Solar energy has become very popular lately, mostly because it represents a clean alternative to fossil fuels and also due to the fact that the technology used to harness the power of the Sun is now more affordable.
How Are Solar Panels Made Today?
Today, there are many types of solar modules available on the market, and the most popular ones are using solar cells made of silicon, while others a combination of materials such as Cadmium Telluride (CdTe), Copper Iridium Gallium Selenide (CIS/CIGS), amorphous silicon (a-Si), and organic photovoltaic cells (thin film solar cells).
Solar modules using solar cells made of silicon provide a better efficiency, which means that they are more expensive, but their lifespan is longer.
However, it was reported that a thin film solar panel works much better in low light conditions and even in shade, so from this point of view a thin film solar module that is also flexible can generate more electricity during a rainy day or during the winter even if its efficiency is reduced compared to the efficiency provided by a photovoltaic solar panel.
Let’s see how different types of solar panels are manufactured today.
The Manufacturing Process of Solar Cells Today
Solar panels using silicon cells have in common the Sun and the silica sand that comes from rocks located in a silicon quarry.
After taking out the silicon rocks from the quarry, they are moved to a large furnace (along with a source of carbon) to be melted at a pretty high temperature (a little over 2,000 degrees Celsius), in order to extract the silicon (SiO2 + 2C = 2CO + Si).
The silicon obtained this way is almost 99% pure and needs to be further purified to manufacture monocrystalline and polycristalline solar cells.
Silicon is used to manufacture solar cells, and also to produce glass and computer chips.
The metallurgical silicon obtained after the melting process of the silicon rocks has a purity of only 98 or 99%, which means that needs to be further purified to be used in the solar industry.
To obtain a purity of 99.99% required by the solar industry, the silicon needs to be melted again and cleaned through a distillation process.
Silicon ingots
The pieces of purified silicon are moved to the ingot factory where the silicon ingots will be produced.
A solar cell can convert the sunlight into electricity due to the fact that during the production of the silicon ingots boron is added to the silicon and later during the processing of the solar cell, phosphorus will be diffused into the silicon to produce two different layers.
The region between the layers will create a wall that will block the electrons from reaching the other layer.
The electrons from the bottom layer will pass the wall between the two layers only with the help of the photons present in the sunlight.
The electrons will gather this way on the upper side of the solar cell, and by connecting the upper and the lower side of the cell with a conducting wire, the electrons will be able to return to the bottom side of the cell through the wire.
Monocrystalline Solar Panels
Monocrystalline solar cells will be produced from a single ingot of silicon with 99.99% purity, while polycrystalline solar cells will be produced from chunks of silicon.
To manufacture monocrystalline solar panels a thin rod known as the seed crystal will be submerged into the melted silicon and will be pulled back up very slowly.
In the process, the liquid silicon will accumulate on the seed crystal and will solidify over a period of four days.
The basic round crystal (silicon ingot) obtained this way will be cut into a rectangular shape for practical reasons.
The ingot will be then cut into millimeter thin slices by a machine using hundreds of spinning wires.
Each slice of pure silicon obtained from the original ingot will be called “wafer”and will become the basis of the future solar cell.
Silicon wafers
Once cut, the wafers will be sent through a wash tunnel to remove any piece of dust or dirt that could compromise the solar cell production.
At this moment, the surface of the silicon wafer is very flat (like a mirror), which means that the sunlight will be reflected for the most part and only a small amount will be used to generate electricity.
To reduce the reflection to the minimum, the surface of the wafer is edged and roughened in a chemical bath to obtain a shape that under a microscope shows the pyramid structure of light in which the sunlight is refracted multiple times to use the incoming light in a more effective way.
The next phase of the manufacturing process is called diffusion and here a negatively charged phosphorus layer will be added to the positively charged layer of the wafer.
In an oven heated at 900 degrees Celsius, phosphorus atoms will be injected with the help of nitrogen, and the gaseous mix of phosphorus and nitrogen will be deposited on the wafer.
At the interface between positive and negative charged layers the free charge carriers created by the light are released, which generates an electric current.
A stamp pack press will print a silver alloy grid onto the front of the cells, which will become the typical grid pattern seen on the solar cells.
The silver coating will ensure that the power generated by the solar cell will be transported properly.
A solar PV panel contains one or more solar cells
The solar cells are now complete and they can generate and transport electricity, but because each cell has a different level of electrical conductivity, they will be evaluated and sorted during the tests that will follow.
