Most solar photovoltaic modules use silicon solar cells, which can be divided into two main types: monocrystalline and polycrystalline. Both solar cells are made of high-purity silicon, but have different manufacturing processes.
- Monocrystalline solar cells are cut from a single crystal. The crystals are grown from molten silicon through a highly controlled process.
- Manufacturers make polycrystalline cells by combining several crystals. Therefore, this process does not require the growth of a single crystal of fused silicon.
Monocrystalline solar panels can convert sunlight into electricity more efficiently, but they are more complex and expensive. Polyurethane solar panels are easier and cheaper to manufacture, but less efficient.
The technical details of solar cell manufacturing are complex, but we'll cover each step of the process in the following sections. The next steps are crystalline silicon solar cells, which account for more than 90% of the global market. Other types of panels, including thin film panels, have different manufacturing processes depending on the material.
Silicon mining and processing
Silicon is one of the most abundant elements on Earth, making up 27.7% of the Earth's crust, according to the Royal Society of Chemistry. However, natural silicon combines with other elements such as oxygen, phosphorus and nitrogen. Manufacturers must process this raw material to obtain the pure silicon needed to make solar cells.
The oxygen contained in the silica mineral can be removed at high temperatures, resulting in high purity silicon. The solar industry uses 99.9999% pure polysilicon to make polycrystalline and monocrystalline solar cells.
Multicells have a simpler manufacturing process that involves melting blocks of polycrystalline silicon and cutting them into square wafers, which are used to make photovoltaic cells.
Making single cells is more difficult because solar manufacturers must first ensure that molten silicon hardens into a single crystal. The process is based on Czochralski's method, in which crystals are "grown" by immersing a smaller "seed crystal" in molten silicon. The result is a large cylindrical block of monocrystalline silicon that manufacturers can cut into solar cells.
Production of photovoltaic cells
Manufacturers can increase the efficiency of photovoltaic cells by adding controlled amounts of boron and phosphorus. The efficiency of a solar panel is a measure of how much sunlight can be converted into energy.
The added elements act as semiconductors. phosphorus creates n-type silicon and boron p-type silicon.
- N-type semiconductors have a larger number of free electrons, which carry a negative charge in motion.
- P-type semiconductors contain "electron holes" that carry a net positive charge.
- P-type and n-type silicon are layered in a "PN junction", which is the basic principle of a solar cell.
- Under the influence of a light source, the electrons of the n-type silicon receive energy, moving through the "holes" of the p-type silicon, creating an electric current.
In other words, this process converts sunlight into electricity.
Solar cells consist of several photovoltaic cells connected together by silver conductors and copper solder. There are many different sizes of panels, but most home solar panels have 60 or 72 cells. Some manufacturers produce 120 or 144 cell half-cell solar cells in 60 and 72 cell panel sizes.
Embedding and back page
Manufacturers cover solar cells with an anti-reflective coating to increase absorption of sunlight. The solar panels are coated with two layers of ethylene vinyl acetate (EVA) to help protect the panels from dust and moisture. The final assembly includes the panel covered with glass and a resin facing sheet.
