What are half-cut solar panels?
It may sound weird, but a cutting a solar cell in half can make panels more efficient. Here's a guide on why you might want them for your home installation.
Half-cut solar panels are one of the latest manufacturing innovations to improve solar panel efficiency.
A half-cut solar panel is the same size as a standard panel, but the solar cells have been sawn in half then wired together in a way that allows the panel to be more efficient, especially in the shade.
This doubles the number of cells and internal connections: a typical solar panel might have 60 cells, while a half-cut panel would have 120 cells.
It might seem weird that such a seemingly simple thing would make a better solar panel, but there are two ways that half-cut cells improve panel efficiency. This article will explain how half-cut cells work, but first let’s talk about conventional solar panels.
What are standard cut solar cells?
A conventional solar panel is made up of dozens of individual silicon solar cells that are wired together. Each cell generates a little bit of voltage (about half a volt) and electrical current. When all of the cells of the panel are combined, the total output of the panel might add up to as much as 60 volts and over 400 watts.
Solar cells come in different sizes. A common size is 6 inches square. At that size, a residential solar panel will commonly have 60 cells, and a larger panel designed for the utility or commercial market might have 72 cells.
Not all panels have 60 cells. For example, SunPower cuts their cells differently, and uses 96 small cells in their residential solar panels. There is also a trend toward larger solar cells, which has the potential to reduce manufacturing costs.
What are half-cut solar cells?
With half-cut solar cells, the initial manufacturing process is the same. That is, the solar cells start as a conventional size, such as 6 inches square.
The next step is to saw the cells precisely in half using a diamond wire saw or even a laser. This means that a cell that started as 6 inches square would end up 6″x3″.
What does a half-cut solar panel look like?
The overall dimensions of a solar panel with half-cut cells is the same. The most noticable difference is a distinct line through the middle of the panel:
This line exists because the panel is electrically wired into two separate halves that combine their electrical current. The reason for this is described later in this article.
What advantages do half-cut cells have?
Earlier, we talked about the extra manufacturing step of sawing cells in half with a diamond saw or laser. Not only does the step add a little more complexity, but the cutting step has the potential to break cells and increase wastage. So why bother?
There’s two big reasons, and both contribute to improved panel efficiency.
Advantage 1: reduced electrical resistance
You might remember from high school science class that electrical resistance increases when current increases. If you ever use a hair dryer on full blast, you know that the plug can get pretty warm after a few minutes. That’s due to electrical resistance.
But if the hair dryer is on low power - that is, if you reduce the amount of current that the appliance is using - the plug doesn’t get quite as warm. This is because with less current draw, the electrical resistance drops too.
This is one reason why half-cut cells make more efficient panels. When a solar cell is half the size, it has half the surface area to collect light, and so it will generate only half the current of the original cell.
With the maximum electrical current cut in half, a half-cut cell has 25% less resistance than the original full-sized solar cell.
Advantage 2: better shade tolerance in some conditions
Because the number of cells is doubled in a half-cut solar panel, if they were wired together in a conventional manner, the voltage would be doubled as well.
This would make the panel incompatible with standard inverters. To get around this, the panel is divided into two halves that are wired together in parallel, which doesn’t increase the voltage. This parallel wiring allows a half-cut panel to have the same voltage as a conventional panel.
Because a half-cut solar panel is really two smaller panels working together, it has better shade tolerance than a conventional panel.
You can read our article on shading and solar panels to learn more, but a quirk of solar panels is that shade falling across a panel can drop the power output by more than the number of cells that are shaded, because shaded cells have a tendency to block the electrical current of neighboring cells.
With twice the connections of a conventional panel, half-cut solar panels have more opportunity for electricity to bypass any shaded cells.
The diagram below illustrates the wiring of a half-cut solar panel. As you can see, the panel is made of two halves wired together:
The improved shade tolerance of a half-cut solar panel depends on where the shadow falls. If it falls in such a way that is covers both halves, the benefit is reduced. However, if the shadow covers only one half, the other half doesn’t experience any impact at all, approximately doubling the shade tolerance of the panel.
Benefits of half-cut cells over other technologies
There are other technologies in common use that increase solar panel efficiency, such as PERC cells and hetereojunction cells.
Both have disadvantages. For example, PERC cells that aren’t manufactured to a high standard may have higher failure rates, and heterojunction cells add manufacturing complexity.
Half-cut cells add some manufacturing complexity too, but is simpler than PERC or heterojunction cells. This may be one of the reasons why half-cut technology is currently being offered by so many manufacturers.
Manufacturers that offer half-cut solar panels
There are hundreds of solar panel manufacturers globally, and many of them offer panels with half-cut cells. Here’s a partial list of solar companies popular in the North American market that have half-cut solar panels in their product lineup:
- Canadian Solar
- Hanwha QCells
- JA Solar
- REC Solar
- Trina Solar
This is not a complete list, so check your favorite manufacturer to see if they offer half-cut cells.
Are half-cut cells worth it?
Compared to some other technologies used to increase solar cell efficiency, half-cut cells don’t rely on exotic materials, but a change in manufacturing process. While this does add complexity and expense, the large number of manufacturers offering half-cut panels suggest that the cost-benefit may be worth it.
Manufacturers also combine the half-cut approach with other technologies. For example, several manufacturers offer solar panels that use half-cut PERC cells, combining two technologies to push panel efficiency higher.
Should you use half-cut solar panels for your project? There is perhaps a small risk of increased manufacturing defects, but solar panel manufacturing across the industry is generally very good, and that’s especially true for the top tier solar manufacturers listed above. Because of that, the downside risk of half-cut cells is probably minimal.
In exchange, you get a solar panel that may perform noticeably better in shaded conditions. If a shady roof is something you’re contending with, half-cut solar panels would be a good choice.
Are half-cut cell modules the future? (PV Magazine)