The solar panel has becoming an increasingly common sight on the roofs of our neighborhoods, but how are they made? There are three different kinds of silicon crystal cell structure in use, these are poly-silicon, mono-silicon and thin film. Due to the best efficiency to cost ratio, the most commonly used type of crystal used in solar panels today, is the poly-silicon crystal. Due to it’s popularity, the poly-silicon process is the sole focus of this article.
Solar panels are created via a four part process that involves creating the silicon crystals, wafering them, manufacturing a solar cell and assembling the solar panel. Each step is vital to the efficient operation of the panel and a detailed breakdown of the whole process follows.
1. Creating the Silicon Crystals
Silicon crystals make up the composition of the solar cell, but they must be grown first in order to process them further later. The process begins with mined poly-silicon rocks. These are placed in a quartz crucible in a blast furnace. The crucible is charged with a boron dopant that will form an electrical orientation that has a positive potential. The furnace is then heated to approximately 2,500°F, the poly-silicon rock melts into slurry and a suspended silicon seed crystal is injected into the material. The crucible then turns as the seed crystal remains static, this causes the slurry to move around it and begin to freeze upon it. As the silicon slurry sets it will match the seed crystals structure and become crystalline. As this stage concludes the new crystal is carefully removed and set aside to cool for a few days.
2. The Wafering Process
The growing stage produced a silicon crystal that now needs to be processed further in order to create a crystal with the correct shape and thickness. Initially the crystals are cut up into chunks that are manageable to work with and of uniform size. After this stage the material is referred to as an ingot and it’s cylindrical in shape. The ingot is then cut again to create square uniform edges and smooth rounded corners. Once the ingot has reached this stage it’s in a form that is suitable for the final cutting process. A very accurate computerized saw is then used to cut the ingot into wafer thin slices.
3. Turning the Slices into Solar Cells
The wafer thin slices of silicon crystal need to be formed into a solar cell using chemicals and heat. The wafers have their surfaces etched with acid, they are diffused and coated with silicon nitride which turns them dark blue in color. The silicon nitride reduces reflection on the surface of the solar cell, this means that the cell can absorb more light.
4. Final Assembly of the Solar Panel
The solar cells are now strung together and created into clusters. The clusters are then soldered together to ensure that all the solar cells are connected and create a circuit. The two current industry standard sizes are 60 cell and 72 cell panels. The clusters are placed into an aluminum frame to provide additional strength and fixing points for the installation. A glass cover, an insulation layer and a protective resin or glass base make up the rest of the unit. If assembled correctly the panel will be protected not only from physical damage, but also from humidity and excess heat. The solar panel is then fitted with a junction box or an inverter and is now ready to be connected singly or in series to a solar energy system.
The whole manufacturing process from start to finish is quite complex and the end result is an efficient photo-voltaic solar panel that can harness the energy of the sun. This process has been refined over the years, although new even more efficient methods are being explored. Future panels will be lighter and more efficient, but it’s unlikely they will be available anytime soon as there is a current worldwide oversupply.