1 INTRODUCTION
The non-renewable energy sector in today's economy relies heavily on solar energy, which converts the sun's energy into electricity. The main point about solar energy is that the energy is absorbed by the sun's rays and so it is necessary for the solar cell to be opaque in order for it to absorb the light energy and so it cannot be transparent and let the sunlight simply pass through it. . Therefore, a solar panel, besides being a solar panel, cannot multitask like anything else. It just adds an extra layer on top of a base layer. Making the solar panel transparent is scientifically impossible, but it can be circumvented by manipulating the absorption of a certain segment of the electromagnetic spectrum.
A team of researchers at Michigan State University created a completely transparent solar cell in August 2014. Unlike the traditional solar cell, it allows photons to pass completely through it, allowing people to see through them. It uses ingenious manipulation of the properties of materials through the use of materials science and chemistry. The team is led by Richard Lunt, an assistant professor at Michigan State who founded the company Ubiquitous Energy to commercialize this technology. Lunt is confident that this product will be useful for implementation in large buildings with many windows or mobile device screens to reduce the load on the primary power source. In this article, we will discuss how they manage to overcome a huge limitation of the conventional solar cell. First we will understand the concept of Luminescent Solar Concentrator (LSC) and then we will apply this logic to understand how it can become transparent.
two LUMINESCENT SOLAR CONCENTRATORS
Currently, conventional photovoltaic solar panels are quite expensive to install in homes where people are looking for a clean environment. The high costs are attributed, firstly, to the use of expensive photovoltaic semiconductors to generate electricity in response to receiving sunlight, and secondly, to the fact that they are currently not very efficient. The trivial solution would be to work on increasing the efficiency of the photovoltaic energy itself, but it is more economical to make adjustments to the solar panels so that they are more exposed to sunlight during their uptime. Achieving this goal is the aim of two main projects, namely solar trackers and luminescent concentrators. Solar trackers are mirrored arrays with mechanisms built to follow the sun across the sky to adjust the solar panels at an ideal angle to receive maximum sunlight. However, solar trackers are expensive because they need to be moved. They also cause the photovoltaics to heat up excessively and therefore require an additional cooling system. Luminescent solar concentrators work by taking radiation energy from a large area and concentrating it into a smaller area, absorbing and emitting directional luminescence.
2.1 PRINCIPLE
Luminescent solar concentrators work by concentrating radiation from a large surface onto a smaller area to improve the effectiveness of solar cells in producing electricity. In principle, it works by converting radiation from a large area into a bright luminescence and is directed to a smaller area, essentially just compressing the light and therefore increasing the power density.
2.2 DESIGN AND CONSTRUCTION
LSCs contain parallel sheets of regular plastic and dye-coated plastic. When sunlight passes through plastic, it is absorbed by the plastic. The dye's electrons are then excited by the addition of radiation energy and jump to a higher level. When they return to the ground state, energy is released in the form of radiation. This radiation is reflected through the plastic sheet through the principle of total internal reflection, that is, when the light exceeds a certain critical angle, it is reflected from a transparent surface. The light is guided by the total internal reflection waveguides to the smaller surfaces of the concentrator, where it is absorbed by the conventional photovoltaic semiconductor strip. These solar concentrators are cheaper than solar trackers, mainly because they are stationary and do not require an additional cooling system. Furthermore, the yield per unit cost would be higher when used in conjunction with these luminescent concentrators, increasing efficiency by around 50%. The only problem that needs to be solved would be the reabsorption of radiation in the dye as it bounces around inside, leading to a loss of energy. Transparent luminescent solar concentrators are a special type of LSC that replace translucent dyes with organic salts that do not absorb the visible spectrum of sunlight and therefore allow photons to pass through.
Figure 1Operating diagram of luminescent solar concentrators
3 TRANSPARENT LSCS – WORKING PRINCIPLE
Figure 2 Close-up of a functional TLSC
The basic concept of the transparent solar cell is that the transparent glass is not actually the solar cell. The glass is actually a transparent luminescent solar concentrator. It consists of organic salts that are complex derivatives of cyanine fused with glass. Cyanine is a synthetic dye used as a fluorescent dye in the field of biomedical imaging, which has a cyan tone as the name suggests and depending on the structure covers the IR to UV spectrum. Specific salt derivatives of the dye cyanine that are precipitated by its reaction with a base, are used to absorb the near-infrared and ultraviolet spectrum, allowing visible light to pass through. to pass through, but it absorbs the ultraviolet and near-infrared region, which are invisible to the human eye. The cyanine derivative luminesces (emits) absorbed energy at a different infrared frequency which is channeled to the edges of the glass by total internal reflection to the edges with the smaller surfaces being coated with conventional small-scale photovoltaic solar cells which are then converted in electricity.
Figure 3 Selective absorption of the UV (ultraviolet) and NIR (near infrared) spectrum of a TLSC
3.1 WHERE YOU GO?
The current TLSC has an efficiency of 1% and therefore still has a long way to go to become a useful addition. Lunt believes it needs to be brought to a value of 10% before it can be effectively used to power buildings where they replace glass windows. They believe they can currently increase this to 5% and work to increase efficiency by adding more effective layers that hinder absorption and reduce energy leakage. With an efficiency of 5%, the windows can be used to power the LED lights present on that floor. With higher efficiencies, they can effectively contribute to reducing dependence on fossil fuels. As an added benefit, it can also protect your interior from harmful UV rays that can cause skin problems. Researchers also believe they can be used to replace smartphone screens to power onboard electronics in combination with lithium-ion batteries to significantly increase the battery life of this generation's heavy smartphones.
4 CONCLUSION
This is also not the first time that researchers have tried to produce transparent solar panels. The researchers also used arrays of microscale solar cells as sheets placed between sheets of glass to allow a nominal amount of light to pass through. However, these panels are noticeable in their opacity as they cast a colored shadow that may not please the people inside. It is in this aspect that TLSCs have the advantage to progress further, as they have almost 90% visible light transmittance. Bearing in mind that this is currently a breakthrough, it's a pretty inspiring concept that cleverly gets around a hurdle in classical physics. Of course there are pros and cons to this invention, but it would be exciting to see how this product can change the way we utilize the raw source of solar energy in an era of self-sustainment.
