If your Question is how does a solar cell work then this article will help you a lot to get proper information.
As we know, Sun is the source of vital force on earth. Every life on earth uses the power of the sun to survive. Humankind is the most dominant life form on earth. We have not only used the power of the sun to survive; now, we are harnessing its power to benefit our livelihood. Solar electricity is an example of it.
Solar electricity is renewable and free. Other traditional sources of power use some kind of fuel such as coal, petrol, and uranium (for nuclear power plants). Solar electricity is generated by sunlight. A solar cell generates electricity.
How does a solar cell create electricity? The basic principle behind a solar cell is known as the photovoltaic effect, or PV for short. In this article, we will explain the working principles and mechanism of a solar cell in detail. Also, we will discuss why solar cells are essential, and what is its future briefly.
What is Solar Cell And How Does a Solar Cell Work
A solar cell is not anything like a battery or so; it looks like a panel. The solar cell is also known as a solar panel. The most popular solar cell is made of silicon (Si). A multi-cell solar panel made of silicon can provide up to 68% efficiency. Gallium Arsenide or GaAs is another popular material used to make solar cells. Gallium and Arsenic are one atomic higher and lower in the periodic table. So, a combination of the two makes the same atomic position of silicon.
Many kinds of the solar cell are being used today; Let’s See Some Important Types of Solar cell
⦁ Crystalline silicon cell
⦁ Polycrystalline thin films
⦁ Single and multijunction cell
⦁ Amorphous cell
⦁ Di-sensitize cell
⦁ Point contact cell
⦁ Plastic solar cell
⦁ Organic solar cell
Some popular types will be discussed later in the article.
Photovoltaic Effect of Solar Cell
Solar cells use the principles of the photovoltaic effect. So before explaining the working principle, we must know what a photovoltaic effect is.
When light is exposed to certain elements, it releases free electrons by absorbing photons. Photon is the energy light carries. This phenomenon produces a direct current within the components. This property of light to create a direct current in objects is called the photovoltaic (PV) effect.
Alexander Edmond Becquerel discovered the photovoltaic effect or PV effect in 1839. He was a French physicist. When he was experimenting with electrodes and electrolytes, he saw that illumination increases conductivity.
The same phenomenon occurred with Willoughby Smith in selenium this time. Later, Albert Einstein explained why this phenomenon occurs. Although his equation was originally developed for the photoelectric effect, it is also applicable to the photovoltaic effect. [energysage.com]
This property of certain materials to produce electricity gave a solar cell the idea of becoming a popular source of power. Based on the research, the most suitable material for the photovoltaic effect to happen is silicon. Other materials react to the PV effect, but silicon has the best efficiency. However, Gallium Arsenide (GaAs) is another suitable replacement for silicon.
Photovoltaic Effect and Photoelectric Effect of Solar Cell
The photovoltaic effect is almost similar to the photoelectric effect. Both the photoelectric effect and photovoltaic effect absorb sunlight, and both release electrons. But some differences separate these two phenomena.
The significant difference between the two effects is that when sunlight is absorbed and free electrons are released, electrons are emitted to space. For the photovoltaic effect, electrons directly enter new materials, creating voltage in the material.
Another significant difference between the photoelectric effect and the photovoltaic effect is that kinetic energy plays a vital role in producing electricity in the photoelectric effect. The photovoltaic effect does not require the kinetic energy of the emitted electrons to produce electricity.
The electrons emitted from the photovoltaic effect are used to generate electricity through the junction of diodes, but there is no potential to generate electricity from junctional diodes. The photovoltaic effect can be seen between two metals that are junctional with each other in a system.
The photoelectric effect occurs in a cathode ray tube by a cathode and an anode connected via an external circuit. The photovoltaic effect occurs when a specific range of photon energy hits subject materials, but the photoelectric effect is difficult to occur.
