Who Says Solar Panels Can't Tap Sun's Energy At Night?

Solar Missing Link Discovered, Giant Step For Humanity

Solar panels have been unable to collect energy at night, a major missing link in renewable energy production until MIT researchers recently presented a solar thermophotovoltaic (STPV) cell, revolutionizing clean, healthy and safe sustainable energy.

“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,” remarked Zhuomin Zhang, a professor of mechanical engineering at the Georgia Institute of Technology, who was not involved in the research. “This achievement paves the way for rapidly boosting the STPV efficiency.”

A new approach to harvest solar energy, developed by MIT researchers, could improve efficiency by using sunlight to heat a high-temperature material that’s infrared radiation would then be collected by a conventional photovoltaic cell, according to MIT News.

This technique could also make it easier to store the energy for later use, the researchers say.

Such a system, the team says, combines the advantages of solar photovoltaic systems, which turn sunlight directly into electricity, and solar thermal systems, which can have an advantage for delayed use because heat can be more easily stored than electricity. The new solar thermophotovoltaic systems, they say, could provide efficiency because of their broadband absorption of sunlight; scalability and compactness, because they are based on existing chip-manufacturing technology; and ease of energy storage, because of their reliance on heat. (MIT News)

Until recently, photovoltaics generate power at night or absorb more than a narrow band of wavelengths from sunlight, as seen in the image below.

MIT reesaerchers have solved both problems with one device: the solar thermophotovoltaic (STPV) cell.

How to tap the sun’s energy through heat as well as light

“The idea is to concentrate sunlight onto a solar cell, grab most of the solar spectrum, and convert it to the wavelength that photovoltaics prefer,” reports Tom Lombardo for Engineering.com. “The multilayer STPV cell incorporates an absorber made of carbon nanotubes that absorb most of sun’s spectrum and convert it to heat, and an emitter made of of a silicon photonic crystal that glows when heated.

“The emitter’s output is tuned to the wavelength at which PV cells operate most efficiently.”

What happens at night? Lombardo explains:

Heat can be stored more easily than electricity, so panels made of solar thermophotovoltaic (STPV) cells can generate electricity at night, assuming they hold on to the heat that they absorbed during the day.

While the researchers are “a little sketchy” about how heat would be stored, Lobardo wonders if the emitter material can have a relatively large thermal mass, so it heats up slowly and retains its heat after the sunlight disappears.

“That way, instead of getting a burst of energy when the sun is shining and nothing after sunset, you’d get a more steady energy production day and night.”

Source: MIT News Office, Engineering.com

Photos: Tom Lombardo