A luminescent solar concentrator (LSC) is a device capable of absorbing and concentrating sunlight to produce electricity. Luminescent solar concentrators capture solar radiation over a large area. Subsequently, they convert this radiation into luminescence and direct it to a smaller target with a photovoltaic receiver.
LSC panels are cheaper than classic photovoltaic panels. In fact, they are made of plastic or glass plates on which the luminescent molecules are deposited.
How Does a Luminescent Solar Concentrator Work?
LSCs are transparent active photographic plates capable of absorbing light from a wide spectrum of solar radiation.
These elements use special luminescent dyes capable of capturing light and emitting it inside the plate. The radiation is then transported to the edges by successive reflections within the plate. At the edges of the panels are photovoltaic cells that convert sunlight into electricity.
The concentration system has many advantages. Silicon cell overheating is reduced, often leading to reduced efficiency and energy loss in the form of heat.
Also, by passing through the solar panels, the incident radiation is converted into wavelengths that maximize the cells' efficiency.
In 2013, researchers at Michigan State University demonstrated the first visibly transparent luminescent solar concentrators. It has a power conversion efficiency of close to 0.5%, efficiencies of over 10% are possible.
Pros of Luminescent Solar Concentrators (LSC)
Among the advantages of luminescent solar concentrators are:
Higher efficiency: They make it possible to shift the solar spectrum's short-wave radiation region to a more extended wavelength range. Within this range, the conversion efficiency of solar cells is higher.
Use of diffuse solar radiation. Achieve a high optical concentration of sunlight in stationary devices due to capturing direct and diffused light.
It prevents solar cells from overheating.
Using the LSC working with a PV system for the production of electrical energy will increase overall efficiency.
The use of small area photovoltaic cells allows the use of more efficient and expensive solar cells. Solar cells are what convert light energy into electricity.
Cons of Luminescent Solar Concentrators (lscs)
This type of solar concentrator has some drawbacks:
The "cone of loss" exerts a relatively significant influence on the efficiency of the structure through which a part of the re-emitted light leaves the volume of the waveguide and can no longer be used for conversion into electrical energy.
To reduce losses within the waveguide is necessary to lower the critical angle by increasing its refractive index. In this case, the loss due to sunlight reflection increases due to a rise in the external acute angle.
The reabsorption of the light re-emitted by a phosphor generates a loss. This loss is inextricably linked to the "cone of loss.”
Uses of LSC Solar Devices
It is possible to integrate solar energy structures consisting of LSCs and PV systems into urban infrastructure using existing artificial surfaces. Building-integrated photovoltaics can be, for example, translucent building structures, such as windows, stained glass, cornices.
The introduction of these systems in mobile electronic devices and fabrics (e.g., backpacks) is promising. The cost of a structure consisting of a luminescent solar concentrator, combined with a solar cell, will be less than the cost of a pure solar cell of similar efficiency. It is because in the first case, the area of the photovoltaic panel will be smaller.
What Materials Are Used in a Luminescent Solar Concentrator?
Plastics, glass, or organic solvents between the plastic or glass sheets can be used as the LSC matrix material. Polymeric materials are best suited for these purposes due to their optical and operational properties and their manufacturability. For these purposes, polymethyl methacrylate and polystyrene are most often used.
Organic dyes, composed of rare earth metal ions and quantum dots, of which the former are the most widely used due to their high quantum yield, ease of use, and low cost, can act as a luminescent material.
When transparent plates are doped with fluorescent materials, the influential design requires that the dopants absorb most of the solar spectrum, re-emitting most of the absorbed energy as long-wave luminescence.
Its concentration for an effective operation does not exceed 1% of the mass, positively affecting the structure's cost. Theoretically, about 75-80 % of the luminescence could be trapped by total internal reflection in a plate with a refractive index roughly equal to that of typical window glass.
Conclusions
Modern solar energy has a sufficient number of unsolved problems, such as:
The high cost of solar cells
The low conversion efficiency of solar cells, which traditional methods cannot increase without high costs,
The discrepancy between the photovoltaic converters' spectral sensitivity with the spectrum of sunlight and the volume of the most efficient ones.
We can solve all these problems separately by improving existing technologies. This approach is time-consuming and costly for materials, making it challenging to develop solar energy as traditional fossil fuel reserves are reduced. Therefore, this new solar window, the luminescent solar concentrator, can be an excellent solution to consider.
