This novel device can wrap around hot surfaces and convert wasted heat to electricity. Tests revealed that it can maintain a 115 per cent power density advantage and produced 56.6 watts of total power output.
An estimated 70 per cent of all energy produced and consumed by humanity is lost as waste heat and released into the environment. For instance, heat radiates off hot water pipes in buildings and exhaust pipes on vehicles. To raise energy efficiency and reduce the consumption of energy, waste heat needs to be reduced or reused. Recently, 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.”
Prior to the study, Penn State scientists have been researching ways to improve the performance of thermoelectric generators, which essentially convert differences in temperature to electricity. Thermoelectric devices are usually made up of small couples, akin to a table with two legs. Most of these two-leg couples are then linked together, forming a flat, square device. When these devices are exposed to a heat source, electrons that move from the hot side to the cold side produce an electric current.
In their previous work, the researchers developed rigid devices that turn wasted heat into clean electricity, which proved to be more efficient than commercial units in high-temperature applications. In the current study, the team innovated a novel manufacturing process to produce flexible devices that provide not only high-power output but also remarkable efficiency. Compared to traditional, rigid devices, flexible devices are a much better fit to address the most common waste heat sources like pipes in industrial and residential buildings and on vehicles. This is because rigid devices need to be glued on surfaces, which reduces efficiency. Flexible devices eliminate the need for glue.
“Think about an industrial power plant with pipes hundreds of feet long,” Priya said. “If you can wrap these devices around an area that large, you could generate kilowatts of energy from wasted heat that’s normally just being thrown away. You could convert discarded heat into something useful.”
To create their new device, the team placed six couples along a thin strip, after which they used a flexible metal foil to connect 12 of such strips together, ultimately creating a device with 72 couples. Then, the researchers added liquid metal between the layers of each strip to enhance the performance of the device. To ensure that the device remains flexible, gaps were left in between the strips to fit around shapes. The gaps also allow for flexibility in modifying the fill factor. The fill factor refers to the ratio between the area of thermoelectric material and the area of the device, which can be exploited to optimise thermoelectric devices for different heat sources.
To assess the performance of their flexible thermoelectric generator, the scientists tested their device on gas flue, from which they discovered that their generator achieved 150 per cent higher power density than other advanced units. Even when scaled up to just over three-inches squared, they were able to maintain 115 per cent power density advantage and produced 56.6 watts of total power output when placed on the hot surface.
“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.” According to the researchers, their 72-couple device successfully achieved the highest reported output power and device power density from a single thermoelectric generator.
“These results provide a promising pathway toward widespread utilisation of thermoelectric technology into waste heat recovery application,” said Wenjie Li, assistant research professor at Penn State. “This could have a significant impact on the development of practical thermal to electrical generators.” [APBN]
Source: Li et al. (2021). Conformal High-Power-Density Half-Heusler Thermoelectric Modules: A Pathway toward Practical Power Generators, ACS Applied Materials and Interfaces, 13, 45, 53935–53944.