How Are Solar Panels Made? What Solar Panels Are Made of How They Are Manufactured
Solar energy’s popularity has rapidly increased in the last several years, making a significant impact on the energy market. According to the Solar Energy Industries Association, the U.S. has installed enough solar to power 13.1 million homes and total U.S. solar capacity is projected to more than double by 2024.
As solar energy use becomes more prevalent, so does information about how it’s harnessed and used. Photovoltaic, or solar, panels can often be found in both commercial and residential areas. How are these panels made, and what materials are used to manufacture them?
The table below outlines the raw materials and parts comprising a solar panel.
Silicon is the basic material for conductive electrical components. Before it can be used, it must undergo a treatment process that removes impurities and converts it to pure silicon, or polysilicon. The industry shouldn’t face material shortages any time soon; silicon is abundant, making up one-quarter of the earth’s crust by weight.
Once the silicon is rid of impurities, it is turned into ingots, which are pure silicon cylinders. The ingots are made from a crystal of silicon that is dipped into polycrystalline silicon. The impurities remain in the melted liquid, so the ingot forms as a completely pure cylinder. From there, the ingot is sliced into.5-millimeter-thick wafers, which are shaped into rectangular or hexagonal shapes so they can fit tightly together.
Boron and phosphorus are added to the wafers through a doping process. The wafers are heated in order to allow atoms from these elements, or dopants, to enter the silicon. When these elements are added to the polysilicon, the first result is an excess of electrons, which is then followed by a deficiency of them. This allows the polysilicon to act as a semiconductor.
To conduct a large amount of electricity, many cells must be connected together by electrical contacts. The group is then connected to the receiver. An anti-reflective coating is applied to the panel to prevent loss of sunlight and wasted energy. The cells are then sealed into a rubber or vinyl acetate, framed in aluminum and covered in glass or plastic.
Silicon: Raw Material in Solar Cells
Silicon is the second most common element in the earth’s crust. According to the Minerals Education Coalition, it isn’t found pure in nature; rather, it’s found combined with oxygen in rocks such as obsidian, granite, and sandstone, in a form known as silica. Silicon can be mined from quartzite, mica, and talc, but sand is its most abundant ore source. The silicon in solar panels is manufactured through a reduction process in which the silica is heated with a carbon material and the oxygen is removed, leaving behind purer, metallurgical-grade silicon.
From there, the grade must be further purified into polysilicon, the solar-grade purity of which is 99.999 percent. To yield polysilicons of different grades, several processes may be applied to the element. For electronic-grade polysilicon, which has a higher purity percentage, 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.
Ingots Wafers: The Backbone of Solar Cells
Several types of wafers are cut from the ingots: monocrystalline, polycrystalline and silicon ribbons. They differ in terms of their efficiency in conducting sunlight and the amounts of waste they produce.
Monocrystalline wafers are thinly cut from a cylindrical ingot that has a single-crystal structure, meaning that it is comprised of a pure, uniform crystal of silicon. A diamond saw is used to cut the wafers off the cylinder, resulting in a circular shape. However, since circles don’t fit tightly together, the circular wafers are further cut into rectangle or hexagonal shapes, resulting in wasted silicon from the pieces that are removed. According to GreenRhinoEnergy.com, this wasted silicon can be recycled into polysilicon and recut. Researchers are trying to find ways to create monocrystalline cells without so much cutting and waste.
Polycrystalline, sometimes called multicrystalline, ingots are made of multiple crystal structures. They may produce less waste, but they are not as efficient as monocrystalline. The ingots are cube-shaped because they are made from melted silicon poured into a shaped cast. This means the wafers can be cut directly into the desired shape, creating less waste.
Silicon ribbons are thin sheets of multicrystalline 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.
Solar Cells: Adding Dopants to Activate the Wafer
While the silicon wafers are complete at this point, they won’t conduct any energy until they go through the doping process. This process involves the ionization of the wafers and the creation of a positive-negative (p-n) junction. The wafers are heated in cylinders at a very high temperature and put into water. Then the top layer of the cylinder is exposed to phosphorus (a negative electrical orientation) while the bottom layer is exposed to boron (a positive electrical orientation). The positive-negative junction of the cell allows it to function properly in the solar panel.
After this step, only a few more things need to happen in order to create a functioning cell. Because silicon naturally reflects sunlight, there is a considerable risk of losing much of the potential energy from the sun that the cells are supposed to absorb. To minimize this reflection, manufacturers coat the cells with antireflective silicon nitride, which gives the cells the final blue color we see in installed panels.
From there, manufacturers implement a system for collecting and distributing the solar energy. This is done through a silk-screen or screen-printing process in which metals are printed on both sides of the cell. These metals make a roadmap for the energy to travel through on its way to the receiver.
