Development Of Thermoelectric Generators Research Articles

Artificial neural network for geometric design and optimization of three-stage segmented thermoelectric generators

The quest for greener power generation is a major driver for the development of thermoelectric generators. Segmented thermoelectric generators are an effective means to significantly improve the efficiency. Given the complexity of multiple geometric parameters in a three-stage segmented thermoelectric generator, the conventional practice is to use software for numerical simulation and geometric optimization before manufacturing. While this method saves time and increases production efficiency, it lacks reproducibility. However, artificial neural networks offer a solution to this problem by further reducing the computational time required. In this work, artificial neural networks are used to replace these processes by using optimization algorithms to guide the neural network in calculating the optimal thermoelectric conversion efficiency. First, a dataset of 3000 three-stage segmented thermoelectric generator configurations is generated using a COMSOL simulation model. A backpropagation neural network is then constructed and trained on this dataset, using particle swarm optimization to adjust the network weights and computational parameters. The trained neural network accurately predicted the conversion efficiency of three-stage segmented thermoelectric generators over various temperature ranges. When compared to COMSOL calculations, the values are generally within the 95% confidence interval of the backpropagation neural network predictions. Finally, genetic algorithms and artificial fish swarm algorithms are used to drive the neural network to calculate the optimal thermoelectric conversion efficiency. Compared to COMSOL, the thermoelectric conversion efficiency increased by 2.48% and 3.61%, respectively. Despite the initial dataset construction time, the artificial neural network can determine the optimal geometric structure and conversion efficiency of a three-stage segmented thermoelectric generator within 5 min. This method is expected to significantly improve the design and production efficiency of three-stage segmented thermoelectric generators.

Feasibility of a Small, Low-Power RTG Concept Utilizing a GPHS Heat Source

Over the past 25 years, the average cadence of National Aeronautics and Space Administration (NASA) missions that employ radioisotope thermoelectric generators (RTGs) or other radioisotope power systems (RPSs) is approximately one per decade. Currently, the only flight-qualified RPS in the NASA inventory for space power applications is the multi-mission RTG, which has a beginning-of-life (BOL) power output of approximately 120 W(electric). In addition, NASA and the U.S. Department of Energy also manage the Next Generation Radioisotope Thermoelectric Generator Development Project, with a projected BOL power of around 245 W(electric). However, if a lower-power RPS unit was available, would there be sufficient mission pull to increase the cadence of RPS-powered missions? We believe the answer to this question is yes, which drove the evolution of a concept study that examines the feasibility of a low-power RPS based on a single general purpose heat source (GPHS) that could be developed rapidly with low risk and cost. This paper discusses the results of a concept study of an RPS system that utilizes novel ruggedized silicon germanium thermoelectric modules with a projected BOL power of 15 W(electric). This new RTG design could help enable a new class of low-powered space exploration missions for NASA, the European Space Agency, or commercial applications. In addition, this paper addresses the next steps required to evolve the concept beyond its current status to conceptual design.

Screening strategy for developing thermoelectric interface materials.

Thermoelectric interface materials (TEiMs) are essential to the development of thermoelectric generators. Common TEiMs use pure metals or binary alloys but have performance stability issues. Conventional selection of TEiMs generally relies on trial-and-error experimentation. We developed a TEiM screening strategy that is based on phase diagram predictions by density functional theory calculations. By combining the phase diagram with electrical resistivity and melting points of potential reaction products, we discovered that the semimetal MgCuSb is a reliable TEiM for high-performance MgAgSb. The MgCuSb/MgAgSb junction exhibits low interfacial contact resistivity (ρc <1 microhm square centimeter) even after annealing at 553 kelvin for 16 days. The fabricated two-pair MgAgSb/Mg3.2Bi1.5Sb0.5 module demonstrated a high conversion efficiency of 9.25% under a 300 kelvin temperature gradient. We performed an international round-robin testing of module performance to confirm the measurement reliability. The strategy can be applied to other thermoelectric materials, filling a vital gap in the development of thermoelectric modules.

Development of Thermoelectric Generator for Energy Saving Device Using Exhaust Waste Heat in Patrol Boat

Development of Thermoelectric Generator for Energy Saving Device Using Exhaust Waste Heat in Patrol Boat

Hybrid Photovoltaic/Thermoelectric Systems for Round-the-Clock Energy Harvesting.

