DNV puts different module formats to the test

The introduction of new wafer formats has driven a rapid increase in both the size and power rating of modules, and significant variations between the products on the market have created challenges for component designers, and left system designers scratching their heads over which is the best module format for their project.

Though standards are emerging to simplify this process, there remain two wafer formats on the market – 182mm and 210mm – and significant differences between PV modules based on the two. These two formats have divided the manufacturing, with both enjoying backing from major players. And while there is likely space in the market for both formats for the time being, gaining a better understanding of how each performs in the field, and the further optimizations that might be needed to get the most out of this new generation of larger modules.

Longi Solar Technology, currently the largest module maker in the world by production capacity, and a key backer of the smaller 182mm wafer format, engaged energy consultancy DNV to conduct a cost comparison for the balance of systems components in three different layouts, and testing 72 cell modules based on the 182mm wafer against 55 and 60 cell modules built with the larger 210mm format.

All modules in the comparison used half-cut cell and multi busbar interconnection. The following table shows the power ratings, dimensions and other characteristics of the modules in the comparison.

Cost comparison

The modules were tested on single axis trackers, two-in-portait fixed tilt, and four-in-landscape racking systems. DNV produced cost calculations for each based on its own experience as well as quotes from equipment suppliers, industry research and ‘typical cost’ estimates for specific parameters provided by market research firm Wood Mackenzie.

For each scenario, DNV made calculations based on a 3.7 MW system located on a flat, rectangular piece of land in Texas. Central inverters were used for the comparison, and number of modules per string calculated based on the maximum voltage of the modules and the inverter.

In all three scenarios, the 182mm module pencilled out at a balance of systems cost slightly lower than the 210mm modules. The cost calculations are provided in the table below.

Same in the end

DNV downplayed the differences in cost between each scenario. “There is little variation in overall prices within each scenario, meaning the module choice has little effect, but it can be seen that certain racking configurations lead to different overall prices,” the company stated, noting that the variation in two string versus three string trackers did produce a noticeable cost difference.

Longi, meanwhile, was keen to note the positive result 182mm products “…under fair and practical boundary conditions of module power, capacity ratio, racking length, selection of electrical equipment and manual installation costs,” reads a statement from the company reviewing the results of the comparison, “the adoption of over-sized modules with an ultra-high current does not show advantage in BOS cost savings than 182-72c modules, as module efficiency is still the critical factor in BOS costs.”

Longi went on to state that DNV’s comparison only takes in BOS costs on the DC; and that there could be further savings possible in the AC system and grid connections lines. “In reality, in the case of large power plants, land resources will usually be fully utilized to maximize installation capacity, meaning that 182 modules will represent a larger capacity (about 2 ~ 3%) with higher module efficiency,” Longi’s statement concludes. “[this means] potentially saving on project development cost per watt and costs arising from booster stations and outgoing utility lines on the AC side, further strengthening the 182 module's potential superiority in overall value.”

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