Solar Cell Structure
The most efficient solar cell design to date is called the Metal Wrap Through (MWT) solar cell. It can provide a 10% higher potential efficiency. Solar cells can be made with the following materials:
⦁ Mono-crystalline silicon
⦁ Poly-crystalline silicon
⦁ Cadmium telluride film
⦁ Silicon thin film
⦁ Gallium arsenide thin film
⦁ Copper indium gallium selenide film (CIGS)
The following procedures make a typical solar cell:
Interconnection Process of Solar Cell
A general solar cell is a combination of silicon semiconductors, which about 156mm x 156mm x 600µm in dimension. The semiconductors are trimmed and consist of up to 16 laser-cut through-holes.
A PV cell consists of both n-type and p-type holes in the same plane. The through-holes are used to transport the free electrons to move around. A specific pattern interconnects the semiconductors, and this pattern is known as a printed link.
This process helps to connect top to top and bottom to the bottom of two semiconductors. The whole process is controlled mechanically.
Insulation
The next step is insulation. This process is mainly for coating the semiconductors to isolate the semiconductor from the back of the cell. There are a lot of coating materials commonly used. Mylar sheet is one of them.
It is about 7-10mm thick—another primary reason for insulation to reduce UV ray penetration. Since UV rays have highly energetic photons, it may damage the silicon semiconductors.
This process is known as UV curing. Insulation also reduces the semiconductors’ inner temperature, which accelerates conductivity and capacity to store free electrons.
Routing
Routing refers to passing the free electrons from the semiconductors to produce electricity. So it works as an internal wire. Since copper has good conductivity and low cost, it is ideal for the routing process.
The copper used for routing is 5 to 20 millimeters thick and 100 to 200 millimeters wide. Sometimes insulation patterns are changed for better efficiency of routing.
Back Panel Installation/ Lamination
The final step of making a solar complete solar cell is the installation of the back panel. The back panels are not meant to be storing any electricity. So it should be shock-proof. Mostly plastic is considered for that purpose.
But it is also a concern not to lose any plastic efficiency so other materials can be considered. The upper cell module is coated with non-electric materials to manufacture a working solar panel and is ready for producing solar electricity.
Working Principle of Solar Cell; Incredible Working Process of Solar Cell
Solar cells use the photovoltaic effect as their primary working principle. When solar radiation hits certain materials, it produces electricity. This is only the basic theory of solar cells. Let us discuss the process elaborately.
Over decades of research, scientists found that silicon (Si) is the most durable element for the photovoltaic effect. When sunray hits silicon, there are three possible outcomes
⦁ Photons go straight through silicon
⦁ Photons reflected by silicon
⦁ Photons absorbed by silicon
The first phenomenon happens when photons carry less energy. The second one occurs when photons have a specific range of energy levels.
But when a photon carries greater energy than the other two cases, it creates electron-hole pair in the silicon. This excites the electrons and set some of them free to move around. Silicon semiconductors are required to utilize this property of silicon properly in the solar cells.
A semiconductor junction consists of a region of high concentrated electrons known as n-type and low concentrated electrons, p-type. The free electrons in the semiconductor then create charge carrier motion and separation of electrons. There are two causes:
⦁ Drift of carriers
⦁ Diffusion of carriers
Drift causes electrons and holes to push separate ways from each other. Diffusion causes electrons to move from higher concentration zones to lower concentration zones.
They work opposite each other. When these two forces work simultaneously, the current of electrons is produced. The current moves toward the n-type zone of the junction and can be wired.
The current can power the electricity load until it reaches the p-type zone. The voltage of the current is equivalent to the difference between the two carriers. [pveducation.org]
The whole system can be represented by a circuit diagram of the solar cell.
