A transparent solar panel that can be placed directly over a window to harvest infrared solar energy has been developed at Michigan State University (MSU). Meanwhile physicists at Harvard University have proposed a device that would generate electric power by releasing infrared energy.
Scientists at MSU have developed a transparent luminescent solar concentrator (LSC) that could enable entire facades on tall buildings to become electricity generators.
The solar harvesting system uses small organic molecules developed by the scientists to absorb specific non-visible wavelengths of sunlight such as ultraviolet and near infrared. Richard Lunt, assistant professor of chemical engineering and materials science at MSU, said these materials then “glow” at another wavelength in the infrared. The “glowing” infrared is then guided to the edge of the plastic panel where it is converted to electricity by a thin strip of photovoltaic solar cells.
It is because the materials do not absorb or emit light in the visible spectrum that they look transparent to the human eye. This transparency will enable the LSC to be discreetly incorporated into fully glazed building facades without changing the building’s appearance. Lunt said the technology “opens a lot of areas to deploy solar energy in a non-intrusive way”.
The technology is still being refined. At the moment it has a solar efficiency of just 1%, but the research team hope eventually to reach efficiencies of 5% or above, which is still short of the 7% efficiency of the best coloured LSC panels. And, because the technology works by absorbing infrared radiation it could also be used to help reduce solar heat gain in buildings.
Jonny Williams, Associate Director of the BRE National Solar Centre welcomed the research,said: “It is fascinating to hear of this development. We welcome any innovation that serves to better integrate the solar, construction and property industries and I look forward to seeing how this technology matures.”
Releasing infrared light to generate electricity
At Harvard University, physicists are also proposing to use infrared emissions to capture energy.
Heated by the sun, the earth is warmer than the vacuum of space which surrounds it. This heat imbalance could be turned into DC power according to the physicists at the Harvard School of Engineering and Applied Sciences.
The team lead by Federico Capasso, professor of applied physics and senior research fellow in electrical engineering, are proposing a photovoltaic panel that works in reverse. Instead of capturing incoming visible light, the device would generate electric power by releasing infrared light.
The amount of power generated this way is small when compared to a conventional solar cell but the technology could be incorporated into solar cells to allow them to produce power at night without the extra installation cost.
The physicists have proposed two possible types of emissive energy harvesters: one that is analogous to a solar thermal power generator and one analogous to a photovoltaic cell. Both would run in reverse.
The first type of device would consist of a hot plate at the temperature of the Earth and a cold plate on top of it which is cooled by radiating heat to the sky. The researchers have calculated that the heat difference between the two plates could generate “a few Watts per square metre day and night”.
The second device relies on the temperature difference between a diode and a resistor in an electrical circuit. If the diode is at a higher temperature than the resistor, it will push the current in a single direction producing a positive voltage. The scientists say the resistor could take the form of an antenna which could be used to cool that part of the circuit to generate a current. According to the researchers a single solar panel could be coated in many of these tiny circuits to generate power at night.
Source: http://www.building4change.com/ Report from – Andrew Pearson