The main components for a solar panel
- Solar photovoltaic cells
- Toughened Glass - 3 to 3.5mm thick
- Extruded Aluminium frame
- Encapsulation - EVA film layers
- Polymer rear back-sheet
- Junction box - diodes and connectors
1. Solar PV Cells
Solar photovoltaic cells or PV cells convert sunlight directly into DC electrical energy. The performance of the solar panel is determined by the cell type and characteristics of the silicon used, with the two main types being monocrystalline and polycrystalline silicon
2. Glass
The front glass sheet protects the PV cells from the weather and impact from hail or airborne debris. The glass is typically high strength tempered glass which is 3.0 to 4.0mm thick and is designed resist mechanical loads and extreme temperature changes. The IEC minimum standard impact test requires solar panels to withstand an impact of hail stones of 1 inch (25 mm) diameter traveling up to 60 mph (27 m/s). In the event of an accident or severe impact tempered glass is also much safer than standard glass as it shatters into tiny fragments rather than sharp jagged sections.
To improve efficiency and performance high transmissive glass is used by most manufacturers which has a very low iron content and an anti-reflective coating on the rear side to reduce losses and improve light transmission.
3. Aluminium Frame
The aluminium frame plays a critical role by both protecting the edge of the laminate section housing the cells and providing a solid structure to mount the solar panel in position. The extruded aluminium sections are designed to be extremely lightweight, stiff and able to withstand extreme stress and loading from high wind and external forces.
The aluminium frame can be silver or anodised black and depending on the panel manufacturer the corner sections can either be screwed, pressed or clamped together providing different levels of strength and stiffness.
4. EVA Film
EVA stands for ‘ethylene vinyl acetate’ which is a specially designed polymer highly transparent (plastic) layer used to encapsulate the cells and hold them in position during manufacture. The EVA material must be extremely durable and tolerant of extreme temperature and humidity, it plays an important part in the long term performance by preventing moisture and dirt ingress.
5. Backsheet
The backsheet is the rear most layer of common solar panels which as acts as a moisture barrier and final external skin to provide both mechanical protection and electrical insulation. The backsheet material is made of various polymers or plastics including PP, PET and PVF which offer different levels of protection, thermal stability and long term UV resistance. The backsheet layer is typically white in colour but is also available as clear or black depending on the manufacturer and module.
The lamination either side of the PV cells provides some shock absorption and helps protect the cells and interconnecting wires from vibrations and sudden impact from hail stones and other objects. A high quality EVA film with a high degree of what is known as ‘cross-linking’ can be the difference between a long life or a panel failure due to water ingress. During manufacture the cells are first encapsulated with the EVA before being assembled within the glass and back sheet.
6. Junction Box And Connectors
The junction box is a small weather proof enclosure located on the rear side of the panel. It is needed to securely attach the cables required to interconnect the panels. The junction box is important as it is the central point where all the cells sets interconnect and must be protected from moisture and dirt.
Solar MC4 Connectors
Almost all solar panels are connected together using special weather resistant plugs and sockets called MC4 connectors. The term MC4 stands for multi-contact 4mm diameter connector. Due to the extreme weather conditions the connectors must be very robust, secure, UV resistant and maintain a good connection with minimal resistance at both low and high voltages up to 1000V.
The connectors are designed to be used with the standard 4mm or 6mm double insulated solar DC cable with tinned copper multi-strand core for minimum resistance. To correctly assemble the connectors a special crimping tool is used to crimp the multi-strand cable to the inner terminal which is then inserted and snapped into the MC4 housing.