Thermoelectric Generation Applications Research Articles

Innovative Technology Strategies for the Sustainable Development of Self-Produced Energy in the Colombian Industry

This research studies the current state of the Colombian industrial sector, which is focused on self-generation processes. The study’s objective is to search for viable technological strategies that strengthen this particular sector’s competitiveness and sustainable development. The analysis shows that internal combustion engines represent 49% of the technologies used for self-generation. The main fuel used in the sector is natural gas, with a percentage of 56%. The lack of strategies for the use of residual heat and technological inefficiencies caused a loss of 36% in the energy used in the Colombian industrial sector. Thermoelectric generators are a feasible way to recover energy from exhaust gases in engines used for self-generation. Additionally, they allow a 4% reduction in fuel consumption and an improvement in the engine’s energy efficiency. The use of hydrogen as fuel allows a 30% reduction in polluting emissions, such as CO2, CO, HC, and particulate matter. Hydrogen production processes, such as water electrolysis, allow the participation of Colombia’s solar energy potential, leading to sustainable hydrogen production, efficiency (60–80%), and a lower economic cost. In general, the application of thermoelectric generators and the use of hydrogen gas allow the improvement of the Colombian industrial sector’s environmental, social, and economic aspects due to greater competitiveness and the reduction in emissions and operating costs.

First principles insight into physical properties of CaX2O4 (X = In, Gd) spinels for optical and spintronic applications

Herein, the calcium based ternary spinel oxides CaX2O4 (X ​= ​In, Gd) are brought under theoretical investigation to study their structural, magnetic, opto-electronic, and thermoelectric features. Thermodynamical and structural stabilities are assured through the assessment of enthalpy of formation (−6.243 and −7.542 ​eV for CaIn2O4 and CaGd2O4, respectively) and tolerance factor (0.96 and 0.86 for CaIn2O4 and CaGd2O4, respectively). DFT ​+ ​U based computations of band structures and density of states define CaIn2O4 as nonmagnetic wide bandgap (Eg) semiconductor (direct Eg of 3.88 ​eV) while CaGd2O4 is found to be half-metallic ferromagnetic spinel (direct Eg of 3.82 ​eV in spin down channel and μTotal ​= ​28 μB). Highly optically conductive and absorptive behavior in UV region has been observed for both oxide spinels, which suggests their prime usability in the field of optoelectronics. Furthermore, thermoelectric (TE) efficiency of both materials is disclosed by determining figure-of-merit (ZT) values which are found to be higher than 0.75 ​at room temperature. Optoelectronic and TE characteristics of both spinel oxides along with greater stability highly suggest their potential applications in various thermoelectric generators. aeronautics and optical devices operating within ultraviolet region of light.

First principles study on structural, mechanical, and thermoelectric properties of half-Heusler alloy (KLiTe)

In this study, the structural, optoelectronics, elastic, and transport properties of KLiTe were estimated from first principles computations using the FP-LAPW technique and semi-classical Boltzmann transport theory The exchange–correlation is addressed employing the generalized gradient approximation with Perdew-Burke-Ernzerhof scheme (GGA-PBE). In order to distinguish between the brittle and ductile properties, the Poisson and Pugh's ratio was calculated. The semiconductor KLiTe is demonstrated to have a direct band gap. The compound under investigation exhibits significant Seebeck coefficient and power factor values. The high-power factor of 8.3 × 1011 W/K2ms. that KLiTe exhibits at 1200 K makes it a potentially viable material for thermoelectric applications. Due to their high figure of merit values, the results obtained indicate that KLiTe could be a strong contender for thermoelectric generator applications at low and moderate temperature.

