Jaziri, Nesrine; Boughamoura, Ayda; Müller, Jens; Mezghani, Brahim; Tounsi, Fares; Ismail, Mohammed: A comprehensive review of thermoelectric generators: technologies and common applications Original published in: Energy reports. - Amsterdam [u.a.] : Elsevier. - 6 (2020), Supplement 7, p. 264-287. Original published: 2019-12-24 ISSN: 2352-4847 DOI: 10.1016/j.egyr.2019.12.011 [Visited: 2021-02-22] This work is licensed under a Creative Commons Attribution 4.0 International license. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/ TU Ilmenau | Universitätsbibliothek | ilmedia, 2021 http://www.tu-ilmenau.de/ilmedia Energy Reports 6 (2020) 264–287 Contents lists available at ScienceDirect Energy Reports journal homepage: www.elsevier.com/locate/egyr Review article A comprehensive review of Thermoelectric Generators: Technologies and common applications ∗ Nesrine Jaziri a,b,c, , Ayda Boughamoura d, Jens Müller b, Brahim Mezghani a, Fares Tounsi a, Mohammed Ismail e a Micro Electro Thermal Systems (METS) Group, Ecole Nationale d'Ingénieurs de Sfax (ENIS), Université de Sfax, 3038, Sfax, Tunisia b Electronics Technology Group, Institute of Micro and Nanotechnologies MacroNano, Technische Universität Ilmenau, Germany, Gustav-Kirchhoff-Straße 1, 98693, Ilmenau, Germany c Université de Sousse, Ecole Nationale d'Ingénieurs de Sousse, 4023, Sousse, Tunisia d Université de Monastir, Ecole Nationale d'Ingénieurs de Monastir (ENIM), Laboratoire d'Etude des Systèmes Thermiques et Energétiques (LESTE), LR99ES31, 5019, Monastir, Tunisia e Department of Electrical and Computer Engineering, College of Engineering, Wayne State University, Detroit, MI48202, USA article info a b s t r a c t Article history: Power costs increasing, environmental pollution and global warming are issues that we are dealing Received 18 July 2019 with in the present time. To reduce their effects, scientists are focusing on improving energy Received in revised form 7 December 2019 harvesting-based power generators. Thermoelectric generators (TEGs) have demonstrated their ability Accepted 10 December 2019 to directly convert thermal energy into an electrical one via the Seebeck effect. Also, they are Available online 24 December 2019 environmentally friendly because they do not contain chemical products, they operate silently because Keywords: they do not have mechanical structures and/or moving parts, and they can be fabricated on many Thermoelectric generator types of substrates like silicon, polymers, and ceramics. Furthermore, TEGs are position-independent, MEMS/LTCC technologies present a long operating lifetime and are suitable for integration into bulk and flexible devices. Wearable devices This paper presents in-depth analysis of TEGs, starting by an extensive description of their working WSNs principle, types (planar, vertical and mixed), used materials, figure of merit, improvement techniques Biomedical including different thermoelectric materials arrangement (conventional, segmented and cascaded), Vehicle engine Aerospace and used technologies and substrates types (silicon, ceramics and polymers). This manuscript also describes the exploitation of TEGs in various fields starting from low-power applications (medical and wearable devices, IoT: internet of things, and WSN: wireless sensor network) to high-power applications (industrial electronics, automotive engines, and aerospace). ' 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Contents 1. Introduction....................................................................................................................................................................................................................... 264 2. Thermoelectric generators basis ..................................................................................................................................................................................... 265 2.1. Main design approaches ..................................................................................................................................................................................... 265 2.2. Fabrication technologies ..................................................................................................................................................................................... 266 2.3. Figure of merit and thermocouples arrangement............................................................................................................................................ 266 3. Common applications ...................................................................................................................................................................................................... 270 3.1. In medical and wearable devices....................................................................................................................................................................... 270 3.2. In wireless sensor networks............................................................................................................................................................................... 271 3.3. In industrial electronic devices .......................................................................................................................................................................... 274 3.4. In automobile engines......................................................................................................................................................................................... 276 3.5. In aerospace.......................................................................................................................................................................................................... 279 4. Conclusion ......................................................................................................................................................................................................................... 282 Declaration of competing interest.................................................................................................................................................................................. 284 References ......................................................................................................................................................................................................................... 284 1. Introduction ∗ Corresponding author. E-mail address: [email protected] (N. Jaziri). The uses of natural gas, fuel, and coal to generate electric- ity have become detrimental for human-beings because of their https://doi.org/10.1016/j.egyr.2019.12.011 2352-4847/' 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). N. Jaziri, A. Boughamoura, J. Müller et al. / Energy Reports 6 (2020) 264–287 265 adverse effects on atmospheric pollution and global warming. where N is the number of connected thermocouples, αAB is the Nevertheless, according to the US Energy Information Administra- Seebeck coefficients of the two joined materials A and B forming tion (EIA), electricity generated from power plants using natural the thermocouple (αAB D αA − αB). When the TCs are connected gas was increasing every year with 28% in 2014, 35% in 2018 and electrically in series, the total internal resistance is proportional 36% in 2019 (U.E.I. Administration, 2018). Furthermore, the world to their number N. So, even though a high number of TCs will consumption and production of liquid fuels increased from 94 increase the voltage delivered by the TEGs, its impact on the million barrels per day in mid-2014 to 100 million in mid-2018, internal resistance is adverse (Fig. 1b). Indeed, the increases of which is leading to an ever-increasing energy cost. To cope with series connected TCs number will lead to a rise of the TEG's this global growth in the consumption of fossil fuels, quite expen- internal resistance which is expressed as (Wang et al., 2013): sive and polluting, other forms of environment-friendly energies ( ) ρALA ρBLB ρCLC arose in the last decades. Indeed, Nicolas Tesla once said: ``Electric RTEG D N C C 2 (2) power is everywhere present in unlimited quantities and can drive SA SB SC the world's machinery without the need of coal, oil, gas or any other where ρA, ρB and ρC are, respectively, the electrical resistivity of the common fuels''. This quote anticipates the current new trend of the materials A, B and the metallic contact. LA and LB are the of harvesting natural energy from the environment to provide thermocouple arms lengths crossed by the heat flow, and LC is unlimited, sustainable, green and cheap electrical power. Nowa- the contact length. SA; SB and SC are, respectively, the A and B days the growing interest in using renewable energy, that can thermocouples and contacts cross-sectional areas. The delivered be scavenged from several natural abandoned sources such as RF output power of the generator is given by: radiation, thermal, solar, vibratory/mechanical energy, etc., and RL converting it into electrical one to supply the world's electronic P D V2 (3) out . /2 devices and machinery, is growing exponentially. RTEG C RL Thermal energy is one of the abundantly available energies where