Solar Cell

Why should we spend our time searching for coal or dumping oil when there is a huge power plant high above us that sends out free and clean energy? The Sun, a smoldering nucleus can provide enough energy to provide power to the Solar System for five billion more years. Solar panels are able to convert this energy into an unending power source.

Although solar power might appear unusual or out of the ordinary, it is already very widespread. A solar-powered clock or calculator for your purse could be on your wrist. A lot of gardeners use solar-powered lights. Solar panels are often found on satellites and spaceships. NASA is one of the American Space Agency, even designed the first solar-powered plane. Global warming is threatening our environment and it is likely that solar energy will become an ever-growing source of energy that is renewable. How do they work?

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

It’s incredible how solar power operates. Each square meter of Earth receives an average 163 watts of solar power. This figure will be discussed in greater detail later. This means that you could put a 150 watt table lamp on every square meters of Earth and utilize the solar energy of the Sun to illuminate the entire planet. Another way to put it is that if we covered only one percent from the Sahara desert with solar panel, then we would create enough solar energy to provide power to the entire globe. The best thing about solar energy is that there’s a lot of it, more than we could ever need.

There is a downside. The Sun’s energy comes as a mixture of light and heat. Both are essential. Light is what helps plants grow and provides food for us. Heat keeps us comfortable enough to live. However, we are not able to use the Sun’s energy or light directly to solar power a TV or car. It is necessary to convert solar energy into a different form of energy is more readily available like electricity. This is exactly the job solar cells perform.

In summary:

The cell’s surface gets illuminated by sunlight
Photons carry energy through the cells’ layers.
Photons transfer their energy to electrons in lower layers
This energy is used by electrons to let electrons escape the circuit, and return into the upper layers.
The energy for a device is provided by the electrons that flow through the circuit.

What are solar cells?

Solar cells are electronic devices which captures sunlight and converts it into electricity. It is about similar to a hand of an adult, octagonal in form, and colored bluish-black. Many solar cells can be put together to form larger modules. They are then joined to form bigger units known by solar panels. (The blue or black-tinted tiles you see on homes typically have hundreds of solar cells per roof) Or chopped into chips (to power small gadgets such as digital watches or pocket calculators).

The cells of solar panels work the same way as batteries. However, unlike a battery’s cells that produce electricity using chemicals, solar panels’ cells are able to capture sunlight and produce electricity. Photovoltaic cells (PV) are able to generate electricity from sunlight (photo is derived directly from Greek word meaning light). The term “voltaic” however, is a reference to Alessandro Volta (1745-1827), an Italian electricity pioneer.

Light can be described as tiny particles known as photons. The sun’s beam is similar to a huge Yellow firehose which releases trillions upon trillions. A solar cell can be placed in the path of these photons to capture them , and later convert them into an electric current. Each cell can generate only a few volts, therefore the job of a solar panel is to combine the energy produced by several cells to generate a useful amount of electric electricity and voltage. The solar cells of today are nearly entirely made of silicon (one the most well-known chemical elements on Earth, found within sand). But, as we’ll discover, other materials could also be possible. The sunlight’s energy blasts electrons out of the solar cells when it’s exposed to sunlight. They can then be used to power any electrical device that runs on electricity.

How are solar cells made?

Silicon is the material from which microchips’ transistors (tiny switches), are made. Solar cells work similarly. The term semiconductor refers to a kind of material. Conductors are substances that permit electricity to flow freely through them, like metals.

Others, like plastics or wood, aren’t able to permit electric current to pass through. they’re known as insulation. Semiconductors such as silicon are not conductors , nor insulators. However we can make them conduct electricity under certain conditions.

A solar cell is composed of two layers of silicon each one of them being treated or doped to allow electricity to flow through it in a specific manner. The lower one has less electrons because it is doped. This layer is referred to as positively-type silicon, also known as p-type. It has too many electrons, which is why it is negatively charged. To give the layer an excess of electrons it is doped with a negative charge. This is referred to as n-type and negative-type silicon. (Read more about doping and semiconductors in our articles on transistors and integrated circuits.

A barrier is formed by the interplay between two layers of n-type and p-type silica. This barrier is the crucial boundary where both kinds of silicon come into contact. The barrier is not accessible to electrons, so even if the silicon sandwich has been connected with a flashlight, the current won’t flow and the lightbulb won’t be able to turn on. However, if you shine light on the sandwich, it will produce some amazing results. The light can be thought of as a streaming stream, or “light particles”, which are energetic, referred to as photons. Photons that enter the sandwich give up their energy to silicon atoms when they move through. The energy that is absorbed knocks electrons from the lower, p type layer. They then cross barriers to get into the n-type above and flow around the circuit. The greater the amount of light then the more electrons leap up and more electricity flows.