Experimental investigation and optimization analysis on thermoelectric water generator integrated with heat pipe

• Thermoelectric water generator integrated with heat pipe (HPTEWG) is proposed. • HPTEWG and thermoelectric water generator (TEWG) are compared experimentally. • HPTEWG can achieve higher cooling capacity than TEWG by 34.11W. • Maximum water generation increment in HPTEWG by 38.95ml/h can be achieved. • Structure configurations of HPTEWG are optimized to gain maximum water generation. As scare freshwater resources have been severely stressed by climate change, population growth and water pollution, demands of efficient water generation methods and devices urgently increase. To further improve the water generation capacity of thermoelectric water generator (TEWG), a novel TEWG integrated with heat pipe (HPTEWG) is proposed and studied by using experimental and simulation methods. Rather than the heat sink of the TEWG, the heat pipe is utilized to precool moisture air before the thermoelectric cooler to achieve the goal. Experimental results show that the maximum improvement in cooling capacity and water generation of HPTEWG can be 34.11W and 38.95ml/h when compared with TEWG under given operating condition. Besides, the effects of the input power of TEWG, inlet air temperature, relative humidity and mass flow rate on the performances of two system are experimentally investigated as well. In addition, a validated theoretical optimization model is built to optimize the structure configuration of the HPTEWG. The maximum water generation of the HPTEWG can be achieved when optimal area allocation ratio of HP and TEWG are chosen under constant total area condition. It is hope that the results can provide theoretical basis for the thermoelectric water generator development and application.

Enhanced Density of States Facilitates High Thermoelectric Performance in Solution-Grown Ge- and In-Codoped SnSe Nanoplates

SnSe single crystals have gained great interest due to their excellent thermoelectric performance. However, polycrystalline SnSe is greatly desired due to facile processing, machinability, and scale-up application. Here, we report an outstanding high average ZT of 0.88 as well as a high peak ZT of 1.92 in solution-processed SnSe nanoplates. Nanosized boundaries formed by nanoplates and lattice strain created by lattice dislocations and stacking faults effectively scatter heat-carrying phonons, resulting in an ultralow lattice thermal conductivity of 0.19 W m-1 K-1 at 873 K. Ultraviolet photoelectron spectroscopy reveals that Ge and In incorporation produces an enhanced density of states in the electronic structure of SnSe, resulting in a large Seebeck coefficient. Ge and In codoping not only optimizes the Seebeck coefficient but also substantially increases the carrier concentration and electrical conductivity, helping to maintain a high power factor over a wide temperature range. Benefiting from an enhanced power factor and markedly reduced lattice thermal conductivity, high average ZT and peak ZT are achieved in Ge- and In-codoped SnSe nanoplates. This work achieves an ultrahigh average ZT of 0.88 in polycrystalline SnSe by adopting nontoxic element doping, potentially expanding its usefulness for various thermoelectric generator applications.

Broad Temperature Plateau for High Thermoelectric Properties of n-Type Bi2Te2.7Se0.3 by 3D Printing-Driven Defect Engineering

High-energy-conversion Bi2Te3-based thermoelectric generators (TEGs) are needed to ensure that the assembled material has a high value of average figure of merit (ZTave). However, the inferior ZTave of the n-type leg severely restricts the large-scale applications of Bi2Te3-based TEGs. In this study, we achieved and reported a high peak ZT (1.33) of three-dimensional (3D)-printing n-type Bi2Te2.7Se0.3. In addition, a superior ZTave of 1.23 at a temperature ranging from 300 to 500 K was achieved. The high value of ZTave was obtained by synergistically optimizing the electronic- and phonon-transport properties using the 3D-printing-driven defect engineering. The nonequilibrium solidification mechanism facilitated the multiscale defects formed during the 3D-printed process. Among the defects formed, the nanotwins triggered the energy-filtering effect, thus enhancing the Seebeck coefficient at a temperature range of 300-500 K. The effective scattering of wide-frequency phonons by multiscale defects reduced the lattice thermal conductivity close to the theoretical minimum of ∼0.35 W m-1 k-1. Given the advantages of 3D printing in freeform device shapes, we assembled and measured bionic honeycomb-shaped single-leg TEGs, exhibiting a record-high energy conversion efficiency (10.2%). This work demonstrates the great potential of defect engineering driven by selective laser melting 3D-printing technology for the rational design of advanced n-type Bi2Te2.7Se0.3 thermoelectric material.

