If you are getting started in the solar energy world, you may be wondering what the solar photovoltaic cells which convert sunlight to electricity are made of. It may surprise you that the answer lies behind one of the most abundant resources on Earth.
Solar panels are made out of silicon wafers that are manufactured through an energy intensive process in which natural beach sand is converted into high grade silicon to be later sliced to form interconnected wafers of micrometric thickness. Silicon is the second most abundant mineral resource on our planet and is extracted mainly from sea sand.
However, for silicon to be extracted and form cells capable of converting sunlight into electricity, a heavy manufacturing process is required in which other elements and materials are involved. This article will explain in detail what materials are used to manufacture solar panels, the structure of solar panels, types of solar panels and their corresponding manufacturing processes.
Solar Panel Manufacturing Industry: Materials and Production
Silicon, doped with phosphorus and boron, is used to make solar panels. Other materials that cover the cells are formed by protective sheets of thermoplastic polymer, glass, and aluminum. Finally, there are the cables capable of allowing the interconnection between solar cells. Each of the materials that make up solar panels is detailed below.
The most commonly used semiconductor materials to make solar panels is silicon which is used to manufacture the most commonly available monocrystalline and polycrystalline solar panels. However, other elements are also used to manufacture other types of modules like selenium, tellurium, gallium arsenide, and indium. These minerals are used as the raw material for solar panels because their semiconductive properties allow to create an electric field in the solar cells that drive electrons’ motion (and therefore, electricity).
It is worth mentioning that most of the monocrystalline and polycrystalline modules are made out of silicon. Silicon is extracted mainly in China, with a production of approximately 5.4 million metric tons by 2020, which corresponds to 70% of the total produced worldwide.
The other semiconductors, such as cadmium telluride, selenium, indium, and gallium are widely used in thin-film solar panels, which have lower solar cell efficiency, but also cost less than conventional solar panels.
Conductive materials such as boron and phosphorus in their pure state are necessary to allow the passage of current, these combine with silicon to create the electric field necessary for the conduction of electric current.
Thermoplastic Polymer, Glass, and Aluminum
The materials that are responsible for protecting solar cells are thermoplastic polymer layers and the anti-reflective glass layer, used for their excellent transmission of solar radiation and for the protection of the cell against atmospheric agents, thus improving the overall lifespan of the panel. In addition, another element necessary for the union of all materials is the aluminum frame. The physical properties of aluminum provide a good level of resistance to the panel.
Solar Panel Structure
As mentioned previously, solar panels are made up of various materials and components, each of them with a specific function, we describe them below:
It gives mechanical robustness to the assembly by joining all the pieces and ensuring their integrity. In addition, the frame of a solar panel allows its insertion in mounting structures (racking) that will group the modules into an array. The material from which it is made is normally aluminum, although it can also be made of other materials resistant to different weather conditions; even extreme conditions, such as hail.
It is an anti-reflective tempered glass with light transmission qualities of more than 90% that has the function of protecting the photovoltaic panel from the action of atmospheric agents.
They are responsible for protecting the solar cells and their contacts. They are mainly composed of glass polymerized with resins and acrylics. Moreover, the materials used (Ethyl-Vinyl-Acetylene or EVA) provide excellent transmission to solar radiation, thus as a null degradation against ultraviolet radiation.
Photovoltaic cells are the most important elements of the solar panel. As already mentioned, they are the semiconductor elements capable of generating electricity from solar radiation. These PV cells are interconnected in rows and columns, by groups of 60, 72, or 96 depending on size and the power target to be achieved.
It is responsible for protecting the back of the panel against atmospheric agents, creating an impenetrable barrier against humidity. They are generally made of acrylic, Tedlar, or EVA materials and are often white as this enhances the performance of the panel due to the reflection it produces on the cells.
It is the place where the terminal outputs of the electrical circuit are installed. It is secured on the rear side of the panel and is waterproof, having the outputs of two cables, one positive and the other negative. Bypass diodes are also included into the junction box of solar panels nowadays which protect the solar cells from phenomena like hot spots.
