New Technology Converts Waste Heat into Electricity and Challenges Thermal Physics Limits

New Technology Converts Waste Heat into Electricity and Challenges Thermal Physics Limits
by Clarence Oxford
Los Angeles CA (SPX) Feb 20, 2025

Researchers at the University of Colorado Boulder's Paul M. Rady Department of Mechanical Engineering have developed an innovative method to transform waste heat into electricity, defying a key thermal physics limitation. This breakthrough, achieved by the Cui Research Group under Assistant Professor Longji Cui, was conducted in collaboration with scientists from the National Renewable Energy Laboratory (NREL) and the University of Wisconsin-Madison. Their findings were recently published in *Energy and Environmental Sciences*.

The technology has the potential to significantly impact manufacturing industries by enabling power generation without the need for high-temperature sources or costly materials. It offers a solution for energy storage, carbon emission reduction, and harnessing thermal energy from geothermal, nuclear, and solar sources worldwide.

Unlocking the Potential of Waste Heat

"Heat is a renewable energy source that is often overlooked," Cui stated. "Two-thirds of all the energy we use is lost as heat. Imagine energy storage and electricity generation that do not rely on fossil fuels. We can reclaim some of this wasted thermal energy to generate clean electricity."

Breaking Thermal Barriers in Vacuum Conditions

Traditional high-temperature industrial and renewable energy processes often rely on thermophotovoltaic (TPV) technology, which converts heat into electricity. However, TPV systems are constrained by Planck's law, which sets a fundamental limit on the usable thermal energy extracted at a given temperature.

"Planck's law is one of the most fundamental principles in thermal physics, defining the limit on how much thermal energy can be captured from a heat source at any given temperature," Cui explained. "Many researchers have attempted to overcome this limitation, but existing methods are too complex to manufacture, prohibitively expensive, and difficult to scale."

The Cui Research Group addressed this challenge by designing a compact TPV device small enough to fit in a human hand. Their approach successfully exceeded the vacuum limit imposed by Planck's law, achieving twice the power density of conventional TPV designs.

"Initially, our theoretical models suggested a significant enhancement in power generation," said Mohammad Habibi, a PhD student leading the research's theoretical and experimental aspects. "Once we conducted experiments and analyzed the data, we realized the improvement was substantial."

Zero-Vacuum Gap Innovation Using Glass

To redefine TPV efficiency, the research team introduced a "zero-vacuum gap" solution. Unlike traditional TPV designs that rely on a vacuum or gas-filled gap between the heat source and the solar cell, their device incorporates a high-index, infrared-transparent spacer made of glass.

This innovation allows thermal radiation to travel more effectively through the device, enhancing power generation significantly. Additionally, glass is an inexpensive material, making the technology economically viable.

"Previously, to boost power density, engineers had to increase temperatures from 1,500C to 2,000C or even higher, which is often impractical and unsafe," Cui noted. "Our device operates at 1,000C but achieves power outputs comparable to those generated at 1,400C in conventional TPV systems."

The team believes this is only the beginning. Future improvements using alternative materials, such as amorphous silicon, could increase power density nearly 20-fold, according to Habibi.

Potential Industrial and Commercial Applications

Cui emphasized that their TPV innovation has the potential to revolutionize portable power generators and decarbonize heavy industries. Optimized versions of the device could be used in high-temperature processes like glass, steel, and cement production, enabling cleaner and more cost-effective electricity generation.

"Our technology integrates seamlessly with existing commercial solutions, making it highly scalable for industrial applications," Cui said. "By recovering wasted heat, we can provide industries with much-needed energy storage at lower operational temperatures."

The research team has already filed a patent application for their groundbreaking TPV technology and is looking forward to advancing the field of renewable energy and heat recovery.

Research Report:Enhanced power density in zero-vacuum-gap thermophotovoltaic devices