How solar panels are made

A solar PV module contains solar cells, glass, EVA, back sheet and frame.Three types of solar panels are available in the market. They are:

•     Mono-crystalline solar panels
•     Poly-crystalline solar panels
•     Thin film solar panels

Therefore, various types of materials are used for manufacturing at cell structure level. They are - mono silicon, poly silicon or amorphous silicon. Mono and Poly crystalline cells have almost similar manufacturing process. For producing a crystalline solar panel following steps are followed:

First Step: Sand

Here sands are used as a raw material. Most solar panels are made of silicon, which is the main component in natural beach sand. Silicon is plentifully available which is the second most available element on Earth. However, converting sand into high grade silicon is a high cost energy intensive process. Pure silicon is produced from quartz sand in an arc furnace at very high temperatures.

Second Step: Ingots

Basically, the silicon is collected in the form of solid rocks. Hundreds of these rocks are being melted together at very high temperatures in order to form ingots in the shape of a cylinder. A steel, cylindrical furnace is used for forming desired shape. All atoms need to be perfectly aligned in the desired structure and orientation during melting process. For providing the silicone positive electrical polarity, Boron is added to the process

Mono crystalline cells are manufactured from a single crystal of silicon. Mono Silicon has higher efficiency in converting solar energy into electricity, therefore the price of mono crystalline panels is comparatively higher.

Poly silicon cells are made from melting several silicon crystals together. After the ingot has cooled down, grinding and polishing are being performed, leaving the ingot with flat sides.

Third Step: Wafers

In this step, wafers are used during manufacturing process. The silicon ingot is sliced into thin disks, also called wafers. A wire saw is used for precision cutting. The thinness of the wafer is similar to that of a piece of paper. As pure silicon is shiny, it can reflect the sunlight. An anti-reflective coating is put on the silicon wafer for reducing the amount of sunlight lost.

Fourth Step: Solar cells

Treating each wafer, metal conductors are added on each surface. The conductors provide the wafer a grid-like matrix on the surface. This confirms the conversion of solar energy into electricity. The coating will ease the absorption of sunlight, rather than reflecting it. In an oven-like chamber, phosphorous is being diffused in a thin layer over the surface of the wafers. This will charge the surface with a negative electrical orientation. Boron and phosphorous combination will provide the positive - negative junction, which is very important for the proper function of the PV cell.

Fifth Step: From Solar Cell to Solar Panel

In this step, using metal connectors, the solar cells are soldered together to connect the cells. Solar panels are made of solar cells integrated together in a matrix-like structure. The current standard offering in the market are:

•     48 cell panels - For small residential roofs.
•     60-cell panels - The standard size.
•     72-cell panels - For large-scale solar power plant.

After putting the cells together, a thin layer (about 6-7 mm) of glass is added on the front side, facing the sun. Highly durable, polymer-based material is used to make the back sheet. This will protect solar panel entering water, soil and other materials from the back. For enabling connections inside the module, the junction box is added.

After assembling the frame, it all comes together. The frame protects the panel from impact and weather. The use of a frame will also allow the mounting of the panel in a variety of ways, for example with mounting clamps. EVA (ethylene vinyl acetate) is the glue which binds everything together. It is crucial that the quality of the encapsulation is high so it doesn't damage the cells under harsh weather conditions.

Sixth Step: Testing the Modules

For ensuring expected performance of the cells, testing is carried in this step. perform as expected. STC (Standard Test Conditions) are used as a reference point. The panel is put in a flash tester at the manufacturing facility. The tester will deliver the equivalent of 1000W/m2 irradiance, 25°C cell temperature and an air mass of 1.5g. Electrical parameters are written down and these results can be found on the technical specification sheet of every panel. The ratings will reveal the power output, efficiency, voltage, current, impact and temperature tolerance.

Besides STC, every manufacturer uses NOCT (nominal operating cell temperature). The parameters used are more close to ‘real life’ scenario:  open-circuit module operation temperature at 800W/m2 irradiance, 20°C ambient temperature, 1m/s wind speed. The ratings at NOCT can be found on the technical specification sheet.

Before shipping the module to homes or businesses, cleaning and inspection are done which is the final step of the production.

The aim of the research and development in the solar energy industry is to reduce the cost of solar panels and increase the efficiency. The solar panel manufacturing industry is becoming more viable and is predicted to become more popular than conventional sources of energy like fossil fuels.