Use Of Thermoelectric Generators Research Articles

A reconfigurable architecture for maximizing energy harvesting of thermoelectric generators in non-stationary conditions

The use of Thermoelectric Generators (TEGs) has proliferated across a multitude of applications for energy harvesting. As more modules are employed to recover greater amounts of energy, the temperature mismatch between them increases. This results in each module operating at a distinct maximum power point, thereby reducing the overall system efficiency. Furthermore, in dynamic applications such as automotive scenarios, the temperatures of the thermoelectric generators are not constant, and the maximum power point accordingly shifts. A fixed architecture is unable to cope with these fluctuating situations. Therefore, this paper introduces a reconfigurable architecture capable of harnessing maximum energy at any given moment, improving energy recovery compared to a fixed architecture. Optimization techniques, lean methodologies, and clustering approaches are employed to efficiently design the reconfigurable TEG, which enables modification of the electrical connections inside the TEG modules and the number of Maximum Power Point Tracking (MPPT) modules. A use case is presented where the reconfigurable TEG is compared with fixed, yet optimized, TEG configurations under mixed driving modes. In this specific case, the results demonstrate that the reconfigurable TEG achieves enhanced performance in dynamic environments with two MPPTs under mixed scenarios, reaching an efficiency of 96.3% and a 0.29% improvement in energy recovery.

Phase transitions and degradation/oxidation mechanisms in lead-free CsSnI3 halide perovskites

Abstract Halide perovskites possess ultra-low thermal conductivity and show high potential for thermoelectric devices. The chemical properties and molecular structure of halide perovskite materials are not completely stable under ambient conditions, which hinders their use in thermoelectric generators. Changes in the properties of bulk halide perovskite thermoelectrics are accompanied by partial phase transitions and surface oxidation processes. In this paper, we conducted a comprehensive study of the transport and structural properties of CsSnI3, which were pristine by vacuum melting followed by spark plasma sintering. The research results on the electrical transport of these materials revealed that exposure to an inert atmosphere does not deteriorate stability and the properties of the materials remain unchanged. However, prolonged exposure to air leads to a significant degradation of the electrical transport properties. Contrary to thin-film samples, the shift to the double perovskite structure from the perovskite one is limited to a specific surface layer. This change significantly influences the electrical transport of the material while maintaining the essential properties of both perovskite types.

Mixed Ionic-Electronic Conducting Hydrogels with Carboxylated Carbon Nanotubes for High Performance Wearable Thermoelectric Harvesters.

Mixed ionic-electronic conducting (MIEC) thermoelectric (TE) materials offer higher ionic conductivity and ionic Seebeck coefficient compared to those of purely ionic-conducting TE materials. These characteristics make them suitable for direct use in thermoelectric generators (TEGs) as the charge carriers can be effectively transported from one electrode to the other via the external circuit. In the present study, MIEC hydrogels are fabricated via the chemical cross-linking of polyacrylamide (PAAM) and polydopamine (PDA) to form a double network. In addition, electrically conducting carboxylated carbon nanotubes (CNT-COOH) are dispersed evenly within the hydrogel via sonication and interaction with the PDA. Moreover, the electrical properties of the hydrogel are further improved via the in situ polymerization of polyaniline (PANI). The presence of CNT-COOH facilitates the ionic conductivity and enhances the ionic Seebeck coefficient via ionic-electronic interactions between sodium ions and carboxyl groups on CNT-COOH, which can be observed in X-ray photoelectron spectroscopy results, thereby promoting the charge transport properties. As a result, the optimum device exhibits a remarkable ionic conductivity of 175.3 mS cm-1 and a high ionic Seebeck coefficient of 18.6 mV K-1, giving an ionic power factor (PFi) of 6.06 mW m-1 K-2 with a correspondingly impressive ionic figure of merit (ZTi) of 2.65. These values represent significant achievements within the field of gel-state organic TE materials. Finally, a wearable module is fabricated by embedding the PAAM/PDA/CNT-COOH/PANI hydrogel into a poly(dimethylsiloxane) mold. This configuration yields a high power density of 171.4 mW m-2, thus highlighting the considerable potential for manufacturing TEGs for wearable devices capable of harnessing waste heat.

Processability of Thermoelectric Ultrafine Fibers via Electrospinning for Wearable Electronics.

