High-Performance Thermoelectric Generators for Field Deployments

Abstract

Thermoelectric power generation is a reliable energy harvesting technique for directly converting heat into electricity. Recent studies have reported the thermal-toelectrical energy conversion efficiency of thermoelectric generators (TEGs) up to 11% under laboratory settings. However, the practical efficiency of TEGs deployed under real environments is still not more than a few percent. In this study, we provide fundamental insight on the operation of TEGs in realistic environments by illustrating the combinatory effect of thermoelectric material properties, device boundary conditions, and environmental thermal resistivity on TEG performance in conjunction with the module parameters. Using numerical and experimental studies, we demonstrate the existence of a critical heat transfer coefficient that dramatically affects the design and performance of TEGs. Results provide a set of concrete design criteria for developing efficient TEGs that meet the metrics for field deployments. High-performance TEGs demonstrated in this study generated up to 28% higher power and 162% higher power per unit mass of thermoelectric materials as compared to the commercial module deployed for low-grade waste heat recovery. This advancement in understanding the TEG operation will have a transformative impact on the development of scalable thermal energy harvesters and in realizing their practical targets for efficiency, power density, and total output power.

Bismuth Telluride Thermoelectrics with 8% Module Efficiency for Waste Heat Recovery Application

“…The magnitude of zT~1.2 is maintained in a broad temperature range up to 150°C in Type (II)-p resulting in high (zT) avg . Better TE properties above room temperature make this material suitable for low-grade waste heat recovery application, such as energy harvesting from hot-water pipes ( Kishore et al., 2020 ). Type (I)-p with higher (zT) peak and lower thermal conductivity at room temperature is appropriate for specific applications that involve high heat sink/source contact resistance such as body heat harvesting ( Nozariasbmarz et al., 2019a ; 2020a , 2020b ; Suarez et al., 2016 ) and body cooling ( Kishore et al., 2019 ).…”

“…These techniques do not assure high conversion efficiency of TEGs mainly due to the low (zT) avg or high device contact resistance. In general, the efficiency of a TEG can be improved by (1) high (zT) avg of TE materials ( Equation 1 ), (2) large temperature gradient ( Equation 1 ), (3) appropriate TEG design to minimize the heat loss ( Rowe and Min, 1996 ; Kishore et al., 2020 ), and (4) small electrical and thermal contact resistances at the junction of TE materials and substrate mainly controlled by the quality of contact metallization of the TE materials, device fabrication process, soldering/brazing material, and interconnect electrodes ( Bjørk, 2015 ; Nozariasbmarz et al., 2019a ). All these factors should be considered in the design and fabrication of the TEGs with high efficiency.…”

“…At the device level, thermal contact resistance at the TE leg/metal interconnect junction and metal interconnect/ceramic substrate, as well as the thermal conductivity of the ceramic substrate affects the temperature distribution and drop across the TEG ( Liu and Bai, 2019 ). Thus, a comprehensive strategy is required for designing high-efficiency TEGs that comprises materials for TE legs, soldering/brazing, metallization, interconnects, and headers ( Kishore et al., 2020 ). This article addresses these aspects ranging from materials to TE modules.…”

Performance Analysis and Optimization of a SnSe-Based Thermoelectric Generator

“…Two dimensionless geometrical parameters connecting leg width ( w ) and module area ( A ) and known as fill fraction ( FF ) and aspect ratio ( AR ) can be defined as , Utilizing eqs and , eq can be rewritten as Under optimal load ( ), the load voltage ( V opt ), TEG power output ( P opt ), and maximum efficiency ( η max ) can be where , ΔT = ( T h – T c ) and T c , T h , S , and ZT̅ represents the cold end temperature, hot end temperature, effective Seebeck coefficient ( S = S p – S n ) and TEG module figure of merit at mean temperature, respectively.…”

“…Although studies on the optimization of a conventional (p–n) Π-TEG and a few unilegged architectures − are available in the literature, most of them have dealt with the isothermal heat boundary condition, where the hot end temperature remains fixed. However, in practical scenarios, most of the heat sources (such as automotive exhaust, industrial flue gas, etc.)…”