Solar panel modules come in a variety of 'designs'. The untrained eyes may be befooled into thinking that they are for style, but for what they truly are, the variations in designs are often a matter of the technology used in their manufacture of the panels than of mere aesthetics. New trends and innovation in the solar module industry quickly follow the latest ones in rapid succession, often times displacing them. The reason being that manufacturers are constantly pushing back the limits of efficiency of their module offerings. In fact, all the top manufacturers have ceased offering panels manufactured from the traditional technologies. There is significant competition between manufacturers, especially the premium brands, in this respect. The efficiency of a solar panel is how well it performs its function of converting sunlight into electricity. The latest solar panel technologies - or designs -, though expectedly far more expensive, come with the highest efficiency ratings.
The traditional technology used in the manufacture are the polycrystalline and monocrystalline technologies. Between the two, monocrystalline is the superior cell technology. Monocrystalline cells are more efficient because they are cut from a single pure crystal ingot. However, because they cost more to manufacture, polycrystalline panels became more popular even though they are inferior to their monocrystalline counterpart. With the drop in manufacturing costs, many manufacturers now use the monocrystalline technology. In fact, even though poly cells are still widely used and very reliable, the top brands have altogether stopped issuing polycrystalline panels and many mid-grade manufacturers are following suit.
By and large, these new solar cell technologies are upgrades on the traditional monocrystalline module technologies. They are listed below in ascending order of efficiency:
PERC - Passivated Emitter Rear Cell
Bifacial Cells
Multi Busbar Cells
Cut Cells
Shingled Cells
Dual Glass Panels - Frameless Double Glass
HJT - Heterojunction Cells
IBC - Interdigitated Back Contact Cells
1. PERC - Passivated Emitter Rear Cell
This is the traditional solar cell technology. PERC stands for Passivated Emitter and Rear Cell or Passivated Emitter and Rear Contact. In PERC cells, a dielectric passivation layer is added to the rear of the cell. The extra layer is to allow more sunlight to be captured and turned into electricity with the goal of increasing the efficiency of PERC cells over traditional solar cells.
PERC technology was invented by a Canadian scientist, Martin Green.
PERC technology comes in two different types, the n-type and the p-type PERC cells. The main difference between p-type and n-type solar cells is the number of electrons. In a p-type cell, the silicon wafer is doped with boron, an element with one less electron than silicon. This makes the cell positively charged. In an n-type, the cell is doped with phosphorus which has one more electron than silicon, making the cell negatively charged.
N-type cells return higher efficiency values than their p-type counterparts. They are also not affected by light-induced degradation unlike their p-type cells.
The International Technology Roadmap for Photovoltaic (ITRPV) predicts that the market share of p-type monocrystalline solar cells will hold around 30% through 2028, while their n-type counterpart will increase to about 28% from barely 5% in 2017. This correlates to the industry demand for more high-efficiency modules so solar buyers can expect more n-type designs entering and disrupting the mainstream.
Trina Solar, Winaico, Q Cells, LONGi Solar, Risen and JA Solar all use advanced variations of the PERC technology in the manufacture of their panels.
2. Bifacial Solar Panels
As is directly implied in the name, a bifacial solar panel is a solar module that is constructed in such a way to expose both the front and backside of the solar cells to sunlight so as to produce electricity from both sides of the panel. In bifacial panels, the top solar cells perform as in traditional monofacial panels: they directly capture sun rays and convert them into electricity. The upgrade is that bifacial modules come with a transparent backside that are able to generate electricity from the sun shining directly on them and also from the sunlight reflected on the opposite side or underneath the panel or off the ground.
Lumos Solar, Era Solar, Prism Solar, Silfab, Sunpreme, Trina Solar and Yingli all offer bifacials.
3. Multi Busbar Cells
Busbars are thin wires or ribbons which run down each cell and carry the electrons through the solar panel. The Multiple-busbars (MBB) solar cell technology is aimed at reducing resistive losses by reducing the amount of current that flows in both the fingers and the busbars.
Traditional flat ribbon busbars shade parts of the cell reducing its performance, but when multiple round wire busbars are used instead, they provide lower resistance and a shorter path for the electrons to travel along the fingers, resulting in higher performance.