High-Performance Functionalized Mg2Si0.9Sn0.1 Thermoelectric Leg Synthesis by a Single-Step Reactive SPS Process

Contact electrodes and their adequate joining are the main bottlenecks in realizing low-cost Mg2(Si,Sn) thermoelectric materials for thermoelectric generator applications. The resistance and diffusion chemistry between the thermoelectric elements and contact electrodes play an essential role in achieving high-performance thermoelectric generators for intermediate-temperature applications. A facile single-step spark plasma sintering process was employed to fabricate Sb-doped Mg2Si0.9Sn0.1 and contact joining simultaneously. The single-step-processed thermoelectric element’s power output characteristics with three different contacts (Ni, MnSi, and FeSi2) were investigated by employing a thermoelectric conversion efficiency evaluation system. Our experimental strategy demonstrated that the single-step processing of Mg2(Si0.9Sn0.1)0.95Sb0.05/Ni joining imparts the lowest internal resistance and high-power output characteristics and eliminates the main obstacle of Mg2(Si,Sn) material integration in thermoelectric power generators.

Enhancement of thermoelectric power factor via electron energy filtering in Cu doped MoS2 on carbon fabric for wearable thermoelectric generator applications

The design and construction of state-of-the-art wearable thermoelectric materials are important for the development of self-powered wearable thermoelectric generators (WTEGs). Molybdenum disulfide (MoS2) has been reported as a noteworthy thermoelectric (TE) material because of its large intrinsic bandgap and high carrier mobility. In this work, Cu-doped two-dimensional layered MoS2 nanosheets were grown on carbon fabric (CF) via a hydrothermal method. The electrical conductivity, Seebeck coefficient, and power factor for the Cu-doped MoS2 were found to increase with increasing temperature. The maximum Seebeck coefficient was obtained for a MoS2 sample doped with 4 at% of Cu (CM4) was ∼10 μV/K at 303 K and ∼13 μV/K at 373 K. The enhancement in the Seebeck coefficient was attributed to an energy-filtering effect caused by the interfacial barrier between MoS2 and Cu. In addition, a thermoelectric device was designed with four pairs of TE materials, where CM4 (4 at%) was used as a p-type material and Cu wire was used as an n-type material. These p- and n-type materials were connected electrically in series and thermally in parallel to generate a voltage of 190.7 μV at a temperature gradient of 8 K.

Potential applications of thermoelectric generators (TEGs) in various waste heat recovery systems

Nowadays the World faces critical issues, such as increasing power costs, environmental impacts of fossil fuel, and global warming. In this respect, scientists are trying to improve the efficiency of the energy harvesting. The enhancement of power generation sectors is focused on the waste heat recovery systems based on thermoelectric generators (TEGs) that have demonstrated the capacity to transfer thermal energy directly into electric energy via the Seebeck effect. TEG uses the available waste heat sources in different applications to produce power, thus it considered as an eco-friendly power source. In the present study, the integration of thermoelectric systems with other technologies for green power production is introduced. This work introduces a background about the common materials used in the fabrication of the TEG. Furthermore, the application of the TEG to harvest waste heat from different sources, i.e., fuel cells, heat exchangers, photovoltaics, internal combustion engine, electric vehicles, and hybrid waste heat recovery systems have been summarized. The characteristics of thermoelectric generators are discussed, considering the different operating and design parameters. Finally, the barriers and challenges facing the applications of the thermoelectric generators for waste heat recovery are also discussed.

