Solar panel has advanced rapidly in recent years in terms of efficiency, and different material. However, despite the massive advancements in technology, basic solar panel construction hasn’t changed much over the years. Most solar panels in the market are still made up of crystalline silicon cells sandwiched between EVA on the front and back typically covered in an aluminum frame and a glass plate on the front side.
How are solar cells made?
Solar cells are primarily grown similarly to the wafers used to make computer processors. The silicon wafers can be either polycrystalline or monocrystalline (more information on different types of solar panels can be found in this article on which solar panels are the best? ). Monocrystalline cells are manufactured using the CZ process (Czochralski process.).CZ process is more energy intensive and they produce high quality and highly efficient solar cells in comparison to the polycrystalline solar cell. Polycrystalline solar cells are less energy intensive and are a more simplified process.
The CZ creates an ingot and then later these ingots are turned into wafers a typical cylindrical ingot will be around 150 – 200 Kg. The typical process of converting SiO2 (quartz) to silicon wafers is given below.
Figure 1: Process flow for making monocrystalline-silicon wafers via Cz crystal growth.
Source: National Renewable Energy Laboratory (NREL)
Multicrystalline DS wafers are fabricated from shorter but much wider and heavier ingots— around 800 kg. The whole process can be seen in the figure below. The standard industry trend was to produce 156.75 mm x 156.75 mm solar wafers. known as the M2 cell size. Since 2020 new PV cell sizes have started entering the market with 182 mm x 182 mm / 210 mm x 210 mm in size.
Figure 2: Process flow of making multicrystalline wafer ingots using Diredctional Solidification process (DS Process)
Source: National Renewable Energy Laboratory (NREL)
Main Components of a solar cell:
- Solar cells
- Front Glass
- EVA film layer
- Polymer back sheet
- Junction box
- Aluminum frame
Figure 3: Typical layers of crystalline solar panel
- Solar 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. The PV market is currently silicon solar cells. (Monocrystalline and Polycrystalline) Monocrystalline and polycrystalline solar panels essentially perform the same function, i.e., capture sunlight and turn it into electricity. The key difference is the type of silicon structure they use. Monocrystalline solar cells are made from a single crystal of silicon. As a single continuous crystal, the electrons inside the cell can move quite easily generating more current and giving out higher cell efficiency. In the case of polycrystalline solar cells, they are manufactured with a nonregular silicon structure as monocrystalline, then electrons cannot move quite easily which leads to reduced cell efficiency.
These first-generation solar cells usually have an atypical thickness of around 170 µm. This is said to decrease even further according to ITRPV. Theoretically, for first-generation solar panels, the thermodynamic efficiency limit for a single junction cell is 33%. Crystalline silicon PV cells have laboratory energy conversion efficiencies of over 25% for single-crystal cells and over 20% for Polycrystalline cells. However, industrially produced solar modules currently achieve efficiencies ranging from 18%–22% under standard test conditions (for more detailed information on how solar cells create energy you can refer this previous article How Does Solar Panel Create Energy )
Glass is by far the largest component by mass in solar panels and it accounts for more than 90% of the total weight. Glass is used in solar power systems to protect components and offer structural strength to the module and encapsulate the cells. The glass helps in transmitting the solar light easily to the solar cells and it can be made to have an anti-reflective coating on one or both sides, making them useful for concentrating sunlight. Most solar panels have tempered glass which is generally tougher and stronger and as a result, they can bear the stress created by strong storm events and snow loads.
- EVA Film:
EVA stands for ‘ethylene vinyl acetate’ which is a specially designed polymer highly transparent (plastic) layer. They are 'rubber-like' in softness and flexibility. This plays an important role in preventing moisture from entering the solar panels. During manufacturing, the cells are encapsulated with EVA before fitting the panel with the back sheet and the aluminum frame.
This is the bottom layer / last layer of the solar panel. It protects the cells from environmental damage and ensures that the panel is electrically insulated. The back sheet is tested under repeated mechanical and environmental stress to ensure the longevity of the panels.
- Anodized aluminum frame:
The Aluminium frame protects the edges of the panel. The Aluminium frame is designed to be lightweight and able to withstand high stress from external forces. The Aluminium frame comes in either silver or black with corner sections that can be clamped together. Anodising is done on these structures to prevent them from rusting. As these structures are exposed to harsh environmental conditions throughout their life.
- Junction Box:
The Junction Box is a bridge between a module and the output. It is therefore the transition gate for the produced energy. Inside a JB there are connections and bypass diodes that prevent the entire module from shutting down in case of partial shading i.e when only part of the solar panel produces electricity while another part of the solar panel is covered with shade due to clouds/trees etc.
Solar panels are assembled in advanced manufacturing facilities. The manufacturing plants must be extremely clean and controlled to prevent any contamination during assembly. Throughout the process, the panels are checked and ensured that all the components are located perfectly and the wafers are in good condition. The final assembly is thoroughly checked using several tests to identify any defects that could lead to potential damage to the solar panels.
Authors: Vidhyashankar Venkatachalaperumal, Afshin Bakhtiari