How to Select Solar Photovoltaic Mounting Systems Based on Requirements?

1. Types of Steel Used in Solar Steel Mounting Systems
Given the simple structure and small size of solar photovoltaic mounting systems, lightweight structural steel and small-section ordinary structural steel are predominantly used in the selection of steel materials.

Lightweight Structural Steel: Lightweight structural steel mainly refers to round steel, small-angle steel, and thin-walled steel. Angle steel, when used as support members, can effectively utilize the strength of the steel and facilitate the overall installation of the mounting system. However, when used as bending or compression members, it tends to produce relatively large deformations. Currently, the range of angle steel models available in national standards is limited for solar mounting systems, highlighting the need for a wider variety of small-angle steel models to adapt to the rapidly developing solar market. For purlin members, thin-walled steel is typically made from thin steel plates with a thickness of 1.5–5 mm, formed into various cross-sectional shapes and sizes through cold bending or cold rolling.

Compared to hot-rolled steel, thin-walled steel can increase the radius of gyration by 50–60% for the same cross-sectional area, while the section moment of inertia and resistance moment can increase by 0.5–3 times. This allows for more efficient utilization of the material's strength. However, the processing of thin-walled steel is mostly carried out in factories, requiring high-precision drilling to align with the screw holes on the back of photovoltaic panels. Factory processing and drilling are necessary before hot-dip galvanizing for rust prevention. During on-site installation, the small cross-section of the steel makes it difficult to operate with tools, complicating the construction process. Currently, most domestic photovoltaic panels cannot be directly installed with thin-walled steel and require additional auxiliary fixing structures (such as clamping blocks).

Ordinary Structural Steel: Ordinary structural steel commonly uses carbon structural steel or low-alloy steel, which are easy to smelt and cost-effective. There are various types of cross-sections, with those commonly used in photovoltaics including I-beams, H-beams, L-beams, and custom-designed special-shaped sections. The processing methods are also diverse. Welded steel sections, for instance, involve selecting steel plates of different thicknesses and welding them into shaped steel in factories according to design requirements. This method allows for the use of steel plates of varying thicknesses in different structural parts based on force calculations for different sections of the photovoltaic project. This approach is more reasonable in terms of stress distribution compared to hot-rolled one-time forming products, making it more suitable for on-site installation and saving steel materials.

2. Performance Requirements for Steel in Solar Mounting Systems
The steel used in solar steel structures should possess the following properties:

1) Tensile Strength and Yield Point. A high yield point allows for smaller cross-sections of steel members, reducing the structural weight, saving steel, and lowering the overall project cost. High tensile strength increases the overall safety margin of the structure, enhancing its reliability.

2) Plasticity, Toughness, and Fatigue Resistance. Good plasticity enables the structure to undergo significant deformation before failure, allowing for timely detection and remedial measures. Good plasticity also helps adjust local peak stresses. Photovoltaic panels are often installed using forced methods to adjust angles, and plasticity allows for internal force redistribution in the structure, making stresses in previously concentrated areas more uniform and improving the overall load-bearing capacity of the structure. Good toughness enables the structure to absorb more energy when subjected to external impact loads, especially in desert power plants and rooftop installations where wind effects are significant. The toughness of steel can effectively reduce risks. Good fatigue resistance also enables the structure to withstand alternating and repetitive wind loads more effectively.

3) Processing Performance. Good processing performance includes cold working, hot working, and weldability. The steel used in photovoltaic steel structures should not only be easily processed into various forms of structures and components but also ensure that these structures and components do not suffer significant adverse effects on strength, plasticity, toughness, and fatigue resistance due to processing.

4) Service Life. Since solar photovoltaic systems are designed for a service life of over 20 years, good corrosion resistance is also an important indicator of the quality of the mounting system. If the mounting system has a short lifespan, it will inevitably affect the stability of the entire structure, prolong the investment payback period, and reduce the overall economic benefits of the project.

5) Under the above conditions, the steel used in photovoltaic steel structures should also be readily available, easy to produce, and affordable.

3. Technical Analysis of New Solar Steel Structure Mounting Systems
The use of angle steel in solar mounting systems is increasingly constrained, primarily due to inconsistent steel quality and the need for extensive on-site drilling, which can lead to rusting. Therefore, new mounting systems are required to replace angle steel systems to reduce corrosion and extend service life.

New Solar Mounting System Main Structural Forms:

1) Special-Shaped Cold-Formed Thin-Walled Steel Mounting System. Special-shaped cold-formed thin-walled steel is a prefabricated, dry-assembled light steel structure system that allows for mass production, rapid assembly, and features low steel consumption, time savings, and labor efficiency. The steel structure mounting system of special-shaped cold-formed thin-walled steel involves connecting factory-prefabricated cold-formed thin-walled steel on-site with bolts to form the structural framework, followed by the installation of photovoltaic panels to complete the array.

2) Factory-Prefabricated Integral Steel Mounting System. This system involves factory-prefabricated steel structures with purlins, which only require on-site assembly and fixing, followed by the installation of photovoltaic panels to form the entire array. It offers fast construction speed and is suitable for large-scale power plants. The installation requirements for this steel structure mounting system are extremely high, typically involving the highest quality steel, excellent surface treatment processes, and thorough pre-communication with photovoltaic component manufacturers to achieve perfect assembly compatibility.

3) Beam-Column Frame-Type Curtain Wall Photovoltaic Mounting System. Photovoltaic curtain walls are suitable for beam-column frame-type steel structure mounting systems. This structure is lightweight and reliable. However, due to its small lateral stiffness, lateral bracing is required to form a braced frame structure when the structure is tall or has large story heights. In the design of high-rise photovoltaic curtain walls, mixed structures combining steel and cast-in-place embedded parts are commonly used to enhance the overall structural resistance to lateral displacement, reduce steel consumption, and lower the total cost.

4. Installation of Components for New Cold-Formed Thin-Walled Solar Mounting Systems:

1) Connection of Steel Structure Members: The new cold-formed thin-walled solar mounting system is assembled from factory-prefabricated steel-plastic hybrid connectors. These connectors come in various models to suit different installation conditions. Correctly selecting the connection forms and methods for hybrid components is a crucial aspect of the overall structural design.

2) Connection of Mounting System to Foundation: The new cold-formed thin-walled solar mounting system is lightweight and features multiple installation holes. Independent foundations are generally used, with reinforced concrete tie beams added when necessary. For areas with poor geological conditions, strip foundations or cross-shaped foundations can be used, while raft foundations are avoided as much as possible. All upper column bases adopt hinged connections, while the embedded parts can use inserted column bases or pre-embedded bolts wrapped with waterproof concrete. Both types of column bases are simple to process, easy to construct, and offer good connection performance.

3) Connection of Mounting System Purlins: There are three types of connection nodes: rigid, hinged, and semi-rigid. Modular manufacturing methods for these connection types are already available. Hinged connections are simple in construction and the easiest to manufacture and install. However, in areas with strong winds, horizontal bracing or diagonal bracing is required to help the wall withstand horizontal loads and provide additional stiffness. When bracing is not installed, the connection nodes between beams and columns should be made rigid. Semi-rigid connections are simpler to construct than rigid connections and offer better performance than hinged connections. However, due to the difficulty in controlling their force distribution, practical application requires experience, and they are rarely used at present. On-site connections typically involve bolted hinged connections followed by welding at both ends.