Numerical study on the performance of the thermoelectric generator with different air-water mixtures

Thermoelectric generators (TEGs) have been widely used to convert thermal energy into electrical energy directly. Nowadays, the most popular TEG applications, such as vehicle heat recovery and geothermal power generation, typically utilize water as the cooling working fluid. Water sources, however, may not be available or extremely limited in some cases. Therefore, in this study, we proposed a new method of mixing water and air as the working fluid to save water. It is necessary to find out the suitable ratio of water to air, under which the performance loss could be minimized. A numerical model of TEG was built utilizing COMSOL Multiphysics to investigate the effect of water mole fraction (WMF, representing water to air ratio) on the performance of TEG, where the properties of the air-water mixture (AWM) could vary with WMF. In this study, 5 cases were considered at different flow velocities, different WMFs, and different combinations of air, water, and AWMs. The effects of these parameters on the voltage and the output power of TEGs were studied and analyzed. The TEG module could generate higher voltage and power output with increasing velocity and WMF. When air fixed on one side, only 0.2 of WMF on the other side could boost over 1.5 times of voltage and 3 times of power generation than only using air. Based on the simulation results, TEGs reach the best performance when the value of WMF is equal to 0.5 on both sides.

Scalable spin Seebeck thermoelectric generation using Fe-oxide nanoparticle assembled film on flexible substrate

We fabricated Fe3O4 nanoparticle (NP)-assembled films on flexible polyimide sheets with Pt or Ta cap layer using a spin coating method and DC sputtering. The films were elaborated for spin Seebeck thermoelectric generator applications, and their spin Seebeck voltages were observed. We showed that the thermoelectric power of [Pt film/Fe3O4 NP]n multilayered films increases with increasing number of stacking n. Additionally, we prepared spin Seebeck thermopile devices in which the Fe3O4 NP-assembled films capped by Pt and Ta are connected alternately in series. We demonstrated that spin Seebeck voltages of the thermopile devices are larger than those of single [Pt or Ta film/Fe3O4 NP]n piece. Our results indicate that the spin Seebeck thermoelectric power of Fe3O4 NPs can be enhanced using a simple fabrication process without lithography technique.

A Linear Thermoelectricity Theory for Thermoelectric Materials

The governing equations of thermoelectricity are nonlinear in general. Herein, a first‐order linear theory of thermoelectricity for thermoelectric (TE) materials is presented, in which the Joule heating contribution is neglected in the energy balance equation as it is usually at least one order of magnitude smaller than the total thermal energy in TE generator applications. The first‐order linear theory is applied to calculate the energy conversion efficiency for homogeneous, functionally graded, and segmented TE generators under 1D heat flow conditions. Energy efficiency for a 2D example is also presented. It is found that the maximum energy efficiencies predicted by the linear theory agree well with those using the general nonlinear theory of thermoelectricity, which indicates that the linear theory is accurate in predicting the energy efficiencies of TE devices. Finally, the peak efficiency for a homogeneous leg under 1D conditions in the linear theory is also characterized by the figure of merit parameter Z as in the nonlinear theory.

Current and Future Trend Opportunities of Thermoelectric Generator Applications in Waste Heat Recovery

Today, with the increase of industrialization, the waste heat emitted by the industrial machines used has started to increase. Therefore, the energy efficiency of these devices also decreases. In addition, this waste heat remains a bad factor that plays a role in the world's climate change. Governments are implementing incentive policies to increase energy efficiency and reduce greenhouse gas emissions. Therefore, both scientists and engineers strive for a cleaner environment and energy. Thermoelectric generators (TEGs) are one of the devices that contribute to energy efficiency and sustainable energy production by ensuring the recovery of a certain part of the waste heat emitted by these machines to the environment. The TEGs have found traditional uses from the waste heat of microprocessors to the waste heat of stoves. However, their proliferation is limited by their efficiency less than 10% and their high purchasing costs. Academicians and engineers continue to work without slowing down to overcome these. The semiconductors with low thermal conductivity and high electrical conductivity are the main subjects studied in this field. With overcoming these difficulties, it is aimed to use thermoelectric generators in the future to convert the waste heat of almost all devices into electrical energy. Therefore, the main purpose of this study is to investigate the current innovations of TEGs and to determine the future trend. Among the main findings of this study, it is predicted that TEGs will be widely used in areas where there is a need for silent and maintenance-free energy in the future.

