A single solar cell can be fragile and can produce a limited amount of power. In reality, PV modules are created by connecting up to 72 solar cells together electrically. A panel/PV module is a group of cells that are sealed in a weatherproof packaging. It is the key element of PV systems.
Completed solar cells undergo optical and electrical testing to ensure quality control. They are then grouped according to their power output or current. Solar cells with the same optical aesthetics and electrical performance are utilized to create a panel.
Below are the functionality and requirements of the different elements of a PV module:
- Front glass- made of tempered glass that has an antireflection cover. The anterior portion of the panel must be safe against oxygen, water, and ultraviolet radiation because these factors may degrade individual cells. There must be low iron content in the glass to ensure high transmission because this hinders light transmission towards solar cells.
- Encapsulant- is a binding medium between layers of a panel, which provides resistance to vibrational failure. EVA (Ethylene Vinyl Acetate) is the standard encapsulant for PV modules made of silicon. Solar cells are coated between EVA sheets. Then, the structure will be heated to 150°C, where the EVA melts. As a result, the cells adhere to each other.
Below are features of EVA that makes it a great choice:
- It highly resists electrical current, therefore, serves as a good insulator.
- EVA films can stand against contaminants and moisture.
- They can protect the panel by absorbing vibrations and shocks.
- It remains stable under excessive ultraviolet exposure.
- It has increased optical transmission and decreased thermal resistance.
- It has a refractive index that is the same as glass, providing efficient light coupling.
- It is not expensive.
There continues to be a significant interest in the industry to discover alternative materials for modules made of silicon. That is to improve reliability or performance and reduce cost. Some encapsulants that are undergoing investigation are ionomers, PVB (polyvinyl butyral), and silicones.
Silicones are very transparent to UV light that the naked eye can see. Its refractive index is almost similar to glass, and it has exceptional hydrophobic properties. PVB was utilized in the beginning days of the PV industry. Nevertheless, their better counterparts have dominated EVA under extreme heat and UV exposure in a 70-day stability assessment. However, they cannot stand against too much moisture. Moreover, ionomer can protect from wearing and have good adhesion for improved durability and easy handling.