Residential solar installers have always had to deal with slight size variances among solar panel brands. Even when the industry was generally working within the same 60-cell footprint, one brand’s bordering white space on a solar panel may be larger than another’s, but only slightly. Today’s competing wafer camps (M10’s 182-mm wafer vs. G12’s 210-mm wafer) provide a wider pool of differing panel sizes for installers to sift through. When the end goal is generating the most energy in the smallest area, installers today have more options than ever for best-fit arrays.

Qcells, the most popular residential solar panel brand among the 2024 Top Solar Contractors class, has designed its current residential module based on energy production, BOS and racking compatibility and logistical efficiency instead of conforming to the previously established 60-cell standard. This has led the company to default to 54-cell designs for the residential market using the larger M10 wafer. The company’s latest Q.TRON BLK M-G2+ panel is 4 in. wider than the older 60-cell panel.

Comparatively, popular residential brand REC has transitioned to the G12 wafer and only uses 44 full-sized cells in its residential line. The REC Alpha Pure-RX panel is 6.5 in. wider than the company’s last 60-cell design.

Those extra inches on each module means installers have to be more creative with designs to optimize roof space. Matt Wrightsman, customer training manager for design platform Aurora Solar, said local safety requirements shouldn’t be overlooked when layouts are creeping closer to the edge.

“With modules getting larger on roofs, it’s more important than ever to pay attention to fire code setbacks and fire pathway requirements,” he said.

Robert Santoleri, president of Pennsylvania installer TerraSol Energies, said larger panels are making it more difficult to meet setbacks while maximizing space, but his company has found success with specific brands.

“I like the REC [line of panels] because they are actually shorter and wider, closer to square,” he said. “While this is still to be determined if it is ergonomic for installers to handle a 48-in. wide panel, it is better for design. We can maximize southern roof exposures with more panels in portrait.”

Even though large-format panels are also larger energy producers — both the Qcells and REC updated modules produce 100 W more than their older 60-cell variants — customers aren’t necessarily choosing fewer panels to more easily meet certain system sizes. TerraSol has found that it’s all about maximizing roof space. Last year’s average system size for the installer was 11.6 kW, while the average is pushing 12.5 kW in 2024.

“For most homeowners, if they have more space available on their roof, they are taking more panels,” Santoleri said. “Most homeowners are either planning on electrical upgrades to their house or are aspirationally looking at an EV purchase in the next year or so. They want to plan ahead for more electric usage.”

For customers wanting to expand existing arrays or replace outdated panels, a formerly simple swap-out can be difficult now with panel manufacturers focusing only on their large-format designs. Qcells said retrofitting an old 60-cell module-equipped residential array is not ideal with the company’s current module offerings, as “there are both physical and electrical factors that deem this both uneconomical and inefficient.” The easiest route is replacing the old system with a whole new array or updating a small section, said Michael Jimenez, technical sales and warranty claims manager with REC Americas.

“This can be a bit tricky, but there are suitable solutions when this scenario is encountered,” he said. “Typically, the newer modules are added to either a new sub-array or at the end of the existing array. This depends on the existing racking type and availability of roof space, among other site-specific attributes. In some instances, homeowners opt to replace an entire string to either accommodate a traditional string inverter or for aesthetic reasons. Regardless of the need to retrofit existing arrays, there are solutions available.”

Santoleri has concerns about the wide range of panel sizes now used in the residential market. Designing an array is one thing — especially as design programs like Aurora continue to input the latest models into its platform — but installing bigger, bulkier panels every day could eventually impact worker retention and safety in general.

“We do the best we can with tie-offs and ergonomic tools to handle larger and larger panels, but there are limits,” he said. “It is my job as an owner that cares about my employees and clients to try and advocate for change. It’s up to installers to choose manufacturers that at least may be able to change in the future. I like high-performing companies [that also] seem to have limits when it comes to panel size.”