Most manufacturers have moved on from the traditional 3 busbars to 5, 6 or 9 busbars. LG, REC Solar, Trina Solar, and Canadian Solar have gone ahead of others and developed MBB systems using up to 12 or 16 very thin round wires rather than flat busbars.
4. Cut Cells
Traditional full-cell panels are made with 60/72 cells on the entire panel. In a half-cell or half-cut module, the number of cells on the entire panel is doubled into 120 or 144 cells per panel. The panel is however, the same size as a full cell panel but with double the number of cells. (Trina Solar offers a 1/3 cut module.)
A 'line' of space halving the panel is conspicuous in cut panels.
5. Shingled Cells/Overlapping cells
Shingled cells use cut solar cells overlapping thin cell strips assembled either horizontally or vertically across the panel. Shingled cells are made by cutting a normal full size cell in to 5 or 6 strips, and afterwards layering them together in a 'shingle' configuration. Their busbars and fingers are then installed using a special type of connection adhesive. In this way, more surface area is covered as more cells overlap each other above a single busbar. In this still-emerging technology, the gaps between cells are removed, fewer busbars are installed, under the cells and more silicon cells are crammed into one module thus increasing power output and module efficiency.
Shingled or gapless solar panels have become the hot trend among manufacturers. Seraphim were one of the first manufacturers to release a range of shingled modules. SunPower/Maxeon also has a range of shingled cells, the SunPower Performance series. Yingli Solar, Era Solar, REC Solar, LG, Q Cells, Alpha Solar, Hyundai and Znshine now offer shingled solar modules.
6. Dual Glass Or Frameless Panels
Glass-glass or double glass solar panels, not to be confused with bifacial panels have their rear replaced which is often a traditional white plastic backsheet with a glass sandwich. This glass sandwich is by far superior because glass is more stable, nonreactive, UV-resistant and has a longer lifespan. Due to the longer life of glass-glass panels, manufacturers offer 30 year performance warranties on dual-glass panels. Sharp Solar offers double glass panels.
Frameless Panels
Many double glass panels are also frameless since they do not come with the traditional aluminium frame with which modules are coupled. Manufacturers producing dual glass solar panels include Jinko, LONGi, Trina, Yingli and JA.
7. HJT
In HJT (short for Heterojunction Technology) solar cells, as the name 'heterojunction' implies, an additional layer of thin film silicon are added on either side of the cells creating a heterojunction. The different photovoltaic layers absorb light of different wavelengths thus boosting net cell efficiency. The next-generation heterojunction cells have the potential to dramatically boost increase efficiency with lab testing achieving cell efficiencies up to 26.5% when combined with IBC technology.
Following initial work on the HJT technology at Sanyo, which was later acquired by Panasonic, Panasonic developed the 'HIT™' range of panels (NeON 2) and until the Alpha Series by REC group which added 16 microbusbars and reached about 21.7% efficiency, were the leaders in HJT cell technology for many years.
According to a 2019 “International Technology Roadmap for Photovoltaic” report, HJT cells are expected to gain a market share of 12% in 2026 and 15% by 2029.
8. IBC
The IBC short for 'Interdigitated Back Contact' solar cell technology the fingers and busbars are fitted on the backside of the solar cell sheet, so that the front of the solar cell sheet facing the sun is completely black, and the metal wires installed on the front of traditional solar cells are completely invisible. (IBC cells are also called 'all-black' or nonbusbar cells.) This not only brings more effective power generation area to users, but also helps to improve power generation efficiency. Also, with a crisp appearance and an all-black aesthetic, IBC solar panels are by far the most beautiful of the different designs.
The world's most efficient and best performing solar panels so far are manufactured using IBC n-type monocrystalline silicon cells. They are also the most expensive, but the most reliable and highest quality panels available. The two best solar panel manufacturers in the world, SunPower and LG offer IBC n-type panels.
These different technologies are often combined for higher efficiencies and durability. For instance, there are monocrystalline-PERC-shingled panels and half-cut bifacial panels. Et cetera.
The traditional poly and mono panel technologies are fast making their exits from the markets. As newer advances in solar cell technologies continue to push the solar panel industry forward, in a few more years, they would have become collectors items.
For the avoidance of doubt and confusion, SolarKobo helps it clients in Lagos and elsewhere in Nigeria make the best possible choice of solar panels that fits their budget and meets their energy needs.