Scientists from the University of Rochester have invented a new ‘black metal’ solar thermoelectric generator (STEG) etched with femtosecond laser pulses that is 15 times more efficient than the best state-of-the-art STEGs currently available.
Although the technology is still in the development stage, the research team suggests black metal-based energy harvesting devices could power smaller, wearable electronics, or even serve as the basis for “off-grid renewable energy systems” in rural or remote areas, although commercial viability and scalability remain to be demonstrated.
Unlike traditional photovoltaic solar panels that convert light into electricity, STEGs convert heat from the sun into power. The technology relies on the transfer of heat energy between a “hot” side and a “cold” side, which can be converted into electricity through a physical phenomenon known as the Seebeck effect. Still, the best STEG only converts around 1% of the solar energy they absorb. For comparison, the best photovoltaic-based residential solar panels on the market can achieve conversion rates exceeding 20%.
According to Chunlei Guo, a professor of optics and physics and a senior scientist at Rochester’s Laboratory for Laser Energetics, efforts to improve STEG efficiency have focused on semiconductor materials used in their designs. Unfortunately, the researchers note that these efforts have made “modest gains” in overall energy conversion efficiency.
University of Rochester photo / J. Adam Fenster
To develop a STEG that could approach a photovoltaic level of efficiency, the Rochester team took a different approach. In their published study, the researchers explain that they “don’t even touch the semiconductor materials” used in STEGs. Instead, the team said they “focused on the hot and the cold sides of the device” by employing a multi-stage approach.
First, the team reengineered the hot side of the device. The primary material change involved the application of a “black metal technology” previously developed by Guo’s laboratory. The team notes that this layer transforms regular tungsten to “selectively absorb light at the solar wavelengths.”
The primary structural change of the STEG’s hot side involved etching the black metal layer with nanoscale structures with a powerful femtosecond laser.
Compared to a smooth surface, the etched black metal enhances the material’s natural energy absorption by collecting and converting more heat energy. Notably, the etched black metal surface also reduces heat dissipation at other wavelengths, thereby conserving that energy for conversion to electricity.
According to Guo, the team finished reengineering the STEG’s hot side by covering the black metal surface with a thin piece of plastic, effectively creating a mini greenhouse “just like on a farm.” The professor said this simple change can help “minimize the convection and conduction” on the material’s surface, thereby increasing the temperature on the device’s hot side. This increased heat can increase the device’s energy conversion.
The final step in the reengineered STEG involved etching nanostructures into the surface of the aluminum heat sink on the device’s cold side with the same laser. The researchers say that adding these tiny nanostructures to the aluminum’s surface “improved the heat dissipation through both radiation and convection.”
“That process doubles the cooling performance of a typical aluminum heat dissipator,” they explained.
Once completed, the team demonstrated their black metal STEG by powering LEDs. Tests of the device’s output showed it generates 15 times more power than previous solar heat energy conversion devices.
“By combining better solar energy absorption and heat trapping at the hot side with better heat dissipation at the cold side, we made an astonishing improvement in efficiency,” Guo said.
Although still in the lab, the team stated that a commercial version of the technology could provide off-grid power to remote and rural locations at a lower material cost compared to photovoltaic panels. Smaller versions of this black metal technology could also power low-demand applications like wireless sensors for the IoT and wearable devices.
The team also notes that the basic technology behind thermal electric generation makes their etched black metal devices adaptable to hybrid systems that capture heat from both solar and other sources, converting them to electricity.
The study “15-Fold increase in solar thermoelectric generator performance through femtosecond-laser spectral engineering and thermal management” was published in Light Science & Applications.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.