The exhaust of the car also releases heat. deepblue4you/iStock
A compact thermoelectric generator built by researchers at Pennsylvania State University can convert exhaust heat from cars, helicopters, and unmanned aerial vehicles (UAVs) into usable electric energy. The prototype developed by the team achieved a power output of 40 Watts, sufficient to power a light bulb, a press release said.
It is well known that the efficiency of internal combustion engines, which have typically powered vehicles, is only around 25 percent. In other words, when we use a vehicle, three-fourths of the energy stored in gasoline is wasted and let out as heat.
As the world suffers from increasing carbon emissions and trailing developments in clean energy technology that can eventually replace fossil fuels, there is a need for more efficient technological measures that can help reduce emissions from existing technologies.
The research team at the Department of Mechanical Engineering worked to improve the energy conversion of gas-powered engines with a thermoelectric generator that converts waste heat into energy.
Problems with thermoelectric generators
Thermoelectric generators use the temperature difference applied across a material and convert it into energy. The concept has been around for a while and typically uses semiconductor materials to achieve this.
However, the design of the generators is complex and relies on an external cooling system to maintain the temperature difference. This requires using a water-based cooling system, which adds to the size of the generator and makes it less versatile for deployment.
The research team led by Wenjie Li and Bed Poudel at Penn State University addressed these shortcomings with an innovative design approach.
Illustration of the thermoelectric generator fitted into the exhaust pipe of a car. 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. Image credit: ACS Applied Materials & Interfaces 2025
Thermoelectric generator with heat exchangers
Instead of relying on a water-based cooling system, the researchers opted for heat exchangers used in air conditioners to capture heat emitted from exhaust pipes.
The thermoelectric generator was made from the semiconductor material bismuth-telluride, and the team also added an extra component called the heatsink to their design. The role of the heatsink is to increase the temperature difference of the system, which is directly correlated with the amount of energy output generated.
The prototype generator achieved a power output of 40 Watts, which is sufficient to power a light bulb. More importantly, though, the researchers found out that the high airflow conditions in exhaust pipes help improve the energy output from the generator.
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The team then conducted simulations in environments where such conditions exist and found that their system could generate more energy when deployed. For instance, the generator output was estimated to be 56 W when deployed in a car. However, a helicopter exhaust could generate 146 W of energy, the equivalent of 12 lithium-ion batteries.
Since the system can be integrated into exhaust outlets and does not depend on additional cooling infrastructure, it can also be retrofitted on existing vehicles. The researchers are confident that this will pave the way for the incorporation of thermoelectric devices into everyday vehicles and help recover energy that is otherwise being wasted.
The research findings were published in ACS Applied Materials & Interfaces.
