Solar panel manufacturers currently use a rather complicated process that can be simplified somewhat. First, manufacturers create silicon from silicon dioxides such as Quartzite or silica sand using a purification process. The addition of boron or phosphorus (doping) creates a designation as P-type or N-type.
Thin wafers of silicon are cut from a crystalline ingot. The application of a thin layer of the doped silicon (P-type or N-type) forms the PN-junction. Metallic fingers and an anti-reflective layer are next, then flat ribbon busbars or thin wire busbars.
The manufacturing facility takes raw materials, beginning with silica sand, and finishing with a product capable of harnessing the energy of the sun. The overall quality of a solar panel depends on the quality of those base materials. The solar industry and manufacturing process often give no hint about how the raw material transforms into renewable energy.
6 Solar Panel Materials
Solar panels use only six key components in the base construction. Although there are slight differences in the construction of monocrystalline and polycrystalline solar panels, the process and components are similar. Thin-film solar panels add additional materials while not using some components, which affects how much thin-film solar panels cost.
Solar photovoltaic cells are in all solar panels made. Monocrystalline and polycrystalline solar cells use silicon. Each solar panel has a layer of tempered glass which is 3 to 3.5mm thick, except the thin-film solar panels.
Ethylene Vinyl Acetate (EVA) is a copolymer film in use as a sealing element (encapsulation) that ensures the performance and reliability of solar cells. All solar panels include a backsheet and a junction box containing diodes and components for the connection of the panel to a solar system. Solar panels, except thin-film, an aluminum frame.
Silicon Crystalline Wafers
Silicon begins in a crystalline form and is the predominant semiconducting material in use for the production of photovoltaic cells. Crystals melt and form into ingots. Manufacturers slice the ingots into silicon wafers to create solar cells. The purity of the silicon determines the efficiency of the end product. Monocrystalline solar panels use silicon that is 99 percent pure after processing.
The Photovoltaic Solar Cell
These silicon cells are paper-thin wafers cut from monocrystalline ingots. Using the Czochralski (CZ) process, manufacturers create silicon crystals. During the growth period, crystals are doped with boron. The boron-doped wafers are infused with phosphorous to form the p-n junction. Cells typically measure 10-15 cm.
The glass in use for solar panels is up to six times stronger than standard plate glass. This type of glass is also known as safety glass or toughened glass. It is created using thermal or chemical means. Because it is durable, it can withstand normal weather occurrences such as hailstorms.
While seemingly an insignificant part of a solar panel, the anodized aluminum frame plays an important role. Not only do they provide structural stability, but they offer high surface reflectivity.
The frame also provides electrical and thermal conductivity. Although frameless solar panels are available, frames remain an important part of solar panel construction.
Polymer Rear Backsheet
Another important component in a solar panel is the backsheet which is the white plastic, or polymer, on the back of a panel. The purpose of the backsheet is to provide an insulative layer and isolation of the internal circuitry.
Depending on the type of panel, the thickness of the backsheet will range from 30 to 270 microns (µm). In addition to the insulative properties, backsheets also protect against ultra-violet radiation, humidity, dryness, dust, wind, chemicals, sand, and vapor penetration.
The junction box is the output interface. It houses the wiring that connects the internal circuitry of the panel to other panels in the array in series or parallel.
The boxes are sealed against the weather to protect the diodes inside. The diodes have a very important function within the system. They prevent power from back-feeding into the panels if there is no sunshine.
How Are Solar Panels Made? The Process
Solar panel construction begins with Quartzite (quartz sandstone rock or silica sand). The Quartzite transforms to metallurgical grade silicon by combining with carbon in an arc furnace. The result of this initial process is 99 percent pure silicon. From this point, the process differs slightly depending on the type of solar panel.
Making Monocrystalline Solar Panels
To make monocrystalline wafers, doped silicon is formed into solid crystal ingots using the Czochralski process. With this process, melting occurs at a high temperature and under high pressure resulting in the slow growth of a single monocrystalline crystal.
Paper-thin slices of ingots receive an infusion of boron or phosphorous. Building on ethylene-vinyl acetate (EVA) film, silicon wafers are put in place on the EVA. This creates a layer of solar cells with busbars linking them together. A second EVA film layer completes this part. This process is encapsulated and forms the heart of the solar panel.
Monocrystalline solar cells are among the most efficient solar panels available. Their consistency in construction offers the longest lifespan.
Monocrystalline panels are easily recognizable because of their dark black color. The coloration also aids in the panel efficiency, absorbing more sunlight for conversion into electricity.
Monocrystalline panels are very space-efficient, meaning fewer panels are necessary for energy production.
The Czochralski Process
Named after Jan Czochralski, a Polish scientist, the Czochralski process was the result of an accident.
This process is now in use to accelerate the growth of silicon crystals for use in semiconductor components including computer systems, cellular phones, and photovoltaic cells.
Construction of Polycrystalline Solar Panels
Introduced in the 1980s, polycrystalline solar cells are still a popular option.
To create polycrystalline or multi-crystalline wafers, metallurgical-grade silicon undergoes conversion to polysilicon using the Siemens process (chemical purification) or other metallurgical processes.
