Researchers have come up with a groundbreaking method for capturing and storing solar energy.
The efficient process uses "sunlight to heat a high-temperature material whose infrared radiation would then be collected by a conventional photovoltaic cell," a Massachusetts Institute of Technology (MIT) news release reported.
The method allows scientists to capture light wavelengths that have not been utilized in the past.
"[A conventional silicon-based solar cell] doesn't take advantage of all the photons," associate professor of mechanical engineering Evelyn Wang said in the news release.
To convert a photon into electricity the photon's energy level must match that of a photovoltaic (PV) material (bandgap). Silicon's bandgap is compatible with a number of light wavelengths, but lets others go to waste.
The team inserted a two-layer absorber-emitter device in between the PV cell and sunlight source. The device was made from materials such as carbon nanotubes and photonic crystals
"This intermediate material collects energy from a broad spectrum of sunlight, heating up in the process. When it heats up, as with a piece of iron that glows red hot, it emits light of a particular wavelength, which in this case is tuned to match the bandgap of the PV cell mounted nearby," the news release reported.
In the past researchers have proposed a theoretical limit on the "energy-conversion efficiency of semiconductor-based photovoltaic devices." The "Shockley-Queisser limit" puts a 33.7 percent cap on this type of efficiency.
"[With the TPV system] the efficiency would be significantly higher - it could ideally be over 80 percent," Wang said.
Past work has only been able to produce STPV devices with efficiencies of about one percent. This new device already has achieved 3.2 percent efficiency and could reach 20 percent in the near future.
This improvement was made possible by the two-layer absorber-emitter material. The device exposed multiwalled carbon nanotubes to sunlight to absorb the heat; the nanotubes are attached to photonic crystals glow when the light's peak intensity is above the "bandgap of the adjacent PV."
The system employs a solar photovoltaic system which converts the sunlight directly into electricity as well as thermophotovoltaic systems that allow the energy to be more easily stored.
"This work is a breakthrough in solar thermophotovoltaics, which in principle may achieve higher efficiency than conventional solar cells because STPV can take advantage of the whole solar spectrum. ... This achievement paves the way for rapidly boosting the STPV efficiency," Zhuomin Zhang, a professor of mechanical engineering at the Georgia Institute of Technology who was not involved in this research, said.
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