Solar Panels: Assembling Cells Into Useful Devices
Solar panel manufacturers employ different proprietary processes to produce their final solar panel products. But, in general, this is an automated process in which robots do the work. First, the cells must be put together to form a big sheet. According to Solar World, a leading manufacturer of solar panels, its process involves soldering six strings of ten cells each, making a rectangle of 60 cells. Each rectangular matrix is laminated onto glass and quickly becomes a larger panel. From there, the panel needs to be framed so that it is sturdy and protected from any weather it will endure.
In addition, the framing must house the electrical equipment that links the panels together and receives the energy.
Where Does Polysilicon Come From?
Polysilicon has one origin: silica. Silica is mined from the earth and is found in sand, rock, and quartz. Because silica has a dioxide component, it must be taken to a plant, where it is converted to silicon through a heating process. According to the United States Geological Society, there are six domestic companies that produce silicon materials at eight plants. These are all located east of the Mississippi River. Imported silicon comes from all around the world, including China, Russia, Japan, Brazil, South Africa, Canada, Australia, and others.
Types of solar panels: which one is the best choice?
The three most common types of solar panels on the market are monocrystalline, polycrystalline, and thin film solar panels. Which is the best for your specific needs?
Most of the solar panels on the market today for residential solar energy systems can fit into three categories: monocrystalline solar panels, polycrystalline solar panels, and thin film solar panels.
The solar cells that make up the panel determine which type it is. Each type of solar cell has different characteristics, thus making certain panels better suited for different situations.
We’ve created a complete guide to monocrystalline, polycrystalline, and thin film solar panels to help you decide which type is right for your home.
- There are three different types of solar panels: monocrystalline, polycrystalline, and thin film.
- Monocrystalline solar panels are highly efficient and have a sleek design, but come at a higher price point than other solar panels.
- Polycrystalline solar panels are cheaper than monocrystalline panels, however, they are less efficient and aren’t as aesthetically pleasing.
- Thin film solar panels are the cheapest, but have the lowest efficiency rating and require a lot of space to meet your energy needs.
- The brand of solar panels and the solar installer you choose is far more important than which type of solar panel you install.
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Find out how much you can save monthly by installing rooftop solar panels
Three types of solar panels
Monocrystalline solar panels are the most popular solar panels used in rooftop solar panel installations today.
Monocrystalline silicon solar cells are manufactured using something called the Czochralski method, in which a ‘seed’ crystal of silicon is placed into a molten vat of pure silicon at a high temperature.
This process forms a single silicon crystal, called an ingot, that is sliced into thin silicon wafers which are then used in the solar modules.
Fun fact! There is more than one type of monocrystalline solar panel
Nowadays, there are several varieties of monocrystalline solar panels on the market to choose from. Passivated Emitter and Rear Contact cells, more commonly referred to as PERC cells, are becoming an increasingly popular monocrystalline option. PERC cells go through a different manufacturing and assembly process that increases the amount of electricity the cells can produce.
Bifacial solar panels, another monocrystalline technology, can generate electricity on both the front and back side of a module, and are gaining traction in commercial ground-mounted applications.
Polycrystalline panels, sometimes referred to as ‘multicrystalline panels’, are popular among homeowners looking to install solar panels on a budget.
Similar to monocrystalline panels, polycrystalline panels are made of silicon solar cells. However, the cooling process is different, which causes multiple crystals to form, as opposed to one.
Polycrystalline panels used on residential homes usually contain 60 solar cells.
Thin film solar cells are mostly used in large-scale utility and industrial solar installations because of their lower efficiency ratings.
Thin film solar panels are made by depositing a thin layer of a photovoltaic substance onto a solid surface, like glass. Some of these photovoltaic substances include Amorphous silicon (a-Si), copper indium gallium selenide (CIGS), and cadmium telluride (CdTe). Each of these materials creates a different ‘type’ of solar panel, however, they all fall under the thin film solar cell umbrella.
During the manufacturing process, the photovoltaic substance forms a thin lightweight sheet that is, in some cases, flexible.
Solar panel type by performance
Highest performance: Monocrystalline
Efficiency ratings of monocrystalline solar panels range from 17% to 22%, earning them the title of the most efficient solar panel type. The higher efficiency rating of monocrystalline panels makes them ideal for homes with limited roof space, as you’ll need fewer panels to generate the electricity you need.
Monocrystalline solar panels have their manufacturing process to thank for being so efficient. Because monocrystalline solar cells are made of a single crystal of silicon, electrons are able to easily flow throughout the cell, increasing overall efficiency.
Not only do monocrystalline panels have the highest efficiency ratings, they typically also have the highest power capacity ratings, as well. Most monocrystalline panels on the market today will have a power output rating of at least 320 watts, but can go up to around 375 watts or higher!
Mid-tier performance: Polycrystalline
Polycrystalline panel efficiency ratings will typically range from 15% to 17%. The lower efficiency ratings are due to how electrons move through the solar cell. Because polycrystalline cells contain multiple silicon cells, the electrons cannot move as easily and as a result, decrease the efficiency of the panel.
The lower efficiency of polycrystalline panels also means they tend to have a lower power output than monocrystalline panels, usually ranging between 240 watts and 300 watts. Some polycrystalline panels have power ratings above 300 watts.