Some simple formula for calculating current and voltage are:
I = IL – ID – ISH
Here,
⦁ I = output current
⦁ IL = photogenerated current
⦁ ID = diode current
⦁ ISH = shunt current
The voltage can be measured by the following equation:
VJ = V + IRS
Here,
⦁ VJ = voltage across both diode and resistor RSH
⦁ V = voltage across the output terminals
⦁ I = output current
⦁ RS = series resistance
Finally, the electricity generation formula is:
E = A * r * H * PR
Here,
⦁ E = Energy (kWh)
⦁ A = Total solar panel Area (m2)
⦁ r = solar panel yield or efficiency (%)
⦁ H = Annual average solar radiation on tilted panels (shadings not included)
⦁ PR = Performance ratio, coefficient for losses (range between 0.5 and 0.9, default value = 0.75)
Some advanced functions require a higher understanding of mathematical terms. Since they are challenging to interpret, they are not provided here. The equations are Ohm’s Law, Shockley diode equation, physical size equation of cells, etc. [pveducation.org]
Contemporary and Previous Technologies
With the advancement of science in a drastic manner, technologies of Solar cells also have advanced. Let us discuss some of the contemporary technologies and compare them with previous ones.
Today’s cells can be categorized into three types based on the technologies they are made of.
⦁ Wafer-based cells
⦁ Commercial thin films
⦁ Emerging thin films
Wafer-based cells are traditional cells that use crystalline silicon or gallium arsenide. Commercial thin films use non-crystalline amorphous silicon, cadmium telluride, copper indium gallium selenide (CIGS), etc. Most advanced cells are called emerging-thin film cells. they include perovskite, quantum dot (QD), and organic cells. [energy.mit.edu]
The classical wafer-based cells can produce a fair amount of electricity. But according to some scientists, comparing them with today’s available advanced cells such as commercial cells is not very relevant. This is because a higher generation of cells may always have better performance than the previous one. But there are cases where traditional silicon cells still have some advantages over newer technologies.
But there should be some criteria that can provide a good measurement. Scientists have found some ways to compare the cells. Firstly, scientists found a way of differentiating cells by the material’s complexity in their molecular structures.
Silicon is very simple in structure. But in reality, silicon is hard to turn into a wafer or solar cell. Because to reach 100% purity for a single element is almost restricted. On the other hand, a compound has not had such a frontier to maintain purity. For QD, it can be achieved at a higher cost.
Another criterion can be the power conversion efficiency of the cells. Here, silicon is a clear victor because, to date, it can provide up to 33% efficiency with actual consistent efficiency of 26%. On the contrary, commercial thin films are locked at 10% to 20%.
But scientists are finding ways to develop a better photon absorb rate for this type of cell. Emerging thin-film cells are still in laboratory experiments in that case. Although they show promising results for smaller-scale cells, opening them for commercial usage is always a challenge.
For additional comparison, the external structure of the cells can be a factor. Traditional crystalline cells are a little heavier and require more space.
The film-structured cells are lighter, flexible, and somewhat robust in their structure. This can allow them to be portable and easily maintainable. But these are smaller details. So, it is really up to the users to decide which one is beneficial for them.
Latest Solar technologies
Although emerging commercial films can be considered the latest solar cells’ latest technology, some other technologies can be highlighted in this portion.
The light-sensitive nanoparticles are commonly known as colloidal quantum dots. A group of scientists from the University of Toronto made the discovery. They believe that is new technology can provide reduced cost and more flexibility.
Scientists claim that this technology is an outdoor functioning one, which can change the solar cell market. The basic theory is that the traditional cells, which consist of n-type semiconductors, can bind with oxygen or other materials, reducing efficiency.
But for colloidal quantum cells, there are no such issues. So it can absorb a better amount of photons. Studies showed that it could provide an 8% extra absorption rate.
Advancement in other aspects of a complete solar system can be seen too. For batteries, there are a few new theories. One of them is molten salt storage technology. The idea is to transfer the heat generation of cells to molten salt, reducing the cells’ operating temperature and increasing efficiency. [energy.mit.edu]
Another new technology for storage is a built-in battery of solar cells. This is to reduce the cost of batteries for a total solar system. It is claimed that the built-in batteries can provide 25% better storage efficiency and 20% cost reduction.
Maintenance
Here are some useful tips for solar cell maintenance:
⦁ When cleaning, use specific solar panel cleaning kits. Cleaning with the usual cleaning apparatus may harm the solar panel.
