I. Introduction
In February 2025, the National Intellectual Property Administration released information indicating that a domestic enterprise had obtained a patent named "Steel Frame for Photovoltaic Modules and Photovoltaic Modules", with the patent number CN 222441628U and the application date set for February 2024. According to insiders, the company has started to purchase a certain quantity of new steel frames from enterprises including Baosteel Baoma on a regular basis this year. At this time, the domestic market for aluminum alloy frames of photovoltaic modules is highly competitive, and the entire industry is suffering losses. The "comeback" of steel frames may put the aluminum alloy frame industry in an even worse situation with both internal and external troubles, and once again spark discussions within the industry about whether steel frames will replace aluminum frames.
The application of aluminum alloy frames has a long history and still holds an absolute market share at present
Photovoltaic modules are composed of core components such as solar cells, tempered glass, EVA film, backsheet, frame and junction box. Among them, the frame is an important component of photovoltaic modules, mainly serving to fix and seal the photovoltaic modules. As a frame structure material, the frame largely determines the service life of photovoltaic modules. Downstream module manufacturers have strict requirements for their processing accuracy, mechanical strength, corrosion resistance, weather resistance, and service life.
By material classification, solar frames include aluminum alloy frames, galvanized aluminum-magnesium steel frames and composite material frames. Among them, aluminum alloy frames have been in use for the earliest time and started along with the photovoltaic module industry. After years of development, the global photovoltaic industry now widely adopts aluminum alloy frames, with a domestic market share of over 95%, holding an absolute dominant position. In contrast, the market share of galvanized aluminum-magnesium steel frames, composite materials and frames made of other materials is less than 5%.
Third, the comprehensive advantages of aluminum alloy frames are the most prominent
Aluminum alloy frames are made from 6-series aluminum alloy (the current mainstream grade is 6005) as raw material. The final product is obtained through production processes such as melting and casting, extrusion, oxidation and deep processing. They have the advantages of light weight and high specific strength. The dense and continuous oxide film on the surface of the aluminum alloy frame makes it have excellent weather resistance, and its service life can be as long as more than 25 years. Meanwhile, the aluminum alloy frame features high processing precision, very small dimensional deviation and an attractive appearance. Its elastic modulus is 69Gpa, which is close to that of photovoltaic glass. The two can deform synchronously and are less likely to cause component breakage. Although its usage cost accounts for approximately 14.2% of the cost of photovoltaic modules, ranking second only to silver paste, and its usage cost is relatively higher compared to composite frames and zinc-aluminum-magnesium frame materials, from the perspective of the entire service life cycle, the maintenance cost of aluminum alloy frames is low, and its excellent recyclable economic value is also unmatched by other frame materials. Therefore, taking everything into account, the comparative advantages of aluminum alloy frames are the most prominent.
Composite material frames have been around for over a decade. They are mainly made of glass fiber, polyurethane and other resins, and are produced through five processes: glass fiber roving arrangement, injection of glue, extrusion molding and curing, cutting by traction machine and spraying. Among the three types of frames, they have the lowest application cost, which is 20% lower than that of aluminum alloy frames. Meanwhile, the composite material frame has good weather resistance (resistance to moisture, heat, light and radiation) and corrosion resistance (resistance to acid, alkali and salt spray), making it suitable for extremely harsh and complex environments, especially for use in offshore photovoltaic projects. Its system does not require grounding, which helps to reduce the risk of PID (Electromotive Force Induced Attenuation) effects and enhance the safety of system operation and maintenance. In addition, the composite material frame is lightweight, aesthetically pleasing and convenient for transportation and installation. However, the organic materials it uses, such as rubber, are prone to weathering, which not only reduces its service life but also easily causes certain environmental pollution. From the perspective of actual application scenarios, composite material frames are indeed only used in offshore photovoltaic projects at present, and are rarely seen in ground-mounted centralized and distributed photovoltaic projects. The reason for this is that its usage strength (tensile but not shear) and service life have shortcomings, which makes downstream component enterprises have doubts. Apart from the ship-grade corrosion-resistant environment, they still dare not use it rashly in other application scenarios.
