How Solar Panels Are Made Step By Step?

Solar panels have become an increasingly important source of renewable energy over the past few decades. The photovoltaic effect, which allows solar panels to convert sunlight into electricity, was first discovered in 1839 by French physicist Edmond Becquerel. The first solar cells made from selenium were introduced in 1883. However, solar panels did not become widely used until the space race beginning in the 1950s, when they were used to power satellites. Since then, advancements in materials and manufacturing have driven down costs, making solar power competitive with fossil fuels in many parts of the world.

Solar panels work by absorbing photons from sunlight and using their energy to knock electrons loose from atoms, generating a flow of electricity. Solar cells are assembled together into solar modules, which can then be linked into larger solar arrays. While sunlight is free, there are costs associated with manufacturing, installing, and maintaining solar panels. However, the costs are dropping each year, and solar power holds great potential to reduce reliance on fossil fuels and provide clean renewable energy around the world. With climate change threatening environmental catastrophe, transitioning to solar and other renewables has taken on great urgency. Widespread adoption of solar power will be critical for reducing greenhouse gas emissions and preventing the worst impacts of global warming.

Table of Contents

Silicon Purification

Silicon is abundantly found in sand, but needs to be purified in order to be used for solar cells. Raw silicon has impurities like iron, aluminum, and titanium that need to be removed. The silicon purification process starts by converting sand into metallurgical grade silicon. This involves heating quartz rock with carbon at high temperatures to reduce it down to silicon.

Next, this metallurgical grade silicon goes through a purification or refining process. This involves treating it with hydrochloric acid to convert it into trichlorosilane gas. The trichlorosilane is then distilled to remove boron and phosphorus impurities. After distillation, the trichlorosilane goes through a chemical vapor deposition process to produce polysilicon rods of ultra-pure silicon with 99.999999% purity levels.

This polysilicon is then melted and recrystallized using the Czochralski process to grow monocrystalline silicon ingots. The Czochralski process involves dipping a small monocrystalline silicon seed crystal into melted polysilicon and slowly extracting the seed while rotating it. This allows the silicon atoms to arrange themselves in the same crystallization pattern as the seed crystal, forming a large cylindrical ingot.

Ingot Creation

After the silicon is purified, it moves on to ingot creation. This involves melting down the purified silicon and casting it into ingots, which are brick-like blocks of silicon.

The purified silicon chunks are loaded into a quartz crucible and melted down at temperatures reaching over 1400°C. As silicon has a very high melting point, an electron beam or arc heating method is typically used to generate sufficient heat. Once the desired temperature is reached, the molten silicon takes on a shiny metallic appearance.

The molten silicon is then allowed to cool and solidify into a rectangular ingot inside a mold. The ingot mold gives the silicon a controlled shape and size for the next manufacturing stages. Multiple silicon ingots can be cast from one crucible of melted silicon. The ingots are then removed from the mold and inspected to ensure they are defect-free and ready for slicing.

Wafer Slicing

Once the silicon ingots are created, they need to be sliced into thin wafers that will be used to make the individual solar cells. This wafer slicing step is a critical part of the solar panel manufacturing process.

The ingots are mounted and sliced into wafers using a steel wire or blade that cuts the silicon with a sawing motion. The thickness of the wafers is very important – they need to be thin enough to be flexible, but thick enough to efficiently absorb sunlight. Most solar panel wafers are between 150-200 microns thick (equivalent to about 15 sheets of paper).

The slicing is usually done with specialized machines called wire saws. The steel wire is constantly moved up and down to slice through the length of the silicon ingot, cutting many wafers simultaneously. The wafers are separated and cleaned once the slicing is complete. Controlling wafer thickness and minimizing material loss during slicing is key to achieving high solar cell efficiency and minimizing cost.

Cell Fabrication

Once the silicon wafers have been sliced to the proper thickness, the next step is fabricating the individual solar cells. This process starts by adding impurities to the silicon to change the properties of the material. Phosphorous is added to create an N-type silicon with extra free electrons. Boron is added to create a P-type silicon with extra electron holes. When a thin layer of the N-type silicon is placed on top of a thicker layer of P-type silicon, it creates a P-N junction.