Due to their emission-free operation and high efficiency, photovoltaic cells (PVCs) have been one of the candidates for next-generation "green" power generators. However, PVCs require prolonged exposure to sunlight to work, resulting in elevated temperatures and worsened performances. To overcome this shortcoming, photovoltaic-thermal collector (PVT) systems are used to cool down PVCs, leaving the waste heat unrecovered. Fortunately, the development of thermoelectric generators (TEGs) provides a way to directly convert temperature gradients into electricity. The PVC-TEG hybrid system not only solves the problem of overheated solar cells but also improves the overall power output. In this review, we first discuss the basic principle of PVCs and TEGs, as well as the principle and basic configuration of the hybrid system. Then, the optimization of the hybrid system, including internal and external aspects, is elaborated. Furthermore, we compare the economic evaluation and power output of PVC and hybrid systems. Finally, a further outlook on the hybrid system is offered.

A Novel Method for Thermoelectric Generator Based on Neural Network

The growing need for renewable energy and zero carbon dioxide emissions has fueled the development of thermoelectric generators with improved power generating capability. Along with the endeavor to develop thermoelectric materials with greater figures of merit, the geometrical and structural optimization of thermoelectric generators is equally critical for maximum power output and efficiency. Green energy strategies that are constantly updated are a viable option for addressing the global energy issue while also protecting the environment. There have been significant focuses on the development of thermoelectric modules for a range of solar, automotive, military, and aerospace applications in recent years due to various advantages including as low vibration, great reliability and durability, and the absence of moving components. In order to enhance the system performance of the thermoelectric generator, an artificial neural network (ANN) based algorithm is proposed. Furthermore, to achieve high efficiency and system stability, a buck converter is designed and deployed. Simulation and experimental findings demonstrate that the suggested method is viable and available, and that it is almost similar to the real value in the steady state with the least power losses, making it ideal for vehicle exhaust thermoelectric generator applications. Furthermore, the proposed hybrid algorithm has a high reference value for the development of a dependable and efficient car exhaust thermoelectric generating system.

Thermoelectric Generator: Materials and Applications in Wearable Health Monitoring Sensors and Internet of Things Devices

AbstractWearable sensors and biomedical devices have attracted a great deal of attention among users. Despite technological advancements in this field, a mixture of both progress and setbacks has been witnessed. The limited battery life of these devices for long‐term operation remains a major challenge. In this context, thermoelectric generators have emerged as potential candidates for harvesting energy from temperature gradients to power wearable sensors and devices. This review focuses on the working mechanism of a thermoelectric generator, as well as the current progress of a variety of promising and widely used inorganic and organic thermoelectric materials. Encouragingly, the highest ZT values of 2.27, 2.5, 2.8, 2.3, and 1.85 are obtained for bismuth telluride, lead telluride, tin selenide, copper selenide, and magnesium antimonide, respectively, at various temperature ranges. Meanwhile, organic materials such as poly (3,4‐ethylenedioxythiophene) polystyrene sulfonate, polyaniline composite, and graphdiyne showed the highest ZT values of 0.75, 0.74, and 4.8, respectively, at near‐room temperature. Furthermore, numerous novel thermoelectric generator‐powered wearable health monitoring sensors and Internet of Things devices are also presented. Finally, the current challenges and perspectives on the future development of thermoelectric generator, in particular for efficient materials and self‐powered devices, are also discussed.

Artificial neural network enabled accurate geometrical design and optimisation of thermoelectric generator

The ever-increasing demand for renewable energy and zero carbon dioxide emission have been the driving force for the development of thermoelectric generators with better power generation performance. Alongside with the effort to discover thermoelectric materials with higher figure-of-merit, the geometrical and structural optimisation of thermoelectric generators are also essential for maximized power generation and efficiency. This work demonstrates for the first time the application of artificial neural network, a deep learning technique, in forward modelling the maximum power generation and efficiency of a thermoelectric generator and its application in the generator design and optimisation. After training using a dataset containing 5000 3-D finite element method based simulations, the artificial neural networks with 5 layers and 400 neurons per layer demonstrate extremely high prediction accuracy over 98% and are able to operate under both constant temperature difference and heat flux conditions while taking into account of the contact electrical resistance, surface heat transfer and other thermoelectric effects. Coupling with genetic algorithm, the trained artificial neural networks can optimise the leg height, leg width, fill factor and interconnect height of the thermoelectric generator for different operating and contact resistance conditions. With almost identical optimised values obtained, our neural networks can realise geometrical optimisation within 40 s for each operating condition, which is averagely over 1,000 times faster than the optimisation performed by finite element method. The up-front computational time for the neural network can be recovered when more than 2 optimisations are needed. The successful application of this data-driven approach in this work clearly represents a new and cost-effective avenue for conducting system level design and optimisation of thermoelectric generators and other energy harvesting technologies.