Galvanized aluminum-magnesium steel frames first appeared in 2021. They are made from galvanized aluminum-magnesium steel plates through stamping and bending processes. This type of product features high mechanical properties. Its yield strength and tensile strength can exceed 450MPa and 510MPa respectively, and its elongation can reach 14%, both of which are higher than the corresponding mechanical values of 280MPa, 300MPa and 8% for aluminum alloy frames. Meanwhile, steel frames are inexpensive, being 15% to 20% lower than aluminum alloy frames. However, the drawbacks of steel frames are also quite prominent. It is made by stamping and cold-bending steel plates, and its processing accuracy is hard to reach that of aluminum frames. Take the 45-degree cross-section corner seam as an example. The gap of the steel frame is within 0.5mm, while that of the aluminum frame and the composite material frame can be controlled within 0.1mm and 0.2mm respectively. The larger the corner gap, the greater the chance of internal corrosion while it affects the appearance. Meanwhile, the very thin galvanized aluminum-magnesium layer on its surface still cannot guarantee that the product meets the hard requirement of a service life of more than 25 years, especially in the cutting surface and the grounding hole puncture layer, where rust is prone to occur. In addition, steel frames are heavier than other frame materials. Besides being inconvenient for transportation and installation, they also increase the risk of load-bearing under wind pressure and snow loads. Therefore, they are not suitable for distributed photovoltaic projects. Therefore, steel frames are a material choice with both obvious advantages and disadvantages. So far, apart from a few enterprises that have used it on a small scale, no other major domestic component enterprises have adopted it, and the same is true in foreign markets.
The advantages emphasized by steel frame products are not yet obvious at present
Since its emergence, steel frame products have always emphasized several major advantages in their promotion and publicity, such as low cost, high usage strength, and low carbon footprint of the product. However, judging from the current market recognition and practical application effects, these advantages are not yet obvious and have not truly contributed to its promotion and application.
From the perspective of the entire life cycle, the cost advantage of steel frames is not obvious
Due to the low cost of raw materials, the selling price of steel frame products can be 15% to 20% lower than that of aluminum alloy frames. This caters to the cost reduction demands of downstream battery component enterprises and is also the main reason why the industry has launched steel frame products in an attempt to replace aluminum frames. However, as downstream component enterprises pay more attention to the service life of their products and safe operation and maintenance, price is not their top priority in procurement. Therefore, steel frames have several major shortcomings that greatly reduce their overall cost performance. Judging from the market response after several years of promotion, steel frames have only achieved certain breakthroughs in a few mid-to-low-end applications at present, occupying a small market share and having a relatively low market presence.
Meanwhile, as the recycling value of steel is significantly lower than that of aluminum alloy frames after reaching the end of its service life, the initial procurement cost advantage of steel frames is also weakened when measured from the perspective of the entire product life cycle.
(2) From a technical perspective, the strength advantage of steel frames is not obvious
In terms of the mechanical properties of the material itself, steel frames are superior to aluminum alloy frames in terms of yield strength, tensile strength and elongation. On the other hand, aluminum alloy frame manufacturers have been constantly improving alloy formulas and production processes in recent years, ensuring that the main mechanical performance indicators can all meet customer requirements and are significantly higher than the YS/T 773-2020 "Aluminum Alloy Profiles for Solar Cell Frames" industry standard for non-ferrous metals released in 2020. At present, the mainstream 6005 alloy used for domestic aluminum alloy frames has a maximum yield strength of up to 280MPa, a tensile strength of 300MPa, and an elongation of over 8%, all of which are higher than the industry standards of 225MPa, 245MPa, and 6%.