How efficient are Solar Panels?

The conservation energy law is a basic principle of physics, states that energy cannot be produced or made to disappear into the air. It is only possible to transform it from one type of energy to another. A solar cell is unable to produce more energy than it absorbs from light every second. As we’ll see, the majority of solar cells convert between 10-20% from the power they get to electricity. The theoretical maximum effectiveness of a typical one-junction solar cell is about 30%. This limit is known as the Shockley Queisser Limit. Since sunlight has a broad spectrum of wavelengths and energies, any single-junction silicon solar cell will only capture photons within a limited frequency range. All other photons will be wasted. Certain photons that hit the solar cells are too weak to produce enough electrons. Others have too much energy and end up being wasted. In the most ideal conditions, laboratory cells with advanced technology may be able to achieve just below 50% efficiency. They employ multiple junctions to capture photons with various energies.

A typical domestic panel could have an efficiency of around 15 percent. Single-junctionsolar cells of the first generation won’t achieve the 30 percent efficiency limit established by Shockley-Queisser, or the record set by the laboratory that is 47.1 percent. There are many variables that can affect the nominal effectiveness of solar cells, like how they’re built, angled and placed, whether they are ever in shadow, how clean they are and how cool.

Different types of Photovoltaic Cell

A majority of the solar cells that you see on rooftops are silicon sandwiched. They have received the designation of “doped” to improve its electrical conductivity. The classic solar cells are referred to as first-generation by researchers to distinguish them from the two newer technologies, second- and third-generation. What is the difference?

First-generation Solar Cells

More than 90 percent of the world’s solar cells are made of wafers made up of the crystalline silicon (abbreviated “c-Si”), which are cut from huge ingots. This process can take as long as a month and takes place in super-clean laboratories. Ingots may be single crystals (monocrystalline solar panels) or multi-crystalline (polycrystalline solar panels) dependent on whether they contain multiple crystals.

The first-generation solar cell functions the way we’ve shown them in the picture above. They use one, simple junction between n and p-type layers of silicon, which is cut out of separate ingots. The n-type ingot is created by heating tiny pieces of silicon using tiny amounts (or antimony, or even phosphorus) as dopants. For a p-type, one uses boron. The junction is formed by fusing slices of p type and N-type silicon. There are additional bells and whistles which can incorporate into photovoltaic devices (like an antireflective coating, which improves light absorption and gives them their blue color) and connections made of metal that allow them to be wired into 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: by shining sunlight onto silicon sand they produced electricity.

Second-generation Solar Cells

The most common solar cells are thin solar cell wafers. They’re typically only tiny fractions of millimeters in thickness (around 200 micrometers or 200 millimeters). They’re not as thick like second-generation solar cells (TPSC), or thin film solar cells, which are 100 times thinner (several millimeters or millionths of a meter deep). Though the majority are still composed of silicon (a type of silicon known as amorphous silu (a-Si)), in which particles are distributed in random crystal structures however, some are made of other materials , such as Cd-Te, cadmium-telluride or copper indium gallium dielenide (CIGS).

The second generation cells are thin and light and are able to be laminated with skylights, windows as well as roof tiles. They can also be used with all kinds of “substrates”, which are backers like metals and plastics. Second-generation cells are less flexible than the first generation ones, however they still perform better than their predecessors. A top-quality first-generation cell may achieve efficiency of 15-20 percent, however the amorphous silicon cells struggle to achieve over 7%) While the most efficient thin-film CdTe cells manage only about 11 percent, and CIGS cells are no better than 7-12%. This is among the main reasons why the second-generation solar cells aren’t enjoyed much success on the marketplace despite their numerous advantages.

Third-generation Solar cells

The latest technologies combine the best qualities of 2nd and first generation cells. They promise high efficiency (up 30 percent or more) as do the first generation cells. They tend to be composed of substances other that silicon (making second-generation photovoltaics (also known as OPVs) as well as perovskite crystals. Furthermore, they could have multiple junctions (made from multiple layers from different semiconducting material). They are more affordable, more efficient, and feasible than first or second-generation cells. The record-setting global record of efficiency for third-generation solar cells stands at 28.9. It was reached in December 2018 by a tandem perovskite-silicon solar cell.