Polymer-based thermoelectric generators hold great appeal in the realm of wearable electronics as they enable the utilization of body heat for power generation. Fibers produced from conducting polymers for use in thermoelectric generators have high porosity and good flexibility, providing comfort-based performance advantages over thin films for wearable electronics. Some fiber processing techniques have been explored to produce textile-based thermoelectric generators; however, they fail to approach the conductivities of polymeric thin films. Ultrafine fibers solution processed through electrospinning yield fiber diameters on the nanoscale, allowing for high surface area to volume ratios and thus low thermal conductivity; however, a number of processing challenges in electrospinning conducting polymers limit the success of preparing high performing thermoelectric textiles. In this work, the specific processing challenges inherent to electrospinning conducting polymers are addressed for both n- and p-type materials. For the p-type polymer, 63 wt % PEDOT:PSS fibers are fabricated through solution formulation improvements yielding a conductivity of 3 S/cm and a power factor of 0.1 μW/mK2. The first of their kind n-type poly(NiETT)/PVA electrospun fibers were created yielding a conductivity of 0.11 S/cm and a power factor of 0.0036 μW/mK2. These nonwoven ultrafine fiber mats show progress toward achieving textile-based thermoelectric materials with equivalent performance of comparable polymeric thin films. This work shows the feasibility of creating ultrafine fibers for use in thermoelectric generators through electrospinning including the first demonstration of poly(NiETT)/PVA fibers.

Evolution of Thermoelectric Generators: From Application to Hybridization.

Considerable thermal energy is emitted into the environment from human activities and equipment operation in the course of daily production. Accordingly, the use of thermoelectric generators (TEGs) can attract wide interest, and it shows high potential in reducing energy waste and increasing energy recovery rates. Notably, TEGs have aroused rising attention and been significantly boosted over the past few years, as the energy crisis has worsened. The reason for their progress is that thermoelectric generators can be easily attached to the surface of a heat source, converting heat energy directly into electricity in a stable and continuous manner. In this review, applications in wearable devices, and everyday life are reviewed according to the type of structure of TEGs. Meanwhile, the latest progress of TEGs' hybridization with triboelectric nanogenerator (TENG), piezoelectric nanogenerator (PENG), and photovoltaic effect is introduced. Moreover, prospects and suggestions for subsequent research work are proposed. This review suggests that hybridization of energy harvesting, and flexible high-temperature thermoelectric generators are the future trends.

Thermoelectric generator for high temperature geothermal anomalies: Experimental development and field operation

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.

Printing Liquid Metal Elastomer Composites for High‐Performance Stretchable Thermoelectric Generators

AbstractContinuous powering of wearable electronics and personalized biomonitoring systems remains a great challenge. One promising solution is the use of thermoelectric generators (TEGs) that convert body heat to electricity. These energy harvesters must conform to curved surfaces and minimize thermal barriers to maintain efficiency while still exhibiting durability under large deformations. Here, highly efficient, stretchable thermoelectric generators made of inorganic semiconductors and printed multifunctional soft matter are introduced. Liquid metal elastomer composites with tailored microstructures are printed as highly conductive thermal interface materials and stretchable interconnects. Additionally, elastomer composites with hollow microspheres are formulated to print a deformable and lightweight thermal insulator within the device. These stretchable thermoelectric wearables show an excellent performance by generating an open‐circuit voltage of 392 mV and a power density of ≈650 µW cm−2 at ∆T = 60 °C and withstanding more than 15 000 stretching cycles at 30% strain. Furthermore, the additive manufacturing process is leveraged by direct writing of the TEGs on textiles to demonstrate their seamless integration and by 3D printing of stretchable heatsinks to maintain a large temperature gradient across the device and to study the effect of convective heat transfer on device performance.

