How Are Solar Panels Manufactured? The Ultimate Guide
March 06, 2019
Solar energy has been the superstar of all the renewable energies available. In the last few years, it has entered the mainstream focus as the cheapest energy source available. Unlike other energy sources, solar energy is cheap, available in abundance and most importantly, the best available “green energy”.
So much has been written about solar energy, its uses, its advantages, its disadvantages but not many people know about the technology that makes the solar energy so efficient i.e. solar panels.
It is the invention of solar panel technology that led to the revolution of this renewable technology. Humans have known the importance of sun for many centuries, but it was only a few decades ago that we were able to harness the energy available from this ball of fire. And it is all possible due to the invention of solar panels.
So, today I am going to tell you everything you need to know about solar panels. Like the history of solar panels, how solar panels are made, the manufacturing process etc.
This Ultimate Guide contains all the information related to the solar panels & its manufacturing process. Information like:
- What are solar energy panels? (How it Works?)
- The history of solar panels
- Materials used in solar panel manufacturing
- The manufacturing process of solar energy panels
- Quality control
- Future of Solar energy
What Are Solar Energy Panels? (How it Works?)
In simple words, solar panels work simply by allowing photons to interact with the electrons present in the solar energy panels, generating a flow of electricity. Solar panels are manufactured by using photovoltaic materials (Photovoltaic materials are nothing but cells which converts sunlight into electricity).
The History of Solar Panels (How the Manufacturing of Solar Panels Evolved?)
The discoveries of various properties of light made solar panel what it is today. Though we use solar energy efficiently from the last six decades, the solar panel invention is 200 years old. Here is the chronology followed by solar energy panels:
The year 1839: Photovoltaic effect is discovered
French scientist Edmond Becquerel first discovered the photovoltaic effect in materials in 1839. The effect occurs when a photosensitive material is exposed to sunlight, the resulting interactions creates an electrical voltage.
1873 – 1876: Photoconductivity of selenium is discovered
In 1873, British electrical engineer discovered the photovoltaic effect in selenium, meaning that selenium could generate electricity when exposed to sunlight. Three years, in 1876, William Grylls Adams and Richard Evans Day discovered that selenium could produce electricity without any heat or mechanical motion. Unlike other conventional energy sources like – coal and fuel.
1883: The first solar panel is manufactured
New York based scientist Charles Fritts manufactured the first solar panel by coating photoconductive selenium with a thin layer of gold. The manufactured solar panel produced an efficiency of 1%. Meaning the solar panel could convert 1% of total solar energy exposed to the panel into electricity. The modern solar energy panels have an efficiency of 15-20%.
1887: Photoelectric effect is observed
German physicist, Heinrich Hertz first observed the photoelectric effect, where light is used to release electron into a vacuum space to generate electricity. Unlike, a photovoltaic effect where electrons enter a different material to generate electricity. Later in 1905, Albert Einstein was awarded Nobel prize for explaining the photoelectric effect. Modern day solar panels use the concept of the photoelectric effect to generate electricity.
1953 – 1956 – The first commercial commercial solar cells are manufactured
In 1953, Bell laboratories discovered that silicon has better efficiency than selenium and thus made the first solar panel with 6% efficiency. In 1956, western electrics started commercially licensing their PV technologies.
1958: Solar panels are used in space technology
After years of experimentation and countless efforts of making solar panels commercially available, finally, in 1958, solar energy got a push when they decided to power a space orbit using solar panels. This paved the way for more research and a decrease in the manufacturing cost of the panels.
1995: First retractable RV solar panel are manufactured
Solar energy started moving in other sectors, Thomas Faludy filed a patent for the first manufactured retractable awning with integrated solar cells. This was one of the first time when solar panels were used in recreational vehicles.
1996-2005 – The efficiency of solar panels reach a new level.
As solar technology kept improving, the efficiency of solar panels reached new heights. Residential rooftop solar systems became popular and the production of solar energy panels gained momentum on a large scale.
Material Used In Manufacturing Of Solar Energy Panels
Raw Materials –
Silicon is the basic material used in the manufacturing of solar panels. Silicon’s atomic number is 14 in the periodic table, it is a non-metal with conductive properties. Silicon is not found in pure form when extracted from the earth’s crust. It is often combined with oxygen in the form of obsidian, granite and sandstone. The silicon found in solar panels is obtained by the reduction process. Where silica is treated with carbon to remove oxygen in the form of carbon dioxide leaving pure silica in the metallurgical form.
Next, the silicon used in solar energy panels must have a high percentage of purity. The metallurgical-grade silicone must pass through hydrogen chloride at extremely high temperatures and undergo distillation. But to yield a solar-grade end product, the silicone goes through a chemical refinement process. In this process, gases are passed through melted silicon to remove impurities such as boron and phosphorus. In its pure form, solar-grade silicon is then turned into cylinders called ingots, which are then sliced into the small conductive pieces that absorb the sunlight in solar panels.
Image Source – Silicon Video
Wafers & Ingots –
Different types of wafers are cut from ingots:- Monocrystalline, polycrystalline and silicon ribbons.
