NRGUtility Ltd Half-Cell Solar Cells: What Are the Proven Benefits?
What is a half-cut or half-cell Solar PV module?
The biggest selling solar PV module for NRGUtility Ltd at the moment is our new range of half-cell or half-cut panels. There are many reasons why customers are choosing these new modules. We explore the reasons below.
In a traditional silicon cell-based PV module, the ribbons interconnecting neighbouring cells can cause a significant loss of power during the current transport. Cutting solar cells in half has been proven to be an effective way to lower resistive power loss.
The half-cut cells generate half the current of a standard cell, reducing resistive losses in the interconnection of solar modules. Less resistance between the cells increases the power output of a module. Solar Power World Online has noted half-cut cells can potentially boost power output between 5 to 8 W per module, depending on the design.
With a higher power output on module that costs relatively similar, it speeds up ROI. This makes the cells a great idea for end users who want a quicker turnaround on their investment.
After conducting a series of tests of half-cut and PERC solar cells in a large-area PV module during in a controlled environment, the Institute for Solar Energy Research Hamelin broke the previous record for module efficiency and peak power output, PV-Tech reported. While they’re not the only organization performing ground-breaking work on half-cut cells, the record, which was independently confirmed by TUV Rheinland, demonstrates the viability of using these modules to bring PV development to its most advanced and lowest cost yet
What’s the benefit of a half-cut solar cell?
While the solar module comprises the costliest component of a total solar system, technological advancements have contributed a significant drop in prices with further declines anticipated in the coming years. From 2015 to 2016, the price of solar panels dropped nearly 40 percent on average, according to recent research from International Technology Roadmap for Photovoltaics.
Despite these price improvements, the panels still constitute roughly 45 percent of the total cost of a PV system. However, experts expect this to fall to 29 percent by 2027. The reasoning behind these estimates stem from the introduction of innovative new technology, processes and solutions that boost efficiency, increase power output and improve performance gains. Combined, these factors are contributed to help lower the overall prices of solar PV systems. Half-cut solar cells are part of a revolutionary new breed of PV technologies working in concert bringing down the module price tag
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Benefits of half cut cells
- Lower resistive losses. A half-cut cell carries half the current and a quarter of the resistance of a full cell. So a complete half-cell module has the same current but half the resistance of a regular module. Resistance = wasted power, meaning a half cell solar panel can boost output by around 3%.
- Durability. Since the cells are physically smaller, they are more averse to cracking.
- Shade resistance. A regular panel is made up of 3 rows of cells connected in series with bypass diodes. If one cell is shaded, a third of the panel’s output can be lost. But in a half-cut panel, there are 6 rows of cells. So, if one of the cells is shaded, only a sixth of the output is lost.
- Less chance of hotspots. With a lower current in each cell, there’s less heat concentration.
- Reduced installation area. Roof space can be saved using half cell technology
What are half-cut solar cells?
Just as bifacial solar panels and PERC solar cells provide small boosts in the efficiencies of silicon solar panels, implementing half-cut cells in solar panels can help improve the power output of a solar panel system. Half-cut solar cells are exactly what their name suggests – they are traditional silicon solar cells that have been cut in half using a laser cutter.
Half-cut cells provide several benefits over traditional solar cells. Most importantly, half-cut solar cells offer improved performance and durability. Performance-wise, half-cut cells can increase panel efficiencies by a few percentage points. And in addition to better production numbers, half-cut cells are more physically durable than their traditional counterparts; because they are smaller in size, they’re more resistant to cracking Due to these advantages, solar panels built with half-cut solar cells have the potential to provide
quicker solar payback periods for property owners installing solar energy systems. Especially for
installations where shading and limited space are constraining factors, half-cut cells can make a solar
panel installation even more worth the upfront cost.
How do half-cut solar cells improve panel performance?
There are a few main ways that half-cut cells can boost solar panel output and performance:
1. Reduced resistive losses
One source of power loss when solar cells convert sunlight into electricity is resistive losses, or power lost during electrical current transport. Solar cells transport current using the thin metal ribbons that cross their surface and connect them to neighbouring wires and cells, and moving current through these ribbons leads to some energy lost. By cutting solar cells in half, the current generated from each cell is halved, and lower current flowing leads to lower resistive losses as electricity moves throughout cells and wires in a solar panel.
2. Higher shade tolerance
Half-cut cells are more resistant to the effects of shade than traditional solar cells. This is not due to the cells being cut in half, but rather a result of the wiring methods used to connect half-cut cells in a panel. In traditional solar panels built with full cells, the cells are wired together in rows, known as series wiring. In series wiring schemes, if one cell in a row is shaded and not producing energy, the entire row of cells will stop producing power. Standard panels typically have 3 separate rows of cells wired together, so shade on one cell of one row would eliminate a third of that panel’s power production
Wiring scheme for a standard solar panel. There are three separate “rows” of cells wired together in parallel. Source: www.solarquotes.com.au
Half-cut cells are also wired in series, but because panels made with half-cut cells have double the number of cells (120 instead of 60), there are also double the number of separate rows of cells. This type of wiring allows panels built with half-cut cells to lose less power when a single cell is shaded because a single shaded cell can only eliminate a sixth of the total panel power output.
