Modules with 182 mm wafers are ideal for reducing LCOE in power plants

This article is a free translation, with adaptation and technical revision of the Canal Solar, from the document “Module based on 182 mm wafer: Optimal Module Solution for Achieving Lower LCOE of Utility Photovoltaic Power Station”, signed by the companies JA Solar, Jinko Solar and LONGi. The article presents the advantages of modules with 182 mm wafers over their predecessors (with 166 mm wafers and smaller) showing that this new family of modules provides a reduction in the implementation costs of solar plants.

At the same time, the article argues that 182 mm is the ideal wafer size, as it allows an increase in generation efficiency without substantially changing the dimensions of modules already standardized on the market and without causing radical changes in the other components of the plants (mainly inverters and structures fixation).

On the other hand, the paper suggests that ultra-high power modules based on 210mm wafers would not be as advantageous. In these modules, the increase in power is accompanied by an increase in mechanical and electrical dimensions, which requires adaptations at all levels (from the mounting structures to the inverters), in addition to the presence of more fragile mechanical characteristics.

Background – size evolution of silicon photovoltaic wafers

Basically two aspects need to be considered when analyzing the evolution of the size of silicon photovoltaic wafers: (1) the influence of the wafer size on the cost of the module production chain and (2) the influence of the wafer size on the module size, on the electrical parameters and module application mode in photovoltaic systems.

In the past, photovoltaic cells were similar to the wafers used in the manufacture of electronic chips and equipment and process costs were relatively high. Increasing wafer size can significantly reduce cell manufacturing cost. With the maturation of the photovoltaic industry, currently the cost of manufacturing a cell is about US$0,03/W, dozens of times lower than the cost of primitive cells.

At the same time that the size of the silicon wafer and the cell evolved, going through variations M1 (156,75 mm wide wafers, obtained from 205 mm diameter ingots), M2 (156,75 mm wide wafers , obtained from 210 mm diameter ingots) and M4 (161,7 mm wide wafers, obtained from 211 mm diameter ingots), among others, the wafer thickness has become increasingly smaller.

In the industry, after the standard silicon wafer size remained stable at 156,75 mm for several years, G1 (158,75 mm wide, ingot diameter 223 mm) and M6 (166 mm) versions have recently emerged wide, ingot diameter 223 mm). On the one hand, these slightly larger wafer sizes are compatible with older solar cell and glass production lines, allowing for immediate cost savings.

Furthermore, the module size increases by less than 10% and the original M2 module can be replaced in all applications. The BOS (balance of system) cost can be maintained to a certain extent while design conditions remain unchanged on the system side (i.e., if the increase in wafer size and module power allows the use of the same power plant components solar panels, without changes).

With the rapid expansion capacity of the photovoltaic industry's production chain, manufacturers began to consider other sizes of wafers, not being bound by the limitations imposed by existing manufacturing plants, being able to update their production lines to manufacture larger modules. dimensions.

In short, manufacturers decided to update their production lines, bearing the necessary costs, to produce a new paradigm of photovoltaic modules with large wafers, taking the photovoltaic industry to a new level — breaking with previously existing barriers to increasing power. of photovoltaic modules.

Some manufacturers have introduced the 12” G12 silicon wafer (210 mm wide, produced from 295 mm diameter ingots), aiming to further reduce the cell manufacturing cost and system cost through the module manufacturing strategy. high power, with increased physical dimensions.

However, the reason for using the M10 wafer (182 mm wide, obtained from 247 mm diameter ingots) is that the manufacturing cost of the photovoltaic cells is not the main factor to be considered for changing the size of the modules. ; The constraints encountered in the design of photovoltaic systems and the application of photovoltaic modules must be comprehensively considered, so the size of the silicon wafer must be determined from the ideal size of the photovoltaic module.

Learn more: What is LCOE and how to use it in photovoltaic projects?

