In , solar equipment manufacturer REC introduced a strange new solar panel - one with half-cut cells. Traditionally, full-sized panels came with 60 or 72 cells in them, and all of them were whole cells, without any perceived need for cutting them in half.
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Few people would have imagined that half-cut cells would quietly claim the &#;next big thing&#; title in less than a decade. But if you look at the reasoning behind the technology, it makes perfect sense. Half cell panels offer a few crucial advantages over traditional panels. Let&#;s discuss the same in more detail, starting first with an overview of half cell panels.
Here&#;s a quick revision on traditional solar panels - a panel comprises an array of solar cells sandwiched between a few other components such as glass and back sheet. The cells themselves are made from super-thin wafers cut from rods made of silicon. These cells are arranged in rows and columns, connected together for power flow. Here&#;s how they look -
Image - Typical solar panel with full cells (source - Canadian Solar)
Half-cell panels, on the other hand, look like this -
Image - typical half cell panel (source - REC)
This type of solar panel is essentially two smaller panels joined together, where both the smaller panels have all the cells cut in half, and the top half works independently of the bottom half. Now why would someone choose to complicate a perfectly working thing by adding the delicate work of cell-cutting, soldering, etc.?
The greatest advantage of a half cell panel over a traditional solar panel is its improved efficiency. But this is a very general way to put it, and to understand how the efficiency is improved, we will first have to look at the major drawbacks of a full cell panel.
In a typical full cell panel, all the individual cells are connected in series, meaning the positive terminal of one cell connects to the negative of the next, and so on. In a series connection, voltages of individual entities add up. So for instance in a 60 cell panel where each cell&#;s voltage is about 0.5 V, connecting all the cells in series gives us a panel voltage of 60 x 0.5 V = 30 V.
There&#;s just one problem with this type of design - series connections are extremely vulnerable to partial shading. If part of a panel is shaded, the entire panel shows a serious drop in production (same when one panel in a series string is shaded) - like a high-school project team where nobody is willing to take up someone else&#;s tasks and the entire project gets stalled because one of the kids doesn&#;t show up!
One way to solve this problem is to connect the cells in parallel, but then we would have very low, almost unusable voltage output per panel, and we would need really heavy cables to transmit all that added current (parallel connections lead to addition of current outputs), since more current means more losses. And speaking of current brings us to the second important drawback of full cell panels - resistive losses.
In the most ideal scenario, you would want to have the highest possible voltage and the lowest possible current, since even a small increase in it increases power losses. This is why in any solar panel, you will find cells connected in series. Even the 30 or so milliamperes generated per sq. cm. of a cell can have noticeable losses.
While many people were scratching their heads about these problems, some smart individuals found a way to halve the current while keeping the voltage the same - by simply cutting the cells in half.
Enter half cell panels!
Resistance is the characteristic of any material to oppose the flow of current. Plastic and rubber are extremely stubborn at resisting power flow, while metals usually allow it. However, even the best electrical conductors will have some resistance in them. &#;What does this have to do with half cell panels?&#;, you may ask. The answer lies in a simple formula -
Here, Ploss is the power loss, R is the resistance, and I is the current flow. The higher the current flow, the higher the losses (notice that the I is squared so it is not a linear increase - a little increase in current leads to a large increase in losses).
By cutting solar cells in half, the voltage remains the same (great news!), while the current is slashed into half - meaning the power loss goes down by a factor of 4. Ultimately, this gives us what everyone in the solar power world is always desiring - more efficient panels!
As we discussed earlier, partial shading means all the cells in a panel slow down. When cells are cut into half, we essentially have 120 or 144 small cells instead of 60 or 72. These are then split into two series batches of 60 or 72 each and connected in parallel. This type of wiring means that even if one batch is affected by shading, the other batch keeps generating power.
In a full cell panel, when a single cell in a cell string is shaded, all the neighbouring unshaded cells can dump the energy they produce into the first shaded cell as heat. This creates a hotspot, which, given enough time, can severely damage the solar panel.
In a half cell panel, twice the cell strings means only half the heat. In other words, there are more cells to dump the heat into, and it will be dumped in a more dispersed manner.
Image - Hotspot on a solar panel due to shading (source - syswe.de)
The solar cells in half cell panels are usually manufactured using an innovative technology known as &#;Passivated Emitter and Rear Contact&#; (PERC). These cells have an additional layer on the back of traditional solar cells. This layer helps capture more sunlight and turn it into electricity.
PERC modules have on average about 5% more efficiency compared to traditional modules.
No new technology is devoid of drawbacks. Half cell panels are relatively new and though they deliver on a lot of pros, there are a couple of cons worth noting.
Cutting cells into half and putting together a panel seems like an incredibly simple solution to traditional panels&#; problems. But simple does not mean easy! Cutting cells into half and soldering them together means increased work - increased time, increased energy consumption and increased machinery requirement in production. This leads to a noticeably higher cost.