Fabrication and testing of Mg2Si1-xSnx based thermoelectric generator module

Mg2Si1-xSnx solid solutions have been of great interest for the advantages they hold as prospective thermoelectric (TE) materials. Despite this, the development of thermoelectric generator (TEG) modules fabricated entirely from these materials has not been reported. In this work, a TEG module consisting of Mg2Si0.3Sn0.7n and p legs has been fabricated, and its thermoelectric generator characteristics were studied as a function of the applied temperature gradient. For the n and p doped legs, compositions with peak zT values of ~1.6 and ~0.44, respectively, were synthesized using induction assisted melt synthesis. Mono-block sintering technique was adopted as a single-step compaction cum contacting technique. In order to create low resistive well-bonded contacts, an additional interfacial layer was placed between the TE material and the outer Cu layer. The TE legs were assembled into a skeletal module comprising of two unicouples electrically connected by Cu bridges. The transient state I-V characteristics of the TE device were measured at various temperature gradients (ΔT). A maximum power output value of 192mW (corresponds to a power density of 0.52 W/cm2) and open-circuit voltage of 200 mV were measured for a ΔT of 331 K. The measured I-V and power output data showed good agreement with the simulated power output values with a variation of only 3% until ΔT = 300 K and 5% at ΔT = 331 K. The TE module simulator was further used to estimate the device efficiency (η) and indicated a maximum value of 5%. This is the highest reported conversion efficiency of a silicide based module (in the studied temperature range) and highlights the possibility of their commercialization in the near future.

Enhancement of p-type thermoelectric power factor by low-temperature calcination in carbon nanotube thermoelectric films containing cyclodextrin polymer and Pd

The p-type properties of carbon nanotubes (CNTs) in organic thermoelectric devices need urgent improvement for large-scale, low-grade thermal energy applications. Here, we present a suitable approach to significantly enhance the power factor (PF) by increasing the electrical conductivity through the low-temperature calcination-induced pyrolysis of the insulating γ-cyclodextrin polymer (PγCyD), which is used as a solubilizer of film-like CNTs. The low-temperature calcination method, which can be used to realize good electrical contact between CNT bundles, shows enhancement behavior as a universal phenomenon for not only PγCyD but also other commonly used polymers for CNT films. To moderate the calcination temperature, the Pd catalyst was added, and the optimal temperature was reduced from 340 °C to 250 °C. Consequently, the PF value of the CNT film was 570 μW m−1 K−2, which was found to be more than twice that of the original CNT film. In addition, we demonstrated the energy harvesting capability of a thermoelectric generator based on this p-type CNT film; a thermoelectric generator with 10 p-type thermoelectric elements showed a maximum power output of 10.3 μW with a temperature difference of 75 °C, which is comparable to the maximum power output of some of the best single-component organic thermoelectric devices demonstrated to date. This outstanding output power shows that easy-to-handle CNT films with low-temperature heat treatment can open new avenues for the development of thermoelectric generators.

Bismuth Telluride/Half‐Heusler Segmented Thermoelectric Unicouple Modules Provide 12% Conversion Efficiency

AbstractThe rapid enhancement of the thermoelectric (TE) figure‐of‐merit (zT) in the past decade has opened opportunities for developing and transitioning solid state waste heat recovery systems. Here, a segmented TE device architecture is demonstrated in conjunction with heterogeneous material integration that results in high unicouple‐level conversion efficiency of 12% under a temperature difference of 584 K. This breakthrough is the result of success in fabricating bismuth telluride/half‐Heusler segmented TE unicouple modules using a “hot‐to‐cold” fabrication technique that provides significantly reduced electrical and thermal contact resistance. Extensive analytical and finite element modeling is conducted to provide an understanding of the nature of thermal transport and contributions arising from various thermal and physical parameters. Bismuth telluride/half‐Heusler based segmented thermoelectric generators (TEGs) can provide higher practical temperature difference with optimum average zT across the whole operating range. These results will have immediate impact on the design and development of TEGs and in the general design of devices based upon heterostructures that take advantage of gradients in the figure of merit.