How are they made?

You can observe the seven steps to making solar cells.

1. Purify Silicon

The silicon dioxide is heated up in an electrical furnace. To release the oxygen, a carbon arc can be applied. The result is carbon dioxide and molten silica which is used to construct solar cells. Even though this yields silicon with a 1% impurity, it’s not quite good enough. The floating zone technique is a method that allows the 100% pure silicon rods to be passed through a heated zone several time in the exact direction. The process eliminates all impurities that are present on one side of the rod and permits it to be sucked out.

2. The Making of Single Crystal Silicon

The Czochralski method is the most popular method to create single-crystalline silicon. This involves placing a seed crystal made of silicon in melted silicon. The result is a boule or cylindrical ingot, by spinning the seed crystal as it is being removed from the silicon melting.

Stage Three Make cuts in the Silicon Wafers

A second boule stage is utilized to slice silicon wafers by using a circular saw. This task is best accomplished with diamond, which produces the silicon chips that are able to then be cut into hexagons or squares. Although the cutting marks of the saw are eliminated from sliced wafers, some manufacturers leave them because they believe that more light could be captured by the rougher solar cell efficiency.

Fourth Stage Doping

After cleansing the silicon at an earlier point, it’s possible to introduce impurities to the silicon. Doping involves the use of an accelerator that ignites phosphorus ions in the ingot. You can control the depth of penetration by controlling the speed of the electrons. You can avoid this step by using the conventional method of inserting boron while cutting the wafers.

Phase Five: Add electric contacts

The electrical contacts are used for connecting the solar panel to act as receivers of the electricity generated. The contacts, which are made of various metals, including palladium and copper, are thin enough to let sunlight into the solar cell in a way that is efficient. The metal is either deposited on the cells that are exposed or vacuum evaporated using a photoresist. The thin strips of copper lined with Tin are typically placed between cells after the contacts have been installed.

Stage Six: Apply the Anti-Reflective Coating

Because silicon shines, it can absorb up to 35% of sunlight. To minimize reflections, a silicon coating is applied to it. The process involves heating the substance until the molecules are boiling off. The molecules move on to the silicon and expand. A high voltage can also be utilized to detach the molecules, and then deposit them onto the silicon at another electrode. This is called “sputtering”.

Stage Seven: Encapsulate and Seal the Cell

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

What amount of electrical energy can solar cells produce?

Theoretically speaking, it’s quite a bit. For the moment, let’s put aside solar cells and focus on pure sunlight. Every square meter of Earth can receive up to 1000 watts of solar power. That’s the estimated power of direct sunlight on a clear day. The solar rays are directed perpendicularly towards the 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. meter in northern latitudes, even on days with no clouds. This translates to about 2-6 kWh/day. When you multiply the whole year’s production, it produces 700- 2500 kWh for every sq. meters (700-2500 units) of electricity. The sun’s energy potential in the hotter regions is definitely more than Europe. For instance Middle East Middle East receives between 50 to 100 percent more solar energy per year than Europe.

The problem is that solar cells are only 15 percent efficient, so you can only harvest 4-10 watts per square foot. This is the reason panels that harness solar power have to be massive in size. The amount of area the area you can cover by cells will affect the power you can generate. The typical solar panel comprised with 40 solar cells (each row of 8 cells) produces around 3-4.5 watts. But a solar panel composed of 3-4 modules can generate many kilowatts, which would be enough to supply a house’s peak energy needs.

How about Solar Panel Farms?

But, what happens is the best option if we require large amounts of solar energy? You will need between 500 to 1000 solar roofs in order to generate similar amounts of power as a large wind turbine, with the peak power of around 2.5 or 3.0 megawatts. In order to compete with huge coal or nuclear power stations (rated as gigawatts) the requirement is about 1 000 solar rooftops. This is equivalent to approximately 2000 wind turbines or perhaps a million of them. The calculations assume that solar and wind generate the highest output. While solar cells do produce clean, efficient power, they cannot claim to be effective in the use of land. Even the huge solar farms being built across the country generate only a small amount of power, typically about 20 megawatts or 1 per cent less than a 2 gigawatt coal or nuclear plant. Nevada Solar Power Installers, a renewable business estimates that it will take approximately 22,000 solar panels for 12 hectares (30-acres) area to produce 4.2 megawatts. It’s about the same amount that two wind turbines with large capacities. The turbine also produces enough power to power 1,200 homes.

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