A photovoltaic solar panel is an electronic equipment made up of dozens of semiconductor cells that use solar radiation to generate electricity. When sunlight hits the cells of the panel, its photons are absorbed by the semiconductor material in the cell and an electric current is generated.
Since the individual cells produce very little energy, the cells are assembled in series and in parallel to form a panel. Series connections increase the voltage for the same current while parallel connections increase the current for the same voltage. Knowing that power is the product of current by voltage, the power of a panel is proportional to the quantity of cells it contains. The more powerful a solar panel is, the more energy it can produce. Generally, solar panels have 60 to 72 cells, although some panels have up to 144 cells.
There are three types of photovoltaic cells: amorphous cells, monocrystalline cells, and polycrystalline cells. The image below shows these three different types of cells (amorphous on the left, monocrystalline in the center and polycrystalline on the right).
The differences in yield are mainly explained by the level of crystal purity of the cells. The more a cell has a high level of purity, the better its interaction with solar radiation and therefore its efficiency. The thickness of the cell also has an impact on the yield, the latter being proportional to the thickness of the cell.
Most photovoltaic cells are made from silicon. This component is used due to its low extraction cost as well as its semiconductor properties. Silicon does not exist in the free state, but rather in different forms of minerals such as sand or quartz. It is very abundant, not to say almost unlimited.
The extraction of silicon from quartz is carried out by carboreduction, that is the extraction of metals from their oxides in the presence of coke at very high temperatures in an electric arc furnace. Very high temperatures (up to 2000 ° C) allow certain chemical reactions to take place, especially the reduction of silica (SiO2 + C ⟶ Si + CO2) and the elimination of oxygen.
The silicon obtained from this process is 99.99% pure. It is only when it reaches this purity that it will be used for the development of photovoltaic cells. That said, the table below shows the elements and their quantity needed to produce a ton of silicon.
|Element||Quantity required (kg)|
|Electricial energy (kWh)||12 000|
The table below from the United States Geological Survey (USGS) shows the top ten silicon producers in 2017.
|Country||Annual production (in thousands of tons)|
1. Ingot drawing: The first step in manufacturing a solar panel is to produce 99.99% pure silicon ingots. To do this, the silicon is baked in an electric arc furnace at a temperature for several hours.
2. Ingot Sawing: Once cooled, the ingots are cut into slices, the thickness of a sheet of paper. These slices are commonly called “wafers”. The wafers are then given an anti-reflection treatment to limit the amount of light they reflect (and by the same time the amount of light they absorb).
3. Phosphorus diffusion: For the wafer to become a photovoltaic cell, impurities must be added. These impurities are so called because they accept or give an electron to bind with the semiconductor of the cells (silicon) and thus generate current.
On the top layer of the cell, the added impurity is an element that has more electrons than silicon (usually Phosphorus). This layer is of type N and is negatively charged.
On the lower layer of the cell, the added impurity is an element that has fewer electrons than silicon (usually Boron). This layer is of type P and is positively charged.
For there to be conduction, a PN junction must be created. Once the junction is created, the wafer is a photovoltaic cell, with one negative side and another positive side.
4. Screen printing Metallization: A silver-based paste is printed before being annealed at high temperature on the surface of the photovoltaic cells, the aim being to be able to collect the electric current that they produce.
5. Strings Interconnections: All the cells of the solar panel are connected together, in series or in parallel.
6. Encapsulation: The cells of the solar panel are encapsulated between a sheet of glass and a polymer to protect them from UV rays, humidity and to insulate them electrically.
7. Framing: This step consists of framing the solar panel in a frame made of aluminum to give it mechanical rigidity. The choice of aluminum is justified by its low weight, its inexpensive cost, and its robustness. The module is finally subjected to mechanical, optical, and electrical tests before being placed on the market.
In summary, monocrystalline solar panels have solar cells made from a single silicon crystal while polycrystalline solar panels have solar cells made from multiple fragments of silicon crystals melted together. Amorphous solar panels are made up of a thin layer of silicon on an amorphous material.
This manufacturing difference means that the spectral response of monocrystalline solar panels is the highest, which gives them better performance. Although they are more expensive, the fact that they can produce more energy offsets their additional cost, especially knowing that their lifespan is at least 25 years. In addition, their black color is more discreet and works better with a conventional shingle roof. Monocrystalline solar panels are the best type of solar panel. However, for those on a more limited budget, polycrystalline solar panels are still a good choice.
That said, do not hesitate to contact us for more information, we will be happy to assist you. Our affordable, reliable and turnkey solar energy systems will fully satisfy you. Give us the chance to impress you and share our solar expertise with you.