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.
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.
Recapping the structure and workings of traditional solar panels
Before 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:
- Printed silver paste (front contact of the cell)
- Anti-reflective coating or anti-reflective glass
- Doped semiconductor (P-N junction)
- Back Surface Field
- Print aluminum paste (rear contact of the cell)
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.
After 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 1983 but officially registered in a paper in 1989. 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.
The 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 panels
Since 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 2016 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 technologies
PERC 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 panels
One 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 panels
One 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 panels
Understanding 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.
- Up to 1% more efficiency than traditional c-Si solar panels.
- Reduced heating absorption, allowing PV systems to perform better at high temperatures.
- Operation on a wider light spectrum.
- Better usage of the available space.
- Cost-effective technology.
- Prices for PERC solar panels will get reduced as the technology becomes more popular.
- PERC solar cells can be combined with IBC or Bifacial technology.
- Relatively larger cost than traditional technologies.
- Light-Induced Degradation (LID) and Potential-Induced Degradation (PID) were a problem in the past for the technology. (Not anymore, since most manufacturers overcame these barriers).
Passivated 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.