Thermoelectric Modules and Applications: An Industrial Perspective

Over the past quarter-century, NASA has maintained a cadence of missions utilizing radioisotope power systems (RPS) at a rate of approximately one mission every ten years. At present, the sole flight-qualified RPS in NASA's inventory is the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), which boasts an initial power output of around 120 watts. Additionally, NASA and the U.S. Department of Energy (DOE) jointly oversee the development of the Next Generation Radioisotope Thermoelectric Generator (NGRTG), expected to provide an initial power output ranging between 250 and 270 watts.<br/><br/>There is currently an unmet need for low-power generators with a projected initial power output of 15 watts. To address this gap, RGS Development and UDRI conducted a concept study to explore the feasibility of low-power RPS based on a single General Purpose Heat Source (GPHS).¹ Thorough thermoelectric calculations were performed to optimize the design of the current generation of RGS Thermagy architecture, which employs an all-silicon-germanium module. This optimization allows for efficient utilization of available heat flux via a suitable heat interface to meet the required power outputs. Furthermore, by concentrating the heat flux on a smaller hot side surface area of the thermoelectric module, a mechanically robust pellet-based next-generation Thermagy module is envisioned.<br/><br/>In terrestrial applications, RGS has undertaken several noteworthy projects focused on power generation through waste heat recovery in various heavy industries, including Tata Steel, Elkem, and ArcelorMittal. These experiences have underscored the need for mid-temperature Thermoelectric Generator (TEG) devices capable of handling high temperatures, reaching up to 600°C. In response to this demand, RGS is advancing the application of nanostructured SiGe materials, known for their higher average ZT values, while concurrently developing telluride-free thermoelectric modules designed to operate at temperatures up to 350°C in a recently funded EU Horizon project.²<br/><br/>RGS has developed significant expertise in various areas, including COMSOL simulations, thermo-mechanical engineering, interface engineering, device aging, and testing, positioning the company to offer TEG solutions for both single-stage and cascaded device architectures tailored to a range of source temperatures and heat flux densities.<br/><br/><br/>¹ K. Sherick, A. Ray, P. Berneron, A. Tolson, C. Barklay, M. D. Heijer, Feasibility of a Low-Power RTG Concept Utilizing a GPHS Heat Source, Proc. of the Nuclear and Emerging Technologies for Space, May 7-11 (2023), Cleveland, Ohio, USA<br/><br/>² https://www.start-heproject.com/