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
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
Geothermal thermoelectric generator for Timanfaya National Park
(2019) Catalán Ros, Leyre; Astrain Ulibarrena, David; Aranguren Garacochea, Patricia; Araiz Vega, Miguel; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
Despite being one of the largest renewable sources, geothermal energy is not widely utilized for electricity generation. In the case of shallow Hot Dry Rock (HDR) fields, thermoelectric generators can entail a sustainable alternative to Enhanced Geothermal Systems (EGS). The present work studies two configurations of thermoelectric generators for Timanfaya National Park (Spain), one of the most important Hot Dry Rock fields in the world, with temperatures of 500°C at only 3 meters deep. The first configuration includes biphasic thermosyphons as heat exchangers for both sides, leading to a completely passive thermoelectric generator. The second configuration uses fin dissipators as cold-side heat exchangers.
Open Access
Energía sostenible: sin malos humos
(Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, 2019) Samanes Pascual, Javier; Pascual Miqueleiz, Julio María; Berrueta Irigoyen, Alberto; Araiz Vega, Miguel; Catalán Ros, Leyre; Aranguren Garacochea, Patricia; Arricibita de Andrés, David; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniería; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Ingeniaritza
¿Puede España ser sostenible energéticamente? Si alguna vez te has planteado esta pregunta, o quieres saber en qué gastamos la energía y de dónde podría ser obtenida, aquí encontrarás respuestas. Nuestros recursos renovables son inmensos, pero también lo es nuestro consumo. Este libro no solo se centra en analizar la situación actual y las posibilidades que las energías renovables tienen en nuestro país, sino que, presentando de forma clara los datos sobre nuestro gasto energético, permite a cada lector identificar sus mayores consumos, de tal forma que pueda considerar cómo reducirlos. Energía sostenible. Sin malos humos es la adaptación al caso español, actualizando los datos, del libro publicado hace una década por David MacKay en el Reino Unido. La sostenibilidad es hoy en día una preocupación creciente en la sociedad. Pero a menudo este interés se ve contaminado por cifras enormes que resultan muy complicadas de comprender. Además, todos hemos oído hablar en algún momento sobre pequeños gestos al alcance de nuestra mano que podrían permitir un cambio hacia un modelo sostenible. Nada más lejos de la realidad, pequeñas acciones solo permiten pequeños cambios, y el cambio de modelo energético al que nos enfrentamos requiere grandes acciones. Para deshacernos de todo este ruido, en este libro se presentan los números de forma clara y sencilla, utilizando unidades a nuestro alcance y que son comprensibles por todas las personas. Esto permite identificar de una forma mucho más personal los consumos energéticos de nuestro día a día. A lo largo de la primera parte del libro se van construyendo dos columnas: una de color rojo, que representa la agregación de consumos, y otra de color verde, que representa la capacidad de generación. Estas columnas ofrecen una comparación muy visual de la infraestructura renovable que sería necesaria para mantener nuestro ritmo de consumo energético actual. Además, utiliza números «gordos» obtenidos de la experiencia del día a día. Por ejemplo, para calcular la capacidad de generación eólica se parte de una velocidad de viento estimada a partir de la velocidad típica de un ciclista urbano. Toda esta información se encuentra en la primera parte del libro, en los capítulos del 1 al 18. Sin embargo, este libro no se centra únicamente en el análisis de la situación actual, sino que da un paso más y propone alternativas al modelo energético actual con el fin de alcanzar un modelo 100% renovable a medio plazo. Estas medidas incluyen un aumento importante en la potencia renovable instalada, un aumento en la eficiencia energética y algunos ligeros cambios en nuestro estilo de vida que permitan una reducción del consumo. Por supuesto, los tres frentes deben ser atacados al mismo tiempo. Estas propuestas se recogen en la segunda parte del libro, en los capítulos 19 a 32. Por último, este es un libro divulgativo al alcance de todas las personas, que busca transmitir toda la información de forma clara e intuitiva sin perderse en complicados cálculos. Pero si eres de los que les gustan las cuentas, al final del libro encontrarás un apartado en el que se explica de forma rigurosa muchos de los cálculos simples realizados en las primeras partes del libro. Estos apéndices técnicos forman la tercera parte del libro, son los apéndices de la A hasta la H.
Open Access
Study of the degradation of heat exchanger materials in the acidic environment of Teide National Park
(2019) Catalán Ros, Leyre; Pérez Artieda, Miren Gurutze; Berlanga Labari, Carlos; Garacochea Sáenz, Amaia; Rodríguez García, Antonio; Domínguez, Vidal; Montañez, Ana Carolina; Padilla, Germán D.; Pérez, Nemesio M.; Ingeniaritza; Institute for Advanced Materials and Mathematics - INAMAT2; Institute of Smart Cities - ISC; Ingeniería
Supplying power to volcanic monitoring stations constitutes a challenge due to both the access difficulties and the acidic environment associated with volcanoes. ELECTROVOLCAN project is developing thermoelectric generators that make use of the temperature of the available fumaroles to directly supply electricity to the stations in a robust, compact and reliable way. The main element of thermoelectric generators are the thermoelectric modules, based on Seebeck effect. Nonetheless, since the efficiency of these modules increases with the temperature difference between their sides, the introduction of heat exchangers becomes essential. The present study analyses the behavior of different materials used in the construction of the heat exchangers in the acidic environment of Teide National Park.
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
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
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
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
Prospects of autonomous volcanic monitoring stations: experimental investigation on thermoelectric generation from fumaroles
(MDPI, 2020) Catalán Ros, Leyre; Araiz Vega, Miguel; Padilla, Germán D.; Hernández, Pedro A.; Pérez, Nemesio M.; García de la Noceda, Celestino; Albert, José F.; Astrain Ulibarrena, David; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
Fumaroles represent evidence of volcanic activity, emitting steam and volcanic gases at temperatures between 70 and 100 °C. Due to the well-known advantages of thermoelectricity, such as reliability, reduced maintenance and scalability, the present paper studies the possibilities of thermoelectric generators, devices based on solid-state physics, to directly convert fumaroles heat into electricity due to the Seebeck effect. For this purpose, a thermoelectric generator composed of two bismuth-telluride thermoelectric modules and heat pipes as heat exchangers was installed, for the first time, at Teide volcano (Canary Islands, Spain), where fumaroles arise in the surface at 82 °C. The installed thermoelectric generator has demonstrated the feasibility of the proposed solution, leading to a compact generator with no moving parts that produces a net generation between 0.32 and 0.33 W per module given a temperature difference between the heat reservoirs encompassed in the 69–86 °C range. These results become interesting due to the possibilities of supplying power to the volcanic monitoring stations that measure the precursors of volcanic eruptions, making them completely autonomous. Nonetheless, in order to achieve this objective, corrosion prevention measures must be taken because the hydrogen sulfide contained in the fumaroles reacts with steam, forming sulfuric acid.