6-16-2015 How Are Silicon Solar Panels Made?
As solar energy becomes more mainstream, silicon solar panels are a common sight on rooftops. They look like rather simple mechanisms soaking up the sunlight and converting it into electricity. However, the process to create silicon solar panels is a complicated one.
The first step in making silicon solar panels is to create a giant crystal. That’s done by heating polysilicon rock with a bit of boron in a cylindrical oven until it melts. Temperatures in the oven usually reach about 2,500 degrees Fahrenheit.
After the silicon is melted, a thin silicon rod, called a seed crystal, is slowly lowered into the liquid. The seed crystal is attached to a wire that slowly spins the rod. The melted silicon freezes onto the seed crystal. As the crystal begins to grow, the rod is pulled up and out of the oven. The result, a giant crystal, is left to cool for a few days.
The cooled crystal is then moved to a new location where a wire saw cuts off its ends so that it’s a uniform width. The crystal is then cut into ingots that measure two feet or less. The ingots are placed on a rack and moved to another wire-slicing machine.
The wire on the machine is arranged in a lattice formation and shears off four rounded segments, leaving the ingots with flat sides. The ingots progress to another wire saw that slices them into thin wafers about the thickness of business cards. Each millimeter of crystal yields about two and a half wafers.
Making Solar Cells
The wafers are the first recognizable piece of the silicon solar panels to appear during the process. After the wafers are cut, they’re sent to a clean room. There, a series of chemical and heat treatments are applied to them. They then undergo a texture etch that removes a tiny layer of silicon, revealing the underlying crystal structure.
The underlying structure should be irregular and have a pattern that resembles pyramids. The pattern is so small that it’s impossible to see it with the naked eyes. However, the pattern is important for boosting a solar cell’s light absorption.
The wafers then move to long, cylindrical chambers where phosphorus is diffused into a thin layer of the wafers’ surface. The phosphorus gives the surface of the wafers a negative potential electrical charge.
The boron added at the beginning of the process gives the underlying layer a positive charge. The differently charged layers create a positive-negative, or P/N junction. This junction is a very important part of a functioning PV cell.
The cells are taken to a heavy vacuum chamber where blue-purple silicon nitride is placed onto their surface. The coating allows the cells to reduce reflection and absorb even more energy. The cells can now absorb light, but they have no way to collect and transfer that energy. To solve this problem, metals are printed on both sides of the cells.
Assembling Silicon Solar Panels
At last, the solar cells are assembled into modules. They’re strung together in strings of 10. Six strings are laid out side by side to form a matrix of 60 cells. Each matrix is laminated onto glass. The laminate is then framed for protection from weather. A junction box is also added to enable connections among modules. The panel is then inspected and shipped to distributors.
Power From the Sun
Silicon solar panels have humble beginnings. They start as lumps of silicon and end as clean power-generating technology. However, the possibilities associated with them are far from lowly. Silicon solar panels have the potential to change how we get our energy, changing how energy has been handled for over a century. That’s not a bad fate for something that started as a hard lump of silicon.