The weekend read: Bigger modules yes, but better…?

From pv magazine 11/2020

For Tier-1 module manufacturers, the switch to larger formats has clear benefits in terms of cost structure – with the adaptation of equipment, they can produce a 600 W module in the same time it takes to produce a 400 W one, effectively increasing their production capacity. The move may also serve to increase market share, leaving smaller producers who lack the upfront cash to adapt equipment to process larger wafers behind, as they are unable to match the power ratings.

While these huge jumps in power rating look impressive on paper, it is often said that there is little innovation behind them – only an increase in size. There is some truth to this – without the increase in size, we’d be looking at increases in the tens of watts range, rather than hundreds. But it was the earlier innovation of half-cut cells that really made this possible. Plenty of hard work has also gone into new interconnection strategies, as well as efforts to reduce the gap between cells to further increase the active surface area.

For manufacturers that have invested in enormous production capacities for PERC cells and modules, there may be few other options open, as new ways to increase efficiency become harder to find, and new cell technologies begin to get closer to PERC in terms of cost per watt. And since this move to larger formats promises to increase energy yield and lower LCOE at project level, it can be argued that it’s as valuable as any other innovation.

Promises, concerns

The manufacturers of these modules promise that it is not only a cost optimization for them. Throughout this year, launches of new modules incorporating 182 mm or 210 mm cells have been accompanied by plenty of fanfare, and promises that the change will lower costs elsewhere in the system design, and ultimately to lead to lower levelized cost of electricity at project level.

First among these is the claim that more powerful modules will bring down costs for the tracker or racking. With the module in the right orientation, the racking system only needs to be made slightly longer in order to accommodate more modules, and more watts per pile.

Another claim common to the majority of new large-format modules is that the combination of cut cells, multibusbar interconnection and “twin” module designs reduces the voltage of the module, again allowing for system designers to fit more energy capacity in the same amount of space.

“The low open-circuit voltage and temperature coefficient of our Tiger module can increase the number of modules at string level,” explains Roberto Murgioni, Head of Technical Service for Europe at JinkoSolar. “And if the DC side capacity of the project is known, the total number of strings in the project can be reduced, which enables power densities of 214 watts per square meter.” Increasing the number of modules per string should in turn serve to reduce the amount of cabling and combiner boxes required, further bringing down BOS costs.

Launching its new Series 7 modules last month, Canadian Solar presented calculations that the new modules, based on a 210 mm wafer, allow engineers to increase the number of modules per string to more than 30. This pushes the power per string up to 20.2 kW, compared with 12.2 kW from a string of around 26 of an older generation Canadian Solar mono-PERC module.

The launch of these modules has also seen several concerns raised over the jump in size. Some have noted that while increasing the size, manufacturers have not made the front glass any thicker, making the module a bit more flimsy. Trina Solar reports, however, that it solved any issues here by strengthening the metal frame, and other manufacturers report their modules are easily able to stand up to the 5,400-pascal mechanical load test specified in the IEC standards. With lower voltage as well comes higher current, leading some to voice concerns over performance degrading hotspots. In response to this, manufacturers point to half-cell and twin-module designs, as well as the smaller gaps between cells, among their strategies to keep the current from running too high. And with smaller gaps between cells – in some module designs the cells are slightly overlapping – better heat dissipation can also help to reduce the likelihood of hotspots forming.

Some have also expressed concern that the sheer size and weight of these modules will cause problems in shipping and for installers. Manufacturers have reported that by packing modules vertically into shipping crates, and exploring other optimizations, they are able to ship high volumes without issue. And on the installation side, Tomaso Charlemont, global solar procurement leader at project developer RES Group, tells pv magazine that the largest of the new PV modules typically weighs in around the 35 kg mark. This is similar to First Solar’s Series 6 modules, which have not caused any major issues for installers since being introduced a couple of years ago.