However, new technologies and manufacturing processes have given the efficiency and power ratings of polycrystalline panels a slight boost over the years, slowly closing the performance gap between mono and polycrystalline panels.
Lowest performance: Thin film
Thin film solar panels have incredibly low efficiency ratings. As recently as a few years ago, thin film efficiencies were in the single digits. Researchers have recently achieved 23.4% efficiency with thin film cell prototypes but thin film panels that are commercially available generally have efficiency in the 10–13% range.
In order to meet your energy needs, you would need to install more thin film panels over a large area to produce the same amount of electricity as crystalline silicon solar panels. This is why thin film solar panels don’t really make sense for residential installations where space is limited.
Fun fact! Thin film panels have the best temperature coefficient
Despite having lower performance specs in most other categories, thin film panels tend to have the best temperature coefficient, which means as the temperature of a solar panel increases, the panel produces less electricity. The temperature coefficient tells you how much the power output will decrease by for every 1C over 25C the panel gets.
The standard temperature coefficient for mono and polycrystalline panels typically falls somewhere between.0.3% and.0.5% per C. Thin film panels on the other hand, are around.0.2% per C. meaning thin film panels are much better at handling the heat than other panel types.
Calculate your solar panel payback period
Solar panel type by cost
Highest cost: Monocrystalline panels
Monocrystalline panels are the most expensive of the three types of solar panels because of their manufacturing process and higher performance abilities.
However, as manufacturing processes and solar panel technology in general has improved, the price difference between monocrystalline and polycrystalline panels has shrunk considerably. According to the Lawrence Berkeley National Laboratory, monocrystalline solar panels now sell for just about 0.05 per watt higher than polycrystalline modules.
Mid-cost: Polycrystalline panels
Historically, polycrystalline panels have been the cheapest option for homeowners going solar, without majorly sacrificing panel performance. Low allowed polycrystalline panels to make up a significant market share in residential solar installations between 2012 and 2016.
But as we said earlier, the price gap between monocrystalline and polycrystalline panels is narrowing. Now, more homeowners are willing to pay a slightly higher price to get significantly better efficiency and power ratings from monocrystalline panels.
Lowest cost: Thin film panels
Thin film solar panels have the lowest cost of the solar panel types, largely because they are easier to install and require less equipment. However, they also have much lower performance abilities and require a substantial amount of space to generate enough electricity to power a home.
Plus, thin film panels degrade much faster than other panel types, meaning they need to be replaced more often, which leads to more long-term recurring costs.
Solar panel type by appearance
Most attractive: Thin film panels
Thin film panels have a clean, all-black look. Their thin design allows them to lie flat against roofs, so they are able to blend in more seamlessly. In fact, with some thin film panels, it’s hard to even see the individual cells within the panel. They also tend to have less wiring and busbars, meaning there’s less white space.
However, because they are so inefficient, you would need to cover your entire roof in thin film panels. which may or may not be your style.
Mid-tier appearance: Monocrystalline panels
Monocrystalline panels have a solid black appearance, making them pretty subtle on your roof. But, the way monocrystalline solar cells are shaped causes there to be quite a bit of white space on the panel. Some manufacturers have worked around this with black packing or shaping the cells differently, but these aesthetic changes can impact both the price and performance of the panels.
Overall, monocrystalline panels still look sleek, but they’re a bit more pronounced than thin film panels.
Worst appearance: Polycrystalline panels
Polycrystalline panels tend to stick out like a sore thumb. The process in which polycrystalline solar cells are manufactured causes the cells to have a blue, marbled look. This means each individual polycrystalline panel looks substantially different from the one next to it. Most homeowners aren’t too keen on the aesthetics of polycrystalline panels.
Fun fact! Crystalline panels are more durable than thin film
Thin film panels tend to have lower wind and hail ratings than mono and polycrystalline panels. So, while thin film panels might look nice at first, one bad storm could cause significant damage.
What is the best type of solar panel for your home?
Monocrystalline solar panels are the best solar panel type for residential solar installations.
Although you will be paying a slightly higher price, you’ll get a system with a subtle appearance without having to sacrifice performance or durability. Plus, the high efficiency and power output ratings you get with monocrystalline panels can provide you with better savings over the lifetime of your system.
If you’re on a tight budget, polycrystalline panels might make more sense for you. We do not recommend thin film solar panels for residential installations. their performance and durability don’t make the low cost worth it, and it’s unlikely you’ll have nearly enough space to install the number of thin film panels you would need to cover your household electricity usage.
Factors to consider besides solar panel type
There are two things we here at SolarReviews think are more important than solar PV cell type when choosing panels for your home: the brand of solar panels and finding the right solar installer.
Going with a high-quality solar panel manufacturer ensures that you’re installing a great product on your roof, regardless of the type of panel it is. Our official ranking of the best home solar panel brands of 2023 can help you find what solar panels will work best on your roof, without sacrificing quality.
