Solar Cell
Solar Cell
Why do we have to dig for coal or digging for oil when there’s a gigantic power plant high above us that provides free, clean energy? The Sun is a glowing ball of nuclear energy, can provide enough energy to power our Solar System for five billion more years. Solar panels can transform the energy into an endless amount of electricity.
While solar power might seem odd or futuristic, it is already very popular. A solar-powered watch or calculator for your purse could be on your wrist. Many gardeners have solar-powered lights. Solar panels are often located on spacecrafts and satellites. NASA, the American space agency, even designed an aircraft powered by solar energy. Global warming is threatening our environment and it is likely that solar power will become an increasingly important source of renewable energy. What is the process?
What is the maximum amount of solar power we can get from the Sun?
It’s amazing how solar power functions. Each square meter of Earth receives an average 163 watts of solar power. This figure will be discussed in more detail in the next paragraph. This means that you could place the power of a table lamp that is 150 watts on every square meter of Earth and use the Sun’s electrical energy to light up the entire planet. Another way of putting it is that in the event that we only covered 1percent from the Sahara desert with solar panel, then we would produce enough solar energy to provide power to the entire globe. The good benefit of solar power is that there’s a lot of it, more than we could ever need.
There’s a down side. The Sun’s energy comes as a mixture of light and heat. Both are essential. The light helps plants grow and provide us with food. The heat keeps us comfortable enough to live. However, we are not able to make use of the sun’s energy or light directly to solar power a car or TV. It is important to transform solar energy into another type of energy that we can use more easily such as electricity. This is exactly the job solar cells perform.
In Summary:
- The cell’s surface is lit by sunlight
- Photons carry energy through the cells’ layers.
- Photons transmit energy to electrons in lower layers.
- The energy used by electrons to let electrons escape the circuit, and return into the upper layers.
- The energy for a device is provided by electrons that move around the circuit.
What are solar cells?
A solar cell is an electronic device that absorbs sunlight and converts it into electricity. It’s roughly equal to a hand of an adult, octagonal in form, and colored bluish-black. A variety of solar cells can be bundled together to create larger units called modules. They are then joined to form bigger units known by solar panels. (The blue or black tiles you see on homes typically have hundreds of solar cells per roof) Or chopped into chips (to provide power to small devices such as digital watches and pocket calculators).
The cells in a solar panel work in similar ways to batteries. However, in contrast to battery’s cells that produce electricity through chemical reactions solar panel’s cells capture sunlight to create electricity. Photovoltaic cells (PV) is a term used to describe solar cells that produce electricity using sunlight (photo is derived in the Greek word meaning light). The term “voltaic”, however, refers to Alessandro Volta (1745-1827), an Italian electrical engineer who was a pioneer in the field.
Light is often described as tiny particles known as photons. A beam of sunlight is similar to an enormous Yellow firehose which releases trillions of trillions. Solar cells can be placed within the path of these photons to capture them , and later transform them into an electrical current. Each cell can generate only a few volts, therefore the job of a solar panel is to combine energy from many cells to produce an appropriate amount of electric current and voltage. Nowadays, solar cells are almost entirely made of silicon (one the most well-known chemical elements found on Earth and is found in sand). But, as we’ll see, other materials may be a possibility. The sunlight’s energy blasts electrons out of the solar cell when it’s exposed to sunlight. Then, they can be utilized to power any electrical device that is powered by electricity.
How are solar cells made?
Silicon is the material used to make microchip transistors (tiny switches), are made. Solar cells work in a similar way. The term semiconductor refers to a type of material. Conductors are the materials that allow electricity to flow freely through them, including metals.
Others, like plastics or wood, don’t permit electric current to pass through; they are called insulation. Semiconductors, like silicon, are not conductors , nor insulators. However we can make them conduct electricity under certain conditions.
A solar cell is made up from two silicon layers, each of which has been doped or treated so that electricity can move through it in a specific manner. The lower layer has slightly less electrons due to it being doped. This layer is called the p-type or positive-type silicon. It has too many electrons and therefore is negatively charged. To give the layer an excess of electrons it is charged with a negative charge. This is known as negative-type and n-type silicon. (Read more about semiconductors and doping in our articles on transistors and integrated circuits.
A barrier is formed at the junction between two layers of n-type and silica p-type. This barrier is the crucial boundary where the two types of silicon come into contact. It is unaccessible to electrons, so even if the sandwich has been connected with a flashlight, the current won’t flow and the light bulb won’t switch on. However, if you shine light onto the sandwich, it’ll produce some amazing results. The light could be considered as a streaming stream, of light or “light particles” which are energetic, and are referred to as photons. Photons that enter the sandwich release their energy to the silicon atoms as they pass through. The incoming energy is able to knock electrons away from the lower, p type layer. They then cross barriers to get into the higher n-type and move around the circuit. The more light that is available, the more electrons will rise and more current flows.
