Normal silicon-based photovoltaics can only convert electricity at efficiency levels of up to 33.7 percent, according to the Shockley–Queisser limit. However, new thermophotovoltaic (TPV) technology being developed at the Massachusetts Institute of Technology (MIT) may be able to surpass that.
Part of the problem with traditional silicon photovoltaics is that they can only absorb solar radiation from the visible spectrum of light.
“Our solar TPV system absorbs a broad range of wavelengths of sunlight—generally including UV, visible, and infrared—as heat, while suppressing thermal reradiation via angular and wavelength selectivity,” said Dr. Peter Bermel, the MIT research scientist that led the research, which was recently published in Nanoscale Research Letters. “The heat is then sent to a selective emitter designed to thermally radiate photons with a narrow range of energies onto a TPV cell. A TPV cell works much like a silicon PV cell, except that it is usually made from different materials, such as gallium antimonide.”
He said this method may allow for efficiencies as high as 80 percent for concentrated sunlight.
It’s not likely to reach that level.
“Achieving temperatures closer to 1,500 kelvin and efficiencies of 37 percent, above the Shockley-Queisser limit of 31 percent for unconcentrated sunlight, seems achievable, according to my calculations,” he said.
That’s significantly higher than the 10 percent efficiency limit that TPV cells have yielded thus far.
The device would operate at high temperatures, similar to a concentrating solar power system (CSP), like a tower or trough system. As such it would need some time to warm up.
“The turn-on time at midday could be chosen on a case-by-case basis to be anywhere from a minute to a day for baseload continuous power generation. If the system started cold at sunrise, it could potentially take several hours to reach nearly full performance with a static design,” Bermel said. “We're also looking into ways to get better performance over the whole day with dynamic design elements.”
The device also has the advantage of being simple to manufacture with standard chip-fabrication technology, according to MIT. The next step will be to produce and test more devices tuning the materials for the highest efficiencies.