Doping is the process of adding trace amounts of boron or phosphorous to the polysilicon to create N-type or P-type silicon. Following the initial doping process, the polysilicon is cast into rectangular blocks.
Unlike the processing for monocrystalline cells, the polysilicon is poured into a square mold from its liquid form. This creates less waste, eliminates the cutting process, and makes polycrystalline solar panels more affordable.
Affordable, but with Some Disadvantages
There are some disadvantages to polycrystalline solar panels. They are slightly less efficient, requiring more solar panels to produce the same amount of energy. These panels are also more susceptible to heat.
Polycrystalline solar panels have a bluish hue and are easily recognizable. They are an affordable option for homeowners in moderate climate regions.
The Siemens Process
The Siemens process accounts for almost 75 percent of the world’s polysilicon production. It is the method most commonly in use for polysilicon production.
The process begins with metallurgical-grade (MG) silicon ground into small particles. The particles react with hydrogen chloride (HCI), producing trichlorosilane (SiHCl3, or TCS), which is highly volatile. With a boiling point of 31.8° Centigrade (C), the TCS can undergo purification easily.
During the chemical vapor deposition (CVD) step, slim filaments of silicon undergo a heating process to 1,150 °C in a reactor where they grow into polysilicon rods. The final diameter of the rods is 15 to 20 cm.
Purity Levels Determine the Final Use
Depending on the degree of TCS distillation, silicon reaches different levels of purity. The resulting polysilicon receives a grade rating of multi-grade, mono-grade, or electronic grade.
As the process continues to improve, costs are seeing a downward trend which will lower solar panel cost in the future.
Thin Film Construction
The construction of thin-film differs from standard first-generation solar panels. The components of a thin-film solar panel system include photovoltaic material, a conductive sheet, and a protective layer. This makes thin-film panels the least expensive to produce.
The semiconducting (photovoltaic) material converts sunlight into solar energy. A conductive sheet, or layer, prevents loss of electricity and increases conductivity. The protective layer is necessary to improve durability, protect the panels from environmental concerns, and extend the lifespan.
There are currently three types of thin-film solar cells:
- Amorphous Silicon (a-Si)
- Cadmium Telluride (CdTe)
- Copper Indium Gallium Selenide (CIGS) or Gallium-free (CIS)
The manufacturing process for the three types of thin-film panels is the same.
Amorphous Silicon is non-crystalline. This makes a-Si thin films less expensive and easier to produce than both monocrystalline and polycrystalline cells. It is non-toxic, using chemical vapor deposition during the manufacturing process. The vapor deposition applies a thin layer of silicon on a plastic, glass, or metal base.
As the oldest thin-film technology, a-Si initially appeared in handheld devices.
It can absorb light in a wide range along the light spectrum. Although it performs well in low-light conditions, a-Si may also discharge rapidly.
Unfortunately, with an efficiency rating of 13.6 percent, it is the least effective of the thin-film family.
Cadmium Telluride (CdTe) is the second-most common type of solar cell technology currently available. Although Cadmium Telluride is great at capturing and converting sunlight to energy, it includes drawbacks.
Among the detractors are its rarity and toxicity. The rarity means that it is not easy for mass production to fill demands.
Because CdTe is highly toxic it requires cost-prohibitive precautions for handling and processing, driving up the end cost. Despite the near-record efficiency ratings possible with CdTe, the detractors make it a difficult sell in the world market.
Copper Indium Gallium Selenide and Copper Indium Selenide
Copper, Indium, Gallium, and Selenide (CIGS) can be layered. This creates a semiconductor that converts sunlight into energy very efficiently. A version without the Gallium (CIS) is also in use.
Using co-evaporation or co-deposition, CIS and CIGS cells blend into photovoltaic material. When the resulting material rests between a conductive layer and a transparent layer, the solar cell can begin collecting sunlight and converting it into energy.
Bi-Facial Solar Cells
Thin-film solar panels can be bifacial, which means they can process sunlight on either side of the solar panel. Backsheets in bifacial panels are clear to allow the sun to create solar energy from either side.
The attributes of thin-film solar panels can be beneficial in several applications. The idea to utilize this technology on a larger scale offers more options for home solar systems.
Recent advancements in efficiency for thin-film solar panels can increase usage tremendously.
Anti-reflective coatings (ARC) have a place of importance. Solar panels made these days include this coating as a part of the manufacturing process. Solar panels made without this coating lose efficiency as the ARC increases the amount of sunlight that the panel could absorb.
The ARC improves light transmittance, increasing the efficiency of all solar panels made.
Anti-reflective coating is an integral ingredient for any panels at installations around airports or flight paths. Solar panels made without ARC could potentially blind pilots flying overhead.
The Solar Panel Efficiency Is on the Rise
Manufacturers are improving solar panel specifications regularly by refining the processes of construction. As thin-film technology continues to improve, the industry is more than ready to face the future. Current testing models are reaching efficiency levels nearing 50 percent. Incredibly, one test has even topped out at a whopping 113 percent efficiency!
The Future Is Bright
While those advancements are not currently ready for mass production, they are on the drawing board. If you are planning on installing solar panels, you should still invest in current technology. Solar panels great candidates for recycling if you upgrade at a later time. In the meantime, you will be able to convert sunlight into electricity to produce solar power.
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