How efficient are Solar Panels?
The conservation energy law, a fundamental rule of physics, stipulates that energy can’t be made or transformed in the air. It is only possible to convert it from one form of energy to another. Solar cells cannot generate more electricity than it gets in light each second. As we’ll see, the majority of solar cells convert between 10-20% of the energy they receive to electricity. The theoretical maximum effectiveness of a typical single-junction silicon solar panel is approximately 30 percent. This limit is referred to by The Shockley Queisser Limit. Because sunlight is a wide spectrum of wavelengths and energies that a single-junction silicon solar cell will only collect photons within a narrow frequency range. All other photons will go to waste. Some photons that strike the solar cell are too weak to produce enough electrons. Some have too much energy and go to waste. In the most ideal conditions, lab cells that use advanced technology may achieve just below 50 percent efficiency. They use multiple junctions to capture photons with various energy levels.
A real-world domestic panel might have an efficiency of approximately 15 percent. Single-junctionsolar cells of the first generation won’t achieve the 30 percent efficiency limit set by Shockley-Queisser, or the lab record that is 47.1 percent. There are many factors that could affect the efficiency of solar cells, including how they’re constructed, angled , and placed and whether or not they’re in shadow and how clean they are, and how cool they look.
Different types of Photovoltaic Cell
A majority of the solar cells that you see on rooftops are silicon sandwiches. They have had their silicon “doped” to enhance the electrical efficiency of their cells. These solar cells of the past are referred to as first-generation by researchers to distinguish them from two more advanced technology, second- and third generation. What is the difference?
First-generation Solar Cells
More than 90 percent of the world’s solar cell production is made from wafers containing crystalline silicon (abbreviated “c-Si”), which are sliced from large ingots. This process can take up to one month and is carried out in ultra-clean labs. Ingots could be single crystals (monocrystalline solar panels) or multi-crystalline (polycrystalline solar panels) in the event that they contain multiple crystals.
Solar cells of the first generation function as we’ve shown them in the above box. They use one, simple junction between n and p-type layers of silicon. The latter is cut from separate ingots. An n-type ingot is made by heating tiny pieces of silicon using small amounts (or antimony or phosphorus) as the dopant. A p-type one would use boron. The junction is made by combining slices of p-type and n-type silicon. There are additional bells and whistles which can be added to photovoltaic cells (like an antireflective coating, which improves light absorption and makes them blue) and connections made of metal to allow them to be wired into circuits. However, a basic p-n junction is the one that most solar cells depend on. Photovoltaic solar cells have been working since 1954, when Bell Labs scientists pioneered it by shining light onto silicon sand they produced electricity.
Second-generation Solar Cells
The traditional solar cells are thin film solar cell wafers. They’re usually only tiny fractions of millimeters thickness (around 200 micrometers or 200mm). They’re not as thick than second generation solar cells (TPSC) or thin-film solar cells that are 100 times thinner (several millimeters, or millimeters of a meter deep). Although the majority of them are still made of silicon (a type of silicon known as amorphous silu (a-Si)), in which the atoms are placed in random crystalline forms Some are composed of different materials like Cd-Te, cadmium-telluride and copper indium gallium diselenide, (CIGS).
The second generation cells are thin and light and can be laminated to windows, skylights as well as roof tiles. They are also compatible with all kinds of “substrates” which are backers such as metals and plastics. Second-generation cells have less flexibility than first-generation ones, but they still perform better than their predecessors. A top-quality first-generation cell may have an efficiency of 15 to 15 percent, however, Amorphous silicon is struggling to reach higher than 7 percent) and the top thin-film CdTe cells achieve just 11 percent efficiency, with CIGS cells can’t even reach 7-12 percent. This is among the main reasons why second-generation solar cells haven’t been able to make a mark in the market , despite their numerous advantages.
Third-generation Solar cells
These innovative technologies blend the best features of first- and 2nd generation cells. They are expected to have high efficiency (up to 30 %) as do first-generation cells. They tend to be constructed from substances other that silicon (making second-generation photovoltaics (also known as OPVs), as well as perovskite crystals. Additionally, they may feature multiple junctions (made by multiple layers made of different semiconductor materials). They would be more affordable, more efficient, and feasible than first or second-generation cells. The record-setting global record of efficiency of the third generation solar cells stands at 28.9. This was achieved in December of 2018 with the perovskite-silicon tandem solar cell.
How are they made?
