Researchers at Penn State and the National Renewable Energy Laboratory have developed a new flexible thermoelectric generator that can wrap around pipes and other hot surfaces and convert wasted heat into electricity more efficiently than previously possible.
“A large amount of heat from the energy we consume is essentially being thrown away, often dispersed right into the atmosphere,” said Shashank Priya, associate vice president for research and professor of materials science and engineering at Penn State. “We haven’t had cost-effective ways with conformal shapes to trap and convert that heat to useable energy. This research opens that door.”
Researchers have been working to improve the performance of thermoelectric generators – devices that can convert differences in temperature to electricity. In their work, the team has developed a new manufacturing process to produce flexible devices that offer higher power output and efficiency.
Thermoelectric devices are made up of small couples, each resembling a table with two legs. Many of these two-leg couples are connected together, typically forming a flat, square device. Researchers placed six couples along a thin strip. They then used flexible metal foil to connect 12 of the strips together, creating a device with 72 couples. Liquid metal was used between the layers of each strip to improve device performance.
During the tests conducted on a gas flue, the new device exhibited a 150% higher power density than other state-of-the-art units. A scaled-up version, just over 3-inches squared, maintained a 115% power density advantage. That version with 72-couple hH legs exhibited a total power output of 56.6 watts under a temperature difference of 570 °C.
These results provide a promising pathway toward widespread utilization of thermoelectric technology into the waste heat recovery application. This could have a significant impact on the development of practical thermal to electrical converters.
“As you scale up these devices, you often lose power density, making it challenging to fabricate large-scale thermoelectric generators,” said Bed Poudel, associate research professor at Penn State. “This illustrates the extraordinary performance of our 72-couple device.”
The gaps between the strips provide the flexibility to fit around shapes like pipes and also allow for flexibility in altering the fill factor, which can be used to optimize thermoelectric devices for different heat sources.