Efficiency Measurement and Modeling of a High‐Performance Mg2(Si,Sn)‐Based Thermoelectric Generator

Mg2(Si,Sn) is an attractive material class due to its excellent thermoelectric (TE) properties, its eco‐friendly constituents, its low mass density, and its low price. A lot of research has been done on optimizing its TE properties; however, works on its use in thermoelectric generators (TEG) are scarce. Herein, the first conversion efficiency measurement of a functional, fully Mg2(Si,Sn)‐based TEG, approaching a maximum value of 4% for an applied = 375 °C, is shown. A maximum power density of 0.9 W cm−2 (related to the cross‐sectional area of the TE legs) at =375 °C is also reported, which is among the highest performance of silicide‐based modules reported in literature. Efficiency measurements can be tricky due to the uncertainty of heat flow measurement and parasitic heat losses; therefore, assessing the measurement reliability by confronting it to theoretical calculations is necessary. TEG device simulation in a constant property model is used to compare measured data to expected values and a good match is found (<1% deviation for current at maximum power, <4% difference for maximum power output, deviation within measurement uncertainty range for heat flows and efficiency). The significant discrepancy between measurement and calculations of the inner electrical resistance reveals room for improvement. Cracks form due to thermally induced mechanical stress, which dramatically increase the inner electrical resistance. It is shown that by avoiding those cracks, the maximum power output and conversion efficiency of the TEG could be improved by 30%.

Experimental and Theoretical Studies on Possibility of Void Filling by Magnesium in Mg-Doped Tetrahedrites.

Tetrahedrites, due to their promising thermoelectric properties, are one of the materials being investigated for use in thermoelectric generators. One problem is the lack of n-type tetrahedrites, which would be beneficial for the design of tetrahedrite thermoelectric modules. Preliminary theoretical studies have shown that elements from groups I and II can be introduced into the structural voids of tetrahedrite, acting as donor dopants, and should enable n-type conductivity. Therefore, in this work, an attempt was made to obtain and study magnesium-doped tetrahedrites. A series of samples, MgxCu12Sb4S13, with different magnesium contents were obtained and their phase and chemical compositions were characterized. It was observed that the structural changes occurring upon doping indicate that Mg atoms are likely to be embedded in the structural voids. The experimental studies have been supported by electronic structure calculations indicating that the most likely location of Mg is in the structural voids at the 6b Wyckoff position. Seebeck coefficient and resistivity measurements showed that doping with Mg reduces the concentration of holes, which is consistent with the predicted donor character of the dopant. However, the introduction of magnesium in sufficient amounts to achieve n-type conductivity was not successful.

The use of thermo electric generator to utilize the waste heat from the biomass stove into electricity

Indonesia has a huge potential for biomass energy resources. In 2013, the estimated potential of forest biomass in Indonesia for bioenergy was 132 PJ, 50.4% from harvest residues and 49.6% from wood processing residues. Until now, the technology of burning biomass using a stove continues to develop. Biomass stoves are designed, modified and tested to get maximum performance, at least approaching the performance of LPG-fueled stoves. Several studies concluded that about 14.66% of the total heat loss is on the walls of the biomass stove. The purpose of this study was to investigate whether the waste heat in the wall of a biomass stove can be used to generate electricity. Many researchers have studied the heat loss on the walls of the biomass stove, this heat loss can reduce the thermal efficiency of the stove and can cause the stove user to feel uncomfortable. Based on the Seebeck effect method where the temperature difference can be converted into electricity. If there is a temperature difference between the two sides of the thermoelectric, electricity will arise. This principle is used by thermoelectric generators. To maximize the temperature difference, the cold side of the Thermoelectric Generator (TEG) needs a cooling system. In this study, the TEG was attached to the wall of the biomass stove, then the voltage generated by the TEG was measured for each type of biomass fuel. the highest average voltage produced by wood chips, followed by candlenut shells, corn cobs and coconut shells. This is unique, although the calorific value of coconut shells (19,5 MJ/kg) is higher than hard wood (18,8 MJ/kg) and corn cobs (5.32 MJ/Nm3 ), but the highest average voltage is produced by wood 1.30 volts, then 1.12 volts of candlenut shells, 1.08 volts of corn cobs, and 0.79 volts of coconut shells.

High-performance thermoelectrics and challenges for practical devices.

Thermoelectric materials can be potentially employed in solid-state devices that harvest waste heat and convert it to electrical power, thereby improving the efficiency of fuel utilization. The spectacular increases in the efficiencies of these materials achieved over the past decade have raised expectations regarding the use of thermoelectric generators in various energy saving and energy management applications, especially at mid to high temperature (400-900 °C). However, several important issues that prevent successful thermoelectric generator commercialization remain unresolved, in good part because of the lack of a research roadmap.

