A solar cell starts as a grain of sand. Or rather tons of silica sand. Carbon is added to the sand in an arc furnace to produce 100% pure silicon. The silicon is converted into Polysilicon using a chemical process called the Siemens Process.
Finally, impurities in the form of boron or phosphorous are added to make the silicon more conductive as raw silicon is a poor conductor of electric current.
Metal conductors are used to provide interconnection between solar cells. Metal is used because it has better conductivity, allowing electric current to flow with less resistance. Solar cells are wired to each other using metal busbars that are made from copper, silver, and aluminum. Busbars are connected to the front and back of a solar cell and allow the flow of electricity out from the cell to where it will be used.
A solar panel consists of multiple solar cells wired together. But how are they joined together? That is the subject we want to look at in-depth in this article.
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Interconnections conduct the electricity generated by a solar cell. In simple terms, they carry electricity out from a solar cell. So, what are they made from, and are they the same thing as busbars? Keep reading to find out.
What Material Is Used For Interconnection?
A metal conductor is used to provide interconnection between solar cells. Metal is used because it has better conductivity, allowing electric current to flow with less resistance.
Which Metal Is Used In Interconnection Of Solar Cells
Solar cells are wired to each other using metal busbars that are made from copper, silver, and aluminum. Busbars are connected to the front and back of a solar cell and allow the flow of electricity out from the cell to where it will be used.
A solar cell is the smallest unit in a solar panel. It is the most important part of a solar panel as this is where sunlight is converted into electricity. A solar panel can have between 32 to 96 cells, with each cell having a voltage of 0.5V. The current depends on the size of the cell. Generally, they produce between 0.028 to 0.035 amps per square centimeter. Source
|SOLAR CELLS||TOTAL VOLTAGE (V)|
Busbars are the long silver-colored vertical strips that run down the front and back of a solar cell. These busbars conduct the electricity produced by the cell. They are typically made from copper coated with silver. The silver coating helps improve the conductivity of the copper busbar while also reducing rusting.
Running across the busbars are what are called fingers. They are the thin strips that run horizontally across a solar cell. The fingers collect the current generated by the solar cell and deliver it to the busbars they are connected to.
From the busbars the current moves to the tab or string wires where it will finally make its way out of the solar cell and into the junction box of the solar panel. From there the current is distributed either to an inverter or battery.
Solar cells will either have three (3BB), four (4BB), or five (5BB) busbars. Older solar cell technologies used two busbars. The number of busbars determines shading and resistance losses. Generally, the more busbars a solar cell has the shorter the distance between them. This means current travels faster which makes for a more efficient solar cell.
Coating busbars with silver increases the cost of a solar panel. This is why solar manufacturers are replacing silver with metals like tin and nickel which are far much cheaper.
Which Method Is Used For Interconnection Of Cells In Solar Panels?
Busbars are screen printed onto solar cells. In terms of this process, a silver paste is deposited onto the solar cell using a strip screen.
What Metals Are Used In Solar Panels?
Solar panels are made of different metals including silicon, copper, silver, zinc, cadmium, gallium, aluminum, indium, selenide, tellurium, and lead. Silicon is by far the most commonly used metal in solar panel manufacture. More than 90% of the world’s solar panels are made from silicon.
Solar panels are split between silicon-based solar panels and thin-film solar panels.
Silicon solar panels
Owing to its abundance, at more than 28% of the Earth’s crust, silicon has been used for thousands of years. The first to use it were ancient Egyptians to make glassware and beads. Today, silicon has much more sophisticated uses like making semiconductor chips and of course solar panels.
Crystalline silicon or C-Si solar panels dominate the market. This is because they have a higher efficiency than their thin-film counterparts. In its rawest form, a silicon cell starts as Quartzite or silica sand before it is purified and refined.
Crystalline silicon solar panels come in two variations. These are monocrystalline and polycrystalline.
Monocrystalline is the most efficient single-junction solar panel. Made from a single silicon crystal it has a dark black color. The process of fabricating a monocrystalline solar cell is complex and energy-intensive which is why monocrystalline is typically the most expensive solar panel.
Polycrystalline has a bluish color. They are made from a simpler process compared to monocrystalline which leads to a much cheaper solar panel. They are, however, less efficient than monocrystalline. Source
Thin-film solar panels
Thin-film solar cells are made by depositing one or more layers of photoconductive material on glass, metal, or plastic. They can be deposited on almost any material and are lighter and more flexible than silicon solar panels.
As they are made through a simpler process, thin-film solar panels are cheaper than silicon. They are, however, up to 50% less efficient. The most common thin-film technologies are cadmium telluride, copper indium gallium selenide, and amorphous silicon.
Cadmium telluride (CdTe) makes up about 5% of solar panels and half of the thin-film solar panels in the world. They are made by combining cadmium and tellurium with the latter being almost as rare a metal as platinum.
Copper indium gallium selenide (CIGS) is made by combining copper, indium, gallium, and selenide. CIGS solar panels make up 2% of the PV market.
Amorphous silicon is the only silicon-based thin-film solar panel. The very first solar-powered calculators used amorphous silicon cells. Source
Aside from the solar cells themselves, metal is also used elsewhere in the solar panel. The frame that holds the components of a solar panel together is made from aluminum. Then there are the wires or conductors that connect the solar cells.