For engineers and project developers, it’s early days working with these modules. And while many manufacturer claims appear valid, there are more factors at work that will only become clear once we see modules being used in actual projects. Tino Weiss, head of purchasing at BayWa r.e. Solar Projects, says he can see the reduction in cabling costs playing out in the field. Cost reductions on the tracker/racking system are likely as well, but there will be a limit to how much longer/wider you can go without increasing the cost of the structure, he says. And he warns that the increased current might result in a need for higher rated fuses, increasing the price for combiner boxes. “The real question is how much of these BOS savings are eaten up by the module price,” says Weiss. “Ultimately whether you can count on these BOS savings will always be dependent on your system design.”

Large, and then larger

The appearance of larger wafers, and then larger module formats, has seen the industry quickly divide itself into two main camps, promoting either the 182 mm or the 210 mm wafer. Manufacturers are certainly ensuring that new cell and module lines are able to process sizes up to and even beyond 210 mm, but this is viewed by some as hedging their bets against the possibility of having to do a second round of costly upgrades within a couple of years. In terms of actual production plans, the industry appears split between those who view the bigger jump in power output enabled by the 210 mm wafer as a goal worth pursuing immediately, and those who value the more incremental jump to 182 mm as a less risky and disruptive route to higher energy yields and lower LCOE.

In a recent pv magazine Webinar, Trina Solar presented a case study based on 100 MW fixed tilt, 1500 V system, comparing its Vertex module, utilizing 210 mm cells, to a competitor’s module utilizing 182 mm. This showed that Trina’s module allowed up to 36 modules in a string, compared to 27 for the rival, and a 35.8% increase in power per string. And this further cascades down to a reduction of 62 piles, 3.5 kg of steel and 1 kilometer of cabling per megawatt installed.

But bigger changes mean more uncertainty and higher risks. The largest and most powerful of these new solar modules is already requiring redesigns at tracker and inverter suppliers, as well as overall system layouts, for project developers and investors to reap their benefits. While the potential rewards are such that some will surely take the risk, it will take a few years at least for a track record to develop and for such changes to become accepted and understood by more investors.

Meanwhile, modules based on 182 mm wafers still reach power outputs well in excess of 500 W, and in comparison, require only minor optimizations to existing components and plant layouts. “The 182 mm module is the most mature and bankable product,” argues JinkoSolar’s Murgioni. “And it offers guaranteed yield and production capacity for the existing cell and module manufacturing process in the industry.”

In the short term, at least, those working on full systems favor the less disruptive route. Baywa r.e. says that modules deploying 182 mm cells in a half-cut layout appear to be the optimal solution.

Tomaso Charlemont of RES Group also says that without a track record, 210 mm technology would be too disruptive for the company to look at today, although he will not rule it out in the future. “When they tell you that you can make strings of 30-plus modules, the entire design of the project is impacted, e.g., trackers need adjustment and inverters need different fused protection.” he explains. “It involves a completely different layout. That’s not going to happen overnight.”

Charlemont goes on to explain, however, that working with 182 mm modules, RES has already been able to take an existing project originally planned with M6 (166 mm) modules, and recalculate for the larger 182 mm format. And the new calculations have shown capex savings of around $0.01/W.

“You still remain within limits that you can evaluate quickly with the manufacturers of inverters and mounting structures using current solutions. We can take the 182 mm module to an investor and tell them ‘here is a validated number, approved by an independent engineer.’ It is a different module but it is a straightforward implementation,” Charlemont explains. “You can understand why manufacturers are so confident, because they know what we have done is work that is both easy and bankable.”

The move up to 210 mm wafers and modules rated at 600 W and higher, however, is a step into new territory, and some track record of performance will be needed for investors to view systems designed with these modules as bankable. But the industry has already taken notice, and some larger players will likely be willing to take the risk on a new iteration of existing and well understood technologies such as this. Tracker and inverter suppliers as well are working quickly to optimize their offerings to fit the largest of modules, and manufacturers are already reporting sales of both 182mm and 210mm modules, and seem very much convinced that the move will be a success.

For now, whether 182 mm or 210 mm, it appears the larger wafer and module formats are here to stay. Analysts including Wood Mackenzie (see chart on p.34) and PV InfoLink forecast these two sizes to represent around 90% of the market by 2025, with 210mm beginning to gain an advantage in the later years – reflecting the time needed for the new move to establish itself and achieve bankability.