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How Are Solar Panels Made? A Step by Step Process

June 23, 2020
By John Cole

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You may have wondered how solar panels are made. It’s likely more simple, and more complex, then you have imagined. In this article, we will explain the step-by-step process for the manufacturing of solar panels.

Solar panels are made from the second most abundant element in the earth’s crust, silicon. This is found across the globe in a rock known as silicon dioxide. These stones are melted, purified, melted again, and cut into thin slices called wafers. The wafers are then prepped, given an anti-reflective coating, wired, glued into a frame, and ready for use as a solar panel.

But this is just a simple explanation for a multi-step process that lasts weeks. To explain it all, it is easiest to place the individual steps into two categories: manufacturing the photovoltaic (PV) wafers and compiling the solar panels.

Category One: Manufacturing the PV Wafers

Step One: Gathering the Raw Materials

PV cells are primarily composed of the element silicon. Thankfully for the solar industry, silicon is the second most abundant element within the Earth’s crust, just behind oxygen. It is typically found in the form of silicon dioxide. Silicon dioxide, in turn, is refined from natural materials such as quartzite gravel, crushed quartz, or even natural beach sand.

Being the second most abundant element on the earth, this shiny black rock can be mined from numerous places across the globe. While it may be difficult to believe that solar panels come from nothing more than a rock on the beach, the overabundance of this material is a good sign for the solar industry. The process to refine silicon is fascinating.

Step Two: Purifying the Silicon

Next, solar manufacturers must convert silicon dioxide into silicon. As its name suggests, silicon dioxide is a material composed of one part silicon and two parts oxygen. To release the oxygen from the materials, manufacturers place the rocks into a carbon arc furnace. This type of furnace produces incredibly high temperatures that melts the silicon rock into a white hot liquid. The heat from this process causes the oxygen particles to combine with the carbon particles from the furnace. The direct result of this process is that two particles of oxygen are released from the silicon, attach to the carbon, and are released into the atmosphere as carbon dioxide.

At this point, the purifying process is still incomplete. Though the material is no longer silicon dioxide, it is not yet pure silicon either. The carbon arc furnace yields silicon with a 1% impurity, which is not efficient enough for solar technology. To remove that last 1%, the silicon is cooled slightly and then sent through a heated zone multiple times. With each pass through the zone, the impurities are dragged to one end until the silicon is deemed pure enough to meet standtards. The impure end is then removed.

Step Three:  Making Silicon Ingots

Now this is where the process truly gets crazy. The pure silicon rocks are then transferred to a quartz cylindrical furnace to make ingots. Ingots are silicon cylinders, typically 8 inches in diameter and approximately 6 feet in length. One ingot may weigh as much as 250 pounds. Once the rocks are collected, a bit of boron is added to ensure that the finished crystal will have a positive electrical orientation.

Approximately 250 pounds of silicon are placed into the furnace. The furnace then melts the material into a shimmery liquid at 2,500 degrees Fahrenheit. Once the rocks have been liquified, the quartz furnace starts to turn. A seed crystal of silicon is attached to a rotary device and lowered into the vat of liquid metal. The seed then rotates in the opposite direction as it is slowly removed from the quartz furnace. And when I say slowly, I mean this process takes approximately three and a half days.

Step Four: Making Silicon Wafers

Once the pure silicon ingots, or cylinders, are grown, the tops and tails are removed and they are trimmed to workable lengths of two feet. These round cylinders are placed on a rack sixteen at a time. Saw wire is then used to square off the edges in order to fit more PV cells into the finished product.

Once the ingots are cut into either a rectangular or hexagonal shape, they are sliced into paper thin cells called wafers. These wafers form the basis for the solar panel. Once fully prepped, they will be considered solar cells. In the meantime, they are polished to remove any potential saw marks or imperfections.

Category Two: Compiling the Solar Panels

Step One: Polarizing the Wafers

Now that we have pure silicon wafers ready to absorb the power of the sun, we need to convert that energy into electrical energy. To aid this process, the wafers are sometimes given what’s called a texture etch. This removed a tiny portion of the silicon to create an irregular pattern of pyramids on the surface of the wafer causing it to absorb even more light.

Once textured, some of the wafers are then diffused into a phosphorus gas at a very high temperature. This molecular reaction causes these wafers to have a negative electrical orientation. When paired with their positive counterparts, they create a positive-negative connection, or a P/N junction. Once this polarization is complete, electrical processes will begin similar to what you experience with a AA battery. Positive on one side, negative on the other.

Step Two: Anti-reflective Coating

The treated wafers are then moved to the coating phase. By itself, silicon will reflect approximately 35 percent of the sunlight it receives. Manufacturers coat these metal wafers with chemicals such as silicon nitride, titanium dioxide, or silicon oxide, which gives them that recognizable violet tint. This hue helps to prevent further reflection within the energy-dense blue end of the light spectrum.

