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Solar Cell

Why do we have to dig for oil or shoveling coal when there’s a massive power station high above us that sends out free, clean energy? The Sun, a smoldering ball of nuclear energy is able to supply the energy needed to supply power to our Solar System for five billion more years. Solar panels can transform this energy into an unending amount of electricity.

While solar power might seem odd or futuristic however, it’s already popular. A solar-powered clock or calculator to keep in your pocket could be in your wrist. Many gardeners are equipped with solar-powered lighting. Solar panels are commonly located on spacecrafts and satellites. NASA, an American Space Agency, has even created an aircraft powered by solar energy. Global warming is threatening the environment and it is likely that solar energy will be an increasingly important source of energy that is renewable. What is the process?

What is the maximum amount of solar power we can get from the Sun?

It’s amazing how solar power operates. Each square meter of Earth receives an average 163 watts solar energy. We’ll discuss this figure in more detail in the next paragraph. It means you could install a 150 watt table lamp on every square inch of Earth and use the Sun’s electrical energy to illuminate the entire globe. Another way of putting it this way, If we could cover just 1percent of the Sahara desert in solar panels, we could create enough solar energy to power the entire world. The good benefit of solar power is that it has a large amount of it, more than we’ll ever need.

There’s a down side. The Sun’s energy is an amalgamation of heat and light. Both are vital. Light is what helps plants grow and provides food for us. Heat keeps us comfortable enough to live. However, we are not able to make use of the sun’s light or heat directly to solar power a car or TV. It is necessary to convert solar energy into another type of energy that can be used more efficiently 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 cell’s layers.
  • Photons transmit energy to electrons that reside in lower layers.
  • The energy used by electrons to escape from the circuit, and return into the upper layers.
  • The power of the device is generated by electrons that move around the circuit.

What are solar cells?

The solar cell can be described as an electrical device that is able to capture sunlight and transform it into electric energy. It’s about similar to a hand of an adult with a shape that is octagonal and colored bluish-black. Numerous solar cells are able to be joined together to create bigger units, also known as modules. These are then connected into bigger units known by solar panels. (The blue or black-tinted tiles that you see on your homes - usually with hundreds of solar cells per roof) Or cut into chips (to provide power to small devices such as digital watches and pockets calculators).

The cells in a solar panel work in the same way as a battery. However, unlike a battery’s cells, which generate electricity through chemical reactions the cells of solar panels capture sunlight to create electricity. Photovoltaic cell (PV), as they generate electricity from sunlight (photo originates from the Greek word that means light). The word “voltaic” however, is a reference to Alessandro Volta (1745-1827), an Italian electric pioneer.

Light is considered as tiny particles called photons. The sun’s beam is similar to a huge white firehose, which shoots trillions of trillions. Solar cells can be placed within the path of these photons to collect them and transform them into an electrical current. Each cell produces some volts, and the purpose of a solar panel is to combine energy from several cells to generate an appropriate amount of electric electricity and voltage. The solar cells of today are nearly all made of slices of silicon (one the most well-known chemical elements that are found on Earth and is found in sand). But, as we’ll discover, other materials could be a possibility. The sun’s radiation blasts electrons away from the solar cell when it’s exposed to sunlight. Then, they can be used to power any electronic device that runs on electricity.

How are solar cells made?

Silicon is the substance that microchips’ transistors (tiny switches), are made. Solar cells also work in a similar manner. It is also a form of material. Conductors are the materials that allow electricity to flow freely through them, such as metals.

Others, like plastics and wood, don’t permit the flow of electricity through them; they are called insulation. Semiconductors like silicon are not conductors , nor insulators. However they can conduct electricity in certain conditions.

A solar cell is composed consisting of two different layers of silicon each one of them being modified or doped to allow electricity to flow throughout it in a specific way. The lower layer contains slightly less electrons because it is doped. This layer is referred to as the p-type or positive-type silicon. It is awash with electrons, which is why it is negatively charged. To provide the layer with an excess of electrons it is doped to the other direction. This is called negative-type and n-type silicon. (Read more about doping and semiconductors in our articles on integrated circuits and transistors.

A barrier is created by the interplay between two layers of n-type and silica of the p-type. This is the vital border where both types of silicon meet. The barrier is not accessible to electrons. Therefore, even if the sandwich is connected to a lamp but the current isn’t flowing and the bulb will not turn on. If you shine light onto the sandwich, it’ll produce an amazing effect. The light is thought of as an evaporation stream as well as “light particles” which are energetic, called photons. Photons entering the sandwich give up their energy to the silicon atoms they pass through. The incoming energy knocks electrons out of the lower layer, which is p type. They then cross the barrier to reach the higher n-type and move around the circuit. The greater the amount of light the greater chance that electrons will jump up and more current flows.