Perhaps the most important thing to consider when going solar is the installer. A solar panel system will be on your roof for at least 25 years, so you need an installer you can trust for two-plus decades! We recommend local, reputable solar installers with high customer review scores as they give the most personalized customer service on solar projects.
Comprehensive Guide to Solar Panel Types
The push for renewable energy sources has led to a surge in solar energy use. In the past decade alone, the solar industry grew by almost 50%, buoyed by federal support such as the Solar Investment Tax Credit and strong commercial and industrial demand for clean energy.
As the solar sector continues to rise, it’s worth studying the backbone of the solar industry: solar panels.
This guide will illustrate the different types of solar panels available on the market today, their strengths and weaknesses, and which is best suited for specific use cases.
What is a Solar Panel?
Solar panels are used to collect solar energy from the sun and convert it into electricity.
The typical solar panel is composed of individual solar cells, each of which is made from layers of silicon, boron and phosphorus. The boron layer provides the positive charge, the phosphorus layer provides the negative charge, and the silicon wafer acts as the semiconductor.
When the sun’s photons strike the surface of the panel, it knocks out electrons from the silicon “sandwich” and into the electric field generated by the solar cells. This results in a directional current, which is then harnessed into usable power.
The entire process is called the photovoltaic effect, which is why solar panels are also known as photovoltaic panels or PV panels. A typical solar panel contains 60, 72 or 90 individual solar cells.
The 4 Main Types of Solar Panels
There are 4 major types of solar panels available on the market today: monocrystalline, polycrystalline, PERC, and thin-film panels.
Monocrystalline solar panels
Also known as single-crystal panels, these are made from a single pure silicon crystal that is cut into several wafers. Since they are made from pure silicon, they can be readily identified by their dark black color. The use of pure silicon also makes monocrystalline panels the most space-efficient and longest-lasting among all three solar panel types.
However, this comes at a cost — a lot of silicon is wasted to produce one monocrystalline cell, sometimes reaching over 50%. This results in a hefty price tag.
Polycrystalline solar panels
As the name implies, these come from different silicon crystals instead of one. The silicon fragments are melted and poured into a square mold. This makes polycrystalline cells much more affordable since there is hardly any wastage, and gives them that characteristic square shape.
However, this also makes them less efficient in terms of energy conversion and space, since their silicon purity and construction are lower than monocrystalline panels. They also have lower heat tolerance, which means they are less efficient in high-temperature environments.
Passivated Emitter and Rear Cell (PERC) panels
PERC solar panels are an improvement of the traditional monocrystalline cell. This relatively new technology adds a passivation layer in the rear surface of the cell that enhances efficiency in several ways:
- It reflects light back into the cell, increasing the amount of solar radiation that gets absorbed.
- It reduces the natural tendency of electrons to recombine and inhibit the flow of electrons in the system.
- It allows greater wavelengths of light to be reflected. Light waves over 1,180nm can’t be absorbed by silicon wafers and simply pass through, so they end up heating the cell’s metal back sheet and reduce its efficiency. The passivation layer reflects these higher wavelengths and stops them from heating up the back sheet.
PERC panels allow greater solar energy collection in a smaller physical footprint, which makes them ideal for limited spaces. They are only slightly more expensive to produce than traditional panels, due to the added materials needed, but they can be manufactured on the same equipment, and can end up having a lower average cost per watt due to their efficiency.
To get a better feel for the benefits of PERC panels, check out our blog 5 Important Benefits of PERC Solar Panels You Need to Know.
Thin-film solar panels
Thin-film panels are characterized by very fine layers that are thin enough to be flexible. Each panel does not require a frame backing, making them lighter and easier to install. Unlike crystalline silicon panels that come in standardized sizes of 60, 72, and 96-cell counts, thin-film panels can come in different sizes to suit specific needs. However, they are less efficient than typical silicon solar panels.
Thin-Film Solar Panel Variations
Unlike crystalline panels that use silicon, thin-film solar panels are made from different materials. These are:
- Cadmium telluride (CdTe)
- Amorphous silicon (a-Si)
- Copper indium gallium selenide (CIGS)
Cadmium telluride (CdTe)
CdTe has the same low-cost advantage as polycrystalline cells while possessing the lowest carbon footprint, water requirement, and energy payback time of all solar panels types. However, the toxic nature of cadmium makes recycling more expensive than other materials.
Amorphous silicon (a-Si)
Amorphous silicon panels (A-Si) derive their name from their shapeless nature. Unlike mono-and polycrystalline solar cells, the silicon is not structured on the molecular level.
On average, an a-Si cell requires only a fraction of the silicon needed to produce typical silicon cells. This allows them to have the lowest production cost, at the expense of efficiency. This is why a-Si panels are suited for applications that require very little power, such as calculators.
Copper indium gallium selenide (CIGS)
CIGS panels use a thin layer of copper, indium, gallium, and selenium deposited on a glass or plastic backing. The combination of these elements results in the highest efficiency among thin-panel types, though still not as efficient as crystalline silicon panels.
