A new flexible thermoelectric generator wraps around hot surfaces to convert waste heat into electricity more efficiently than was previously possible, scientists claim.
Penn State researchers have been working to improve the performance of thermoelectric generators that convert temperature differences into electricity. When the devices are placed near a heat source, electrons moving from the hot side to the cold side produce an electric current.
“A large amount of heat from the energy we consume is essentially wasted, often dispersed directly 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 capture that heat and convert it into usable energy. This research opens that door.”
In previous work, the team rigid devices made that were more efficient than commercial units in high temperature applications. Now the team has developed a new manufacturing process to produce flexible devices that offer higher power and efficiency.
“These results offer a promising path to widespread use of thermoelectric technology in the application of waste heat recovery,” said Wenjie Li, assistant research professor at Penn State. “This could have a significant impact on the development of practical thermal to electrical generators.”
MORE FROM ENERGY & ENVIRONMENT
Flexible devices are a better match for the most attractive waste heat sources, such as pipes in industrial and residential buildings and on vehicles, the scientists said. In addition, they do not need to be glued to surfaces like traditional rigid devices, further reducing efficiency.
In tests conducted on a flue pipe, the new device showed a 150 percent higher power density than other units, the scientists reported in Applied materials and interfaces. A scaled-up version, just over 3 inches squared, retained a 115 percent advantage in power density. That version showed a total power of 56.6 W when placed on the hot surface, the scientists said.
“Think of an industrial power plant with pipes hundreds of meters long,” Priya said in a statement. “If you can wrap these devices around such a large area, you can generate kilowatts of energy from wasted heat that would normally just be thrown away. You could turn wasted heat into something useful.”
Thermoelectric devices are made up of small pairs connected together to form a flat, square device.
When creating the new device, scientists placed six pairs along a thin strip. They then used flexible metal foil to connect 12 of the strips together, creating a device with 72 pairs. Liquid metal was used between the layers of each strip to improve the performance of the device.
“When you scale these devices, you often lose power density, making it a challenge to fabricate large-scale thermoelectric generators,” said Bed Poudel, an associate professor of research at Penn State. “This illustrates the extraordinary performance of our 72-pair device.”
The 72-pair device showed the highest reported power output and device power density of a single thermoelectric generator, the scientists said.
The gaps between the strips provide the flexibility to fit around shapes such as tubes. The openings also allow for flexibility in changing the fill factor, or the ratio between the area of thermoelectric material and the area of the device, which can be used to optimize thermoelectric devices for different heat sources, the scientists said.