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How efficient are Solar Panels?

The conservation energy law is a basic principle of physics, stipulates that energy can’t be made or transformed into thin air. We are able to only transform it from one type of energy to another. A solar cell is unable to produce more energy than it absorbs in light each second. As we will see, the majority of solar cells convert between 10-20% of energy that they receive to electricity. The theoretical maximum effectiveness of a typical mono-junction silicon panel would be around 30%. This is known by The Shockley Queisser Limit. Because sunlight is a wide spectrum of wavelengths and energies that a single-junction silicon solar cell can only be able to capture light in a very narrow frequency range. The rest of the photons will go to waste. Certain photons that hit the solar cell aren’t strong enough to create enough electrons. Others are too energy-intensive and are wasted. Under the ideal conditions, laboratory cells with advanced technology may be able to achieve just below 50% efficiency. They use multiple junctions to capture photons of various energy levels.

A typical domestic panel could be able to achieve an efficiency of about 15 percent. First-generation solar cells with a single junction won’t achieve the efficiency of 30 percent set by Shockley-Queisser, or the record set by the laboratory that is 47.1 percent. There are a myriad of factors that could affect the efficiency of solar cells like how they’re constructed, angled and positioned and whether or not they’re in shadow and how clean they are and how cool they are.

Different types of Photovoltaic Cell

Most solar panels that you see on rooftops are just silicon sandwiches. They have received the designation of “doped” to enhance their electrical conductivity. These solar cells of the past are referred to as first-generation by researchers to distinguish them from two newer technology, second- and third-generation. What is the difference?

First-generation Solar Cells

Over 90 percent of the solar cell production comes from wafers containing the crystalline silicon (abbreviated “c-Si”), that are then cut out of large ingots. The process can last for as long as one month and is carried out in super-clean laboratories. Ingots may comprise monocrystalline (monocrystalline solar panels) or multi-crystalline (polycrystalline solar panels) in the event that they contain multiple crystals.

The first-generation solar cell functions as we’ve shown them in the above box. They are based on a single, easy junction between n and p-type layers of silicon. The latter is cut from separate ingots. The n-type ingot is created by heating tiny pieces of silicon using tiny amounts (or antimony and phosphorus) as dopants. In a p-type ingot, you would use boron. The junction is created by combining slices of p-type and the n-type silicon. There are additional bells and whistles which can be added to photovoltaic cells (like an antireflective coating, that increases the absorption of light and makes them blue) as well as metal connections so they can be connected to circuits. But a simple P-N junction is the most common solar cells rely on. This is how photovoltaic solar cells have been working since 1954 when Bell Labs scientists pioneered it using sunlight to illuminate silicon sand they produced electricity.

Second-generation Solar Cells

The most common solar cells have thin of solar wafers. They’re typically only a fraction of millimeter thickness (around 200 micrometers, or 200 millimeters). They’re not as thick like second-generation solar cells (TPSC) which are thin-film solar cells, which are 100 times thinner (several millimeters or millionths of a meter deep). Although the majority of them are still made of silicon (a form known as amorphous siliu, a-Si) where the atoms are placed in random crystal structures Some are composed of other materials such as Cd-Te, cadmium-telluride or copper indium gallium dielenide (CIGS).

Second-generation cells are extremely light and thin and can be laminated to skylights, windows and roof tiles. They are also compatible with all kinds of “substrates” which are the backers, such as metals and plastics. Second-generation cells have less flexibility than those of the first generation, but they are still superior to the first generation. The top first-generation cells can attain efficiency of around 15%, but amorphous silicon struggles to get higher than 7%) and the top thin-film CdTe cells achieve just 11 percent efficiency, with CIGS cells can’t even reach 7-12%. This is among the reasons that second-generation solar cells have not been able to make a mark in the market despite their many advantages in practical use.

Third-generation Solar cells

The latest technologies combine the best features of first- and 2nd generation cells. They are expected to have high efficiency (up to 30 percent) similar to the first generation cells. They are more likely to be composed of substances other as silicon (making second-generation photovoltaics (also known as OPVs) and perovskite crystals. Furthermore, they could have multiple junctions (made up of several layers of different semiconducting material). They will be less expensive as well as more efficient and feasible than first or second-generation cells. The current worldwide record in efficiency of 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?

As you can see there are seven steps involved in making solar cells.

