The long read: A limit to PV module size

From pv magazine 12/2021

Large format modules have gained market share but face a number of hurdles, including shipping, comparable efficiency rates, and balance of system (BOS) considerations. What is the key to Longi’s strategy regarding the trend to high power?

Hongbin Fang, director of product marketing, Longi Solar: The 182 mm wafer and cell size is the optimal dimension arrived at after thorough analysis across the whole cell and module manufacturing processes. We believe this is also true relating to the module deployment processes, including shipping and installation – it is the maximum wafer/cell size with conventional six row stringing within each module that still fits 40HC containers using the current best-known method of shipping modules: double stacking of pallets inside 40HC and landscape packing of modules within each pallet.

With module voltage kept the same as previous smaller format modules and current only modestly higher, only minor adjustment is required on downstream BOS equipment to make them compatible. We have worked diligently with various BOS component partners to ensure compatibility. Based on this, Longi believes the 182-72 cell module is the optimized solution for utility projects. That has helped our customers to reduce BOS cost and achieve significantly lower LCOE.

You’ve mentioned voltage and logistics, but what about modules installed in the field. Why do you believe that the 182-72 cell format is better than larger modules, some of which are now up over 600 W?

PV projects are designed to work reliably for 25 to 30 years. But extreme weather conditions are becoming more and more common, and we need to include sufficient margins in our system and component design, so that the whole project can survive extreme weather conditions and perform well throughout their lifetime. With the same efficiency, higher power modules require a larger footprint, which creates challenges for deployment and increases reliability risks. For example, under the same mechanical load, 40% to 60% higher deformation is observed on 600 W and plus modules compared to 182-72 cell modules, increasing the chance for cell u-crack formation and glass breakage.

Other areas of higher reliability risks include larger shear stress at mounting position under dynamic load, smaller safety margin at junction box, higher resistive loss at connector contacts and lower glass strength due to larger dimensions. In order to fit into 40HC, oversized modules (600 W+) have to adopt vertical loading (portrait orientation) within each pallet, significantly raising the center of gravity and posing challenges during unloading process on unfriendly site conditions.

So, do you believe we have reached the threshold for module sizes?

Using large-format modules to improve power output from each module has been an effective way to reduce BOS cost and improve LCOE in the last couple of years. Analysis has shown that BOS cost has reached a plateau with approach of increasing module size and power without efficiency improvement. At the same time, using the same 2mm plus 2mm double glass construction, increasing module dimensions even further will bring higher risks on reliability, as I’ve already addressed.

At Longi, we think there are significant reliability risks using oversized modules (more than 2.8 m² in area or more than 1.2 m in width). As such, we will not pursue larger module dimension than 182-72 cell format. Instead, we will focus on cell and module efficiency improvement for future technology advancement and bring better value to our customers with higher efficiency modules.

If you won’t go bigger, how do you continue to push up efficiencies?

With significant investment in advanced technology development, the PV industry is progressing nicely on efficiency improvement and cost reduction to bring advanced technology into high-volume production. Our recent announcements showing TOPCon and HJT cell efficiency world records on commercial size wafers are good testaments to recent progress. The market will see more and more advanced high-efficiency technology in volume production in the next few years.

There is an increasing focus on carbon footprints in production. What steps is Longi taking to further decarbonize and green its supply chain, while also addressing module end-of-service issues?

We are in the green energy business and committed to making our manufacturing green. Since 2015, we have intentionally located most of our new ingot and wafer manufacturing capacity in Yunnan province in China and Sarawak in Malaysia, to take advantage of local grids mostly powered by clean hydropower. Longi has also joined the RE100 initiative and is committed to power 100% of our operations by renewables by 2028. To help deep decarbonization, we have also established Longi Hydrogen Company focusing on green hydrogen equipment development.

What two or three measures can Longi take to drive down the cost of solar further?

We truly believe with technological innovations, solar cost will be further reduced. Manufacturing processes in ingots, wafers, cells and modules can be further optimized, and material consumption further reduced, combined with continuous improvement on cell and module efficiency, module cost per watt will continue to drop.

With improvements on cell and module efficiency, higher power is achieved with the same module dimension. Energy yield will also be further improved with the introduction of advanced technology. Both will help to reduce BOS cost and achieve lower LCOE at system level.

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