In the never-ending quest of the solar industry to improve photovoltaic (PV) technology and achieve the highest possible efficiency, researchers have tested many technologies, materials, and combinations. One option that outstands from the rest is the Passivated Emitter and Rear Contact (PERC) solar technology which allows for the creation of PERC solar panels.
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The PERC solar panel is a highly efficient and improved type of PV technology that uses Crystalline Silicon (c-Si) and fixes some inconveniences of this traditional technology. In this article, we will do a deep and detailed analysis of what is a PERC solar panel, how it compares to older and other advanced technologies, as well as the different applications for PERC solar panels.
WhistlingBird, Silicon solar cell (PERC) front and back, Redesign, CC BY-SA 4.0Recapping the structure and workings of traditional solar panelsBefore diving into PERC solar panel technology and its benefits, it is important to have a proper understanding of traditional solar panels and how they work. Traditional solar panels are called monocrystalline and polycrystalline silicon solar panels, depending on their manufacturing materials. The basic structure of c-Si solar cells is comprised of the following layers:
The c-Si solar panels generate power by harvesting solar energy under the photovoltaic effect. The most important component to generate solar power is the doped semiconductor or P-N junction manufactured with an N-doped layer which is negatively charged with extra electrons, and a P-doped layer which is positively charged and therefore it has holes (missing electrons). The P-N junction works as the main structure generating solar energy in the cell.
On a simple basis, the load is connected to the solar cell and it is energized by the power generated from the cell, but it is important to understand the inner functioning of the solar cell. This will also help us understand more about PERC solar panels in the following sections.
When the P-N junction or photovoltaic material is hit with a photon, the electron within the semiconductor is excited. The electron is then moved to the conduction band, creating an electron-hole (e-h) pair.
Flow from the electron through the load - Source: The Physics of Solar Power from Colorado CollegeAfter the e-h pair is created, the electron usually goes to the front contact and the hole to the P-doped layer. During this process, the electron flows through the load, which creates the flow of electric current.
After the electron goes back to the solar cell through the rear contact, it recombines with a hole, ending the electrical current flow for that particular pair. This process is constantly ongoing whenever photons hit the surface of solar cells.
What are PERC solar panels?While the recombination of the e-h pair under the aforementioned circumstances is the regular process generating an electric current for traditional solar cells, there is also another type of recombination called surface recombination, which produces losses for traditional crystalline silicon technology.
The surface recombination process occurs when a hole combines with an excited electron that did not go through the contact. This recombination process translates as a reduced solar cell efficiency since the e-h pair combines without generating an electric current or solar power.
On top of the surface recombination, traditional crystalline silicon solar panels can produce losses due to inefficiency in capturing light, reflection by the solar cell itself, and partial shading by materials in the module. To reduce efficiency losses, researchers in the solar industry developed the PERC solar cell.
PERC technology was first described in the University of New South Wales in but officially registered in a paper in . The PERC solar cell finally allowed PV modules to move over the 20% conversion efficiency that has been the norm for several years in the industry.
Structure of a PERC solar cell - Source: ENF SolarThe PERC solar cell technology includes dielectric surface passivation that reduces the electron surface recombination. At the same time, the PERC solar cell reduces the semiconductor-metal area of contact and increases the rear surface reflection by including a dielectrically displaced rear metal reflector. This allows photons to be absorbed when going into the cell or out of it, and it also reduces heat absorption.
This highly efficient and improved version of c-Si technology results in PERC solar panels having a 0.86% or more increment in the efficiency of the solar cell. This provides several perks like a reduced installation time, fewer space requirements, and cost reductions by requiring fewer wires, connectors, racks, and other components that you would require when installing the same PV capacity with traditional technology.
Mono PERC vs. Poly PERC solar panelsSince PERC is a technology implemented on traditional crystalline silicon solar cells, PV modules under this technology are divided between mono PERC solar panels and poly PERC solar panels.
Poly PERC solar cells are manufactured by blending or melting different silicon fragments together, while mono PERC solar cells are manufactured using a single silicon crystal, free from grain limits (2D defects). Since mono PERC solar cells have a higher level of purity, these PV modules are more efficient, but they are also slightly more expensive.
Studies performed in provide us with enough data to have a deeper understanding of PERC technologies and how they compare to traditional panels.
Poly c-Si solar cells with 18.46% efficiency get an increased efficiency of 18.61% when manufactured with PERC technology, the difference is even more notorious with mono c-Si solar cells. A traditional mono c-Si panel has a 19.55% efficiency, but this efficiency increases by 0.86% to achieve 20.41% for mono PERC solar panels.
Mono PERC solar panels tend to have a relatively higher price, but considering the performance and technical specifications against the price, this technology is much better than poly PERC solar panels.