All solar cells that have passed the tests will be assembled and soldered together to form a structure that will be used to build a solar panel.
During the lamination process, the solar cells mounted on the panel will be covered by glass to protect them from the outside conditions.
Monocrystalline solar cells produced this way will provide the highest efficiency available on the market today for photovoltaic solar cells.
Polycrystalline Solar Panels
To manufacture polycrystalline solar panels, the chunks of silicon will be put into a crucible and the boron will be added.
The crucible full of chunks of silicon will be then placed in the crystallization oven where the silicon will be melted.
By regulating the cooling process in the oven, the unwanted impurities will be removed and the purity of the silicon will be improved.
Once the silicon is cooled and solidified, the crucible will be removed and the silicon ingot will be moved into a machinery that will cut the ingot into columns and then the columns of silicon will be put inside a machine full of spinning wires that will slice the silicon column into very thin wafers.
In the next phase, the silicon wafer will be turned into a polycrystalline solar cell.
In the first step, the silicon wafer is precisely measured to ensure a high-quality end product, and after that the surface of the wafer will be roughed by running the wafer through a chemical fluid.
In an oven at a temperature of 900 degrees Celsius phosphorus will be diffused on one side of the solar cells, and after that a grid of fine silver stripes will be printed on each cell.
Poly solar panels are more affordable
Several cameras will then check the solar cells resulted, and the efficiency of the cells will be measured.
All solar cells that have passed the tests will be selected and then sent to the module factory.
At the module factory, many packs of solar cells with similar electrical characteristics will arrive and the solar cells will be placed in rows next to each other and connected.
To ensure a long lifespan of the solar panels, a sheet of glass will be placed on the module to protect the solar cells and an extra foil to repel the water.
In the final phase, the solar module will be bonded in an oven, and after that will be tested if it works properly.
If the solar panel passes all the tests, will be packed and shipped to the customer.
Thin Film Flexible Solar Modules
The manufacturing process of the thin film flexible solar modules begins with the creation of the core of the solar module, which consists of a very thin (30 microns thick) and long roll of plastic.
The roll of plastic goes through a sequence of deposition machines to put down a back metal contact (on the back of the solar module) that will be followed by six layers of semiconductor amorphous silicon and then a top conductive layer that is also transparent.
From the deposition machines, the film will be loaded into a laser scribing machine where laser heads will scribe intersections on the material to create the individual solar cells on the roll.
The film will then be moved to the printing stage where electrical insulators will be printed between the individual solar cells in order to isolate the positive and the negative sections.
The roll is then run through a silver print machine that will print conductive silver ink particles to increase the electrical conductivity of the module.
Thin film solar panels work well on different surfaces
Once tested, the roll will go through a process in which a copper busbar will be soldered on the module to create the electrical connection, and after that a laminate (a Teflon type product) will be put on the front and the back side of the module to ensure a high resistance of the solar module in the outside conditions such as water, chemicals, moisture, etc.
The roll will then be loaded into a die-cutting machine where the film is aligned and cut into individual modules.
Thin film flexible solar modules will then be tested electrically and the ones that will pass the tests will be loaded into a large machine (the pick-and-place machine) where a robotic arm will pick up the individual modules will check them for orientation and will place them onto a fabric surface.
The robot will keep placing solar modules on the fabric following a pattern previously selected by the computer.
Once finished, a laser will cut the piece of fabric to form the outline of the foldable solar panel.
The panels will be taken by operators from the pick-and-place machine in order to connect the modules together on the fabric using a flexible multi stranded wire.
Solar panels are very well insulated to withstand harsh weather conditions
Soldering iron will be used by the operator to burn away small sections of lamination over the conductive tape and create multiple connections to ensure that the solar panel will still be operational even if a wire will break.
After that, the solar modules will go through a final lamination process, which is actually a high heat lamination process that will bond everything together and will seal the panel from moisture, chemicals, water and other destructive agents.
In the next phase, the flexible solar modules will reach the sewing cell where the edges of the panels will be sewn, and a top fabric wrap will be added along with the product labels and strips that will be sewn over the wire attachment points.
In the finishing cell, the operator will add a circuit board and a connector, and also a few strong points at the corners to strap down the solar panels in windy conditions.
The completed units will then be taken outdoors for the final tests prior packaging, and all the units that will pass the tests will be moved to the shipping department.
Conclusion
As time passes, solar technology improves and becomes more affordable, which creates the opportunity for a cleaner environment for us and the future generations.
