Your Car Is Wasting Energy and Scientists Just Found a Fix

Waste Heat Recovery System — Researchers design and test a waste-heat recovery system, illustrated here, that attaches to a car tailpipe and converts heat from exhaust into energy. The fanned grooves on the outside of the pipe are the cold side of the device’s heatsink and the triangular components inside the pipe are plate-fin heat exchangers. Credit: Adapted from ACS Applied Materials & Interfaces 2025, DOI: 10.1021/acsami.4c18023

Most fuel in gas-powered vehicles is wasted as heat, but a new study reveals a way to convert this lost energy into electricity.

Researchers have developed a thermoelectric generator that captures exhaust heat and transforms it into usable power. Unlike previous systems, which are heavy and require extra cooling, this new design is lightweight, efficient, and works in high-speed environments.

Wasted Energy in Combustion Engines

Gas-powered combustion engines waste about 75% of their fuel’s energy as heat, with only a quarter being used for motion. A new study in ACS Applied Materials & Interfaces explores a way to harness this lost heat and convert it into electricity. Researchers have developed a prototype thermoelectric generator that could improve fuel efficiency and reduce carbon dioxide emissions, offering a potential boost to sustainable energy efforts.

Turning Waste Heat into Electricity

Fuel waste not only reduces efficiency but also increases greenhouse gas emissions, highlighting the need for better waste-heat recovery systems. Thermoelectric systems, which use semiconductor materials to generate electricity from heat differences, offer a solution. However, most existing designs are bulky, complex, and require additional cooling water to maintain effectiveness.

Now, a research team led by Wenjie Li and Bed Poudel has developed a more compact thermoelectric generator that efficiently captures and converts exhaust heat from high-speed vehicles — including cars, helicopters, and unmanned aerial vehicles — into usable energy.

Innovative Thermoelectric Generator Design

The researchers’ new thermoelectric generator contains a semiconductor made of bismuth-telluride and uses heat exchangers (similar to those used in air conditioners) to capture heat from vehicle exhaust pipelines. The team also incorporated a piece of hardware that regulates temperature, called a heatsink. The heatsink significantly increases the temperature difference, which directly influences the system’s electrical output.

Their prototype achieved an output power of 40 Watts, about enough to power a lightbulb. Importantly, the results indicate that high airflow conditions, like those found in exhaust pipes, enhance efficiency, thereby increasing the system’s electrical output.

High-Speed Simulations and Future Potential

In simulations mimicking high-speed environments, the waste-heat system demonstrated great versatility; their system produced up to 56 W for car-like exhaust speeds and 146 W for helicopter-like exhaust speeds, or the equivalent of five and 12 lithium-ion 18650 batteries, respectively.

The researchers say their practical system can be integrated directly into existing exhaust outlets without the need for additional cooling systems. As the demand for clean energy solutions escalates, they add that this work could pave the way toward the practical integration of thermoelectric devices into high-speed vehicles.

Reference: “Thermoelectric Energy Harvesting for Exhaust Waste Heat Recovery: A System Design” by Rabeya Bosry Smriti, Wenjie Li, Amin Nozariasbmarz, Subrata Ghosh, Na Liu, Christopher D. Rahn, Mohan Sanghadasa, Shashank Priya and Bed Poudel, 7 January 2025, ACS Applied Materials & Interfaces.
DOI: 10.1021/acsami.4c18023

The authors acknowledge funding from the Army Rapid Innovation Fund Program; the National Science Foundation Industry-University Cooperative Research Centers Program through the Center for Energy Harvesting Materials and Systems; and the Office of Naval Research.