Solar Panel Types by Efficiency
Among all panel types, crystalline solar panels have the highest efficiency.
- Monocrystalline panels have an efficiency rating over 20%.
- PERC panels add an extra 5% efficiency thanks to their passivation layer.
- Polycrystalline panels hover somewhere between 15-17%.
In contrast, thin-film panels are usually 2-3% less efficient than crystalline silicon. On average:
- CIGS panels have an efficiency range of 13-15%.
- CdTe ranges between 9-11%.
- a-Si have the lowest efficiency at 6-8%.
Solar Panel Types by Power Capacity
Monocrystalline cells have the highest power capacity, thanks to their single-crystal construction that allows a higher output rating in a smaller package. Most monocrystalline panels can generate up to 300w of power capacity.
Recent advances in solar technology have allowed polycrystalline panels to bridge the gap. A standard 60-cell polycrystalline panel is now capable of producing between 240-300w. However, monocrystalline panels still beat polycrystalline in terms of power capacity per cell.
Because thin-film panels don’t come in uniform sizes, there is no standard measure of power capacity, and the capacity of one thin-film panel will differ from another based on its physical size. In general, given the same physical footprint, conventional crystalline panels output more power than a thin-film panel of the same size.
Solar Panel Types by Cost
Monocrystalline panels (or modules as they are technically known) carry a hefty price tag, due to its energy-intensive and inefficient manufacturing process with only a 50% yield for every silicon crystal.
Polycrystalline modules are cheaper because they make use of the crystal fragments leftover from monocrystalline production, which results in a simpler manufacturing process and lower production costs.
Among thin-film solar panels, CIGS is the most expensive, followed by CdTe and amorphous silicon. Apart from the lower acquisition cost, thin-film modules can be easier to install thanks to their lighter weight and flexibility, which lowers the cost of labor.
While the total cost of residential systems has declined by more than 65% over the last decade, the soft cost of a system has actually risen from 58% of total system cost in 2014 to 65% in 2020.
For more information about soft costs, check out our article on the soft costs in the solar industry. and what’s being done to reduce them.
|Panel (Module) type||Average Cost per Watt|
|Monocrystalline||1 – 1.50|
|Polycrystalline||0.70 – 1|
|Copper indium gallium selenide (CIGS)||0.60 – 0.70|
|Cadmium telluride (CdTe)||0.50 – 0.60|
|Amorphous silicon (a-Si)||0.43 – 0.50|
Note that these figures don’t include the cost of installation and labor. With labor and other overhead factors, the total can rise to 2.50 to 3.50 per watt.
Other Factors to Consider
The temperature of a solar panel can affect its ability to generate energy. This loss of output is reflected through the temperature coefficient, which is a measure of the panel’s decrease in power output for every 1°C rise over 25°C (77°F).
Monocrystalline and polycrystalline panels have a temperature coefficient between.0.3% / °C to.0.5% / °C, while thin-film panels are closer to.0.2% / °C. This means that thin-film panels can be a good option for hotter environments or places that experience more sunlight throughout the year.
The updated International Building Code of 2012 requires solar panels to match the fire rating of the roof where they are installed. This is to ensure that the modules do not accelerate the spread of flames in the event of a fire. (California goes one step further by requiring the whole PV system, which includes the racking system, to have the same fire rating).
As such, solar panels now carry the same classification rating as roofs:
- effective against severe fire test exposure
- flame spread should not exceed 6 feet
- required for wildland-urban interface areas, or areas with high fire severity and wildfire risk
UL 1703 and UL 61703 standards address hail storms, by dropping 2-inch solid steel spheres on solar panels from a height of 51 inches, and by firing 1-inch ice balls on PV panels with a pneumatic cannon to simulate hail impacts.
Because of their thicker construction, crystalline panels can withstand hail hitting at speeds of up to 50mph, while thin-film solar panels carry a lower rating due to their thin and flexible nature.
While there is no formal solar classification rating for hurricanes, the Department of Energy recently expanded its recommended design specifications for solar panels to safeguard against severe weather.
The new recommendations include:
- Modules with the highest ASTM E1830-15 rating for snow and wind loading in both the front and back.
- Fasteners with true locking capability based on DIN 65151 standard
- The use of through-bolting modules with locking fasteners instead of clamping fasteners
- The use of 3-frame rail systems for improved rigidity and support against twisting
- Tubular frames over open-shaped C channels
- Perimeter fencing around PV systems to slow down wind forces
Light-Induced Degradation (LID)
LID is a performance loss commonly seen in crystalline panels during the first few hours of sun exposure. This happens when sunlight reacts with oxygen traces left over from the manufacturing process, which affects the silicon lattice structure.
The LID loss is directly tied to the manufacturing quality and can range from 1-3%.
Summary: Solar Panel Types Compared
|Initial Cost||Highest||High||Middle||Highest to lowest:|
So, Which Solar Panel Type Should You Use?
