What is Half-Cut Cell?
Half-cut cell mono PERC solar modules have solar cells that are cut in half, which improves the solar module’s performance and durability. Traditional 60-cell and 72-cell solar panels will have 120 half-cut cells and 144 half-cut cells, respectively. When solar cells are halved, their current is also halved, so resistive losses are lowered and the solar cells can produce more power.
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.
Smaller cells experience reduced mechanical stresses, reaching a decreased opportunity for cracking. Half-cut cell PV modules have higher output ratings and are more reliable than conventional solar panels.
Did you know that even a little shading can have severe detrimental effects on an entire string of solar modules? And exposing to extreme temperatures can cause hot spots, decreasing a whole module string’s power output.
Today new solar module generation technology has increased the module output of up to 15 watts per module, compared to standard solar modules. Boasting the efficiency of up to 19.79%.
The new solar module series based on the latest trend of half cut cell technology is not only cutting the cells into half but also reducing the cost, ensuring a lower LCOE.
How do half-cut solar cells improve PV panel performance?
There are a few main ways that half-cut cells can boost solar panel output and performance:
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 neighboring 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.
Higher shade tolerance
A conventional solar panel typically contains sixty 0.5V solar cells wired up in series. Voltages add in series, so the solar panel operates at 30V.
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.
If half cut cells were wired together as in a standard panel, they would produce half the current and twice the voltage. This would not be appreciated by installers using normal solar inverters .
To make them operate like standard panels they are wired together differently. There are 2 lots of 60 series-connected cells that operate at 30V each. These two 30V halves are then connected in parallel. Voltages in parallel stay the same, so the panel remains at the standard 30V.
Instead of having 3 panel cell-strings like a standard solar panel, the half cut panel has 6 panel cell strings making it a 6 string panel. Thanks to bypass diodes (shown in red below), one small spot of shade on a panel, caused by say a leaf or bird poop, will knock one entire cell string out of action, but not affect the others. Because the half-cut panel has more strings, the effect of partial shade is less severe.
On a roof without shade in an area where the birds are not particularly incontinent, this will make very little difference in overall generation, probably less than 1%, but that’s still an advantage. On a roof with a significant amount of shading I would expect a modest improvement in output. But it won’t be great because shade is basically solar panel kryptonite.
A regular solar panel has 3 cell-strings, each of which can be bypassed with a (red) bypass-diode. One shaded cell will shut down one-third of the panel.
A half cut solar panel has 6 separate cell-strings (but only 3 bypass diodes), offering better partial-shade tolerance. If half of the panel is shaded (e.g the LHS), the other half can still operate.
Hot Spots Not So Hot?
When one solar cell in a panel cell string is shaded, all the preceding unshaded cells can dump the energy they produce into the first shaded shaded cell as heat. This creates a hot spot that can potentially damage the solar panel if it lasts for a long time. Twice as many panel cell strings means only half as much heat, but as the shaded cell only has half the area to radiate heat as a normal cell, I’m not sure there will be much of an improvement. But the decreased total amount of heat produced should be less damaging to the panel so there is likely to be an improvement in resistance to hot spot damage.
Split Junction Box
Standard solar panels have one junction box that cables come out of located on the back of the panel near the top. Panels with half cut solar cells can have junction boxes that are split into three, as you can see in this picture of a REC Twinpeak half cut panel. The middle box is for the middle bypass diode.
At first I thought that since the junction box, or boxes, were in the middle of the panel it made no difference which way up it was installed. But then I was reminded that one cable is positive and the other is negative and it’s probably best not to confuse them. While there is enough length in the cables to cross them over if necessary, the thought of doing that gives me the creeps. It is not an elegant solution.
Reduce Power Loss
Half cell technology reduces resistive losses in the interconnection of solar modules. Less resistance between the cells increases the power output of a module.
Improved Heat Dissipation
The use of three separate smaller junction boxes with each containing one bypass diode reduces internal resistance and enables new layout design for increased output.
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