Solar cells are made from materials that directly convert sunlight into electricity.
Today, most commercially used solar cells are made of silicon (chemical symbol: Si). Silicon is what is known as a semiconductor. This chemical element is found throughout the world in the form of sand, which is silicon dioxide (SiO2), also called quartzite.
Another application of semiconductor silicon is in the microelectronics industry, where it is used as a base material for computer and appliance chips.
|
|
| 1. | sunlight (photons) | 4. | deflection layer |
| 2. | front contact | 5. | positive layer |
| 3. | negative layer | 6. | later contact |
For the planning, construction and installation of solar panels, get our Graphic, Practical and Illustrated Guide to Building Low Cost Solar Panels. Click Here
Structure of a solar cell
Silicon solar cells can be monocrystalline, polycrystalline, or amorphous; monocrystalline being the most efficient, although compared to polycrystalline, the difference is not much, nor is the difference in power significant.
The main difference between them lies in the way the silicon atoms are arranged, that is, in the crystal structure of each cell.
There is also a difference in the efficiency of each cell. Efficiency refers to the percentage of sunlight that is converted into electricity. Monocrystalline and polycrystalline silicon solar cells have almost the same and higher level of efficiency compared to amorphous silicon.
A typical solar cell is made up of layers. First there is a back contact layer and then two layers of silicon. At the top are the front metal contacts with an antireflection coating, which gives the solar cell its typical blue color.
During the last decade, new types of solar cells made of various materials have been developed, among which we find, for example, thin-film cells and CIS (copper indium diselenide) and CdTe (cadmium telluride) cells. ). These are beginning to be marketed.
| Solar cell efficiency: | |
| Monocrystalline: |
12-15% |
| Polycrystalline: |
11-14% |
| Amorphous: |
6-7% |
| Cadmium telluride: |
7-8% |
How many solar cells do I need to build a solar panel?
First you need to know how much electrical energy each solar cell produces to define the power in watts that the finished solar panel will generate. For example, the solar cell shown to the right generates 0.5 volts and 3.3 amps each, this is an average power of 1.65 watts. Therefore, if you need to build a 60-watt photovoltaic panel, just divide this number by 1.65 to find out how many photovoltaic cells you need for each panel:
60w / 1.65 w = 36 solar cells per panel.
Now, it is important to understand the concept of:
- Serial connection; and,
- Parallel connection.
When you join solar cells to create a solar panel. Solar cells are connected in series when we solder the positive poles of the first cell with the negative poles of the next cell. This type of connection is used to add the cell voltage without increasing the amperage.
Two groups of solar cells are connected in parallel when the positive poles of the first group are connected to the positive pole of the second group, adding the amperage without increasing the voltage.
The front blue part of the cell contains two white vertical lines which are the negative poles (bus bars) and the back of the cell contains 6 white squares which are the positive poles.
The white color of the poles is a silver compound which should not be scratched or removed. The metal strips used to join the cells must be soldered to the negative poles of the first solar cell and to the back 6 frames of the next solar cell (positive poles) to create a series connection.
Thus, we could build 4 strips of 9 solar cells each. Each group of 9 solar cells can be connected again (in series) with the next group until you have a total of 4 groups of 9 solar cells all connected in series. That is, 9 x 4 = 36 solar cells in series, at 1.65 watts per cell, this gives us a total of 60 watts for each solar panel.
To test the correct operation of a photovoltaic cell, it is necessary to expose the cell to direct solar radiation and measure its voltage with a multi-meter connecting to the terminals of the solar cell.
Specifications per photovoltaic cell
Power (Watts): 1.65 Wp
Average Current (Amps): 3.3
Average Voltage (Volts): 0.5
Width 200μm = 0.2mm
Exact dimensions: 3 1/4 inches x 6 inches, or 80 mm by 150 mm
Weight: 6 grams
Cost of photovoltaic cells to assemble solar panels
If you are ready to build your first solar panel, ask us via email at support@daprose.com about our kits for building solar panels. If you want to save time in the construction of solar panels, we recommend the packages that include pre-soldered solar cells (tabbed solar cells).
