Carbon nanotubes are getting an overhaul by researchers at Rice University, who are developing a version that is more efficient.
Researchers Gururaj Naik and Junichiro Kono of Rice’s Brown School of Engineering, who showcased their technology in ACS Photonics, developed a hyperbolic thermal emitter that can absorb heat, fit it into a narrow bandwidth and emit it as a light that can be used to create electricity. The heat would otherwise be emitted into the atmosphere and wasted. With this technology, it could make solar cells much more efficient.
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“Thermal photons are just photons emitted from a hot body,” Kono said in a press release announcing the results of the research. “If you look at something hot with an infrared camera, you see it glow. The camera is capturing these thermally excited photons.”
As it stands, any hot surface emits light in the form of thermal radiation. But Naik said the problem is the thermal radiation is broadband. In order to convert light into electricity, the emission has to be in a narrow band, and thus the invention. The researchers discovered nanotubes are a way to isolate the photons that would be wasted. The nanotube films act as conduits that absorb the waste heat and turn it into the narrow-bandwidth protons.
Waste Heat Motivated the Researchers
The researchers said they were motivated to do the research because of the heat that is wasted. Naik pointed to a study by Rice graduate student Chloe Doiron who found around 20% of energy consumption is waste heat. He said that's about three years of electricity needed to power the state of Texas.
“The most efficient way to turn heat into electricity now is to use turbines, and steam or some other liquid to drive them,” he said. “They can give you nearly 50% conversion efficiency. Nothing else gets us close to that, but those systems are not easy to implement.” Naik said. The researchers plan to develop a compact system that doesn't have any moving parts to make the process that much easier.
More Efficient Solar Cells to Come?
So what does this mean for society? According to the researchers, it could increase the efficiency of solar cells which currently peak around 22%. “By squeezing all the wasted thermal energy into a small spectral region, we can turn it into electricity very efficiently,” said Naik. “The theoretical prediction is that we can get 80% efficiency.”
Rice University researchers aren't the only scientists trying to make solar energy more efficient. With the planet warming at an alarming rate, there is a race to make alternative energy sources more efficient. Researchers at MIT spent several years developing a new approach that gets high-energy photons that hit silicon to knock out two electrons instead of one, which is how the current systems work. Even if the photon is carrying double the energy it can only loosen a single electron.