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With the increase in the number of modules being launched in the higher watt-peaks segment of 600 Wp+ and even higher, its important that we assess the empirical evidence and test them on reliability which is really critical for ensuring the long-term performance of the solar systems. Bigger is not always better and therefore it’s critical that we base our judgement on on-ground data from plants.
Below is the white paper, on the Empirical comparison of the energy yield and reliability of the modules in China, where they were tested on strict guidelines and criteria.
- Background and Overview
The long-term developing direction of PV module technology is to improve efficiency and reduce internal losses. High internal losses in the module will reduce power and efficiency on the one hand, and on the other hand will lead to higher operating temperature, affecting the energy yield performance. Therefore, in recent years, the industry has widely used half-cut and multi-grids technology to reduce the current, striving to avoid internal heat losses. The application of these technologies makes it feasible to moderately increase the size of the wafer, but the pursuit of ultra-large current is not the right developing direction of PV evolution.
According to both literature reports and empirical evidence of energy yield of LONGi’s module at the China National Electric Apparatus Research Institute’s Hainan base, half-cut modules usually have a energy yield advantage over high-current whole-cell modules1. And the higher the irradiance and ambient temperature are, the more obvious the energy yield advantage will be. Ultra-large current modules with G12 wafers have a short-circuit current of 18A or even more on the front side, which is expected to have a similar phenomenon in energy yield performance compared to mainstream products. JA was the first to compare the energy yield performance of M10 (which is based on 182mm wafers) modules with ultra-large current modules (both are bifacial modules) at CPVT’s Yinchuan empirical base, with preliminary results displayed in the “Joint White Paper on 182 Module Products “2 and subsequent reports showing M10 modules have energy yield gains of 1.9%3 over ultra-large current modules (February,2021 to August,2021). LONGi has also conducted empirical researches in Xi’an and Taizhou, and the recently obtained data can be confirmed with the above-mentioned studies: M10 modules usually outperform ultra-large current modules in terms of energy yield performance, and the higher the irradiance is, the more obvious the advantage will be.
- Empirical results of Xi’an Zhongsen Power Plant
The empirical power plant is located on the rooftop of Zhongsen Company in Xi’an Economic Development Zone (34.4 °N, 108.9 °E). The empirical work is carried out by a third party, Zhongsen Company, relying on its testing platform, using one of LONGi M10 bifacial modules (Hi-MO 5) and one of ultra-large current bifacial modules. The modules are connected to micro-inverters to achieve MPPT tracking and meters to accurately measure the power generated on the DC side. The modules were exposed to the sun for a week, tested for initial power before starting the empirical test. The installation manner, ground type (gray gravel), and cable length were all kept consistent.
The plant has been in operation since November 17, 2021, and as of the end of February 2022, the average power output of LONGi M10 modules is 2.9% higher than that of ultra-large current modules. As shown in the graph below, the M10 module has a significant advantage on days with high irradiance, whlie the ultra-large current module has a slight advantage on cloudy days with poor irradiance. Due to the long PV cables in this empirical project, excluding the less than 2% difference in line loss, the M10 module generates about 1% more power per watt than the ultra-large current modules.
- Empirical results of Xi’an Taizhou Power Plant
This empirical power plant is located at the base of LONGi Taizhou Product R&D Center (32.5 °N, 120.0 °E), which uses string inverters to compare the energy yield performance of LONGi M10 modules and ultra-large current modules, with four pieces of each bifacial modules and grass on the ground. The Taizhou empirical power plant also uses meters to collect energy yield data on the DC side, which excludes the influence of cable line loss to facilitate the detailed study of the energy yield capacity of the modules.
The empirical power plant in Taizhou was officially put into operation on February 23, 2022. The collected data of the first 10 days showed an obvious regularity: the average energy yield gain of M10 bifacial modules over G12 ultra-large current modules is up to 0.96%. And the higher the daily energy yield and the ambient temperature are, the higher the energy yield gain of M10 modules will be. On March 1, the energy yield of the two modules was comparable at a daily energy yield of 3kWh/kWp.
In order to further investigate the performance of the two modules under each irradiance value, we did a comparative analysis of the single-day power curves of each module in Taizhou. Figure 5 shows the data of different time in a day from March 1, 2, 3, and 5, 2022 (showing 9:00 to 15:00, with 1-minute intervals). Ultra-large current modules outperform M10 modules in the morning when irradiance is low; while when the irradiance reaches 600~700W/m2, the energy yield of both modules is comparable, but the energy yield advantage of M10 modules increases significantly with further increase of irradiance. The energy yield gain of the M10 modules is about 1% when the irradiance is 800W/m2 and about 2% when the irradiance is 900W/m2. While in the afternoon, the threshold irradiance value is around 500W/m2 of M10 modules that are comparable to the energy yield capacity of ultra-large current modules due to higher temperatures. Considering that the irradiance level of these 10 days in Figure 4 is better than the annual average, and the temperature level is slightly lower than it, the estimated power gain of M10 modules in Taizhou power plant is slightly less than 0.96% for the whole year.
Combining the empirical results of LONGi in Xi’an and Taizhou with JA and CPVT in Yinchuan, as well as the comparison of former M2 half-cut modules and whole-cell modules, it can be established that the lower internal losses enable M10 modules to have a clear energy yield performance advantage over ultra-large current modules under normal circumstances, which increases with richer light resources in project ground. It is expected that in regions with ordinary light resources, the energy yield advantage of M10 modules over ultra-large current modules is about 0.5~1%; while in regions with rich light resources, the average daily energy yield of bifacial modules can reach up to 5.5~6kWh/kWp, and the power gain of M10 modules over ultra-large current modules can be 2% or even more.
The empirical results of M10 modules energy yield confirm the assertion in the white paper of ‘LONGi＆JA＆Jinko’: M10 modules are the product that can achieve the lowest cost of electricity after considering the manufacturing situation of the whole industry chain, BOS cost of power station, module energy yield performance and module’s life cycle reliability.
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