This does not mean that half cell panels are not worth the price - it depends on your requirement. If you are never going to face shading issues and if you are not very concerned about a little difference in efficiency, then you can opt for traditional panels.
Soldering is used to connect solar cells to one another using solar ribbons that run throughout the panel. Think of it as an adhesive bond created by locally melting a little conducting metal to stick the solar ribbon to the cells.
This method is not fool-proof and may have defects, and twice the number of soldered points means twice the likelihood of soldering defects, aka internal cell defects.
Despite their nominal drawbacks, half cell panels are rapidly gaining popularity. The ninth edition of the International Technology Roadmap for Photovoltaics (ITRPV) predicts the market share of half cells will grow from 5% in to nearly 40% in .
With advancing machinery and production techniques, the extra time and cost incurred in half cell panel production is bound to go down. As such, it will not be a surprise if we are at a point where the market is completely dominated by half cell panels.
In a relatively short span of time, following the pioneer REC, nearly all major solar panel manufacturers have launched half cell panels. Particularly in NZ, there are at least five different brands to choose from, and we are sure that number will grow fast.
In case you are interested, here&#;s a list of all the half cell models available currently in NZ:
In summary, half cell panels seem to be the obvious upgrade over traditional, full cell panels. Their ability to significantly reduce shading as well as current losses is almost revolutionary, which is why the market predictions seem to make total sense. Half cell panels might actually be, or are - truly the next big thing in solar panel tech!
Half-cut solar cell technology is a new and improved design applied to the traditional crystalline silicon solar cells. This promising technology reduces some of the most important power losses in standard PV modules, allowing the solar panels and a PV system, in general, to perform better.
The advantages of half-cut solar cells are great and there are no remarkable disadvantages to this technology when compared to traditional modules. In this article, we will provide a detailed explanation of half-cut solar cell technology, how it works, its advantages & disadvantages, and even compare it against traditional and PERC technology.
Novergy Solar, Half-cut solar panels, Cropping and Redesigning, CC BY-SA 4.0What is a half-cut solar panel?Half-cell modules or commonly known as half-cut solar panels are the new trend in manufacturing technology. If you are wondering what is a half-cut solar panel? Here we explain it in detail:
Components and materials of the half-cut solar cellHalf-cut solar cell modules are not a technology developed with new and innovative chemical components added to the cell. Actually, the half-cut solar cell technology is based on the traditional crystalline silicon (c-Si) solar cells. This means that the components and materials used to manufacture a half-cut solar cell are the same as the ones for c-Si solar cells, which are the following:
While the half-cut solar cell itself shares the same technology as the traditional ones, the fact that sets them apart is a change in the design, which focuses on improving performance and reducing electrical losses from traditional panels.
Cutting in half of the solar cellHalf-cut solar cells start to differ from regular cells because they are cut in half with a process called cleaving, applied to monocrystalline and polycrystalline solar cells. The cleaving process uses high-tech laser technology to cut the cell in half, with the cell delivering the same voltage but half the current.
Since this technology is based on cutting a traditional crystalline silicon solar cell, this means that the conversion efficiency for the half-cut solar cell is theoretically the same as the traditional c-Si cell. Other types of solar cells like PERC and bifacial can be used to manufacture half-cut solar cells.
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Structure of half-cut solar panelA half-cut solar cell panel allocates twice the cells in the same area of a regular module. This means two times the arrays of solar cells within one module, with half-cut solar cells having half the width, keeping the area of the panel the same.
Whole-cell vs. Half-cell solar panel | Source: GSES Global Sustainable Energy SolutionsGenerally, modules with 60 solar cells include three substrings of 20 cells in series. The equivalent half-cut solar cell modules have 120 solar cells, divided into six substrings of 20 cells. Each side of the half-cut solar panel has three substrings in parallel, with both sides also connected in parallel. Besides, there is one bypass diode per substring pair. The same case is analog for panels with 72 solar cells or more.
Working mechanismA half-cut solar panel works the same way a whole-cell one, but it has a few more substrings. Arrays of half-cut solar panels can be connected as well in series or parallel, replacing traditional whole-cell modules, with the voltage being the same in both cases.
Major differences from halving solar cells and increasing the substrings are the production of less current per cell which translates in reduced losses, and the increased tolerance against partial shading.
Advantages of half-cut solar panelsAre you wondering what are the benefits of half-cut solar panels? Here we will list and explain the benefits achieved by implementing half-cut solar cell technology:
Reduced power lossesThe main improvement of half-cut solar cell modules is the reduction of electrical losses caused by Joule's Law, which is based on the following equation:
Since half-cut solar cell produces half (1/2) the current per cell, and Joule&#;s Law considers the square current to calculate losses, these cells produce one-fourth (1/4) the power losses, or about 75% less electrical losses. On the other hand, when evaluated at the module level, there is an increased overall current output of 2-4%, which also increases the power output by that same percentage.