Stage 1: Purify Silicon

It is then heated up in the electric oven. In order to release oxygen carbon arcs can be applied. It results in carbon dioxide, and then molten silicon which is utilized to create solar cells. However, even the silicon is produced with only 1% impurity it’s still not sufficient. The floating zone technique is a method that allows the silicon rods that are 99% pure to pass through a zone that is heated several time in the exact direction. The process eliminates all impurities from one end of the rod and permits it to be cleaned.

2. Making Single Crystal Silicon

Czochralski Method is the most well-known method to create single-crystalline silicon. This involves placing a crystal of seed made of silicon inside melting silicon. The result is a boule or cylindrical ingot by rotating the seed crystal when it is removed from the melted silicon.

Stage Three Cut the Silicon Wafers

The second stage boule is used to cut silicon wafers with circular saws. This is the best job to do with diamonds, which create silicon slices that can be further cut to make squares or hexagons. Although the cutting marks of the saw are eliminated from the cut wafers, some producers leave them because they believe that more light could be captured by the rougher solar cells.

Stage 4: Doping

After cleansing the silicon at an earlier point, it’s possible to introduce impurities to the silicon. Doping is the use of a particle accelerator to ignite the phosphorus ions within the ingot. You can regulate the penetration depth by controlling the speed of the electrons. You can avoid this step by using the conventional method of inserting boron during cutting the wafers.

Step Five: Add the electrical connections

Electrical contacts are used for connecting the solar panel and serve as receivers for the current generated. These contacts, composed of metals like palladium and copper, are thin enough to allow sunlight to enter the solar cell in a way that is efficient. The metal can be deposited on the exposed cells or vacuum evaporated using a photoresist. Thin strips of copper coated with tin are usually placed between the cells following the contacts have been inserted.

Step Six Application of the Anti-Reflective Coating

Since silicon has a shiny appearance, it has the ability to be able to reflect as much as 35% of sunlight. To reduce reflections, a silicon coating can be applied. The process involves heating the material until the molecules boil off. The molecules move on to the silicon and begin to condense. The high voltage could also be used to eliminate the molecules and then deposit them onto the silicon on an opposite end of the electrode. This is known as “sputtering”.

Stage Seven: Encapsulate and Seal the Cell

The solar cells are then enclosed by silicon rubber or ethylene vinyl Acetate. Then, they are put inside an aluminum frame, with a back sheet and glass cover.

What amount of electrical energy can solar cells produce?

Theoretically, it’s an enormous amount. For the moment, let’s forget about solar cells and instead focus on pure sunlight. Every square meter of Earth can absorb up to 1100 watts of sun energy. That’s the estimated energy of direct sunlight on a clear day. The sunlight’s rays are fired perpendicularly to Earth’s surface, resulting in the greatest illumination.

When we adjust for Earth’s tilt and the time we will receive between 100 and 250 watts per square. meters in northern latitudes even on days with no clouds. This translates to about 2-6 kWh per daily. Multiplying the entire year’s production results in 700-2500 kWh for every sq. m (700-2500 units) of electricity. The sun’s energy potential in hotter regions is clearly more than Europe. For instance the Middle East receives between 50 and 100 percent greater solar power each season than Europe.

However, solar cells are just 15 percent efficient, so we only get 4-10 watts per square meter. This is why panels with solar power must be large in size. The amount of area you are able to cover by cells will affect the power you can generate. An average solar panel comprised with 40 solar cells (each row of eight cells) produces around 3-4.5 watts. However, a solar panel made up of 3-4 modules can generate several kilowatts, which is enough to meet a home’s highest energy demands.

How about Solar Panel Farms?

What do we do if we have to produce huge amounts of solar energy? You’ll need between 500 and 1000 solar roofs in order to generate approximately the same quantity of power as a wind turbine with the peak power of around 2.5 or 3.0 megawatts. To compete with large coal or nuclear power plants (rated in gigawatts) the requirement is around 1,000 solar roofing systems. This is roughly 2000 wind turbines, and possibly a million of them. These comparisons assume that our solar and wind generate the highest output. While solar cells do produce clean, efficient power, they cannot claim to be efficient in the use of land. Even the massive solar farms appearing all over the country generate only a small amount of power, typically around 20 megawatts or 1 per cent less than a 2 gigawatt coal or nuclear plant. LA Solar Group, a renewable energy company, estimates that it takes approximately 22,000 solar panels for 12 ha (30-acres) space to generate 4.2 megawatts. This is about the same amount as two large wind turbines. It also generates enough energy to power 1200 homes.

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Solar energy can reduce the cost of electricity and also help you be more eco sustainable. You could be eligible to get paid if you have an agreement between the company that provides electricity to supply solar energy in return to the grid.



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