayo, Sergio; Aranguren Garacochea, Patricia; Araiz Vega, Miguel; Catalán Ros, Leyre; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
The use of thermoelectric heat pumps for heat, ventilation, and air conditioning in nearly-zero-energy buildings is one of the most promising applications of thermoelectrics. However, simulation works in the literature are predominately based on the simple model, which was proven to exhibit significant deviations from experimental results. Nine modelling techniques have been compared in this work, according to statistical methods based on uncertainty analysis, in terms of predicted coefficient of performance and cooling power. These techniques come from the combination of three simulation models for thermoelectric modules (simple model, improved model, electric analogy) and five methods for implementing the thermoelectric properties. The main conclusion is that there is no statistical difference in the mean values of coefficient of performance and cooling power provided by these modelling techniques under all the scenarios, at 95% level of confidence. However, differences appear in the precision of these results in terms of uncertainty of the confidence intervals. Minimum values of uncertainty are obtained when the thermal resistance ratio approaches 0.1, being ±8% when using temperature-dependent expressions for the thermoelectric properties, ±18% when using Lineykin's method, and ± 25% when using Chen's method. The best combination is that composed of the simple model and temperature-dependent expressions for the thermoelectric properties. Additionally, if low values of resistance ratio are anticipated, empirical expressions from the literature can be used for the thermal resistance of the heat exchangers; for high values, though, experimental tests should be deployed, especially for the heat exchanger on the hot side.
Open Access
Thermoelectric generator with passive biphasic thermosyphon heat exchanger for waste heat recovery: design and experimentation
(MDPI, 2021) Araiz Vega, Miguel; Casi Satrústegui, Álvaro; Catalán Ros, Leyre; Aranguren Garacochea, Patricia; Astrain Ulibarrena, David; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Gobierno de Navarra / Nafarroako Gobernua
One of the measures to fight against the current energy situation and reduce the energy consumption at an industrial process is to recover waste heat and transform it into electric power. Thermoelectric generators can be used for that purpose but there is a lack of experimental studies that can bring this technology closer to reality. This work presents the design, optimizations and development of two devices that are experimented and compared under the same working conditions. The hot side heat exchanger of both generators has been designed using a computational fluid dynamics software and for the cold side of the generators two technologies have been analysed: a finned dissipater that uses a fan and free convection biphasic thermosyphon. The results obtained show a maximum net generation of 6.9 W in the thermoelectric generator with the finned dissipater; and 10.6 W of power output in the generator with the biphasic thermosyphon. These results remark the importance of a proper design of the heat exchangers, trying to get low thermal resistances at both sides of the thermoelectric modules, as well as, the necessity of considering the auxiliary consumption of the equipment employed.
Open Access
Experimental development of a novel thermoelectric generator without moving parts to harness shallow hot dry rock fields
(Elsevier, 2022) Alegría Cía, Patricia; Catalán Ros, Leyre; Araiz Vega, Miguel; Rodríguez García, Antonio; Astrain Ulibarrena, David; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
Nowadays, geothermal energy in shallow hot dry rock fields is not exploited enough due to the high economic and environmental impact as well as the lack of scalability of the existing technologies. Here, thermoelectricity has a great future potential due to its robustness, absence of moving parts and modularity. However, the efficiency of a thermoelectric generator depends highly on the heat exchangers. In this work, a novel geothermal thermoelectric generator is experimentally developed, characterizing different configurations of biphasic heat exchangers to obtain low thermal resistances that allow the maximum efficiency in the thermoelectric modules. As a result, robust and passive heat exchangers were obtained with thermal resistances of 0.07 K/W and 0.4 K/W in the hot and cold sides, respectively. The geothermal thermoelectric generator was built with the most effective heat exchangers and was experimented under different temperature and convection conditions, generating 36 W (17 W by a prototype with 10 modules and 19 W by a prototype with 6 modules) for a temperature difference of 160 °C between the heat source and the environment. Furthermore, the experimental development showed that it is possible to increase electricity generation with a more compact generator, since a decrease in the number of modules from 10 to 6 increases the efficiency from 3.72% to 4.06%. With this research, the feasibility of a novel and robust geothermal thermoelectric generator whose working principle is phase change has been experimentally demonstrated, as well as the importance of compactness to maximize its efficiency and thus, power generation.