Holistic Development of Thermoelectric Generators for Automotive Applications

One of the major challenges of the future automotive development is to achieve the required reductions of the CO2 emissions. Therefore, it is necessary to investigate all potential technologies for efficiency improvement. In a combustion engine, about 2/3 of the chemical energy of the fuel is dissipated as waste heat. Due to its high temperature level, the waste heat in the exhaust gas is very promising for the technology of thermoelectric generators (TEG). In this work the methodology for a holistic TEG optimization for automotive vehicle applications will be presented. Thereby, all system interactions between the vehicle and the TEG are modelled and the CO2 reduction can be optimized within the vehicle system. Moreover the costs are calculated for each TEG design, and the method realizes an optimization of the cost–benefit ratio in a direct way. The optimization method is applied with a highly integrated TEG design, which has been developed to be compact and lightweight. Through the combination of improvements in TEG design and system optimization, a gravimetric power density of 267 W/kg and a volumetric power density of 478 W/dm^3 could be achieved. These power densities are about 900% and 700%, respectively, higher than the state of the art. The optimization method was applied exemplarily to a conventional vehicle (Volkswagen Golf VII) and a hybrid vehicle (Opel Ampera/Chevrolet Volt). As a result, reductions in consumption and CO2 emissions of up to 2.2% for the conventional and 3.4% for the hybrid vehicle could be achieved within the worldwide harmonized light duty driving test cycle. The cost–benefit optimum is 81.3 €/(g/km) for the conventional vehicle and 54.8 €/(g/km) for the hybrid vehicle in charge sustaining mode.

(Invited) Tubular Thermoelectric Generator for Enhanced Power Generation

Thermoelectric generators are interesting energy harvesting option due to its clean nature, silent operation and it harnesses the power from otherwise wasted heat. While most of the research has been directed toward high thermoelectric performance based material innovation, we have focused on its architecture and how to connect hot and cold ends when they are far apart. From that perspective, we have devised an effective integration strategy to roll-up otherwise ultra-thin layers of thermoelectric materials to form tubular architecture and to integrate them in array for high power thermoelectric generator development. We have used widely used thermoelectric materials such as bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3). We also offer an analytical methodology to deduce the effective mechanics of the strain associated with the thermoelectric materials and the used polymeric materials (as stressor and as support layers). Experimentally we have shown seamless 4 cm (and further expandable) tubular arrays of thermoelectric piles. Such a long length allows us to connect to far apart hot and cold end for higher power generation as we also maintain higher temperature difference for longer time. We also compare its effectiveness with solid slab and wire of the same tube from its performance and cost perspective. At the initial stage we report up to 5 μW (8 pairs of p and n-type thermopiles) through a temperature difference of 60 °C. We also show how this can be improved further and potential integration strategy with 2D material system.

Development of Thermoelectric generator based on Ionic Liquids for high temperature applications

Current, Seebeck-coefficients (SE) and maximal power output (Pmax) of thermoelectric generators using Ionic Liquids (ILs) were measured to determine the optimal temperature window for their use as thermoelectric generators (TEGs) in the range between room temperature (RT) and 300°C. The IL was sandwiched in a thermoelectric cell between a heated and a cooled electrode, allowing temperature-dependent current, voltage, and power-output characterization. Dissolving redox-couples (e.g. I2/I-) enables charge transfer from the IL to the electrode. It was found, that protic ILs degraded irreversibly at 140°C. Aprotic ILs, however, in combination with LiI/I2 redox couples exhibit higher temperature stability being finally limited either by redox-couple-electrode reactions, by temperature-induced redox couple degradation or by reaching at the boiling point at about 280°C. ILs being solid at room temperature could successfully be activated, as soon as at least the hot electrode of the set-up was heated above the melting point (m.p.) of the IL. As a striking observation, the thermo-voltage (linked to the SE) changes the sign as soon as the cold electrode was kept below the m.p. when Ethylammonium tetrafluoroborate (EA BF4) was used. Another IL, Tetrabutylammonium tetrafluoroborate (TBA BF4) exhibited in the full temperature range negative SE as high as 7 mV/K.

Method and Apparatus for Determining Operational Parameters of Thermoelectric Modules

The main aim of this work was to construct and test an apparatus for characterization of high temperature thermoelectric modules to be used in thermoelectric generator (TEGs) applications. The idea of this apparatus is based on very precise measurements of heat fluxes passing through the thermoelectric (TE) module, at both its hot and cold sides. The electrical properties of the module, under different temperature and load conditions, were used to estimate efficiency of energy conversion based on electrical and thermal energy conservation analysis. The temperature of the cold side, Tc, was stabilized by a precise circulating thermostat (≤0.1°C) in a temperature range from 5°C to 90°C. The amount of heat absorbed by a coolant flowing through the heat sink was measured by the calibrated and certified heat flow meter with an accuracy better than 1%. The temperature of the hot side, Th, was forced to assumed temperature (Tmax = 450°C) by an electric heater with known power (Ph = 0–600 W) with ample thermal insulation. The electrical power was used in calculations. The TE module, heaters and cooling plate were placed in an adiabatic vacuum chamber. The load characteristics of the module were evaluated using an electronically controlled current source as a load. The apparatus may be used to determine the essential parameters of TE modules (open circuit voltage, Uoc, short circuit current, Isc, internal electrical resistance, Rint, thermal resistance, Rth, power density, and efficiency, η, as a function of Tc and Th). Several commercially available TE modules based on Bi2Te3 and Sb2Te3 alloys were tested. The measurements confirmed that the constructed apparatus was highly accurate, stable and yielded reproducible results; therefore, it is a reliable tool for the development of thermoelectric generators.

