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China is widely recognized as the world's manufacturing center for photovoltaic modules, shipping to all corners of the globe by sea, road, rail and air.
With factors such as delivery cycle, capacity and cost to consider, sea transport has become the preferred mode for shipping and with this being the case, maximizing container capacity utilization is now a subject receiving great market attention.
1) Packaging methods for photovoltaic modules
Vertical packaging is commonly seen as the ideal method, due to problems with the horizontal stacking alternative.
Vertical packaging solves the three main problems of horizontal stacking, namely module frame deformation, glass breakage and invisible cracks caused in transit, and the vertical landscape solution has become the common choice over the portrait alternative.
2) Maximum size allowed with vertical packaging
Meeting the ultimate objective of reducing the proportion of broken products or products with invisible cracks upon arrival, vertical landscape packaging has a lower center center with the consequent lower risk of modules tipping over during packaging and unpacking, due to its design-for-performance advantage of operational security.
This is the main reason for its preferential status, better meeting the requirements of reliability in maritime transport, packaging stability and safety of the employees involved. According to the door height of a container, the maximum allowable height for ideal packaging can be determined. The logical relationship is shown below:
3) Questions about vertical stacking in portrait mode for large modules
The operating margin for loading and unloading containers is extremely limited, theoretically with only about 7 cm available. Longi's Hi-MO 5 products are designed to have an operating margin of 10 cm for loading and unloading containers.
However, this redundancy in operating height for larger modules in a vertical packaging scenario is reduced to about 7 cm once the height, packaging paper thickness and pallet height are taken into account, which means the total height will exceed 2.5m – and the container door is 2.575m.
Although tightly packaged goods can be loaded and unloaded by skilled workers in a factory environment with equipment such as a loading dock, there are no such facilities available in overseas warehouses or on project sites.
Workers are at greater risk of injury when turning packages that are heavier and have a higher center of gravity. Compared to the weight of the bifacial Hi-MO 5 of 32.3 kg, the weight of a larger module exceeds 38.7 kg, an increase of almost 20%.
Larger modules are also packaged via the vertical method in portrait format, which means the package height will exceed 2.5 m (see Figure 5a). The barycenter height is almost double compared to the Hi-MO 5, increasing the possibility of tipping over and subsequent injury.
Taking an initial tilt angle of 75° as an example, the weight of the largest module is 38.7 kg, with a 31-unit pallet having an overall gravity as shown below:
G = 38.7 × 31 × 9.8 ≈ 11760 N
The pressure on the beveled side of the support:
F = G × cos 75° ≈ 3043 N
The coefficient of static friction between the support and the sand is considered 0.4, with its equilibrium relationship with the horizontal force as follows:
Fmax = (Msupport × 9.8 + F × cos 75°) × 0.4 ≥ F × sin 75°
As per the above, the weight of the support must reach over 660 kg to maintain non-slip status, with the use of a support of this weight in a project with larger modules being a challenge during the construction and installation phases.
The weight of the stand can also be calculated under different tilt angles. The smaller the unpacking angle, the greater the risk of the support slipping.
If an installer is unpacking, the modules can also be turned by the wind reaching the fifth scale when the number to be unpacked is less than 10 units and the tilt angle is greater than 85° (e.g. figure 4.)
In summary, larger packaged modules stacked vertically in portrait orientation are at greater safety risk, with additional limitations in terms of unpacking in ground-mounted PV plants.
During the initial stage of construction of a large-scale ground-mounted photovoltaic plant, care must be taken to position the packaged modules to prevent them from tipping over, which makes traction more difficult on uneven terrain.
Compared to the weight per pallet of Hi-MO 5 bifacial modules, that of the larger modules shows an increase of 20%, resulting in a net weight of over 1.2 tonnes.
For this reason, a forklift or lifting machinery with a large load capacity is required for safe transportation, increasing labor and equipment costs to complete the installation within the construction period. When installing larger modules, there is also the possibility of lower efficiency and a higher rate of invisible cracks.
As shown in Figure 5b, it may be difficult for workers to handle a larger module, needing to place a corner on the ground, with the added concern of exceeding the recommended maximum weight of just under 35 kg for two-person handling (the maximum weight for handling by one person is 20 kg to 25 kg, with the coefficient for two people 0.666, i.e. 25 × 2 × 0.666 = 33.3 kg – see HSL Guide for Weight Limit in Manual Handling).
According to research, the breakage rate of Hi-MO 5 bifacial module is generally lower compared to that of larger modules during installation, while the invisible cracking rate for larger modules increases by more than five times.
In conclusion, LONGi adheres to the proven reliability of vertical landscape packaging solution for its Hi-MO 5 modules, this minimizing shipping costs and making unpacking and installation more convenient for on-site workers.
One Response
Great article. I contracted for the purchase/installation of a photovoltaic kit, with 20 panels of 560 W each, for my home. I try to read everything I can find about solar panels and how to avoid damaging them. What is the MAXIMUM TORSION that modules can be subjected to without damage?