Strength in numbers: How half-cut solar cells conquer the market

Half-cut cell technology was introduced by Norwegian brand REC in 2014. The European company called their new panel line Twinpeak. The first model was polycrystalline, but the new design made it powerful enough to compete with naturally more efficient monocrystalline panels.

Since then the technology has been adopted by other manufacturers: Trina Solar, Panasonic, Q CELLS, Certainteed, Mission Solar all use half-cut cells. Experts from INRPV (International Technology Roadmap for Photovoltaic) expect the share of half-cell solar panels to increase even further: from around 20% in 2020 to more than 60% in 2030.

The engineers build upon their success with half-cut cells and test how far they can go using the same idea. Trina Solar started making large 210mm square cells that are split into three pieces. This format is used for high-output panels that reach 600W in power. Some study the possibilities of splitting cells in four, five, six sections, but so far these projects haven’t turned into the market product.

To make a half-cut cell solar panel, engineers split a standard solar cell in two smaller ones with a laser. It’s tricky, because a solar cell is fragile by itself and it’s often paired with Passivated Emitter Rear cell technology. PERC makes a cell more efficient but more complex as well. What we get in the end are 120-cell and 144-cell panels that are the same size as traditional 60 and 72-cell ones.

Since cells are smaller, the space between them doesn’t have to be as wide. It gives room for engineers to split the whole module in two smaller ones, just like REC did with Twinpeak. You can think of a split cell panel as two modules that are encased together and are wired in parallel. But what are the benefits of splitting the cells and panel in two?

When engineers cut solar cells in half, the current is also divided by two. The resistance decreases, resistive losses fall, which results in more electricity produced. Higher output per square foot means that panels with half-cut cell design can reach higher in wattage. This is why half cut cell solar panels are a good choice for mobile solar installations, like an RV or a boat system, since space is typically limited there.

Making cells smaller increases their durability. Therefore the half-cut cell panel is less susceptible to microcracks compared to the original design. It is also better protected against hot spots development. As a result, a split cell solar panel is more likely to outlast a traditional one and energy losses caused by cracks are also going to be lower.

Panel of a standard design usually has three bypass diodes which split the module into three strings. When one solar cell gets shaded, the performance of a whole string goes down, because cells are connected in series.

Half-cut cell design means that there are two independent halves in one panel and suddenly you have six strings instead of three. Let’s say, we have two 330W panels, one has 60 cells and the other has 120 cells. One shaded cell would lower the performance of a first panel by up to 110W while in the other one the performance would only go down by 55W maximum.

The advantages of split cell design are impressive, but what about the downsides? Well, these panels are more expensive than traditional ones, because manufacturing costs are higher.

• Splitting solar cells with a laser is a delicate process. You need precise and quality equipment plus skilled employees to perform the task well.
• To make two sides of solar panels independent from each other, manufacturers make smaller and multiple junction boxes. That, of course, drives the costs up by a bit.
• More busbars are added for better cell connection. Again, you need precise equipment for this kind of job since cells themselves become so much smaller. Recently, some manufacturers replaced ribbons with wires, because ribbon busbars slightly shade a cell. Trina Solar is the pioneer of multi busbars technology.

Aside from higher price, the compatibility with microinverters is also at question, and you should check this detail before the purchase. Older microinverters were designed to be paired with 60 or 72-cell panels and not all of them can be connected to half-cut cell modules. Modern models, like Enphase IQ8, work with half-cut cell panels just fine.