Step Three: Printing

Even though the wafers are now capable of harnessing energy from the sun, they still must be prepped for the transference of that energy. A mesh of metal strips, typically made from tin-coated copper, are placed across the surface of the wafers. These strips are arranged in thin, frail fingers and cris-crossed with larger bus bars. The intention is to leave as much exposure to the sun as possible while still making electrical connections across the wafers. At this point, the silicon wafers now graduate to solar cells.

Step Four: Encapsulating the Cells

Now the cells are gathered and arranged in accordance with the desired size of the panel. Solar panels are frequently found in 48, 60, or 72 cell arrangements.The number of cells will impact the amount of energy the panel will produce. Each cell is connected to the next through metal contacts. Precision robots will solder these connections together in rows. These contacts ensure that electricity will be able to travel freely across the panel and to the output at the junction box.

The desired arrangement of the cells are placed on a polymer-based backsheet to prevent the intrusion of water, dust, or other volatile material. The cells are glued to the backsheet using EVA, or ethylene vinyl acetate. Likewise, EVA is placed on top of the cells to adhere them to the protective glass or plastic cover.

Once all of these layers are combined, the solar cells are placed within an aluminum frame and conjoined with a junction box that houses the wiring for the panel. Aluminum is a strong, lightweight metal with poor electrical conductivity making it the ideal choice for the frame. Once everything is attached, a baby solar panel is born.

Step Four: Testing the Panels

The solar panel is then sent to quality control to ensure that each cell is performing as expected. Solar manufacturers use Standard Test Conditions (STC) as a frame of reference. These STCs involve 1000W/m2 irradiance, 25deg C, and an air mass of 1.5g. These consistent criteria should produce near identical results in terms of efficiency, voltage, current, impedance, impact and temperature intolerance. Solar panels are constructed to work under severe weather conditions and must be built to withstand mother nature.

In addition to STCs, the criteria are lowered to a less-than-ideal situation to test the panel under poorer circumstances. The energy input and temperature are lowered to 800W/m2 irradiance and 20deg C. If the panels pass quality control, they are cleaned, packaged, and ready for shipment.

Variances

There are a handful of variances in the process above based on the particular manufacturer at the time. Early on in the process, boron is added to the silicon before melting it in the cylindrical furnace. This ensures that the crystal will bear a positive potential electrical orientation. Some manufacturers have learned that they can wait to produce a positive orientation by shooting phosphorus ions into a silicon ingot. The variable speed of the ions impacts the depth they reach.

Also, the processes above are for the most common type of solar panels, monocrystalline solar panels. There are two other types, however. Let’s take a moment to highlight the three main types of solar panels and note any manufacturing differences.

Monocrystalline – These panels are made from silicon wafers sliced from silicon ingots. They are labor-intensive to manufacture, but are rigid, efficient, and effective.

Polycrystalline – These are produced by melting silicon crystals together. Once melted, these crystals are then re-fused onto the panel itself, resulting in an inexpensive, but less efficient panel. Cylindrical ingots are not generated using this method.

Amorphous Silicon – These solar cells are non-crystalline and are directly adhered to glass, plastic, or metal. Usually, this substrate is flexible so that the softer solar cells can flex and bend. Imagine mounting a solar panel atop an RV so that it follows the bend of the root. That’s what amorphous panels can do. These panels are more flexible in the installation, but far less energy efficient.

Environmental Concerns

While solar energy is considered green energy, it is far from perfect. Manufacturing solar is an incredibly complicated and intensive process. We’ll break down the risks here:

1. Deep mining industries – Although silicon is an abundant mineral, it still must be mined in quarries. The amount of pollution and waste that comes from the mining industry is quite large. But as it is, there is no alternative to get the amount of silicon needed for the booming industry.

2. Energy intensive processes – Silicon is melted down to a white hot liquid at least twice. This requires an excess of 2,500deg F. This temperature is maintained for nearly 4 days in order to produce a single ingot.

3. Carbon-dioxide by product – In addition to the amount of energy needed to melt stone, carbon dioxide is generated as a natural byproduct of the chemical process. Silicon dioxide is two parts oxygen, one part silicon. The two parts oxygen leaves the silicon and attach to the carbon from the carbon arc furnace resulting in carbon dioxide being released into the atmosphere. This does not account for the carbon dioxide produced by the power plants supplying the energy needed.

4. Water usage – Solar is a water hog. The manufacturing process uses a massive amount of water for cooling, chemical processing, dust control, and cleaning. When I say a lot of water, I mean that one facility might use 1.5 billion liters of water during the construction process.

5. Toxicity – Many volatile and toxic compounds such as hydrofluoric acid are used during the manufacturing process. While it’s possible to manage the waste from the plants, we are relying on either government regulations or the goodwill of solar manufacturers to do so. But this doesn’t always happen. In 2011, for example, one Chinese company, Jinko Solar Holding Co. was found dumping hydrofluoric acid into the river, killing fish and decimating the local farmland.

For more information about solar energy and its impact on the environment, visit greenenergygeeks.com. Green Energy Geeks are a group of clean energy activists who are dedicated to making the world more sustainable through green energy.

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