PERC solar panels vs. Other advanced panel technologiesPERC is only one of the available technologies to improve efficiency and applications for solar panels. There are other advanced technologies like Interdigitated Back Contact (IBC) and Bifacial Solar Cell (BSC) technology. Manufacturers can use either one or even combine PERC with IBC or BSC. In this section, we compare IBC and BSC against PERC technology, to fully understand the perks of this technology.
PERC panels vs. IBC solar panelsOne interesting improvement performed to solar cells is the implementation of Interdigitated Back Contact technology. Most cells (PERC included) have a thin strip of conductors in the front, which are called busbars, these conductors are used to transport the electric current through the cells.
While the space occupied by the busbars is not that large, it is still a surface area of the solar cell that could receive photons to generate solar power. To reduce losses, IBC solar cells place the conductors on the back of the cell, leaving the frontal surface entirely exposed to the sun, allowing the whole IBC solar cell to receive photon impacts and generate solar power.
Efficiency for IBC solar cells is higher in general, but the highest recorded efficiency for both technologies is similar. The highest efficiency for PERC solar cells was recorded at 25.0%, while IBC solar cells achieved a 25.4% conversion efficiency.
The biggest downside for IBC technology is that it has a higher cost than PERC solar panels. An advantage is that manufacturers can combine both technologies and obtain an even higher-performing PV module.
PERC panels vs. Bifacial solar panelsOne of the most underused resources in solar applications is albedo. This is the diffuse solar radiation reflected from surfaces onto the PV module. To fully take advantage of this solar resource, manufacturers implement reflective rear sides or dual-panel glass, creating bifacial PV modules.
Bifacial technology can absorb direct light coming from the sun (like PERC solar panels), but it can also generate power from albedo light being reflected on the rear side of the module. Bifacial c-Si PV modules can deliver a higher performance ratio (PR) for the PV system, delivering 6% more PR than monocrystalline silicon modules, while PERC modules can deliver around 1% more efficiency than traditional technologies.
The good news for the solar industry, is that bifacial and PERC technologies can be combined, to create bifacial PERC PV cells. These new and innovative solar cells can deliver up to 18% more power than monofacial solar cells.
Key takeaways: Pros and cons of PERC panelsUnderstanding how PERC solar panel technology works, is key to understanding the pros and cons of different applications. In this section, we round up the major pros and cons of PERC solar panel technology and highlight some of its best features.
ProsPassivated Emitter and Rear Contact (PERC) technology is an excellent improvement that allows solar cells to achieve higher efficiencies. While this technology presented several cons in the past like LID and PID, manufacturers found ways to solve this, resulting in high-efficiency PERC solar panels without the cons of the technology in the 80s.
Since manufacturers can either design regular PERC solar panels or combine them with IBC or bifacial technology, the range of applications for this technology is quite broad. PERC solar panel technology can be used on residential, commercial, and industrial applications (including utility-scale applications).
For residential purposes, PERC solar panels can be used as regular rooftop photovoltaics, EV solar roof chargers, and solar sheds. For commercial and industrial applications, this technology can be used for ground photovoltaic power stations (especially when combined with bifacial technology), Building Integrated Photovoltaics (BIPV), water surface power stations, and much more.
The use of this technology is quite convenient for the solar industry in general. With the rise of PERC solar panels, homeowners and utilities can benefit by using less space, fewer installation components, and using PV modules with higher performance and an infinity of applications.
Conventional silicon photovoltaic (PV) cells have long been the standard in the solar industry. But as the technology matures and approaches hard efficiency limits, researchers and manufacturers have started to embrace a relative newcomer &#; the Passivated Emitter and Rear Contact (
PERC
) solar cell.
In this article, we&#;ll look at the
core benefits
of PERC solar cells, how they work, how they&#;re made, and even how to sell them. But first, let&#;s get into some background about how conventional solar cells work and what limitations they present.
Traditional solar cells contain two layers of silicon, commonly called &#;n-type&#; and &#;p-type&#; for their negative and positive charge behavior. A solar panel
creates electricity
when sunlight hits the solar cells, knocking electrons loose from the n-type layer as the p-type layer accepts them.
These flowing electrons are what create an electric field &#; and by extension &#; clean solar power for the customer&#;s home or business.
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Although this basic design has served the solar industry well, plain PV cells suffer from several
types of efficiency losses
, including:
Insufficient sunlight capture either due to light reflecting off panel surfaces or because of wires and other components blocking light
Excessive heat buildup, especially as light hits the back-most surface of the PV cells
Free electrons being knocked out of alignment due to scattered light refraction
Electrons recombining with the silicon material on the front and back of the solar cell
Fortunately, some of these efficiency losses can be mitigated with technology.
For example, adding a front passivation layer can help stop front-side recombination. This strategy also helps to reduce some reflection. To prevent unwanted electrons from moving through the cell and hitting the rear contact, it&#;s possible to add a back surface field layer or place all the wires on the back of the panel during the manufacturing process.
