Collecting solar power in cloudy days is really a problem for the solar industry, since it can make this source of energy unreliable and pretty intermittent. An MIT researcher, Carmen Rotschild, presented a solution that would be perfectly suited for this.
At the Optical Society of America’s Frontiers in Optics 2010 she discussed the possibility of capturing light, turning it into a laser beam, which is then sent to a photovoltaic cell to create electricity with very little loss. The device is called Luminescent Solar Laser.
So far, only devices that use incoherent light have been created, and they are called luminescent solar concentrators (LSC). But turning to a laser means that the light, incoherent by its nature, should be processed and turned into a coherent form (in which all the wave fronts have the same phase, hitting the target at the same time).
Incoherent LSCs use the principle of total internal reflection to harvest a beam of light through a dye-coated slab of clear plastic, which reradiates it in a lower wavelength band and makes it reach the end of the slab. There, the photovoltaic cell harvests the concentrated light much more efficiently than it would have done without the slab.
However, part of the light’s energy is lost because the dye reradiates it in all directions, since it’s incoherent (some photons with different phases pass through).
What Rotschild and her colleagues propose is to create microring lasers made of three materials. One layer’s output-wavelength band will match the following layer’s absorbtion-wavelength band, so the chain is theoretically perfectly light-conductive.
From the outside to the inside of the Luminescent Solar Laser, a very thing outer dye coating absorbs and reradiates light very efficiently, but doesn’t transmit it very well. The second material absorbs the first layer’s reradiated light and re-emits it in a longer wavelength (just like in the LSC). This re-emission has a longer transmission length, fact which leads the light to enter the laser cavity. The cavity, which has a high Q factor (lower rate of energy loss), has a very low absorbance, but this is compensated by its high Q factor. This cavity absorbs the light from the second material and produces a coherent laser light by all classic principles.
More research has to be done in order to have a fully functional unit. However, experimentation has led the researcher to promising results, but the need for knowing which materials are best suited for such a device and studying their perfect geometry leads to a delay.
Both the luminescent solar laser and the classic LSC could be used perfectly to harness the sun’s energy from any angle, without the need for tracking devices. Furthermore, their concentration abilities make them become the hope of every solar panel enthusiast, especially in cloudy areas of the world.