As crystalline and thin-film panels have their own pros and cons, the choice of solar panel ultimately comes down to your specific property and condition settings.
Those living in a dense area with limited space should opt for highly efficient monocrystalline modules to make the most of the physical space and maximize utility savings. If budget permits, going for PERC panels can lower energy generation costs even more in the long run.
Those with a sufficiently larger property can save on upfront costs by using polycrystalline solar panels, where a bigger panel footprint can offset the lower panel efficiency. However, a larger footprint could also mean added labor costs, so it’s not necessarily cheaper to get a higher quantity of less expensive panels. While the initial cost may be low, it may eventually be offset by reduced efficiency and higher operating expenses in the long term.
As for thin-film solar panels, these are best suited for locations where the heavy and labor-intensive installation of crystalline silicon is not feasible. Such locations can include commercial buildings with tight spaces or thin roofs; compact spaces such as recreational vehicles and watercraft; and areas that require flexible installation instead of rigid paneling.
Keep in mind that solar panels are designed for long-term installation, which can be as long as 25 years. So whatever type you choose to go with, make sure to do your homework to ensure that it’s the best option for your needs.
Silicon cost per watt down 96% over last two decades
Since 2004, the volume of polysilicon per watt is down by 87%, and the inflation adjusted price for polysilicon is also down by 76%.
Silicon is the semiconductor material at the heart of most solar cells. Thanks to advancements in technology, solar is now powering the world with a lot less silicon.
Research by Fraunhofer ISE shows that since 2004, the material usage of polysilicon per watt of solar cell has dropped by approximately 87%. The data suggests that in 2004, 16 grams of silicon were needed to produce a single watt of solar cell. By 2021, that number had shrunk to just over 2 grams.
For example, when the world’s largest solar farm – at just over 5 MW – turned on in Germany in 2004, it was using 150 watt solar panels. At the time, constructing one of these modules would have consumed 2,400 grams of the processed material.
In 2021, Maxeon signed a deal that 1.8 million of its Performance 5 UPP solar modules would be the powerhouse of the world’s 8th largest solar facility – the Primergy Solar farm in Nevada. If we assume that this 545 watt panel uses 2.2 grams of silicon per watt, we get 1,199 grams per module.
That’s approximately 360% higher output per solar panel — using only half of the silicon!
Of course, we’re going to use massively more silicon in 2023 than we did in 2004. In 2004, we deployed 1,044 MW of solar power, using just over 16,000 t of silicon globally. According to Bloomberg. 268 GW of solar was deployed in 2022, which is over 250 times more capacity than what was deployed in 2004. At 2.2 grams per watt, the 268 GW used approximately 590,000 ktg of silicon, or 35 times more silicon than was used in 2004.
The volume of silicon used is only half the story.
During the 2004 to 2022 window, the price of polysilicon actually did not stray too far from its original price, if we ignore inflation, and a few “bumps” along the way.
Bernreuter Research’s excellent history on those bumps in polysilicon pricing shows that in 2004, the price of the material was roughly 45 per kilogram. Between the end of 2003 and the end of 2004, the price of silicon nearly doubled, due to an expansion of German solar programs. But the price movement didn’t stop there. As the world’s installed solar capacity grew over 600% between 2004 and 2008, the price of polysilicon grew by about 1000%.
The price increases led to bankruptcies and lawsuits.
What followed was another dramatic price movement, as the manufacturing might of the Chinese government took the industry by storm. The growing nation determined that solar energy would be a national security consideration, and as a result, polysilicon plunged. Over the next two decades, we saw the price below 10/kg – with spot market moments in the 6/kg range. 6/kg is only 1.3% of polysilicon’s 2008 peak price of 460/kg.
In the past two years, we’ve seen the price of polysilicon increase to nearly 45/kg on heavy demand. And in the last month or two, we have seen pricing falling 54%, to 17. as a potential 536 GW of manufacturing capacity comes online.
The last variable to complete our analysis is inflation.
When accounting for inflation of the U.S. dollar. the 45/kg cost in 2004 is equal to about 71/kg in 2022. If we consider that it took 16 grams to make a single watt in 2004, then the inflation-adjusted cost per watt of polysilicon in 2004 was approximately 1.14/watt. In 2022, at 2.2 grams per watt at 17/kg – the price is 0.04/watt.
So, the real cost per watt of silicon has come down by 96.7%.
This article was ameded tno change the unit from kg to t in the following: In 2004, we deployed 1,044 MW of solar power, using just over 16,000 t of silicon globally. At 2.2 grams per watt, the 268 GW used approximately 590,000 t of silicon, or 35 times more silicon than was used in 2004.
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John Fitzgerald Weaver
Commercial Solar Guy is a commercial utility solar developer, general contractor for commercial and residential solar, as well a consultant. We construct projects in MA, RI, NY, and soon PA.
Solar Cell Production: from silicon wafer to cell
In our earlier article about the production cycle of solar panels we provided a general outline of the standard procedure for making solar PV modules from the second most abundant mineral on earth – quartz.