⦁ Make sure that dust does not stack on the system, whether it is the panel or the batteries.
⦁ Take necessary safety measures for dismounting panels, advised by the experts.
⦁ A performance monitoring meter is an excellent way to maintain the system.
⦁ Automated cleaners are available in the market; this can be an excellent investment to make user has less time to put on the solar system.
⦁ Keep the solar panel out of shade as they might become blunt or inactive.
⦁ Watch out for energy surges as they might damage the system, built the system in a cooler and safer place.
⦁ Keep an eye on other components such as inverters, batteries, or cables. Replace them with consultancy.
⦁ Never use harsh materials to clean solar cells as they might damage the inner structures.
⦁ Check for performance ups and downs; contact the technicians if the panels are underperforming.
Troubleshooting
Some of the common problems of solar systems and their troubleshooting process are as follows:
Loose Wiring: Many often, the wiring of the system becomes loose. This can happen for several reasons. One possible explanation can be temperature. Wires are made of plastic or rubber coating, which tends to increase with heat.
Another reason can the wires have become old. So, the troubleshooting is easy for this, change the cables, for the whole system or components. Use technicians’ directions before doing the process. [fluke.com]
System Overheating: Overheating is a problem for everything; the same goes here. Every component of a solar system should come with a reference heating manual.
If the system or any component is overheating, it means that there is something wrong with it. Contact the technician, in that case, to solve the overheating or replace the components.
Bad Connection: For bad connections, make the connections stable. Users should be able to do that by themselves with the user manual help that comes with the system. if the problem is severe, contact the system provider. [fluke.com]
Solar Cell Defect: If the solar cell becomes defective, there is nothing much a user can do since the cells are highly complex in structure. Replacing or returning the cells are the only options.
Low Voltage: if the system is giving low voltage levels despite being well operational, it might be because of shading. Check for shade on the cells and remove them if possible. Another reason for low voltage can be defective components. Seek the technician’s advice in that case.
Future development of Solar cells
⦁ Bio-solar cells: The biological solar cells or bio-solar cells are the most promising futuristic technology for solar power systems. This cell uses bacteria to increase the photon consumption rate of the cells. The particular bacteria is called cyanobacteria. They can be found almost everywhere. The technique is to produce extra electricity from the photosynthesis and respiratory activity of the bacteria. Though the production increases very little than the traditional cells, it holds outstanding potential. [altenergy.org]
⦁ Photo-bioelectrochemical cells: This is an entirely new idea for solar cells. The idea is to use the biochemical process of microbes, enzymes, and plants to enhance cell efficiency. This cell’s working principle is described in papers from the Hebrew University of Israel and the University of Bochum, Germany. But to unite photosystems with enzymes is a real challenge. [mit.edu]
⦁ Floating Solar cells: as the traditional silicon-powered solar cells are getting cheaper and more efficient, scientists proposed a floating solar farm on water bodies. The study suggests that floating PV cells can generate a huge amount of electricity. The cooling effect from water can increase power generation by up to 10% more than regular land-based cells. But the maintenance is a bit costly. A floating solar power plan already exists in California at Napa Valley.
⦁ Solar Fabric: Researchers are trying to create a solar fabric that can produce solar power on the go. The main idea is to use solar radiation everywhere since it is available everywhere. The fabric will use photovoltaic treads. Another project is to combine PV panels with solar fabric. Solar fabric may be used to charge phones on the go or even keep the cloth warm in winter. [mit.edu]
Conclusion
We hope You have got every single point how does a solar cell work. We also clarify that the solar cell is an emerging way of powering the earth. To better understand society’s needs, people should know more about solar cells and how they work. Also, knowledge of solar cells will help users understand their value and usage capacity.
This knowledge needs to be spread because the world is in ever need of electricity. One day the traditional means of producing electricity will stop because of scarcity.
Solar cells can produce renewable electricity; it is also a cheaper way of producing power. It is ideal for an individual power supply. So the knowledge of solar cells and solar systems is necessary.