Increased partial shading toleranceStandard vs. Half-cut solar cell module with shade covering 1/3 of the panel | Source: GSES Global Sustainable Energy SolutionsWhen a PV module is partially shaded, this causes major power losses for the module and the array. Half-cut solar cells include twice the substrings, meaning that shading a single area of a panel will cause reduced losses. Studies show that half-cut solar cell panels produce up to 50% fewer power losses in an array.
Reduced hot spots and temperature in generalHot spots are a consequence of partial shading in solar panels. When some cells are shaded, instead of producing power they act as resistances, consuming electricity and therefore increasing their temperature. Half-cut solar cells reduce the current per substring, which in turn reduces the temperature of hot spots, this technology can reduce the peak temperature of hot spots by up to 20ºC.
Higher Cell-to-Module powerWhile conversion efficiency for a single half-cut solar cell depends on the type of solar cell technology, half-cut solar cells have a higher Cell-to-Module power (CTM) which translates into higher power output. Traditional PV modules have a 94.8% CTM power while half-cut solar cells have a 99.4% CTM power before factoring laser-cut losses, or 98.4% after factoring them.
Integration with different solar cell technologiesHalf-cut solar cell technology is a modification in the manufacturing process of PV modules that uses solar cells manufactured under the traditional c-Si technology. As a consequence, half-cut solar panels can be manufactured in combination with PERC and/or bifacial technologies, which can translate as PV modules with fewer power losses, a higher power output, and several other advantages.
How about their disadvantages?Half-cut solar cell technology is quite beneficial; however, there are a couple of disadvantages to consider:
Manufacturing of Half-cut solar cells represents a large investment in manufacturing equipmentTo manufacture the same number of half-cut solar cell modules compared to whole-cell modules, manufacturers need to invest in doubling their tabber & stringers and acquire a piece of equipment to cleave the solar cells. Studies show that half-cell modules cost 0.6-1.2% more than whole-cell modules, but thanks to the power increase, their cost per watt is reduced by 0.8-1%.
Manufacturing half-cut solar cell modules means twice the soldered connections, which translates as twice the probability of bad contacts. Halving the solar cell also increases the probability of causing defective cells which is a downside to the technology for manufacturers. While this is a problem to consider, a manufacturer with proper quality control will not be greatly affected by this.
Half-cut vs. Standard solar panels (Comparison table)To fully understand the scope of half-cut solar cell technology, it is important to compare it against the standard Al-BSF technology. In this section, we compare both technologies, considering aspects like the number of cells, voltage, current, and others.
Traditional c-Si solar panels use a simple technology that produces several losses and has poor CTM power. Since half-cut solar cell technology is an improvement of traditional crystalline silicon solar technology, reduces loses, increases CTM power, and it provides additional benefits.
Half-cut solar technology reduces electrical losses by 75%, increases CTM power by 3.6%, increases the resistance of the module against partial shading, reduces the operating temperature by handling less current per cell, and reduces hot spot by up to 20ºC. The main disadvantage of half-cut solar cell technology is the slightly higher cost and reduced aesthetics of the module (although for all-black solar panels is barely noticeable).
Half-cut vs. PERC solar panelsPERC solar technology improves the structural design of Al-BSF c-Si solar cells. This technology reduces losses due to the surface recombination process, increases the efficiency by implementing a reflecting metal at the rear surface of the cell, and reduces heat absorption. Comparing PERC against half-cut solar cell technology can provide an insight into which is the best one.
While half-cut solar panels produce 2-4% more power than standard modules, PERC solar cells increase this output by 6%. While this is an important advantage, it is its only point in favor of PERC against half-cut solar cell technology.
Even though PERC technology absorbs less heat from the sun, this technology shares the same shading intolerance and electrical losses as the standard solar panels. Half-cut solar panels might not have the same increased performance as PERC solar modules due to the surface recombination process, but they perform better when partially shaded and have an important reduction in ohmic losses. Moreover, the potential reduction in energy losses caused by shading is something that PERC technology cannot compete with, particularly for the residential sector applications where major obstructions and trees can cause high shading.
However, the good news is that there is no need to choose between PERC and half-cut cells because both technologies can be integrated. This means that a PERC mono half-cut solar panel can be manufactured, including reduction of electrical losses, a higher tolerance against partial shading, reduced heat absorption from the sun, improved efficiency due to reducing surface recombination, and an increased CTM power, all at the same time.
Are half-cut solar panels worth your investment?Half-cut solar technology is one of the latest attempts of the solar industry to achieve higher efficiency for PV modules. The technology only costs 0.6-1.2% more than standard c-Si PV modules, but it represents a higher power output of 2-4%. This makes it better for limited spaces requiring fewer PV modules.
Implementing half-cut solar panels is not only better for locations with limited space, but also provides better performance in areas that are being frequently shaded. By including more substrings, the system can be partially shaded without causing the large losses that some regular systems have.
While you might worry that with smaller solar cells, the PV module will also be more delicate, this is not the case. Since modules are covered with protecting glass, mono half-cut solar panels will have the same durability as a regular solar panel, making it one of the best investments that can be made in the solar panel industry.
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