In chemical terms, quartz consists of combined silicon-oxygen tetrahedra crystal structures of silicon dioxide (SiO2), the very raw material needed for making solar cells.
The production process from raw quartz to solar cells involves a range of steps, starting with the recovery and purification of silicon, followed by its slicing into utilizable disks – the silicon wafers – that are further processed into ready-to-assemble solar cells.
Only a few manufacturers control the whole value chain from quartz to solar cells. While most solar PV module companies are nothing more than assemblers of ready solar cells bought from various suppliers, some factories have at least however their own solar cell production line in which the raw material in form of silicon wafers is further processed and refined.
In this article, we will explain the detailed process of making a solar cell from a silicon wafer.
Solar Cell production industry structure
In the PV industry, the production chain from quartz to solar cells usually involves 3 major types of companies focusing on all or only parts of the value chain:
1.) Producers of solar cells from quartz, which are companies that basically control the whole value chain.
2.) Producers of silicon wafers from quartz – companies that master the production chain up to the slicing of silicon wafers and then sell these wafers to factories with their own solar cell production equipment.
3.) Producers of solar cells from silicon wafers, which basically refers to the limited quantity of solar PV module manufacturers with their own wafer-to-cell production equipment to control the quality and price of the solar cells.
For the purpose of this article, we will look at 3.) which is the production of quality solar cells from silicon wafers.
How are silicon wafers made?
Before even making a silicon wafer, pure silicon is needed which needs to be recovered by reduction and purification of the impure silicon dioxide in quartz.
In this first step, crushed quartz is put in a special furnace, and then a carbon electrode is applied to generate a high-temperature electric arc between the electrode and the silicon dioxide.
That process, called carbon arc welding (CAW), reduces the oxygen from the silicon dioxide and produces carbon dioxide at the electrode and molten silicon.
This molten silicon is 99% pure which is still insufficient to be used for processing into a solar cell, so further purification is undertaken by applying the floating zone technique (FTZ).
During the FTZ, the 99% pure silicon is repeatedly passed in the same direction through a heated tube. This process pushes the 1% impure parts to one end, with the remaining 100% pure parts remaining on the other side. The impure part can then be easily cut off.
Crystal seeds of silicon are in the so-called Czochralski (CZ) process put into polycrystalline silicon melt of the Czochralski growth apparatus. By extracting the seeds from the melt with the puller, they rotate and form a pure cylindrical silicon ingot cast out from the melt and which is used to make mono-crystalline silicon cells.
In order to make multi-crystalline silicon cells, various methods exist:
1.) heat exchange method (HEM)2.) electro-magneto casting (EMC)3.) directional solidification system (DSS)
DSS is the most common method, spearheaded by machinery from renowned equipment manufacturer GT Advanced. By this method, the silicon is passed through the DSS ingot growth furnace and processed into pure quadratic silicon blocks.
During the casting of the ingots, the silicon is often already pre-doped before slicing and selling the wafer disks to the manufacturers. Doping is basically the process of adding impurities into the crystalline silicon wafer to make it electrically conductive.
These positive (p-type) and negative (n-type) doping materials are mostly boron, which has 3 electrons (3-valent) and is used for p-type doping, and phosphorous, which has 5 electrons (5-valent) and is used for n-type doping. Silicon wafers are often pre-doped with boron.
Once we have our ingots ready, they can then – depending on the geometrical shape requirements, for solar cells usually space-saving hexagonal or rectangular shapes- be sliced into usually 125mm or 156mm silicon wafers by using a multiwire saw.
Processing of silicon wafers into solar cells
The standard process flow of producing solar cells from silicon wafers comprises 9 steps from a first quality check of the silicon wafers to the final testing of the ready solar cell.
Step 1: Pre-check and Pretreatment
The raw silicon wafer disks first undergo a pre-check during which they are inspected on their geometric shape and thickness conformity and on damages such as cracks, breakages, scratches, or other anomalities.
Following this pre-check, the wafers are split and cleaned with industrial soaps to remove any metal residues, liquids or other production remains from the surface that would otherwise impact the efficiency of that wafer.
Light reflection difference between a non-textured flat silicon wafer surface and a silicon wafer surface with a random pyramid texture
Step 2: Texturing
Following the initial pre-check, the front surface of the silicon wafers is textured to reduce reflection losses of the incident light.
For monocrystalline silicon wafers, the most common technique is random pyramid texturing which involves the coverage of the surface with aligned upward-pointing pyramid structures.
This is achieved by etching and pointing upwards from the front surface. The proper alignment of the pyramids etched out is a result of the regular, neat atomic structure of monocrystalline silicon.
The regular, neat atomic structure of monocrystalline silicon also benefits the flow of electrons through the cell as with fewer boundaries electrons flow much better. Therefore, monocrystalline silicon has an electrochemical structural advantage offering more efficiency over the grainy atomic structures of multi-crystalline silicon.
