Open Access
Computational study of geothermal thermoelectric generators with phase change heat exchangers
(Elsevier, 2020) Catalán Ros, Leyre; Araiz Vega, Miguel; Aranguren Garacochea, Patricia; Astrain Ulibarrena, David; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
The use of thermoelectric generators with phase change heat exchangers has demonstrated to be an interesting and environmentally friendly alternative to enhanced geothermal systems (EGS) in shallow hot dry rock fields (HDR), since rock fracture is avoided. The present paper studies the possibilities of the former proposal in a real location: Timanfaya National Park (Canary Islands, Spain), one of the greatest shallow HDR fields in the world, with 5000 m2 of characterized geothermal anomalies presenting temperatures up to 500 °C at only 2 m deep. For this purpose, a computational model based on the thermal-electrical analogy has been developed and validated thanks to a real prototype, leading to a relative error of less than 8%. Based on this model, two prototypes have been designed and studied for two different areas within the park, varying the size of the heat exchangers and the number of thermoelectric modules installed. As a result, the potential of the solution is demonstrated, leading to an annual electricity generation of 681.53 MWh thanks to the scalability of thermoelectric generators. This generation is obtained without moving parts nor auxiliary consumption, thus increasing the robustness of the device and removing maintenance requirements.
Open Access
Thermoelectric generator for high temperature geothermal anomalies: experimental development and field operation
(Elsevier, 2023) Alegría Cía, Patricia; Catalán Ros, Leyre; Araiz Vega, Miguel; Casi Satrústegui, Álvaro; Astrain Ulibarrena, David; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In the current climate and energy context, it is important to develop technologies that permit increase the use of renewable sources such as geothermal energy. Enhancing the use of this renewable source is particularly important in some places, due to its availability and the enormous dependence on fossil fuels, as is the case of the Canary Islands. This work proposes the use of thermoelectric generators with heat exchangers working by phase change to transform the heat from the shallow high temperature geothermal anomalies on the island of Lanzarote directly into electricity, since the use of conventional geothermal power plants would not be possible because they would damage the protected environment. To bring this proposal to reality, this work has succeeded in developing and field-installing a geothermal thermoelectric generator that operates without moving parts thanks to its phase-change heat exchangers. This robust generator do not require maintenance nor auxiliary consumption, and produces a minimal environmental impact, it is noiseless, and the use of water as working fluid makes it completely harmless. The developed device consists of a thermosyphon as hot side heat exchanger, thermoelectric modules and cold side heat exchangers also based in phase change. Tests were carried out in the laboratory at various heat source temperatures and varying the number of thermoelectric modules. It was determined that installing more modules decreases the efficiency per module (from 4.83% with 4 modules to 4.59% with 8 modules at a temperature difference between sources of 235 °C), but for the number of modules tested the total power increases, so the field installation was carried out with 8 modules. After the good results in the laboratory, it was satisfactorily installed at Timanfaya National Park (Lanzarote, Spain) in a borehole with gases at 465 °C. This generator presents a maximum output power of 36 W (4.5 W per module), and is generating 286.94 kWh per year, demonstrating the great potential of the developed thermoelectric generators to build a larger-scale renewable installation.
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
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
Field test of a geothermal thermoelectric generator without moving parts on the Hot Dry Rock field of Timanfaya National Park
(Elsevier, 2023) Catalán Ros, Leyre; Alegría Cía, Patricia; Araiz Vega, Miguel; Astrain Ulibarrena, David; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Although in the last years thermoelectric generators have arisen as a solution to boost geothermal power generation, tests on field are still scarce. The vast majority of the available studies focus on computational simulations or laboratory experiments, mainly with active heat exchangers that require pumps or fans, and, consequently, present moving parts and auxiliary consumption. The present paper demonstrates for the first time the suitability of a geothermal thermoelectric generator (GTEG) with passive phase change heat exchangers, and therefore, without moving parts nor auxiliary consumption, on the shallow Hot Dry Rock (HDR) field of Timanfaya National Park (Canary Islands, Spain), where 173 °C air anomalies can be found. The device has been in operation without maintenance for 2 years now, producing more than 520 kWh of energy. In terms of power generation, since the installed device is in turn composed of two prototypes with 10 and 6 thermoelectric modules, it has been confirmed that installing more modules leads to a lower generation per module, although total generation can be higher. In fact, the prototype with 10 thermoelectric modules generated a maximum of 20.9 W (2.09 W per module) with a temperature difference between sources of 158 °C, while the prototype with 6 thermoelectric modules obtained 16.67 W (2.78 W per module) under the same conditions. These results open the door for a large-scale exploitation thanks to the intrinsic advantages of modularity, reliability, robustness, and minimal environmental impact of the developed device.