Ni substitution improves the high-temperature thermoelectric performance of electronegative element Se-filled skutterudite Se0.05Ni Co4-Sb12

The electronegative element-filled skutterudite (EN-SKD) has become an interesting thermoelectric material in the mid-temperature region in recent years. However, the strong intrinsic excitation above ~650 K affects its thermoelectric performance, limiting the practical applications in thermoelectric generators (TEG). To alleviate this situation, a series of EN-SKD compounds with different Ni substitutions, Se0.05NixCo4-xSb12 (x = 0.1, 0.2, 0.3, 0.4) are fabricated by solid-state reaction. It is found that the substitution of Ni for Co significantly suppresses the bipolar effect as the temperature above ~700 K due to the increase of electron concentration, reduces the lattice thermal conductivity (κL) by introducing phonon scattering centers, and consequently performs a significant enhancement of zT. Se0.05Ni0.4Co3.6Sb12 realizes a zT value two times higher than Se0.05Ni0.1Co3.9Sb12 at 823 K. This work demonstrates an approach to optimize thermoelectric performance by Ni substitution at Co sites in EN-SKD through the suppression of the bipolar effect on S and κ.

Adiabatic and isothermal configurations for Re4Si7 transverse thermoelectric power generators

Transverse thermoelectric generators (TTEGs) have the potential to overcome two challenging problems that limit the commercial application of classical thermoelectric generators (TEGs): the significant irreversible efficiency losses in the contacts and the thermal degradation of the contacts at the hot end. TTEGs are built from a single material that can generate a thermoelectric current in a direction that is orthogonal to a temperature gradient. They only require a single set of contacts that are displaced away from the hot end. Here, we experimentally explore the device design considerations for optimizing the performance of this far less explored class of thermal-to-electric generation devices. We fabricate Re4Si7 TTEGs and show that there is no measurable loss in efficiency with a single set of contacts that are midway between the hot and cold ends. We show that a new effect must be considered: the appearance of transverse thermal gradients that lead to significant differences between the performance of TTEGs implemented in isothermal and adiabatic geometries. The isothermal TTEG configuration leads to much higher device efficiencies. Overall, this work highlights how different the design of TTEGs is from that of conventional TEGs and the importance of controlling the device geometry for optimum waste heat recovery.

Tetrahedrite Thermoelectrics: From Fundamental Science to Facile Synthesis

Thermoelectric materials have a long and storied history in the research and development of semiconductor materials, being the first such class of materials to be investigated. Thermoelectrics may be used to convert heat to electricity or, alternatively, to liberate or absorb heat upon electrical excitation. They thus find application in thermoelectric generators for converting heat from a primary source or a waste stream to useful electrical power, and as solid state heating and cooling devices. In spite of their great potential in such important applications, thermoelectrics have suffered from a number of drawbacks that have hindered their utilization on a large scale. Chief among these is the fact that most high performance thermoelectric materials are comprised of elements that are in relatively low abundance. Additionally, their synthesis typically involves complex and multi-step processes, hindering manufacturability. Thermoelectric materials derived from Earth-abundant sources are thus of strong current interest, from both scientific and economic points of view. One of these, the family of semiconductors based on tetrahedrite compounds, has generated enormous interest over the last decade due to not only its potential low cost, but also for its fascinating science. In this review, we summarize the state of the art of tetrahedrite as a thermoelectric, with special emphasis on the relationship between crystal structure and bonding in the crystal and its unusually low lattice thermal conductivity; on its fascinating electronic structure; and on the wide array of compositions that have been synthesized and whose thermoelectric properties have been studied. We further highlight some rapid and facile synthesis techniques that have been developed for these compounds which, in combination with their potential low material cost, may open the door to widespread application of these fascinating materials.

