Thermoelectric generators for waste heat recovery: A review of module and system integration

Thermoelectric generators provide a promising route for converting low- and medium-grade waste heat into electricity in sustainable energy systems. Although substantial progress has been achieved in thermoelectric materials, practical system performance remains strongly governed by the structural design and integration of thermoelectric modules and heat exchangers. This review systematically examines recent advances in thermoelectric leg and module configurations, including conventional π-type, segmented, multi-stage, annular, unileg, coaxial, flexible, and linear architectures, with emphasis on their operating principles, application suitability, and engineering limitations. Plate-type, cylindrical, polygonal, heat pipe-based, vapor chamber-assisted, and stacked heat exchangers are also reviewed for automotive exhaust, industrial processes, geothermal resources, building energy systems, and distributed low-grade heat recovery. Particular attention is given to coordinated module–heat exchanger design through thermal-resistance and power-loss pathways, geometry and topology matching, thermal-field and material compatibility, interface reliability, and system-level trade-offs. The review shows that no universally optimal configuration exists, because suitable designs depend on heat-source characteristics, duty cycles, installation constraints, durability requirements, and economic objectives. More importantly, structural optimization should be evaluated not only by peak power or conversion efficiency, but also by time-integrated net energy recovery, parasitic losses, service life, scalability, manufacturability, and life-cycle cost under realistic operating conditions. By linking component-level innovation with application-specific energy-system requirements, this review provides practical and interdisciplinary guidance for reliable deployment, improved waste heat utilization, transportation and industrial energy efficiency, distributed power generation, and low-carbon energy-system development.