SOLAR CELLS OPTIMIZE THERMAL RADIATION
Did you know solar cells can ‘see’ only a portion of the solar radiation? Close to 20 percent of all the energy in the solar spectrum is not available to silicon cells. For instance, they cannot utilize short wavelength infrared radiation for powergeneration.
That is about to change. Researchers have demonstrated how this unusable radiation can be tapped into with the help of an up-converter. Although the technology to convert infrared into usable light has existed since the 60s, we did not investigate this technology for its potential use in solar cells.
Recent research conducted at the Fraunhofer Institute in Switzerland produced the biggest improvement in terms of energy efficiency. Which is good news because traditional solar cells only convert thirty percent of the sunlight that falls on them into electrical energy. With the help of up-converters, this amount can go up to 40 percent.
LIGHT PARTICLE LADDER
You might be thinking – how can the up-converter tap into infrared radiation in a solar panel? As radiation from the sun falls on the solar panels, they absorb the near-infrared and visible light. The infrared portion of the light isn’t absorbed. It goes right through the cells.
In the new system, the unabsorbed radiation is made to fall on a up-converter, which is basically a micro crystalline compound made of sodium yttrium fluoride, embedded inside a polymer. Some of the yttrium is replaced with erbium, which tends to be active in the optical range and is responsible for the up-conversion. As the light falls on the converter, it excites the erbium ions, which raises them to a higher energy state.
The reaction is not very different from climbing up a ladder. The electron uses the light particle’s energy to climb over to the next step. Ions that have been excited this way can come back down from the highest state. When it does, it emits light energy that is equivalent to all the light particles that helped it climb up the ladder. The up-converter then converts the energy of these particles and transfers it all to a single one. The solar cells can then “see” it and utilize it.
CAN TRADITIONAL SOLAR CELLS USE THIS TECHNOLOGY?
It goes without saying that traditional solar cells will have to be modified to accommodate this. Usually, the metal is deposited on the backside through chemical vapor deposition, which makes it possible for current to flow out of the cells. So, no light can shine through. These solar cells will be equipped with metal lattices on the rear and the front so that infrared light can pass through them.
Moreover, light can be used by both cell faces. The researchers call it a bi-facial solar cell. They applied special anti-reflective coatings to the rear and front of the solar cell. These cancel all the reflections at the surfaces and make it possible for the cells to absorb as much light as they can. The potential of this new technology is vast and will go a long way into making solar panels more efficient.