After an in-depth analysis of the entire production chain (manufacturing, transportation, installation, power generation performance and system suitability), it is concluded that modules based on the M10 wafer (182 mm wide) are a good option for reducing of costs in the market.

Conditions that affect the size of modules

Packaging and shipping

Photovoltaic modules are generally packaged vertically in landscape orientation to ensure stability and minimize damage during transportation. If placed horizontally in packaging, the weight and vibration during transportation will likely introduce microcracks and damage the modules.

If packaged vertically in portrait orientation, stability is compromised and the risk of tipping is much greater, posing significant challenges when unpacking. In 40ft containers (40HC) commonly used for international shipping, double stacking of pallets is a common practice, therefore the height of two module pallets cannot exceed the container door height of 2,57m.

Furthermore, considering the surface undulation at the project site, it is necessary to leave about 10 cm of operating margin for forklift unloading, and the width of the modules is limited to about 1,13 m. Under these conditions, modules with the typical six-cell row layout have the wafer width limited to 182 mm.

Handling and installation of modules

Within a certain range, the size and weight of PV modules can be increased to reduce handling and installation costs per watt. Beyond a certain limit, manual installation will become more difficult as workers will be prone to fatigue and the rate of breakage during installation may be significantly increased.

The width of older PV modules used to be around 1 m and installers could hold the modules with open arms. After the width is increased to about 1,13 m, two people can still move them safely on level ground. However, the width of the module must not be increased further to ensure stability during handling.

The weight limit for repetitive handling by a single person is approximately 20-25 kg, and the weight limit for two people is not simply multiplied by 2, but the coefficient of 0,666 needs to be considered, that is, the weight limit for handling by two people is: 25 kg * 2 * 0,666 = 33,3 kg < 35 kg. For this reason, the weight of the module must be kept as close as possible to 33,3 kg and the maximum weight must not exceed 35 kg.

The 72c-182 double-glass bifacial photovoltaic module (72 cells of 182 mm) weighs about 32 kg, which can be easily handled and installed by two people in almost all scenarios except rugged mountainous regions, thus saving the cost of labor. manpower compared to the more traditional 72c-166 modules (72 cells of 166 mm).

Module mechanical load capacity

The main factor that determines the mechanical load capacity of photovoltaic modules is the glass, followed by the frame. In consideration of module cost and weight control, the glass thickness of double-glass bifacial photovoltaic module is preferably 2mm. On the premise of double glass structure (2mm + 2mm) and reasonable control of structure cost, the module size must be within a limit, otherwise its ability to resist static and dynamic loads will be seriously weakened.

Under laboratory testing and outdoor application conditions, structure damage, glass explosion and large amounts of microcracks are likely to occur, leading to excessive degradation of the module's power during its service life. Based on theoretical analysis, the module with a 182 mm wafer is within the safe load limit (the image in Figure 3 shows the simulation of mechanical stress of the structure under load of 5400 Pa).

Obviously, increasing width leads to a greater increase in mechanical stress than increasing length. Under a static load of 3600 Pa, when no beam is installed at the rear, a 1,13 m wide module has smaller deformation, and the power degradation of the module is less than 2%. Therefore, from the perspective of risk control of the return on investment of the photovoltaic power plant, the module size, especially the width, should not be increased further.

Product Profile

Dimensions, weight, electrical parameters

Based on the above analysis, and considering the limitation of module size and weight, the same assumptions can be applied to half-cell modules also employing 182mm wide silicon wafer. The area of ​​182mm (M10) silicon wafer is 330,15cm², which is 20,4% larger than the area of ​​166mm (M6) wafer, which is 274,15cm².

Thus, we can see that the area, weight and electric current of the module are increased correspondingly. Typical parameters of 72-cell modules with 182mm and 166mm wafers are listed below:

It can be seen that the module with 182 mm wafer offers an optimal solution for large-scale photovoltaic power plants due to its relatively reasonable size and weight.