Now, with such a pyramid structure in place, the incident light does not reflect back and gets lost in the surrounding air but bounces back onto the surface.
Another, less common texturing technique is the inverted pyramid texturing. Instead of pointing upwards from the front surface, the pyramids are etched into the wafer’s surface, similarly achieving reflection losses of incident light trapped in the inverted pyramid holes.
The texturing of multi-crystallin silicon wafers requires photolithography – a technique involving the engraving of a geometric shape on a substrate by using light – or mechanical cutting of the surface by laser or special saws.
Step 3: Acid Cleaning
After texturing, the wafers undergo acidic rinsing (or: acid cleaning). In this step, any post-texturing particle remains are removed from the surface.
Using hydrogen fluoride (HF) vapor, oxidized silicon layers on the substrate can be etched away from the wafer surface. The result is a wet surface that can be easily dried.
By using hydrogen chloride (HCl), metallic residues on the surface can be absorbed by the chloride and thus removed from the wafer.
Step 4: Diffusion
Diffusion is basically the process of adding a dopant to the silicon wafer to make it more electrically conductive. There are basically 2 methods of diffusion: solid-state diffusion and emitter diffusion.
While the former method basically involves the already mentioned uniform doping of the wafers with the p-type and n-type materials, the emitter diffusion refers to the placing of a thin dopant material-containing coating on the wafer bypassing the wafers through a diffusion coating furnace.
Wafers that have already been pre-doped with p-type boron during the casting process are during the diffusion process given a negative (n-type) surface by diffusing them with a phosphorous source at a high temperature, creating the positive-negative (p-n) junction.
Why diffuse the wafers though? This junction of electron deficiency in the p-type and high electron concentration in the n-type allows for excess electrons from the n-type to pass to the p-type, a flow creating an electron field at the junction.
Step 5: Etching Edge Isolation
During diffusion, the n-type phosphorous diffuses not only into the desired wafer surface but also around the edges of the wafer as well as on the backside, creating an electrical path between the front and backside and in this way also preventing electrical isolation between the two sides.
The objective of the etching and edge isolation process is to remove this electrical path around the wafer edge by disk stacking the cells on top of each other and then exposing them to a plasma etching chamber using tetrafluoromethane (CF4) to etch exposed edges.
Step 6: Post-Etching Washing
After the etching, particle residues’ potential remains on the wafer and the wafer edges. Therefore the wafers need to undergo a second washing to remove the remains of the previous etching process.
After this second washing, the wafers can further be processed for the deposition of anti-reflective (AR) coating.
Niclas checking cell production at a PEVCD machine
Step 7: Anti-Reflective Coating Deposition
In addition to surface texturing, AR coating is often applied on the surface to further reduce reflection and increase the amount of light absorbed into the cell.
This anti-reflective coating is very much needed as the reflection of bare silicon solar cells is over 30%. For the thin AR Coating, silicon nitride (Si3N4) or titanium oxide (TiO2) is used. The color of the solar cell can be changed by varying the thickness of the anti-reflection coating.
In the semiconductor industry, there are basically three methods to depose layers on wafers, which are:
1.) Atmospheric Pressure Chemical Vapor Deposition (APCVD), which is used only for a few applications and requires high temperatures.
2.) Low-Pressure Chemical Vapor Deposition (LPCVD), which involves the deposition process to be performed in tube furnaces and like the APCVD method requires high temperatures.
3.) Plasma Enhanced Chemical Vapor Deposition (PECVD), which is the most common method for the deposition of AR coating on the wafer.
In the PECVD process, the thin coating exists in a gaseous state and is through a chemical reaction process solidified onto the wafer.
Step 8: Contact Printing and Drying
As the next step, metal inlines are printed on the wafer with the objective to create ohmic contacts. These metal inlines are printed on the rear side of the wafer, which is called backside printing.
Contact Printing and Drying Machinery
This is achieved by printing the metal pastes with special screen printing devices that place these metal inlines onto the backside. After printing, the wafer undergoes a drying process.
Once dry, this process is followed by the printing of the front side contacts, then the wafer is another time dried.
After all, contacts have been printed on the rear and front sides, the screen-printed wafers are passed through a sintering furnace to solidify the dry metal pastes onto the wafers. Then, the wafers are cooled and can already be called solar cells.
Step 9: Testing and Cell Sorting
In this final process, the now ready-to-assemble solar cells are tested under simulated sunlight conditions and then classified and sorted according to their efficiencies.
This is handled by a solar cell testing device that automatically tests and sorts the cells. The factory workers then only need to withdraw the cells from the respective efficiency repository to which the machine assorted the cells.
TO OUR READERS:
In this article we went through the standard production process from silicon wafer to solar cells. However, there are many quality problems that can potentially be created early on in this process. Which potential quality risks are you aware of when processing silicon wafers into solar cells? If you are aware of potential quality problems or have experience in solar cell production, we kindly invite you to share more insights with the Sinovoltaics Community!