Choosing the right large-size module to optimize lifetime returns
By Chengjiang (CJ) Fu and Hongbin Fang, LONGi Solar
Wide format modules are the “big” topic in the industry right now because they can deliver big results. On the face of it, the higher the power each module produces, the greater the cost savings for utility-scale projects, with benefits ranging from lower system costs (BOS) to lower installation costs. But there is a reason that the three largest module manufacturers – LONGi Solar, JinkoSolar and JA Solar – are pushing for the “large”, 1.13 m wide module, instead of the “oversized”, which are larger than 1.20 m wide . If you look beyond the module cost and power to the cost of the lifetime system, it is clear that the 1.13 m module (with 182-mm/M10 wafers) is the most cost-effective solution to maximize lifetime efficiency. to optimize.
Why is bigger not always better? BOS savings generally increase as module power increases, but only to certain levels before other factors act to reduce the savings or introduce additional reliability risks. In terms of reliability, transportation, handling and full system costs, large modules outperform extra large modules (with 210mm/G12 wafers). Large format modules are not just an intermediate solution to achieve larger, more powerful module sizes, but are instead the optimal choice for balancing 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 is becoming a necessity. The reliability of the module throughout the lifetime of PV projects is important to ensure consistent energy yield and return on investment for all PV projects.
As we deal with extreme weather much more frequently, module reliability is becoming increasingly important to ensure long-term efficiency. Increasing precipitation, storms with higher wind speeds and extreme heat are putting pressure on the modules. If we analyze only two of these elements – wind and static load – we see advantages of large format modules compared to the extra large modules.
In wind tunnel tests conducted by LONGi Solar and TÜV Nord, large modules experienced less acceleration during the change of wind speed and less vibration amplitude at constant wind speed. These results can be attributed to the greater structural stiffness of the large module, which means more energy is required for wind-induced module vibrations, a lower risk of failure and ultimately better reliability. In wind tunnel tests with threshers, large modules passed the test when wind speed steadily increased to 134.2 mph, while oversized modules failed with deformed and broken screw holes with bolts at only 100.7 mph.
Perhaps the most convincing test results come from the static load tests performed by LONGi Solar on both monofacial and bifacial modules. When -2,400 Pa pressure was applied to the large and oversized monofacial modules, the cracks of the oversized module were nearly six times larger than those of the large modules, even with reinforcing ribs installed on the back of the oversized modules. In the same test with two-sided modules, the deformation of the extra-large module was 65% greater than that of the large module.
With oversized modules you can certainly carry more watts per shipping container, but with a risk to the modules. Taking into account the height of the container door and suitable accommodation for unloading the forklift, the maximum module width is 1.13 m. In fact, the dimensions of the sea container were the driving force behind the optimal design of large modules. Oversized modules simply won’t fit in a standard shipping container using the vertical double stacking technique – an industry best practice.
It is possible to place larger modules in standard shipping containers using other loading methods, such as flat landscape and vertical portrait stacking, but both methods have drawbacks. Flat, horizontal packaging increases the risk of bursting and vertical upright packaging increases the risk of falling because the packaging is too high and may require a large counterweight for crash bars.
The weight of the container is also a consideration. The double glass that is part of the design of the bifacial module significantly increases the weight, not to mention the added surface area for possible micro-cracks. A 40-ft container completely filled with oversized, two-sided modules will exceed the weight limit on US highways and add restrictions and additional costs to transportation.
Using the vertical landscape packaging method with large modules minimizes module damage during shipment and ensures that the container does not become too heavy.
There are also advantages to handling a large module over an oversized module. A large side module can be safely carried by two people, but the oversized module size and added weight pose a risk when handling the module.
When two people lift an object, the general rule is that its weight should not exceed two-thirds of the total sum of their individual lifting capacities. Large modules weigh 71.2 lbs, which is less than the maximum weight limit of two people (73.4 lbs) according to general industry practice and the Health and Safety Executive (HSE). Oversized modules, on the other hand, weigh 77.8 lbs or more, which exceeds the HSE maximum limit. The added weight leads to increased installer fatigue, increasing the risk of damage to the module and personal injury. Likewise, the width of oversized modules further increases fatigue.
Oversized modules do not necessarily reduce module-level costs due to higher wafer and module bill of materials (BOM) costs. At the system level, you can achieve lower overall costs with large-sized modules, taking into account cable and tracker costs.
For cable, the total cost is lowest when the module current is between 14 and 15 A, which is the working current of the large two-sided module. The cable cost decreases as the maximum working current of the module increases with a decreasing slope, but the resistive cost increases linearly as the maximum working current of the module increases.
And with trackers we are tied to the length of the tracker. With a 1P tracker, oversized modules reduce the number of strings from three to two, meaning the total power of a single tracker is lower and the cost per watt is higher. With a 2P tracker, oversized modules will reduce one set of modules. The total power carried by the tracker will be equal to that of a large module, but there will be a series of modules placed on separate sides of the main shaft, leading to a loss of power due to a mismatch.
Larger modules create exciting opportunities for utility-scale projects to achieve lower BOS costs and improved levelized cost of energy (LCOE). With limited strength when using the same 2+2mm glass or 3.2mm glass + backplate, the module size cannot expand infinitely without sacrificing reliability performance. Choosing large modules can reduce reliability risk and overall cost, while still achieving impressive power.
So what’s next for the innovation race? We cannot keep increasing modules in size without compromising reliability and long-term cost savings and benefits. Module manufacturers need to refocus on module efficiency and field performance to increase power, help customers achieve lower BOS costs and lower LCOE, and move us closer to our climate goals.
Chengjiang (CJ) Fu is the director of technical services and Hongbin Fang is the director of product marketing at LONGi Solar.