Wiring scheme for a solar panel made with half-cut cells. There are six separate “rows” of cells wired together in parallel. Source: www.solarquotes.com.au
What solar panel manufacturers use half-cut cells?
Half-cut cell production lines are not much different from traditional solar cell lines, and any panel manufacturer looking to begin making half-cut cells doesn’t need to completely overhaul existing factories or production processes. There are two additional steps needed when making half-cut cells: a cell cutting step and a stringing step.
Cell cutting is done with a laser and involves splitting standard solar cells into two halves. Solar cells can be very fragile, and laser cutting allows for precise lines to be cut into solar cells.
As with cell cutting, the stringing process needed when making half-cut cells is a very precise task. Stringing is the process of placing the conductive strips, known as busbars, on each half-cut cell. Due to the smaller size of half-cut cells, the busbars used are smaller and require specialized equipment to accurately place them.
Half-cut solar cells are an exciting technology in the solar industry and can be a solution for property
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Every last watt
PERC power: As PERC settles into its position as a mainstream technology, leading module manufacturers are searching for ways to push ever more watts out of their module, and eliminate lingering degradation issues. So far this has included ramping up production capacities for half-cell modules and developing innovative new connection strategies. pv magazine looks into the latest technologies leading to gains in power output and quality at module level.
Thanks to its potential to boost module power output, half-cell technology – whereby silicon solar cells are cut in half prior to layout within a module – is now an industrially relevant concept being adopted by several leading module manufacturers…
Push for power
Chief among the reasons for the growth in half-cell technology is the potential to provide a power boost at module level. In an example provided by Fraunhofer ISE, sample modules incorporating the full cell and half-cell layout were compared when using the same total cell power. The cells utilized have a power rating of 330 W, this translated to module power of 316.7 W for the full cell module, and 325.2 W for the half cell module, an increase of 2.7%. The modules are otherwise identical, although the half-cell module is 1.8% larger, as the design naturally means more cell gaps. Therefore, the efficiency boost is not as strong as the power boost, increasing from 18.84% to 19.12%.
Fraunhofer ISE data showing cell to module power losses and gains.
As shown in the graph, the largest difference in cell to module losses/gains comes at the cell interconnection stage, where a 6.05 W loss in the full cell module is reduced to 1.56 W in the halfcell. Cutting cells in half also halves the electrical current, meaning that resistive losses decrease.
On the other hand, in half cut cell modules, losses due to the area lost between the cells is increased. In half cells, there are just under twice as many cell gaps as in full cells. These losses are partially recovered by multiple reflection of the light. This recovery is higher in half cut cells than in full cell modules, as the losses are higher.
“When light falls into the intercellular space, it is partially reflected again and in turn partially reflected back to the cell at the front glass-air interface,” explains Ulrich Eitner, head of the photovoltaic modules group at Fraunhofer ISE. “In glass-glass modules, for example, this gain does not occur.” As round wire for the cell interconnection can further increase the recovery due to enhanced reflection compared ribbon, it makes sense that Q CELLS also adopted this interconnection concept.
Manufacturers also reports a 3% power increase, attributable to the half-cell layout, in its latest module offering. The largest of the range – the 144 half-cell monocrystalline comes with a power rating up to 395 W. “The first big advantage is the higher power of around 3%,” explains Maximilian Schurade, Director of Technical Marketing Support. “This is the effect of the half-cell itself, and the different interconnection, because you reduce the resistive losses in the module.”
Another reported advantage of half-cell modules is increased mechanical stability. “The half-cut cells are smaller, so it’s much harder to break them,” continues Schurade. He also notes that the choice of process for cutting the cells does not bring additional weakness to the module, and that the improved mechanical stability allowed the company to improve the maximum yearly degradation specified in its warranty from 0.6% to 0.54%.
The slight increase in the size of the module, appears to be negligible “it’s 15mm longer, this is not really an issue though,” says Schurade. “The width is more important for most installations, so the additional 15 mm in length is not really an issue for our customers.”
Separating the cells
Alongside half-cells, innovative strategies for connection can further reduce cell to module losses. Manufacturers have opted for round wire technology in place of ribbon, which it says achieves a power increase of around 2%. According to teamtechnik as well, there is an advantage to using roundwires.
“With a round wire you will get more reflection of incoming light. Light hitting the round wire is reflected back to the glass panel, and from the glass back to active surface of the cell,” says Kramer. “The challenges are the reduced contact area on the busbar, adhesion of the wire on the cell, and the alignment – since you have less contact area it might move around a bit. Handling the round wire is a little more tricky compared to the flat ribbon, but it can be done.”