Evaluating electricity generation from low-grade heat sources

Waste heat is a byproduct of many systems, including power generation, industrial processes, and consumer equipment. Much of this heat, however, is low-grade, below 100 °C in temperature, making it challenging to extract any useful energy from it. Recently, several promising technologies, including thermally regenerative electrochemical cycle (TREC), have been developed that could efficiently apply this type of heat.

Zhang et al. assessed the performance of multiple types of TREC systems across different metrics. Their goal was to clarify the differences between these independently developed systems.

“The great disparities in the scales and testing conditions of reported TREC systems have made their evaluation challenging for practical applications,” said author Qing Wang. “We decided to create evaluation criteria for a fair assessment of the practicability of various TREC systems to promote their development.”

TREC systems generate electricity between heating and cooling cycles and can convert small temperature differences into usable electricity. The team evaluated three types of TREC systems and compared metrics such as thermoelectric efficiency, power density, and net electricity generation.

“Electrically powered TREC systems stand out due to their high apparent thermoelectric efficiency and large net electricity output,” said Wang. “Charging-free TREC systems could achieve continuous heat-to-electricity conversion but are limited by low efficiency. High-current TREC systems could simultaneously provide high-power energy storage and efficient thermal energy conversion.”

Following their evaluation, the authors provided perspective on how to approach existing challenges within the field, including finding materials with better performance, increased stability, and lower internal resistance. They are hopeful about the technology’s potential use as a clean energy source in the future.

Source: “Evaluation of thermally regenerative electrochemical cycle for thermal-to-electrical energy conversion,” by Hang Zhang, Zhiyu Wang, and Qing Wang, Applied Physics Letters (2023). The article can be accessed at https://doi.org/10.1063/5.0146725 .