Solar windows - transparent solar concentrators

A team of researchers from the University of Michigan, led by Richard Lunt, has developed a unique solar concentrator that can convert only part of the solar spectrum into ultraviolet, which is not perceptible to the human eye. The material is transparent to visible light, which means that such transparent solar panels can be easily inserted instead of window glass, while the window will look completely familiar, like ordinary glass in it, but electricity will be generated along the way. The development was called "transparent luminescent solar concentrator."

Colored luminescent solar concentrators are already widely known, in which part of the spectrum of the radiation incident on the concentrator is absorbed in the colored upper layer, then reradiated with a longer wavelength. Then, through a second, transparent layer, the radiation is directed to the lateral face of the concentrator, where the line of photodiodes that convert the radiation into electrical voltage is located.

When direct sunlight hits the top layer of the hub, it has a certain direction. But when re-radiation occurs, after the sunlight is absorbed, the rays of light already have different directions. It turns out that approximately the same amount of light is emitted in different directions.

If the angle of incidence of the reradiated rays at the glass-air interface is greater than a certain value, then the reflection occurs back inside the glass, then the rays fall on the opposite boundary, there they are again reflected at the same angle, and so after a few reflections in the end, the beam hits the side face hub. On the side face is a ruler photodiodes, which converts the energy of rays into electricity.

Due to the fact that light re-emission occurs uniformly in all directions, most of it, almost 80%, falls on the glass borders at an angle that is exactly more than critical, and therefore is transferred to the line of photodiodes on the side faces of the glass.

Thus, solar concentrators have the following advantages:

• firstly, unlike conventional solar panels, where photovoltaic converters cover the entire surface, here the converters are located on the faces, this reduces the cost;

• secondly, due to its transparency, such a hub can be inserted like ordinary window glass.

But there are also disadvantages, the first of which is low efficiency, because here it is much lower than that of conventional solar panelsand the second is that the light falling into the room is not clean, but slightly reddish. In other words, an ordinary transparent solar concentrator is still “color”, and not transparent.

The second flaw was eliminated by researchers from the University of Michigan. Scientists have made the top layer of organic molecules with a special property. They absorb not only the ultraviolet, but also part of the infrared spectrum, then re-emitting it into infrared light, but with a different wavelength.

As a result, scientists obtained a completely new working concentrator, which does not absorb and does not radiate in the visible range of the spectrum, that is, it is perceived by the human eye as ordinary transparent glass.

The obtained parameters allow to widely introduce this technology for various applications. These are the window panes of buildings, including high-rise ones, whose facades can be fully equipped with such transparent panels. These are the screens of various mobile devices, such as e-books, tablets, smartphones.The main task of the developers is to make solar concentrators invisible, like ordinary glasses.

Richard Lunt notes that despite the first step, there is still a lot of work to improve, in the first place - improving the efficiency of the new hub. The efficiency of solar energy conversion by a sample of 1% has now been achieved, but the developers say that at the moment their goal is to increase it to 5%. The efficiency of the best of the painted luminescent solar converters reaches 7%.