The P-N junction is critical to creating an electric field within the cell. The free electrons in the N-type silicon diffuse across the junction into the P-type silicon, while the holes diffuse in the opposite direction. This creates a negative charge on the N-side and a positive charge on the P-side, forming an inherent electric field across the entire junction. When light hits the solar cell, the energy knocks electrons free in both sides, allowing them to flow through the built-in field and generate electricity.

Applying Metallic Contacts

Applying metal contacts to the wafers is an important step in making solar panels. This process helps increase electrical conductivity and allows the cells to be interconnected into modules. Metal contacts are applied to the front and back of the wafers by a screen printing process.

A fine metal paste containing silver, aluminum or copper is used to form the metallic contacts. The paste is pushed through a stainless steel mesh in the desired pattern onto the wafer. The wafer then goes through a high temperature furnace, which forms alloyed electrical contacts on the wafer.

The front contacts collect solar electricity and conduct it out. They are formed into thin parallel metal fingers to allow maximum light exposure. The rear contacts form a continuous sheet to conduct electricity over the entire rear surface. The contact grid pattern maximizes conductivity while minimizing material use and shading.

High quality contacts are crucial for solar cell efficiency and performance. The metal paste ingredients, contact finger geometry, and contact firing process are optimized to provide high conductivity while avoiding damage to the wafer surface. Good electrical contacts allow the cells to work reliably for decades.

Connecting Cells

After the solar cells have been fabricated, they need to be connected together to produce modules with the desired voltage and current output. This process is known as stringing or matrixing.

To string the cells together, thin tabs called interconnect ribbons are soldered to the front and back of each cell. The interconnect ribbons are made of materials like copper or silver-coated copper. They provide an electrical interconnect between adjacent cells.

The soldering is done by heating the interconnect ribbons and applying solder paste or solder wire. The ribbon tabs are then mechanically pressed onto the metallic contacts on the front and back of the cells to form a permanent electrical and mechanical connection after the solder cools and hardens.

The interconnect ribbons connect the cells in series to form cell strings. This increases the voltage of the module. Multiple cell strings are then connected in parallel to increase the current output and form a matrix. The fully assembled matrix then gets laminated in the next step.

Precise soldering is critical to ensure proper electrical connections and maximum power output. Automated soldering and tabbing equipment is often used for production scale manufacturing to ensure consistency.

Laminating

Laminating protects the delicate solar cells from mechanical damage and moisture. This process sandwiches the interconnected solar cells between two sheets of ethyl vinyl acetate (EVA), a type of plastic. EVA bonds well to glass and serves as a moisture barrier and electrical insulator.

During lamination, the EVA sandwich structure is placed in a vacuum laminator and heated. The heat causes the EVA layers to become gooey and sticky, binding firmly to the cells and glass. Air bubbles are removed by the vacuum pump, preventing defects. Once cooled and hardened, the EVA encapsulates the solar cells, shielding them from weather, dirt, and other environmental factors. This protects the panel over its lifetime, which can span decades.

Installing Frame

Once the solar cells have been laminated together, the last step is to install an aluminum frame around the edges. This frame serves several important purposes:

Adding aluminum frame
The aluminum frame provides structural rigidity and helps protect the solar cells from damage. Aluminum is lightweight, corrosion resistant, and durable, making it an ideal choice. The frame pieces are precisely cut and designed to overlap at the corners for stability.

Providing structure and rigidity
Without the frame, the solar panel would be fragile and prone to cracking and breaking. The aluminum frame reinforces the entire perimeter and prevents bending or flexing of the panel. This allows the solar panel to be safely transported, mounted, and subjected to outdoor elements like wind and rain once installed.

The installed frame gives the final solar panel product a neat, finished appearance as well. Once the frame is attached, the solar panel is structurally complete and ready for testing and certification before being shipped out for installation.

Testing and Certification

Once the solar panel construction is complete, the panels undergo rigorous testing and certification.

Testing primarily focuses on three key performance factors – efficiency, durability, and safety:

Efficiency testing measures the percentage of sunlight energy converted to electricity by the panel under standard test conditions.
Durability testing puts panels through stresses like mechanical loading, thermal cycling, humidity freeze, and damp heat to validate a 20-30 year lifetime.