Car exhaust waste heat recovery using hexagon shaped thermoelectric generator

Heat recovery technology using thermoelectric has attracted many research intentions mainly for its ability to generate power passively. The automotive engine usually produces waste heat ranging from 30-40% due to the thermodynamic limit. The use of thermoelectric generator (TEG) for waste heat recovery and power generation could increase the efficiency of the internal combustion engine system. This research developed and investigated a heat recovery system using a thermoelectric generator (TEG) for power generation. A thermoelectric generator (TEG) consisted of thermoelectric modules, hexagonal pipe connector and heat sinks was built and connected to an exhaust pipeline. A theoretical model was developed to access the thermal and electrical performance of the TEG system. The theoretical model consisted of the heat transfer mechanism including the thermal resistance networks from the flue gas to TEG and the heat sink. The electrical power output was determined using the Seebeck principle. The early stage of finding reveals that the system was able to produce an open circuit voltage of 0.13 V for a small temperature gradient of 3ᵒC between the cold and hot surface of the TEG. The further improvement of the system is currently under investigation for producing higher power. In the future, this system hopefully could replace the car battery for charging the alternator as well as increasing the overall efficiency of the engine system.

Performance of diesel engine having waste heat recovery system fixed on stainless steel made exhaust gas pipe

Chemical energy is not effectively converted into mechanical energy by an internal combustion engine. Major portion of heat energy get dissipated with exhaust and coolant. Use of thermoelectric generator (TEG) technology is regarded as an environment friendly technique for recovering the waste heat, with which heat energy directly converts into electrical energy. In this study, an experiment is conducted in which TEG technology has been used to recover waste heat going out through exhaust gas from the diesel engine. Thermoelectric modules were fixed on the surface of stainless steel made pipe having square cross-section. It has been found that the power output of thermoelectric generator enhances with the increase in engine load. The maximum electrical power output of TEG has been obtained as 37 W at maximum load of 6 kg. Overall thermal efficiency of diesel engine has also been improved with the use of TEG type of waste heat recovery system.

Use of thermoelectric generators to harvest energy from motor vehicle brake discs

The challenge of reducing vehicle energy consumption and greenhouse gas emissions has become a major orientation of automotive industry research throughout the world. Improving and optimizing power consumption by electric vehicles is of special concern. A novel use of thermoelectric generators in vehicle braking is presented. Thermal analysis of brake pads and discs using finite elements was applied to evaluate the energy potentially available in the form of heat produced by the friction involved in braking. We present stimulations of disc heating during and after braking at three ambient temperatures and reflect on the possibilities of energy recovery in warm as well as cold climates. The results show that although the yield of electrical energy from typical thermoelectric generators is about 0.3% of the total thermal energy associated with braking, at least 4 W can be made available, enough to power on-board instrumentation and vehicle devices and thereby improve the energy efficiency of motor vehicles.

Analysis of the Parameters of the Two-Sections Hot Side Heat Exchanger of the Module with Thermoelectric Generators

One of the methods of converting thermal energy into electricity is the use of thermoelectric generators (TEG). The method can be used in low-temperature waste heat conversion systems from industrial installations, but its serious limitation is the low efficiency of thermolectric generators and the relatively low power of the electric waveforms obtained. Increasing the obtained power values is done by multiplying the number of TEGs used, grouped into modules (MTEG). In such systems, the design of the module is extremely important, as it should ensure the best possible heat transfer between both sides of the TEG (hot and cold), and thus obtaining maximum electrical power. The article presents an analysis of a two-section flat plate heat hot side exchanger MTEG. The key parameters like effectiveness of exchange and MTEG efficiency and their impact on the efficiency of heat use and generated electric power were indicated. The tests showed an improvement in these main system parameters for the mixed cycle (co-current and countercurrent—inward direction) of the hot side heat exchanger, compared to the countercurrent flow in both sections of this exchanger.

Thermodynamic and parametric analyses of a thermoelectric generator in a liquid air energy storage system

A thermoelectric generator was applied to the liquid air energy storage system to utilize the excess heat, whereas their coupled thermodynamic characteristics were rarely reported. This article conducted the thermodynamic and parametric analyses on system performance in detail. The effects of the hot water mass flow and outlet temperature of thermoelectric generator, the discharging pressure, and stages of expansion on the performance were investigated. The results showed that the hot water outlet temperature had significant impact on the thermoelectric and energetic characteristics. The optimal hot water outlet temperature of 60–80 °C and discharging pressure of around 16 MPa improved the efficiency by 1.7%. In addition, two different configurations of the thermoelectric generator were presented based on the effective cold energy utilization of the air turbine exhaust. The economic analysis indicated that compared with the organic Rankine cycle and Kalina cycle, the use of thermoelectric generator had economic advantage with a payback period of 2.99 years at an investment cost of $10703.

