Module Size Does Not Determine Efficiency, Safety in PV Plants

As the solar industry continues to innovate, bigger no longer means better when it comes to a key component in solar technology: modules. Module research is targeting efficiency improvement in solar installations alongside performance.

“The idea that the bigger the better is not correct,” said Judy Chen, Product Marketing Manager at LONGi Solar. Instead, module innovation should be based on reducing the Levelized Cost of Energy (LCOE) from 300W to 550W, hence the driving force is to reduce the cost of PV modules or the Balance of System (BOS) cost of PV power plants.

 “Oversized modules do not reduce cost but, rather, they introduce obstacles to the transportation and manual installation of the modules, resulting in a significant decrease in module reliability under extreme weather conditions. Excessive current also affects the efficiency and power generation performance of the modules, which is not beneficial for the reduction of LCOE,” added Chen.

Based on the new build capacity and the entire industry chain, the M10 wafer size has been introduced to standardize the manufacturing and application systems. It also realizes the reduction of module manufacturing costs and system BOS costs. After a thorough analysis of module manufacturing and deployment processes, the optimal module dimension was determined and a corresponding wafer/cell size of 182mm was deduced. These dimensions include considerations regarding production feasibility and cost, module reliability, system compatibility, transportation and installation.

There is a correlation between module efficiency and the BOS cost of PV power plants. Under the same efficiency, the BOS cost is reduced by increasing module power considering three aspects: the cost savings of racks (including pile foundations) due to long racks, the cost savings of DC cables due to high string power, and the cost savings of installation.

“Larger module size emerged to improve production efficiency and save cell manufacturing costs; however, but it is wrong to increase the size of the product infinitely,” said Chen. Since the G12 module was introduced in early 2020, cells’ efficiency, yield and silver consumption have performed to a lesser degree than mainstream M6/M10 cells. “In comparison, the non-silicon cost of M10 cells has more attractive advantages,” continued Chen. Regarding the cost of wafers, theoretically, the thickness of the G12 wafer needs to be increased due to the large area. In 2021, the G12 wafer was 5mm thicker than the M10 wafer. In 2022, the significant reduction in the thickness of the G12 wafer brought potential risks to the modules’ reliability. Moreover, the yield of M10 wafers was also higher than that of G12 wafers, showing that M10 can reduce costs during the manufacturing process.

In terms of reliability, the key factors that determine the mechanical properties of PV modules are glass thickness and strength. The secondary factors are the thickness of the B side of the frame as well as the frame design. For the mono facial (3.2mm) module and bifacial (2mm+2mm) module with a 35mm B-side frame, excellent mechanical properties are maintained by optimizing the frame design when the module area is increased from 2.2m2 to 2.6m2(M10 module). However, with the same design, it is difficult to guarantee the reliability of oversized modules with an area of more than 3m2 (G12 module) due to the excessive size and the decrease in glass edge strength.

To avoid damage to the module during transportation, landscape packaging in wooden boxes is commonly used. For the M10 module, the height of the two wooden boxes is close to the door height of a 40-foot-high cabinet. The M10 modules’ width is 1.13m, leaving a 10cm margin for forklift loading and unloading. In contrast, due to their higher width, G12-60c and G12-66c modules are placed flat in wooden boxes. This position leads to a high damage rate during transportation. As the two-pallet landscape package is not feasible in the container and the package exceeds the 4m height limit for Chinese land transportation, G12 modules can only be transported through the portrait package.

Safety also represents a challenge when transporting bigger and heavier modules. In a project in Zaozhuang, Shandong Province, China, workers were injured by portrait-packaged modules as they tried to transport the modules to the installation. The heavier weight is also a challenge when installing the modules. During the process, the maximum weight carried by one person should not exceed 25kg. The maximum weight for two people should be 33kg considering a coefficient of 0.666. The weight of the M10 module is less than 33kg. However, bigger modules carry excessive weight that will cause fatigue among workers, reducing installation efficiency and significantly increasing the installation damage rate.

The current of the G12 module is 30 percent larger than the M10 module. The high current leads to a higher operating temperature of the module. This difference is even more relevant when the irradiation and the environment temperature are high. Therefore, G12 modules are especially not suitable for areas with rich light resources and high temperatures in daytime, in places such as Western China, the Middle East and Africa, Australia and Mexico.

Similar to half-cell versus full-cell, M10 modules have lower power generation in low light conditions and higher power generation in strong light conditions compared to G12 modules. The power generation under strong light accounts for a high proportion of the total power generation. This is why M10 modules have more advantages in outdoor power generation performance. In areas with general irradiation, the power generation advantage of M10 modules is 0.5~1 percent. In areas with good irradiation, the advantage of M10 modules is 1~2 percent or even higher. Meanwhile, for utility projects, M10 modules have advantages in large-scale ground power stations and mountainous terrains. An appropriate M10 module size allows flexible matching of racks. For Distributed Generation (DG), M10 modules are suitable for industrial and commercial roofs.

If large size and high current are the technical trends, 158.75mm, and 166mm wafers do not need to be cut in half, and 112 and 120 cells modules can be manufactured to achieve 700W power or even higher current and string power. However, excessive current will cause high heat loss and reduce the efficiency of the module. The high operating temperature of the module also reduces the power generation performance. “Such a simple increase in power by enlarging the size is not a great innovation. A reasonable analysis of the value and risk of size increase is beneficial for the whole industry,” explained Chen.

In 2022, M10 modules accounted for 81 percent of total winning bids between January and May, establishing themselves as a market benchmark in China. Based on the latest version as of August 2022, PV InfoLink has also made major adjustments to its shipment forecasts for 2022: the market share for M10 products is projected to increase significantly, to58 percent, while G12 is forecast to decrease to 24 percent.

BOS savings generally increase as module power escalates but only to certain levels before other factors kick in to diminish the savings or bring additional reliability risks. In reliability, transportation, handling and full system cost, M10 modules outperform G12 modules. M10 modules are not just an interim solution to reach larger, more powerful module sizes but instead are the optimum choice to strike a balance between system cost and reliability.

Modules and solar systems are built to last 25 to 30 years, or even longer, and performing well against extreme weather conditions becomes a necessity. Module reliability in terms of performance throughout the lifetime of PV projects is important to ensure consistent energy yield and return on investment for all PV projects.

Mexico is considered among the countries with one of the richest solar energy resources in the world, with an annual average daily level of solar radiation higher than 4.4 kWh/m2. LONGi's M10 modules can take advantage of power generation under conditions of high irradiation. Some projects in Mexico also have complex terrain, therefore, M10 modules can take advantage of flexible installation to save costs.

“When we look beyond the module cost and power output to the lifetime systems cost, it is clear that the 1.13m, M10 module using 182mm wafers is the most cost-effective solution to optimize lifetime returns. All the conditions above make LONGi’s M10 module the best choice for solar projects in the Mexican market,” said Chen.