Solar panels are produced through a multi-step process that transforms raw materials into devices capable of converting sunlight into electricity.
1. Silicon Purification and Ingot Creation
- Silicon Purification: The process begins with purifying raw silicon, typically derived from quartz sand. This involves chemical processes to remove impurities and achieve a high purity level (solar grade silicon).
- Ingot Formation: Purified silicon is then melted and formed into large cylindrical ingots (or blocks). Two main methods are used:
- Czochralski (CZ) process: A seed crystal is dipped into the molten silicon and slowly pulled upwards while rotating, resulting in a single-crystal ingot. This is efficient but produces less uniform silicon.
- Multi-crystalline casting: Molten silicon is poured into a mold and allowed to cool and solidify. This method is less expensive but results in silicon with multiple crystal structures.
2. Wafer Production
- Slicing: The silicon ingot is sliced into thin wafers using a wire saw. These wafers are typically around 150-200 micrometers thick (thinner than a human hair). This process unfortunately creates a lot of waste silicon.
- Cleaning and Texturing: Wafers are cleaned to remove any debris from the slicing process. Then, the surface is textured (usually with chemicals) to reduce reflection and increase light absorption.
3. Solar Cell Fabrication
- Doping: The silicon wafers are "doped" with impurities to create a p-n junction. This junction is essential for generating electricity when light strikes the silicon.
- N-type doping: One side of the wafer is doped with phosphorus, creating an excess of electrons.
- P-type doping: The other side of the wafer is doped with boron, creating a deficiency of electrons (holes).
- Applying Anti-Reflective Coating: An anti-reflective coating (ARC) is applied to the surface of the wafer to further minimize light reflection and maximize absorption.
- Metal Contacts: Metal contacts (thin metal lines) are screen-printed onto the top and bottom surfaces of the wafer. These contacts collect the generated electricity and allow it to flow out of the solar cell.
4. Solar Panel Assembly
- Cell Interconnection: The individual solar cells are connected together in a series to achieve the desired voltage. These strings of cells are then connected in parallel to increase the current.
- Lamination: The interconnected cells are sandwiched between layers of protective materials:
- Front: A sheet of tempered glass provides protection from the elements.
- Encapsulant (EVA): Ethylene-vinyl acetate (EVA) is a clear, cushioning plastic that encapsulates the cells, protecting them from moisture and vibrations.
- Backsheet: A durable backsheet (often made of plastic) provides insulation and further protection.
- Framing: An aluminum frame is attached to the laminated panel to provide structural support and ease of installation.
- Junction Box: A junction box is attached to the back of the panel to provide electrical connections.
5. Testing and Quality Control
- Performance Testing: Each solar panel undergoes rigorous testing to ensure it meets performance specifications (voltage, current, power output).
- Visual Inspection: Panels are visually inspected for any defects.
This process results in a finished solar panel ready to generate clean energy from sunlight.