Evaluation of the use of thermoelectric generators in rooms with excessive heat release

The purpose of the work was to evaluate new methods and new technology for the manufacture of thermoelectric modules for use in rooms with excessive heat release. Investigation of heat release parameters for the possibility of converting them into electrical energy. A new design of the thermoelectric module with a new topological pattern is applied. The research of the parameters of new thermoelectric modules is carried out using the developed installation, with the help of which it was found that the efficiency of the new design is 16.5% higher than that of classical thermoelectric modules. At the same time, it was found that the cost of the new design is 8 times less than that of classical thermoelectric modules. The heat release of the equipment of the operating boiler house, located in the city of Irkutsk, was studied. In the course of research, it was revealed that the technological equipment intended for servicing four fuel oil boilers of the «DE 16-14 GM» type emits heat energy of about 100 kW, which can be converted into electrical energy with an efficiency of more than 30%. The studies have shown that there are innovative technologies, using which it is possible to convert heat losses in buildings with excessive heat release into electrical energy, thereby increasing the efficiency of the equipment used.

Effect of temperature mismatch on the life cycle of thermoelectric generator efficiency for waste heat recovery

Global warming due to greenhouse gases that has been produced by energy generator as a byproduct has becoming a serious issue in recent decades. Thermoelectric module is an alternative method that can generate energy from heat and vice versa. The module is denominated as thermoelectric generator (TEG) when it is used to generate electricity via a process called the Seebeck effect. The use of thermoelectric generator has become more and more demanding due to the low maintenance cost and waste heat availability can be found everywhere in daily life such as car exhaust, roof tiles, and etc. The purpose of this research paper was to determine the effect of temperature mismatch on the life cycle of the thermoelectric generator efficiency using ANSYS simulation. The common used materials for the thermoelectric are bismuth telluride, lead telluride and silicon germanium. Each material has different thermal conductivity, Seebeck coefficient and electrical resistivity. The materials are paired together to form a thermocouple and the thermal gradient of the TEG is being evaluate through the simulation. Generally, the greater the temperature between the hot and cold side of the TEG, the higher the power generated. Bismuth telluride has a highest temperature difference between the hot and cold side followed by lead telluride and silicon germanium. The combination of BiTe(N) - BiTe(P) has the lowest minimum heat flux compared to the rest of the thermoelectric material combination. This proves that thermal and electrical properties and combination of thermoelectric material plays a vital role in the thermal gradient of the TEG.

High-energy laser detection through thermoelectric generators

Detection of high-energy laser strikes is key to the survivability of military assets in future warfare. The introduction of laser weapon systems demands the capability to quickly detect these strikes without disrupting the stealth capability of military craft with active sensing technologies. We explored the use of thermoelectric generators (TEGs) as self-powered passive sensors to detect such strikes. Experiments were conducted using lasers of various power ratings, wavelengths, and beam sizes to strike 2 × 2 cm2 commercially available TEGs arranged in different configurations. Open-circuit voltage and short-circuit current responses of TEGs struck with 808-, 1070-, and 1980-nm lasers at irradiance levels between 8.5 and 509.3 W / cm2 and spot sizes between 2 and 8 mm are compared. TEG surface temperatures indicate that the sensor can survive temperatures nearing 400°C. TEG open-circuit voltage magnitudes correlate more strongly with net incident laser power than with specific irradiance levels, and linearity is limited by Seebeck coefficient variation with temperature. Open-circuit voltage responses are characterized by 10% to 90% rise times of ∼2 to 10 s despite surface temperatures not reaching equilibrium. With open-circuit voltage as the sensing parameter, detection thresholds three times above the standard deviation noise level can be exceeded within 300 ms of the start of a laser strike with irradiance levels of ∼200 W / cm2. Potential harvested power levels as high as 16 mW are estimated based on measured electrical responses. A multiphysics finite-element model corresponding to the experiments was developed to further optimization of a lightweight, low-profile TEG sensor for detection of high-energy laser strikes.

Computational study of geothermal thermoelectric generators with phase change heat exchangers

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.