What is a photovoltaic cell?
It has its origin in the year 1839 when Henri Becquerel, a physicist of French origin who dedicated himself to the study of the solar spectrum, magnetism, electricity, and optics, among other things discovered the ability of certain semiconductors to generate electric charges when receiving light incident.
Photovoltaic cells (also called cells or photocells) are an electronic device capable of transforming the energy of the incident light into electricity. This occurs thanks to the photoelectric effect.
How is a photovoltaic cell made?
The main component of photovoltaic cells is semiconductors. To reduce the manufacturing cost, silicon is used, which is the second most abundant element on the earth’s surface.
Photovoltaic cells are made up of two layers of semiconductor silicon charged with different concentrations of electrons. Electrical contacts are placed in each layer to extract the electricity they generate when they receive energy from sunlight.
Solar panels or modules are made up of photovoltaic cells, and therefore the size and characteristics of the module will depend on the cell used.
What is the efficiency or performance of a photovoltaic cell?
Efficiency is the cell’s ability to convert the amount of energy (solar radiation) incident on its surface into electricity. The cell is the generating unit and the active part of the module.
In other words, a cell or module is more efficient if it generates more electricity being the same size as another.
What types of cells exist?
There are different types according to the type of silicon structure and the size of the silicon wafer.
According to the silicon structure:
- Multicrystalline silicon cells, commonly known as Poly or polycrystalline, which have the most competitive cost. Made up of multiple crystals, they tend to be of a non-uniform blue color, and they are cheaper and less efficient because performance is lost at the union of the crystals. The latest manufacturing techniques already give greater uniformity to the appearance of the cell and have become very popular for its good value for money.
- Monocrystalline silicon cells, commonly known as Mono. Consisting of a single crystal, they are usually a very uniform black or dark blue color. The cost of production is higher and they provide better performance under certain conditions.
The performance of photovoltaic cells depends on the internal three-dimensional structure of these silicon sheets.
According to the size of the silicon wafer:
Silicon is cut into wafers of various sizes before making cells. Let’s highlight some.
From 2006 to 2018 almost exclusively, the modules on the market were made of M2 cells (square for Poly and with corner chamfers for Mono), both in full-cell and cut-cell modules. With the same starting wafer, a module was more efficient when it had more power than another of the same dimensions.
From 2019 onwards, we can notice changes in the dimensions of cells almost every 3 months. In addition, the modules made with pieces of cells are no longer only intended for small applications, the 120, 144, and 156 half-cell versions are already very popular, making the panels a little larger than their corresponding 60, 72, and 78 whole cells but also improve their performance.
Dimensions are evolving. However, this development is taking place almost only in the area of Monocrystalline cells and there are hardly any technological advances in Polycrystalline products.
- 6×6 inch (156x156mm) cells (M2) has been with us for more than 10 years after it replaced the 5×5 inch (125x125mm) cell, maximum power 415-420W in a panel with 144 half cells
The width of the module for these types is from 992 to 1040 millimeters, the length from 1650 to 2170 millimeters depending on the version (full cell/half cell or half cell)
- 158.75×158.75mm cells (G1): maximum power 435w-440W in panel 144 half cells
The width of the module for these types is from 922 to 1040 millimeters, the length from 1670 to 2190 millimeters depending on the version.
- 166x166mm cells (M6): 465-475W in panel 144 half cells
The width of the module for these types is from 1030 to 1120 millimeters, the length from 1750 to 2270 millimeters depending on the version.
- 180x180mm cells (M7): 510-530W in panel 144 half cells
The width of the module for these types is 1120 millimeters, the length from 2280 to 2390 millimeters depending on the version.
- 210x210mm cells (M12): 540-560W in 100 thirds of cells
It requires panels with different configurations so as not to exceed the limit dimensions of the glass.
In 2020 we can find 410Wp panels on the market with lower efficiencies than 390Wp panels due to the use of different cell sizes and configurations. For this reason, it is important to know the size of the panel and its efficiency and not just its power.
Every time the market requires and demands more efficient modules at a more competitive price. The reduction in prices is the result of optimization and increased production. However, the production of a reasonably durable module comes at a price, as does the production of a solar cell.
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