The hardest efficiency losses to manage, however, are excessive PV panel heating and back-side recombination. Because of these limits, the maximum efficiency of standard solar modules
hovers around 20%
in the field.
First
introduced in
, PERC panels are modified silicon cells that have an
additionallayer on the back. Because this extra layer is reflective, it is able to send unused light back across the n-type and p-type junctions to generate more energy. Better still, this reflective surface also helps to reduce rear recombination and prevent longer wavelengths from becoming heat that would otherwise impair the cell&#;s performance.
Early commercial implementations of PERC technology ran into trouble &#; largely due to increased
light-induced degradation
. But with
steady improvements over the years, PERC modules have since achieved solar generation efficiencies up to 12% higher than their traditional silicon counterparts.
As a result, solar PV installers are able to
save time
and
reduce costs
when using the newer PERC standard. This is because fewer panels are needed to achieve the same solar power output. Using fewer panels also helps to reduce the amount of
racking
,
wiring
, and
MLPE
devices needed to connect everything together.
For example, even if roof space is not a major concern, it may be possible to savePERC solar modules are structurally similar to other silicon panels on the market, which is a distinct advantage for manufacturers.
Even though there are additional costs when creating passivation and rear contact capping layers, panel manufacturers are able to reuse existing production equipment with minimal retooling required.
This places PERC manufacturing costs on par with conventional silicon cell production. Although PERC panels remain
slightlymore expensive, these costs are largely offset by the increased efficiency gains &#; which yield higher lifetime utility bill savings and carbon offsets for the end user. And as the technology continues to mature thanks to economies of scale and R&D, PERC cells will likely continue to benefit from even larger efficiency gains and cost reductions moving forward.
Monocrystalline solar cells are cut from a single piece of silicon, making them more efficient than polycrystalline panels. Additional PERC layers can be added to help further increase efficiency rates.
Unlike uniform monocrystalline cells, polycrystalline PERC cells are manufactured using a blend of silicon shards. This mix yields lower efficiencies, but polycrystalline cells are cheaper to manufacture.
Just like with monocrystalline cells, adding a PERC layer can significantly increase the efficiency of polycrystalline cells without dramatically increasing their manufacturing costs. But because higher solar power output is the industry&#;s Holy Grail, the more efficient monocrystalline PERC cell is the preferred standard for most new PV installations.
Global demand for PERC modules skyrocketed in the late s and continues to see steady growth. In , the
PERC solar sales market
was estimated at around $150 billion and is projected to hit $290 billion by .
While PERC cells are undoubtedly the top panel on the market, some
industry experts
theorize that PERC cells may be phased out in the next few years, favoring N-type solar cells due to their &#;superior conversion efficiency.&#;
Pros and cons of PERC solar panels
There&#;s a reason PERC cells are the industry standard &#; they&#;re highly efficient and a much-improved type of PV technology compared to traditional solar panels. However, compared to the new development of N-type cells, there are some disadvantages. Let&#;s review the pros and cons of PERC solar panels.
Pros of PERC solar panels
More efficient compared to conventional silicon solar panels
Work better in low light and high heat conditions compared to standard solar cells
Are more affordable than N-type solar panels
Cons of PERC solar panels
Slightly more expensive compared to conventional silicon panels
Don&#;t produce as much power compared to N-type cells
Are more negatively influenced by high temperatures than N-type cells
How offering PERC solar panels can increase solar sales
The main selling point of PERC panels is their efficiency. Because they make better use of space, fewer modules are required to produce the same solar output as a standard silicon panel. For customers who may have space constraints, offering PERC panels is a compelling option. The same case goes for customers who don&#;t get as much direct roof sunlight or customers who live in high-heat areas: PERC cells perform better in these conditions compared to traditional cells.
But even if roof real estate or weather conditions aren&#;t factors, it&#;s possible to
save installation time and costs
by using PERC modules. Because PERC cells are more efficient, less panels will need to be installed.
Side-by-side cost comparison: Traditional vs. PERC Solar Panels
Cost will still be a major consideration for many clients. To seal the solar deal, it&#;s easier to outline how PERC solar panels are a better value in the long run, even if they&#;re a larger upfront investment. The table below provides a good visual.
Want to learn more about the solar industry?You&#;ll hear from industry experts on everything from what to expect for the rest of , to how AI is affecting the industry, and more.For example, even if roof space is not a major concern, it may be possible to save installation time and costs by using higher efficiency PERC modules. If a site takes 40 standard modules or 38 PERC modules to reach the desired annual production, you&#;re able to reduce the amount of racking, wiring , and MLPE devices needed to connect everything together.A knowledgeable customer is one of our best weapons when selling solar. Make sure your customers have all the information by giving them a free Solar Sales Follow Up Kit . It has all the background a customer needs on the basics of solar, and can help set their mind at ease.
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