Mass production

The 182 mm wafer module is a standard size module, which has the advantage of increasing power without radically changing the final dimensions of the product, presenting itself as a game changer in the industry after breaking the barrier of wafer modules 166 mm, or for many years dominated the market.

By the end of 2021, manufacturers LONGi, Jinko and JA each plan to establish at least 30 GW of 182mm cell and module production capacity. The total capacity of 182mm wafer modules will exceed 100 GW for the entire industry by the same time. The first batch of 182mm wafer modules was mass-produced and shipped in the fourth quarter of 2020. The maturity of the industrial chain has been maintained with module size variations of less than 20%.

The 182mm silicon ingot and wafer have the same manufacturing yield found for the 166mm wafer; the conversion efficiency of the 182mm cell also reaches the same level as the 166mm product; the mass production power of 182mm modules is 535Wp to 540Wp, and the load capacity and hot-spot temperature of the modules are all within the safety zone.

Industrial chain compatibility and product standardization

The 182mm wafer module undergoes some changes in size and output current, which sets new requirements for manufacturing components. In terms of bill of materials, there is not much difference in terms of glass and encapsulants; due to the current increase of about 20%, the 182mm bifacial module uses a junction box with a rated current of 25A (the junction box uses 3 large bypass diodes), which maintains a sufficient safety margin and fully guarantees reliability under long-term operation.

Regarding the design of solar plants, the main issue revolves around the choice of the combination of inverter and single-axis horizontal tracking system. Considering a gain of around 15%, bifacial modules with 182 mm wafers that have an Imp current of 13 A require an inverter with an input of 15 A per string, which can be achieved with small adaptations to the inverter designs, without the need to resize the power electronics modules. The products remain backward compatible with 166 mm or smaller modules, thus avoiding the risk of sudden and structural changes in the market.

The length and width of the 182mm wafer module are increased by only about 9%. A tracker can support modules with the same number of strings with only a slight structural reinforcement. Increasing the total power of the modules can reduce the support cost per watt. Currently, the mainstream 1-panel and 2-panel trackers are compatible with the 182mm wafer module.

As described in section 2, it is not advisable to apply wider modules on the tracker (especially the 2-panel tracker) due to the risk of module deformation under wind load and power degradation due to micro-cracks in the cells.

Values ​​on the photovoltaic system side

The BOS (balance of system) savings made possible by high-power modules are mainly associated with 3 aspects:

1. Larger supports are adopted to maximize the total power of photovoltaic modules supported on the same support, in order to reduce the costs of pile supports and foundations per Wp;
2. The total length of the photovoltaic cables that connect the photovoltaic strings and the string-boxes (or inverters) is reduced as the power of the strings increases;
3. The module size is enlarged moderately to reduce labor cost.

For a solar power plant installed on very rough terrain, the length of the structural elements is limited and it is difficult to transport large modules. Therefore, the module with 182mm wafer is preferably applicable on relatively flat terrain. The cost of the solar power plant can be greatly reduced by using longer supporting structural elements and optimizing the pile spacing.

For fixed supports, the length of structural elements should be limited to around 120 m due to thermal expansion and contraction of the steel. The 182 mm wafer module is compatible with designs that employ two rows of vertical modules (2P) and four rows of horizontal modules (4L), and can adapt to different terrain conditions by adjusting the number of strings mounted on a single support. Typical 2P fixed support length is shown in the following table (calculated with 26 modules with 182 mm wafer per string):

Similar to fixed-tilt structures, there is a restriction on the length of the trackers. Further increasing the module size and string power will reduce the number of strings in a single tracker, which cannot improve the total power supported by the tracker and therefore cannot reduce the cost of the tracker.

In terms of cabling cost, as shown in Figure 5, with the increase of module current and string power, the cost of 4mm² photovoltaic cable is slowly and gradually reduced. However, the cost due to cable power loss increases almost linearly.