Open Access
Enhanced behaviour of a passive thermoelectric generator with phase change heat exchangers and radiative cooling
(Elsevier, 2023) Astrain Ulibarrena, David; Jaramillo-Fernández, Juliana; Araiz Vega, Miguel; Francone, Achille; Catalán Ros, Leyre; Jacobo-Martín, Alejandra; Alegría Cía, Patricia; Sotomayor-Torres, Clivia M.; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Heat exchangers are essential to optimize the efficiency of Thermoelectric Generators (TEGs), and heat pipes without fans have proven to be an advantageous design as it maintains the characteristic robustness of thermoelectricity, low maintenance and lack of moving parts. However, the efficiency of these heat exchangers decreases under natural convection conditions, reducing their heat transfer capacity and thus thermoelectric power production. This work reports on a novel heat exchanger that combines for the first time, phase change and radiative cooling in a thermoelectric generator to improve its efficiency and increase the production of electrical energy, specially under natural convection. For this, two thermoelectric generators with heat-pipes on their cold sides have been tested: one with the radiative coating and the other without it. Their thermal resistances have been determined and the electric power output was compared under different working conditions, namely, natural convection and forced convection indoors and outdoors. The experimental tests show a clear reduction of the heat exchanger thermal resistance thanks to the radiative coating and consequently, an increase of electric production 8.3 % with outdoor wind velocities of 1 m/s, and up to 54.8 % under free convection conditions. The application of the radiative surface treatment is shown to result in a more stable electrical energy production, suppressing the drastic decrease in the generated electric power that occurs in thermoelectric generators when they work under free convection.
Open Access
Improvements in the cooling capacity and the COP of a transcritical CO 2 refrigeration plant operating with a thermoelectric subcooling system
(Elsevier, 2019) Astrain Ulibarrena, David; Merino Vicente, Amaya; Catalán Ros, Leyre; Aranguren Garacochea, Patricia; Araiz Vega, Miguel; Sánchez, Daniel; Cabello, Ramón; Llopis, R.; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
Restrictive environmental regulations are driving the use of CO 2 as working fluid in commercial vapour compression plants due to its ultra-low global warming potential (GWP 100 = 1) and its natural condition. However, at high ambient temperatures transcritical operating conditions are commonly achieved causing low energy efficiencies in refrigeration facilities. To solve this issue, several improvements have been implemented, especially in large centralized plants where ejectors, parallel compressors or subcooler systems, among others, are frequently used. Despite their good results, these measures are not suitable for small-capacity systems due mainly to the cost and the complexity of the system. Accordingly, this work presents a new subcooling system equipped with thermoelectric modules (TESC), which thanks to its simplicity, low cost and easy control, results very suitable for medium and small capacity plants. The developed methodology finds the gas-cooler pressure and the electric voltage supplied to the TESC system that maximizes the overall COP of the plant taking into account the ambient temperature, the number of thermoelectric modules used and the thermal resistance of the heat exchangers included in the TESC. The obtained results reveal that, with 20 thermoelectric modules, an improvement of 20% in terms of COP and of 25.6% regarding the cooling capacity can be obtained compared to the base cycle of CO 2 of a small cooling plant refrigerated by air. Compared to a cycle that uses an internal heat exchanger IHX, the improvements reach 12.2% and 19.5% respectively.