Thermal Concentration on Thermoelectric Thin Film for Efficient Solar Energy Harvesting

Thermoelectric generators can directly harvest and convert ambient thermal energy into electricity, which makes it ideal for thermal energy conversion. However, the limited working temperature gradient developed by direct solar radiation severely restricts the performance and the application of solar thermoelectric generators. Here, we report a multilayer thin film integrating a solar selective absorbing coating and a thermoelectric layer, where an in-plane temperature gradient was established. The temperature gradient was relatively large since the absorbed solar energy could only flow through the restricted cross-section of the thin film, representing a high thermal concentration. The fabricated thin-film solar thermoelectric generators (100 mm × 15 mm) achieve an open-circuit voltage of about 300 mV, and an output power of 0.83 μW under AM 1.5G conditions. Our work opens up a promising new strategy to achieve the simple and cost-effective conversion of solar energy into electricity by thermal concentration.

Switched Inductor DC–DC Boost Regulator Using Voltage-to-Time Controller for TEG Applications

This paper presents a switched inductor (SI) DC–DC boost regulator designed for thermoelectric generator (TEG) applications. To boost and regulate the output voltage, two feedback loops are implemented which control the duty cycle of the SI clock. The first loop consists of a pulse skip modulation (PSM) controller that compares the load voltage and reference voltage. Based on the comparison output, the PSM will either pass or bypass the modulated pulse width signal generated from the second loop. The second loop replaces the conventional circuit design of the pulse width modulation (PWM) with a voltage-to-time converter (VTC). The VTC converts the difference between load and supply voltage to time delay resulting in a modulated pulse width. This work is the first to report on utilizing VTC circuit in the SI boost regulator. The proposed SI boost regulator is designed using 65 nm CMOS technology which converts the TEG voltage of 50 mV to support dynamic voltage scaling in the range of 0.6 V to 0.8 V. The PSM and PWM controller loops can tune the duty cycle of the clock in the range of 0 to 70%. It achieves a peak efficiency of 60.9% at 30 μW load power. Comparing the proposed single-stage SI boost regulator with the conventional two cascaded stages of switched-inductor boost converter followed by switched capacitor regulator, the area is reduced by 9.6× and power efficiency is increased by 1.35×.

APPLICATION OF CRYOGENIC THERMOELECTRIC GENERATORS IN ENERGY STORAGE SYSTEMS

Features of application of cryogenic thermoelectric generators in the systems of accumulation of the electric power using liquefied air (LAES) are considered. It is shown that the use of cryogenic thermoelectric generators as a heat exchanger-evaporator of the LAES scheme allows to increase the coefficient of electricity recovery by 10–15 % and reduce the equalized cost of electricity by almost 3 times — up to 0.03 $/kWh. The conclusion on expediency of application of similar schemes of accumulation of the electric power in the distributed power systems of the future is made. Bibl. 15, Fig. 3.

Thermoelectric Generators: A comprehensive review of characteristics and applications

• The open literature on thermoelectric generators is comprehensively reviewed. • Technical aspects of thermoelectric generators is thoroughly discussed. • Device and system-level designs for thermoelectric generators are scrutinized. • Thermoelectric generators applications are broadly elaborated and reviewed. • Recommendations are provided for future studies. Energy crisis and associated environmental issues are the main challenges in today’s changing world, where there is a growing demand for electricity. To address such challenges, modern-day energy conversion systems for which, reliability and scalability are the two most desired features, are in need. Thermoelectric generators are a kind of heat engines capable of offering solutions for these challenges if they reach their expected potentials. The advantages for such technologically advanced devices are manifold; they are environmentally friendly, highly scalable, reliable, and have long lifespan. Additionally, by applying thermoelectric generators, one can improve the existing systems’ efficiency or supply the electricity demand of different systems with high flexibility. Nonetheless, the low conversion efficiency of thermoelectric generators has impeded their wide application, restricting them to an academic subject. Yet, recent advancements in thermoelectric materials and devices are pushing the technology to find its place among state-of-the-art energy conversion systems. The present review explores the recent literature to present a comprehensive and realistic perspective of the state of the technology. Furthermore, this review carefully investigates the feasibility of integrating thermoelectric generators into different systems and applications, and eventually, provides an in-depth analysis with recommendations for future studies.