Monocrystalline wafers are thinly cut from a cylindrical ingot, meaning they only have a single crystal structure. The diamond saw used to cut these wafers cut it into a circular form and since these circular shapes don’t fit together they are reshaped into a rectangle shape. This reshaping causes a lot of material loss. Efforts are being made to manufacture monocrystalline wafers without wasting the material.
Polycrystalline wafers are ingots made from multiple crystal structures. The wafers are made from melted silicon poured into a mould. This produce less waste as the desired form can be obtained without the need for reshaping. Polycrystalline wafers are less efficient than monocrystalline wafers.
Silicon ribbons are thin sheets of polycrystalline silicon. They are so thin that they don’t have to be sliced into wafers. While the thin sheets, or thin films, are flexible, can be used in interesting ways and are less expensive to manufacture, they’re not as durable as wafers and they require more support than other solar panel structures.
While silicon wafers are complete, they are not yet ready to conduct energy. They need to be processed with additional dopants (namely phosphorous and boron) to make them good conductors. The wafers are heated at high temperature and placed into water. Then the top layer is exposed to phosphorous (a negative layer) and the bottom layer is exposed to boron (a positive layer). This positive-negative layer makes it function properly in the solar panels.
Image Source – Lets Go Solar
Anti-reflective coating –
Silicon naturally reflects the sunlight and hence the sunlight received may get lost without providing us with any kind of benefit. To minimize this reflection, the silicon panels are coated with anti-reflective silicon nitride. Which gives panels the blue colour we see on the solar system.
Manufacturing Process of Silicon Panels
Purifying the silicon
- The silicon dioxide is placed into an electric arc furnace. A carbon arc is used to supply oxygen. The products obtained are carbon dioxide and molten silicon. This process yields silicon with 1% impurity. To use the product in solar panels, the product must be further purified.
- The 99 % pure silicon is purified using the floating zone technique. A rod of impure silicon is passed through a heated zone several times in the same direction. At the end of the process, all the impurities get together at one end which can be chopped off, leaving us with silicon in 100% pure form.
Making single crystal silicon
- Solar cells are made from silicon crystals. The most commonly used process for creating the crystal is called the Czochralski method. In this process, a seed crystal of silicon is dipped into melted polycrystalline silicon. As the seed crystal is withdrawn and rotated, a cylindrical ingot of silicon is formed. The ingot withdrawn is unusually pure, because impurities tend to remain in the liquid.
Making silicon wafers
- Silicon wafers are sliced one at a time using a circular saw. Half of the material is lost in making a circular wafer. Next, the circular wafer is then cut into a rectangle shape since they can be fitted perfectly as solar cells, utilising all the space available in the solar panels. Next, the rough edges a
- re smoothened to give solar panels a better aesthetic look.
- The traditional way of doping is to introduce a tiny amount of boron during the Czozhralski process. The wafers are then sealed back to back and heated at a temperature of 1400 degree Celsius in the presence of phosphorous gas. With phosphorous forming a negative layer and boron forming the positive, the solar cell is now ready to conduct electrons. Since the phosphorous and boron junction needs to be uniformly distributed, the operating temperatures are carefully controlled.
Making electrical connection
- Electrical contacts connect each solar cell to another and to the receiver of produced current. The contacts must be very thin so as not to block sunlight reaching the solar cell. Metals such as silver, nickel, or copper are vacuum-evaporated through a photoresist, silkscreened, or merely deposited on the exposed portion of cells that are partially covered with wax.
- After the contacts are in place, thin strips are placed between cells. The most commonly used strips are tin-coated copper.
Applying Anti-reflective coating
- Silicon reflects 35% of the received sunlight and hence a coating must be applied to the silicon wafer. Silicon nitride is the most commercially used anti-reflective coating. The nitrogen containing gas is made to react with silicon to form silicon nitride. Another method is to allow titanium or silicon to heat until the material boils and condense to reach the silicon molecule.
Encapsulating the solar cell
- The solar panels are then sealed into a silicon rubber. The sealed rubber is then placed into an aluminum frame with a tedlar back sheet and a glass or plastic cover.
Quality Control in Solar Panels
Quality control is an important aspect of solar panel manufacturing since it affects the overall performance and efficiency of the solar power system.
The silicon obtained is tested for purity, resistivity, orientation. Solar panel manufacturers also test for the presence of oxygen and carbon dioxide since they affect their strength and resistivity.
During the solar panel manufacturing process, the temperature, pressure, oxygen level in the air, quantity and quality of dopants are closely controlled.
The solar panels are tested in both ideal conditions and the conditions which will occur in the natural environment and based on the performance the efficiencies are noted down. The panels are also tested for vibration, heat, wind and hailstorm.
The ultimate test is when solar panels start functioning in the natural environment, the data available is used to determine the difference between the ideal life expectancy and the actual life expectancy. Since solar is a high one-time investment, life expectancy plays an important role in driving customer decision.
Future of Solar Energy
Considering the present pace with which solar energy is proceeding, we can fairly conclude that solar energy is the energy of the future. With fossil fuels depleting rapidly, it is the adoption of solar energy that is going to determine the future of human society. With the government pushing solar energy and researchers inventing new technologies, we can say that the future of human society being 100% solar dependent is not far away.