Taking these two costs into consideration, the ideal current is about 14~15 A, that is, the working current of the 182 mm bifacial module. Furthermore, the cable cost will be further reduced if two strings are combined in parallel and then connected to the string-box (or inverter) by a 6 mm² photovoltaic cable.

In terms of labor cost, as described in section 2, there is a limit to the weight of the PV module when it is handled and installed by two people. Furthermore, workers are prone to feeling tired after long hours of work — therefore, work efficiency will be reduced and the rate of module breakages will be higher if the module dimensions are too large.

Based on the above analysis, the BOS cost of a solar PV plant was compared and analyzed under various conditions. The results verified by TÜV NORD are as follows:

Conditions in the table below: wind pressure 0,38 kN/m² [25 years], 0,45 kN/m² [50 years]; snow pressure 0,21 kN/m² [25 years], 0,25 kN/m² [50 years]; inclination 34°; the lowest point of the module is 1,5 m above the ground; the cost of the land is calculated based on US$0,127/m²/year and a one-time payment for 20 years.

The results of 2P fixed system calculations meet the following expectation:

• The module with 182 mm wafers has an obvious advantage over the module with 166 mm wafers in terms of BOS cost;
• Compared to the 60c-210 and 55c-210 modules (with 210mm wafers), there is little difference, but with a slight advantage for the 182mm module due to the higher module efficiency;

The BOS costs of 72-cell modules with 182 mm wafers and 55-cell modules with 210 mm wafers installed on a support with 4L arrangement (4 rows of modules horizontally) are compared below.

The results show that the 182 mm module has a slight advantage in support, foundation and land costs due to greater efficiency. Very wide modules are not considered in the comparison due to the low load capacity when there is no beam and the difficult installation of the upper row of modules in the case of 4L type systems.

Excessive working current of a module will lead to a significant increase in heat losses on the metal contact surface of the cell, the metal ribbons (ribbons) and the busbar, which will increase the working temperature of the module to a certain extent.

This was proven by comparing and analyzing the working temperatures of half-cell modules and full-size cell modules. JA and TÜV NORD carried out a comparative study on the power generation capacity of the module with 182 mm wafers and a high current module (with wider wafers), and the data for two months (from February 19, 2021 to April 20, 2021) were obtained. The results are shown in Figure 6.

It can be seen that on a sunny day, the average operating temperature of the module with 182mm wafers is 1,7°C lower than that of the high-current module, and the maximum temperature difference can be as high as 4~5 °C. Meanwhile, the average energy yield per watt of the former is about 1,6% higher than that of the latter. Therefore, the module with 182 mm wafers shows an obvious advantage in power generation.

Application cases

Below are some examples of projects that employ 182 mm modules, listed in order from left to right and top to bottom (according to figure 7):

• Zhongwei, Ningxia, China, 200 MW;
• Hainan Prefecture, Qinghai, China, 42,5 MW;
• Cangzhou, Hebei, China, 200 MW;
• Pernambuco, Brazil, 80 MW;
• Taebaek, Korea, 1 MW;
• Quang Ngai, Vietnam.

Summary

Photovoltaic plants are designed to operate reliably for more than 25 years and can perform well even in extreme weather conditions. Module and system reliability is the basis for ensuring return on investment and realizing value for customers.

The 182mm wafer module is the most cost-effective solution based on in-depth analysis of various conditions including the module manufacturing chain and PV system design. Without improving efficiency, the additional increase in module power through the use of wider wafers (and consequently larger modules) does not allow for a real reduction in the cost of implementing solar plants.

At the same time, there is a significant increase in the reliability risk of photovoltaic systems with large modules, due to mechanical, electrical and thermal issues. Simply increasing the power of the module with increasingly larger dimensions is not a technological innovation. Instead, module size standardization helps maintain the focus of the entire production chain (manufacturing equipment, materials, inverters, trackers, etc.) on improving efficiency and increasing energy generation while reducing costs.