Solar Panel Types and Manufacturing Processes
At the time to manufacture photovoltaic cells, the type of panel that will be produced must be considered. These are the following technology options: monocrystalline, polycrystalline, and thin-film.
The monocrystalline panels are dark in color and their shape is squared with rounded corners to maintain low production costs and a good level of performance.
These cells are manufactured with the Czochralski method. This consists of introducing a rod with a crystal seed at one end of a molten semiconductor bath and make it rise slowly under very controlled cooling conditions. The output of the process is obtaining a single crystal in the form of a rod and without impurities.
A polycrystalline cell is made up of multiple crystals of silicon. This is formed by melting different silicon seeds and pouring it into square molds where it is allowed to cooled down and solidify, then the material is cleaned and textured to add the antireflective layer and finally place the corresponding conductors.
As can be seen, the manufacturing process of a polycrystalline cell is simpler than that of monocrystalline, this makes its performance lower, therefore these panels are considered mid-range in terms of efficiency and price, which has allowed great use.
Thin plates are made by placing several thin layers of silicon on top of each other to create the module. There are different types of thin-film solar cells, and the way they differ from each other comes down to the material used to make them, these are as follows: amorphous silicon, cadmium telluride, copper selenide, indium, gallium, and photovoltaic cells organic.
Bearing in mind that the manufacturing process of the different types of cells has a certain difference, it is important to describe the generic steps that must be followed for the production of a photovoltaic panel:
Step 1: Sand becomes Crystallized Silicone
Crystallized silicon is made from sand at a very high temperature (2000 °C) in an oven. The method of heating the sand in the oven creates solid silicone rocks, which are collected from the bottom once it has cooled.
Step 2: The Formation of Ingots
The crystallized silicone rocks that are collected from the bottom of the furnace are fused together to form cylindrical-shaped silicon ingots. When the silicone melts the operator ensures that the atoms line up throughout the process and infuses boron, that infusion gives the ingots a positive electrical polarity.
Step 3: Grinding, Polishing, and Cell Building
Once the silicone ingots have cooled they are grind and polished to produce smooth, flat sides to cut the discs, which are only a few millimeters thick, to reduce the waste and increase production efficiency.
Step 4: Polarization Conductors
A conductor such as boron is added to the silicon wafers and two types of silicone are formed, the N and the P, the treatment of both creates a power imbalance in the solar panel.
Step 5: Building the solar cell circuit
When the solar panel is formed the P-type and N-type silicones are layered and welded together so that when the sunlight hits the panel, the imbalance stimulates the silicone electrons to move in a closed circuit. This process occurs repeatedly and it is this repetition that generates electricity.
Step 6: Glass and Solar Panel Coating
Glass is added during the manufacturing process and the solar panels are coated with an anti-reflective coating that encourages the absorption of direct sunlight rather than reflecting it.
Step 7: Assembly
Finally, the assembly of the entire module is secured and tighten, leaving it ready for installations.
Frequently Asking Questions
What is the average percentage of each mineral or material in a solar panel?
Conventional photovoltaic modules contain the following materials: 5% silicon (solar cells), 1% copper (interconnections), 8% aluminum (frames), 10% polymers or plastic (encapsulating sheets) and 76% glass (surface of the module).
China is by far the largest solar panel manufacturer in the world with nearly 71% share of the industry. China is followed by Malasya (6%), Korea (6%), United States (3%), Europe (2%), Japan (1%), Taiwan (1%) and India (1%). The remaining 9% is spread through the rest of the world.
The method is named after Jac Czochralski, a polish scientist who developed the method back in 1915. Despite the method was developed over 100 years ago, it’s still the only method used for solar panel manufacturing with silicon ingots.
To take advantage of renewable energy from the sun and transform it into electricity through solar panels, the second most abundant element on the planet is usually used as raw material. Silicon has a complex manufacturing process, which has led to the use of other semiconductor elements, as well as different models for the production of panels, but they still do not meet the same level of efficiency.
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