Current state of thermoelectric material science and the search for new effective materials

The reasons for the recent increased interest in thermoelectricity are considered. Modern thermoelectric materials for practical use are reviewed. Criteria to be met by effective thermoelectric materials are analyzed. It is shown that the solid-solution method has almost completely exhausted itself. Directions in the search for new thermoelectric material classes are analyzed. The development of new bulk thermoelectric materials is connected with the search for and design of materials in which the peculiarities of the structure determine the strong scattering of phonons and decrease in thermal conductivity while maintaining high transport properties of charge carriers. The concept ‘phonon glass–electron crystal’ is of practical interest. Scientific and technological advances over the last decade give hope that more effective thermoelectric materials will be developed in the nearest future. One of the perspective applications of new thermoelectric materials is connected with the development of thermoelectric generators with segmented thermoelectric elements.

Thermoelectric generators: Linking material properties and systems engineering for waste heat recovery applications

Waste-heat recovery with thermoelectric power generators can improve energy efficiency and provide distributed electricity generation. New thermoelectric materials and material performance improvements motivate development of thermoelectric generators for numerous applications with excess exhaust and process heat. However, thermoelectric generator product development requires solving coupled challenges in materials development and systems engineering. This review discusses these challenges and indicates ways system-level performance relies on more factors than traditional thermoelectric material performance metrics alone. Relevant thermo-mechanical and chemical material properties, system components such as thermal interface materials and heat exchangers, and system form factors are examined. Manufacturing processes and total system cost components are evaluated to provide product development and commercial feasibility contexts.

Design and implementation of a measurement system for automatically measurement of electrical parameters of thermoelectric generators

ABSTRACTThe continues development of thermoelectric generators causes a permanent improvement of their characteristics. New types of thermoelectric generators can work at temperatures up to 1000 K. With this, special measurement equipment is needed to control the electrical parameters of the new developed specimens. The devices must be tested over the whole range of operating temperatures. For each temperature value a series of electrical measurements has to be performed. To establish the maximal output power of the thermoelectric generators, a load resistor with variable resistance has to be connected to the output of thermoelectric generator. The measurement system should measure the electrical current through the load resistor and the voltage over this resistor to determine the device parameters. A large amount of measurement data have to be collected and processed to evaluate the electrical characteristics of the specimen and to present them in graphical form, suitable for the comparison with others specimens.

TEG On-Vehicle Performance and Model Validation and What It Means for Further TEG Development

A high-temperature thermoelectric generator (TEG) was recently integrated into two passenger vehicles: a BMW X6 and a Lincoln MKT. This effort was the culmination of a recently completed Department of Energy (DOE)-sponsored thermoelectric (TE) waste heat recovery program for vehicles (award #DE-FC26-04NT42279). During this 7-year program, several generations of thermoelectric generators were modeled, designed, built, and tested at the couple, engine, and full-device level, as well as being modeled and integrated at the vehicle level. In this paper, we summarize the history of the development efforts and results achieved during the project, which is a motivation for ongoing research in this field. Results are presented and discussed for bench, engine dynamometer, and on-vehicle tests conducted on the current-generation TEG. On the test bench, over 700 W of power was produced. Over 600 W was produced in on-vehicle tests. Both steady-state and transient models were validated against the measured performance of these TEGs. The success of this work has led to a follow-on DOE-sponsored TE waste heat recovery program for passenger vehicles focused on addressing key technical and business-related topics that are meant to enable TEGs to be considered as a viable automotive product in the future.

A review on thermocouple for power generation

The factor that has slowed the emergence of thermoelectric generators as a viable alternative for the production of electricity is the relatively low energy conversion efficiency, which is only about 5% to 7% whereas photovoltaic (solar panels) are now in excess of 20%. Unfortunately this low efficiency rating also had a negative impact on further research and development of thermoelectric generators. However, comparing TEGs to PV panels by the watt rating is a grossly inaccurate comparison and makes it appear that TEGs are simply too expensive of an option. In this review article the development and drawbacks of thermocouple at each stage has revealed that greenhouse gases produced by solar radiation can be used as heat source in a thermocouple.