Meanwhile, in addition to the above indicators, downstream component enterprises pay more attention to the mechanical load, positive pressure and back pressure parameters of the frame. Currently, there is not much difference between steel and aluminum frames in this regard. However, steel frame enterprises often use the example of photovoltaic projects in coastal or inland areas where aluminum alloy frames were damaged due to extreme weather such as strong winds, but those using steel frames remained unscathed, to prove that the strength of aluminum alloy frame products is low. But they often overlook that the real reason for the damage to aluminum alloy frames actually comes from factors such as unreasonable installation angles of battery components. Of course, it cannot be ruled out that a few aluminum alloy frame enterprises have reduced product quality to cut costs, but this does not mean that all products in the aluminum alloy frame industry have problems. After all, downstream customers only accept aluminum alloy frame products that meet their usage requirements before using them. Therefore, although steel frames have high strength, they do not differ from aluminum alloy frames in actual use.
(3) From the perspective of product carbon footprint, the potential advantages of steel frames remain to be demonstrated
Under the global background of energy conservation, carbon reduction and green development, customers have begun to pay attention to the carbon footprint of various industrial products and gradually put forward corresponding requirements. In the field of photovoltaic module frame production, domestic downstream customers have not yet put forward clear requirements for carbon footprints, but some overseas customers have already begun to have relevant requirements. In particular, products exported to the EU region in the future will be affected by the official implementation of the Carbon Border Adjustment Mechanism (CBAM).
To compare the carbon footprint of steel frames and aluminum alloy frames, we cited the carbon emission factor data released by the International Iron and Steel Institute and the China Nonferrous Metals Industry Association, as well as the relevant data calculated based on the industry average, and conducted a horizontal assessment according to the calculation formula. The calculation process takes into account the carbon footprint in the raw material production stage, processing stage (including processing and surface treatment), and transportation process, and estimates based on the weight of the steel frame and aluminum alloy frame required for the construction of the photovoltaic power station. The calculation results show that the carbon footprint of all 1GW photovoltaic modules using steel frames is 17,630 tons, while the carbon footprint of aluminum alloy frames produced with common aluminum and green power aluminum is 42,350 tons and 20,120 tons respectively, which is 2.40 times and 1.14 times that of steel frames. If all recycled steel or recycled aluminum is used, the carbon footprints would be 10,890 tons and 8,180 tons respectively, and recycled aluminum alloy frames would have certain advantages.
From the calculation results, it can be seen that currently, steel frames have an advantage in terms of carbon footprint. The carbon footprint of aluminum alloy frames can only be lower than that of steel frames when all recycled aluminum is used. At present, most domestic aluminum alloy frame enterprises directly or indirectly use common aluminum as raw materials for production. There are no cases where all 6005 alloy waste materials such as used aluminum frames and used aluminum formwork are used for production. In the future, as overseas customers increasingly impose strict requirements on the carbon footprint of products, domestic enterprises will also put forward corresponding demands. The potential advantage of low carbon footprint of steel frames may become an "added bonus" for them to expand their market share. In this regard, aluminum alloy frame manufacturers need to pay attention and reverse the unfavorable situation in the competition of product carbon footprint by further increasing the proportion of green electricity aluminum or recycled aluminum used.
V. Problems to be Urgently Solved in the Promotion and Application of Steel Frames
At present, the application scenarios of composite material frames are only limited to offshore photovoltaic projects, while steel frames and aluminum alloy frames are all used in onshore photovoltaic projects. In terms of application scope, steel frames can be regarded as potential competitors of aluminum alloy frames. Compared with aluminum alloy frames, which started early, have been in use for a long time and have an absolute leading market share, steel frames emerged later. Although they have certain advantages in terms of cost, mechanical strength and carbon footprint, their inherent defects are also very obvious. There are many problems that need to be solved in the process of promotion and use, mainly involving the following aspects.
(1) The national standards for the nonferrous metals industry do not mention steel frames
At present, the industry standard YS/T 773-2020 "Aluminum Alloy Profiles for Solar Cell Frames" used in photovoltaic module frames has put forward specific usage parameters and performance requirements for 6063, 6061, and 6005 aluminum alloy frame profiles in the T5 and T6 states. On the basis of industry standards, enterprises have each formulated even stricter product standards to ensure that the performance of their products exceeds the national industry standards. Both aluminum alloy frame profile manufacturers and downstream photovoltaic module users have publicly available technical standards for reference and implementation.
Compared with aluminum alloy frames, steel frames emerged relatively late. Their performance requirements can only be formulated based on the industry standards for aluminum profile frames. Although some of their mechanical performance indicators are still superior to those of aluminum alloy frames, they are still in the process of borrowing and referring to them as a whole. There are deficiencies in their product technical standards, which lack systematicness and have not yet been widely recognized by downstream customers at the technical level.
(2) The short service life of steel frames is the biggest shortcoming restricting their promotion and application
It is well known that steel is prone to corrosion and rusting when exposed outdoors for a long time. If steel frames are to be widely used, they must meet the hard requirement of a 25-year product service life proposed by component enterprises. As there are no industry standards, steel frame manufacturers can only refer to the corrosion resistance experience of other outdoor thin steel plates to carry out protective treatment on the steel frames of photovoltaic modules. The enterprise coated the surface of its products with a zinc-aluminum-magnesium layer about 20 microns thick and also conducted salt spray corrosion tests for 1,000 to several thousand hours accordingly. However, up to now, the steel frame still lacks genuine, effective and industry-recognized experimental test data to support the product promotion claimed by enterprises that it can meet the long-term normal use outdoors.
During the production of photovoltaic module frames, the long and short sides of the frames need to be cut at a 45-degree Angle. For steel frames, although the surface coating has a certain self-healing ability, it is powerless in preventing corrosion of the cutting surface. Judging from the cross-section of the steel frame that has been removed, the corrosion is quite severe, and a similar situation also exists at the grounding hole position. The galvanized aluminum-magnesium layer will form a protective layer on the cutting surface due to its self-healing ability. However, its electrical conductivity is poor. To meet the grounding performance of the conductive holes, the protective layer must be punctured, but this may also cause the grounding holes to rust, thereby affecting the service life of the frame.
Another type of internal corrosion of steel frames stems from their processing techniques. The processing accuracy requirements for the slots of photovoltaic module frames are high. The aluminum alloy frame is formed by die extrusion, and the processing control accuracy of the slot can be less than ± 0.1mm. The steel frame is made by cold bending process. The maximum control accuracy of the bending equipment is generally below 0.5mm, and the minimum can reach ± 0.15mm. Compared with the processing accuracy of aluminum alloy frames, there is still a certain gap. Due to the processing accuracy defects of the steel frame, gaps are prone to occur at the connection points of the frame. This not only affects the appearance yield of the product but also makes it easy for water vapor to seep in and condense, causing water droplets to condense inside the steel frame and subsequently leading to internal corrosion problems.
Given the above situation, there is currently widespread doubt in the industry about whether steel frames can meet the product promotion requirements for 25 years of normal outdoor use. The relatively short service life has also become the biggest shortcoming restricting the market promotion and popularization of steel frames.
(3) The frequent problem of steel frame cracking has deterred component manufacturers
Compared with aluminum alloy frames, photovoltaic modules produced with steel frames are prone to panel breakage problems, which pose a significant threat to the stable operation of photovoltaic power stations and thereby bring the risk of high operation and maintenance costs. At present, the main reasons for the occurrence of board crashes are as follows:
It is caused by the mismatch of the elastic coefficients between the steel frame and the photovoltaic glass
Technical specification data shows that the elastic modulus of the steel frame is 2.06×105N/mm ², which is significantly different from that of glass. Under conditions of large component size, wind pressure and snow load, the deformation of the glass is relatively large, and it is prone to plate cracking. In contrast, the elastic modulus of aluminium alloy is much higher than that of glass