Open Access
Design and experimental development of thermoelectric generators for shallow geothermal anomalies of volcanic origin
(2020) Catalán Ros, Leyre; Astrain Ulibarrena, David; Aranguren Garacochea, Patricia; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
En el contexto energético actual, caracterizado por un incesante aumento en el consumo de energía y una gran dependencia de los combustibles fósiles, resulta imprescindible apostar por sistemas eficientes y basados en energías renovables que contribuyan a un mejor aprovechamiento de los recursos y sean respetuosos con el medio ambiente. En este sentido, la energía geotérmica destaca entre otras fuentes renovables por su carácter permanente, al no depender de las condiciones meteorológicas. Sin embargo, su contribución al sistema energético mundial es mínimo, sobre todo en generación de electricidad. Como alternativa a los ciclos que tradicionalmente se emplean para la generación eléctrica geotérmica, esta tesis doctoral propone la utilización de generadores termoeléctricos debido a sus numerosas ventajas tales como fiabilidad, durabilidad y escalabilidad. Concretamente, la tesis se centra en anomalías geotérmicas superficiales de origen volcánico para dos aplicaciones distintas: la generación eléctrica de media escala en yacimientos de roca caliente seca y el abastecimiento autónomo de estaciones de vigilancia volcánica. Dada la importancia de los intercambiadores de calor en la eficiencia total del sistema, en ambas aplicaciones se ha realizado un profundo estudio para determinar qué tipo de intercambiadores de calor son los más adecuados. En ambos casos, se ha demostrado experimentalmente que los intercambiadores de calor más propicios son aquellos basados en el cambio de fase, ya que aparte de presentar bajas esistencias térmicas, no tienen partes móviles ni requieren de equipos auxiliares, minimizando así el mantenimiento. Asimismo, también ha resultado de gran importancia el desarrollo de un modelo computacional rápido y fiable que tenga en cuenta los intercambiadores de calor, la fuente de calor y el sumidero, sin despreciar ningún efecto termoeléctrico, y considerando los contactos térmicos y eléctricos y la influencia de la temperatura en las propiedades. Este modelo, programado en base al método de las diferencias finitas, se ha convertido en una verdadera herramienta de diseño y optimización para las dos aplicaciones objeto de estudio en esta tesis doctoral, gracias a su error relativo menor al 8%. Los resultados derivados de esta tesis doctoral demuestran que la termoelectricidad puede solucionar las problemáticas de generación eléctrica en los yacimientos de roca caliente seca y en las estaciones de monitorización volcánica, dos aplicaciones inéditas de generación termoeléctrica que pueden hacer que esta tecnología se convierta por fin en una realidad en el ámbito civil.
Open Access
Gamification and a low-cost laboratory equipment aimed to boost vapor compresion refrigeration learning
(OmniaScience, 2022) Aranguren Garacochea, Patricia; Sánchez García-Vacas, Daniel; Casi Satrústegui, Álvaro; Araiz Vega, Miguel; Catalán Ros, Leyre; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The nowadays European educational framework boosts applying the learned theoretical concepts to real situations. Hence, practice sessions are key resources to present students direct applications of the theoretical concepts shown in class. Thus, developing new educational equipment and practice sessions oriented to bringing theoretical knowledge closer to practice should be one of the objectives of teachers. The present work describes a solution proposed by lectures of two Spanish universities looking to increase the knowledge of their engineering students. Along the years, these docents have noticed the lack of connection between the theoretical and practical knowledge among their students, drastically harming their learning procedure. Thus, in order to deepen into practical learning, a teaching methodology involving low-cost prototypes of vapor compression systems and a gamification method to help the students understand the concepts is proposed. The proposed methodology is expected to make a big positive impact on the results obtained by the students, taking into account the preliminary results reached.
Open Access
Corrosion behavior in volcanic soils: in search of candidate materials for thermoelectric devices
(MDPI, 2021-12-21) Berlanga Labari, Carlos; Catalán Ros, Leyre; Palacio, José F.; Pérez Artieda, Miren Gurutze; Astrain Ulibarrena, David; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería; Institute for Advanced Materials and Mathematics - INAMAT2
Thermoelectric generators have emerged as an excellent solution for the energy supply of volcanic monitoring stations due to their compactness and continuous power generation. Nevertheless, in order to become a completely viable solution, it is necessary to ensure that their materials are able to resist in the acidic environment characteristic of volcanoes. Hence, the main objective of this work is to study the resistance to corrosion of six different metallic materials that are candidates for use in the heat exchangers. For this purpose, the metal probes have been buried for one year in the soil of the Teide volcano (Spain) and their corrosion behavior has been evaluated by using different techniques (OM, SEM, and XRD). The results have shown excessive corrosion damage to the copper, brass, and galvanized steel tubes. After evaluating the corrosion behavior and thermoelectric performance, AISI 304 and AISI 316 stainless steels are proposed for use as heat exchangers in thermoelectric devices in volcanic environments.

Catalán Ros, Leyre

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