Very brief history of solar cells
Silicon solar cells make solar panel
Solar cells are semiconductor structures that convert solar radiation in a wide wave-length range into electricity. Solar cells can be connected in series, parallel, or in combination.
It all depends on the projected power of the cell. Residential solar panels usually contain 60 or 72 cells. So we can conclude:A grid of solar cells makes a solar panel.
Solar panel efficiency
Solar cells work in direct current mode (DC), but with a negative current direction.
According to the material from which they are produced, they are divided into : Si, Ga-As, Ge, Cd-Te,In-P,P and organic.
Silicon solar cells - types
Silicon solar cells are the most commercially present, they are divided according to the crystallographic structure into monocrystalline, polycrystalline and amorphous.
Monocrystalline solar cells are the most expensive, and their efficiency coefficient is up to 18%.
Polycrystallines are cheaper, and their efficiency coefficient goes up to 15%. They are an alternative to single crystal cells.
Most efficiency commercial struture
Cheaper and not so efficienc, but affordable.
Solar panels dimensions
- The usual commercial dimensions of a residential PV panel are 1650 mm (40 inches) long and 1000 mm (40 inches) wide. These panels are very price affordable. The large panels consist of 72 cells. Their dimensions are: 2000 mm (79 inches) long and 1000 mm (40 inches) wide. Halfcut cells are doubles inpanels;s forexample, ae panel withdimensions ofs 1650 mmbyx 2000 mm has 120 cells.
Some panels are bigger and have more cells, so they could collect more power. For example, 132 cells (6 x 22) can gain 660 W.
Solar cells structure
The solar cell usually has four layers.
1. The first layer is a protective glass made of SiO2.2and protects the cell from external influences.
2. The next layer is anti-reflective, which reduces light reflection and ensures that as much energy as possible reaches the semiconductor (cell utilization increases).
3—The third layer consists of a system of transparent electrodes, TCO. It contacts a semiconductor with a PN junction, in which a photon of sunlight is captured.
4—The back layer on the underside is metallization—back contact. es here.
How solar cells works - simple explanation
The operation of a solar cell takes place in three steps:
- Photons from sunlight strike the solar panel and are absorbed by semiconductor materials such as silicon.
- Electrons are pushed out of atoms and become free, and can flow freely through the material, thus forming a current. Due to the special construction of solar cells, electrons can only move in one direction.
- A solar cell array converts the sun’s energy into a usable amount of direct current (DC).
How does it made
Building a crystalline silicon solar panel is a medium-complex industrial process. silicon, in the form of silicon dioxide (SiO).2)—sand and gravel. Silicon is the second-most abundant element on Earth.
Before it’s used in a solar panel, silicon dioxide must be turned into pure “metallurgical grade silicon” (MGS). This process uses a lot of energy; producing 1 kilogram of metallurgical-grade silicon requires approximately 15 kWh of power.
The recipe for melting metallurgical-grade silicon is one part silicon dioxide and two parts carbon (coal) in an electric arc furnace. setup the furniture to 2200 degrees Celsius ( steel is melting at 1250 degrees Celsius).
After that, 98% pure silicon and carbon monoxide remain (the carbon will remove oxygen from the silicon dioxide).
This chemical reaction is
Step One: Metallurgical Grade Silicon
SiO2 + 2C-> 2Si + 2CO
Step 2—Silicon purity
The next step is to make silicon 100% pure. To achieve that, we need to upgrade the silicon into an even more pure polysilicon metal using a process that involves hydrochloric acid and hydrogen gas.
Si+3HCl -> HSiCl3 + H2 -> Si + HCl + Cl2 + H2 -> Si + HCl + Cl2 + H2
The result is polysilicon, which is going to melt again with
boron added on one side to obtain a positive charge. The hot silicon cools and forms a single crystal (monocrystalline) called an ignotms
Ignots are typically a rectangular shape, like a bar.
Step 3: Polysilicon wafer fabrication
Ignots have been cut into 0.180-mm-thick layers, and wafers are born. The wafers are heated in the oven, and a thin layer of phosporous is added (diffusion process) to obtain a negative charge and boron on the other side for the positive side.
An anti-reflective coating is added to wafers to prevent sunlight reflections.
At this stage, wafers are fully capable of converting light to
electron movement, which has to be ordered—so silver is added and electric current is obtained.
Silver is one of the best electric conductors, but it takes up 10% of the cost of the solar panel. The silicon wafer is now in the form of a conductive solar cell. Each solar panel usually contains 60 or 72 cells.
Solar cells connected in a grid form make solar panel
The maximum output voltage of a single solar cell is between 600 and 700 mV.
In order to obtain the desired voltage, they are connected in series.
For example, 36 cells connected in series create modules with a nominal voltage of 12 volts.
The power produced by one photovoltaic cell is relatively small, so in practice several cells are connected in a group, which forms a photovoltaic module. According to the designed power, the modules are connected in series and / or in parallel, thus forming a photovoltaic panel that produces current, voltage and power of much higher intensity.
And maybe you should know.
N vs. P type
Unlike P-type modules, the wafer of an N-type module is positively charged on the bottom and negatively charged on the top. This leads to a lower temperature coefficient and thus enables higher yields.
Bifacial Half-Cell Technology
Due to the transparent rear cover and the use of bifacial half-cells, the irradiation on the back of the modules generates up to 30% more energy yield.
Halfcut and Multibusbar Technology
Halfcut cells with additional multibusbar technology increase the efficiency and reliability of our modules. This increases yields by up to 50% when the module is partially shaded.
By converting solar energy into electricity, DC (direct current) is obtained, and for the operation of the device in the house, it is necessary to transform it into AC. With such systems, two ways of connecting have been developed: