Solar screws (also known as photovoltaic screws) are specialized fasteners used in solar photovoltaic systems to fix components, brackets, guide rails, and other parts. Their performance directly affects the stability, safety, and service life of photovoltaic systems. The following the core knowledge of solar screws from aspects such as material, specifications, performance requirements, application scenarios, and selection key points:
Ⅰ. Core Characteristics and Application Scenarios of Solar Screws
1. Core Characteristics
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High Weather Resistance: They need to be exposed outdoors for a long time, withstanding extreme environments such as ultraviolet rays, rain, salt spray, and high/low temperatures (-40°C~80°C).
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Vibration and Wind Load Resistance: Photovoltaic modules may vibrate or displace due to wind, snow, etc., so screws must have anti-loosening ability.
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High Anti-corrosion Grade: Ordinary carbon steel screws are prone to rust, leading to the risk of component falling. Therefore, stainless steel is the mainstream material.
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Easy Installation: To meet the rapid installation needs of photovoltaic brackets, they are often designed as self-tapping screws, drill tail screws, or styles with flange surfaces.
2. Main Application Scenarios
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Fixing photovoltaic modules and brackets
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Self-tapping screws / Drill tail screws
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Penetrating aluminum alloy brackets to fix module frames
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Connecting brackets and guide rails
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Hexagon bolts / Flange bolts
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M8~M12, with nuts and washers
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High-strength connection to bear wind load and snow load
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Grounding screws (with teeth)
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Ensuring good conductive grounding between modules and brackets
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Cross recessed pan head screws
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Fixing cable protection tubes to prevent loosening due to vibration
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Ⅱ. Key Performance Indicators of Solar Screws
1. Material Selection
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Mainstream Materials: Stainless steel (304/316)
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304 stainless steel: Better corrosion resistance than carbon steel, cost-effective, suitable for most inland, non-coastal photovoltaic projects.
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316 stainless steel: Contains molybdenum (Mo) element, with stronger resistance to salt spray, acid, and alkali corrosion, suitable for strongly corrosive environments such as coastal areas, high-humidity regions, and chemical industrial parks.
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Special Scenarios: Hot-dip galvanized carbon steel
Only used in temporary projects or scenarios with strict budget constraints (such as rural distributed photovoltaic pilots). The anti-rust layer needs regular inspection, and it is prone to rust in long-term use.
2. Anti-corrosion Grade
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Salt Spray Test Standards:
Photovoltaic screws must pass≥1000-hour salt spray test(GB/T 10125). 316 stainless steel can usually reach more than 2000 hours, and 304 stainless steel is about 1000~1500 hours.
Stainless steel screws require no additional treatment (relying on surface oxide film for rust prevention); carbon steel screws need hot-dip galvanizing (coating thickness ≥50μm) or Dacromet coating (chromium-free zinc-aluminum coating, environmentally friendly, with salt spray resistance ≥1000 hours).
3. Mechanical Properties
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Stainless steel screws: Commonly A2-70 (tensile strength ≥700MPa) or A4-80 (suitable for high-load scenarios, such as brackets of large photovoltaic power stations).
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Carbon steel screws: At least grade 8.8 (tensile strength ≥800MPa), need to be used with spring washers for anti-loosening.
Flange bolts (with serrated anti-slip), nylon lock nuts, or spring washers are used to cope with high-frequency vibration (such as photovoltaic arrays in typhoon-prone areas).
4. Specifications and Sizes
Metric system is mainly used (M4, M5, M6, M8, etc.). Self-tapping screws have wider thread pitches (e.g., ST4.8, pitch 1.6mm) to facilitate penetration of aluminum alloy.
It is necessary to ensure that after the screw penetrates the fixing part, the exposed thread length is ≥2 times the thread pitch (to avoid virtual tightening). For example, when fixing an aluminum alloy frame with a thickness of 3mm, the screw length should be ≥ (3mm + washer thickness + 2 times thread pitch).
Ⅲ. Key Points for Selecting Solar Screws
1. Select Material Based on Environmental Corrosiveness
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Photovoltaic power stations in Northwest and North China
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Coastal / high-humidity areas
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Coastal photovoltaic projects in Fujian and Guangdong
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Industrial pollution areas (acid rain)
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316L stainless steel (low carbon)
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Photovoltaic projects around steel plants and chemical plants
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Temporary projects / low-cost
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Hot-dip galvanized carbon steel
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Short-term rural household photovoltaic pilots
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2. Select Screw Type Based on Installation Method
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Self-tapping / drill tail screws:
Suitable for aluminum alloy brackets (no prefabricated screw holes). The drill tail tip can directly drill holes and tap threads, with high installation efficiency. However, attention should be paid to avoiding over-tightening leading to thread stripping.
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Hexagon head / countersunk head bolts:
Suitable for steel structure brackets or scenarios requiring high-strength connections (such as fixing guide rails and columns), need to be used with nuts and washers, with stronger tensile force.
Need to be equipped with serrated washers to ensure large contact area and good conductivity, usually installed at the grounding holes of component frames.
3. Anti-loosening and Matching with Installation Tools
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Anti-loosening Solutions:
For outdoor scenarios, double nut locking or anti-loosening glue (such as Loctite 243) must be used; ordinary nuts alone are prohibited.
Use a torque-controlled electric screwdriver, set the tightening torque according to specifications (e.g., torque for M6 screws is about 8~10N·m), to avoid loosening due to insufficient torque or thread stripping due to excessive torque.
Ⅳ. Common Problems and Solutions
1. Component Falling Due to Screw Rusting
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Cause: Using carbon steel screws or inferior stainless steel (such as 201 material), which rust after the surface oxide film is damaged.
Mandatorily use 304/316 stainless steel screws. Check for scratches and cracks on the surface before installation (which are prone to water accumulation and rusting).
Prioritize 316 stainless steel for coastal projects, and apply waterproof sealant (such as silicone glue) at the contact between screws and components.
2. Screw Thread Stripping or Fracture
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Cause: Excessive torque (exceeding the tensile strength of screws) or insufficient material toughness.
Strictly match the torque according to screw specifications (refer toPhotovoltaic Module Installation Manual), for example, the maximum torque of M5 self-tapping screws ≤6N·m.
Choose austenitic stainless steel (such as 304, with good toughness) and avoid martensitic stainless steel (such as 410, which is prone to brittle fracture).
3. Lightning Strike Risk Due to Poor Grounding
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Cause: Grounding screws are not tightened or there is an oxide layer on the contact surface.
Polish the contact surface to a bright finish during installation, use toothed washers to pierce the oxide film, and mark "grounded" on the screw head to facilitate inspection.
Ⅴ. Industry Standards and Certifications
Solar screws must comply with the following domestic and foreign standards:
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China: GB/T 34082-2017Weather-resistant Fasteners for Solar Photovoltaic Systems
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International: IEC 61215 (photovoltaic module standard), ASTM F1554 (anchor bolt standard, suitable for bracket fixing)
Certification Requirements:
Export projects need to pass RoHS certification (environmental protection) and ISO 9001 quality management system certification. Coastal projects may require NACE MR0175 (sulfide corrosion resistance).