Like you see there are seven steps in the process of making solar cells.
1. Purify Silicon
Silicon dioxide gets heated up in the electric oven. To release the oxygen carbon arcs, it is possible to be applied. The result is carbon dioxide and molten silica, which can be used to construct solar cells. However, even the silicon is produced with a 1% impurity, it’s not quite good enough. The floating zone method permits the silicon rods that are 99% pure to pass through a hot zone many at a time, in the direction of. The process eliminates all impurities from one end of the rod, allowing it to be cleaned.
Second Stage: The Making of Single Crystal Silicon
Czochralski Method has become the sought-after method of creating single-crystalline silicon. This involves placing a seed crystal made of silicon inside melting silicon. This creates a boule or cylindrical ingot, by spinning the seed crystal while it is removed from the silicon melting.
Third Stage Cut the Silicon Wafers
Second stage boules are used for cutting silicon wafers using the circular saw. This task is best accomplished with diamonds, which create silicon slices that can be further cut to make hexagons or squares. Although saw marks are removed from the sliced wafers, some manufacturers keep them in place because they believe that more light could be absorbed by rougher solar cells.
4. Stage: Doping
After cleaning the silicon at a earlier stage, it’s possible to introduce impurities into the material. Doping involves the use of a particle accelerator to ignite phosphorus ions in the ingot. It is possible to control the penetration depth by setting the speed of electrons. You can avoid this step using the standard method of inserting boron while cutting the wafers.
Step Five: Add the electrical connections
Electrical contacts are used for connecting the solar panel and serve as receivers for the electricity generated. These contacts, made of metals like palladium and copper, have a thin structure to let sunlight into the solar cell in a way that is efficient. The metal is either deposited on the exposed cells , or it is evaporated by vacuum using a photoresist. The thin strips of copper lined with Tin are usually placed between cells after the contacts have been inserted.
Stage Six Step Six: Apply the Anti-Reflective Coating
Because silicon is shiny, it has the ability to reflect up to 35% of sunlight. To reduce reflections, a layer of silicon can be applied. The process involves heating the surface until the molecules begin to boil off. The molecules move on to the silicon and condense. The high voltage could also be utilized to detach the molecules, and then deposit them onto the silicon on the opposite electrode. This is referred to as “sputtering”.
Stage Seven Step Seven: Encapsulate and Seal the Cell
The solar cells are enclosed with silicon rubber or ethylene vinyl Acetate. Then, they are put in an aluminum frame with the back sheet as well as a glass cover.
What amount of electrical energy can solar cells produce?
Theoretically, it’s quite a bit. For the moment, let’s forget about solar cells and focus on the pure sun. Every square meter on Earth could receive as much as 1100 watts of sun energy. That’s the estimated power of direct sunlight during a clear day. The solar rays are firing perpendicularly to the Earth’s surface and provide the maximum illumination.
After we adjust to the tilt of our planet as well as the time we should receive between 100 and 250 watts per sq. meter in northern latitudes, even on cloudless days. This is equivalent to 2-6 kWh daily. Multiplying the entire year’s production produces 700- 2500 kWh for every sq. m (700-2500 units) of electricity. The sun’s energy potential in warmer regions is evidently more than Europe. For example, in the Middle East receives between 50 and 100 percent more sun energy each year than Europe.
However, solar cells are only around 15 percent efficient so you can only harvest 4-10 Watts per square foot. That’s why panels that produce solar power must be large: how big you are able to cover by cells will affect the power you can generate. The typical solar panel made up with 40 solar cells (each row of eight cells) will produce about 3-4.5 watts. A solar panel composed of 3-4 modules could produce several kilowatts. This is enough to supply a house’s most energy-intensive needs.
How about Solar Panel Farms?
However, what is the best option if we require large amounts of solar energy? You’ll need between 500 and 1000 solar roofs to generate the same amount of electricity as a wind turbine that has an output peak of 2.5 or 3.0 megawatts. To compete with coal or nuclear power plants (rated in the gigawatts), you would need approximately 1,000 solar roofing systems. This is roughly 2000 wind turbines or perhaps a million of them. These comparisons assume that our solar and wind power sources produce the maximum output. Even though solar cells can generate clean, efficient electricity but they are not able to claim to be effective in the use of land. Even the massive solar farms popping up all over the country only produce small amounts of power, typically around 20 megawatts , or one percent less than a 2 gigawatt coal or nuclear plant. Texas Solar Group, a renewable company, estimates that it takes approximately 22,000 panels to cover a 12-hectare (30-acres) space to generate 4.2 megawatts. This is roughly the same as two large wind turbines. It also generates enough power to power 1,200 homes.
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