The Threat of Corrosion to the Long-Term Operation of Solar Power Plants

Solar power plants are typically designed for a service life of 25 years. The stability of the entire structure — racks, panels, and supports — depends on nuts, bolts, and other fasteners. But in reality, many solar installations that use ordinary galvanized or carbon steel nuts develop serious rust problems within just a few years. At best, this causes loose racks and shifting panels. At worst, strong winds can cause racking collapse, posing major safety hazards. On top of that, replacing rusted fasteners later drives up labor and material costs significantly.

Meanwhile, outdoor environments constantly expose fasteners to multiple corrosive attacks, including rain, acid rain, temperature swings between day and night, coastal salt spray, and industrial exhaust. Ordinary corrosion coatings fail very easily under these conditions.

To solve the problem of fast-rusting nuts at its source, stainless steel nuts specifically designed for solar applications have become the industry's recognized long-term solution.

Why Do Outdoor Solar Nuts Rust So Quickly?

Salt Spray and Chloride Attack

In coastal areas, airborne salt particles settle into the threads of nuts. When rain hits, they form an electrolyte solution that quickly breaks through zinc plating and causes pitting rust. Even dozens of miles inland, seasonal winds can carry salt spray that continuously corrodes metal components.

Acid Rain and Chemical Corrosion

In industrial zones and around cities, rainwater is often mildly acidic. Acidic media speed up chemical corrosion. Sulfur compounds and nitrogen oxides stick to nut surfaces and steadily break down protective coatings.

Temperature Swings Damage Coatings

Hot summer sun on panel back sheets, followed by freezing winter temperatures, causes repeated expansion and contraction. This makes zinc coatings on carbon steel nuts crack and peel off. Once the bare metal is exposed, rusting speeds up even more.

Galvanic Corrosion Between Dissimilar Metals

Solar racks are often made of aluminum, while fasteners are typically carbon steel or stainless steel. When rain acts as a conductive electrolyte, the two dissimilar metals create a galvanic reaction. The nut, as the anode, corrodes first and much faster.

Why Stainless Steel Solar Nuts Provide Long-Term Rust Protection

Self-Healing Passive Film

When the chromium inside stainless steel solar nuts comes into contact with air and moisture, it forms an extremely thin, dense, and stable passive oxide film on the surface. This film is so thin and tightly structured that it effectively blocks water, oxygen, and corrosive agents such as acid rain and salt spray around solar panels from reaching the underlying iron.

Even if the surface gets scratched during installation, the exposed metal immediately reacts with oxygen in the air and quickly forms a new protective film. This stops rust at its source.

Resistance to Salt Spray, Acids, and Alkalis

The alloy composition of stainless steel is stable. It resists acid rain, salt spray, and industrial corrosive gases far better than zinc-plated parts. It does not peel or flake as coatings do. Quality stainless steel nuts can withstand long-term chloride attack without rapid pitting.

Handles Extreme Temperature Swings

The thermal expansion and contraction rate of stainless steel is stable. Large day-to-night and seasonal temperature swings do not damage its corrosion-resistant structure. It stays fully rust-resistant even after years of outdoor sun exposure and freezing.

304 or 316? Which Stainless Steel for Outdoor Solar Nuts

304 Stainless Steel Solar Nuts

Composition: Contains roughly 18% chromium and 8% nickel—a standard austenitic stainless steel with stable basic rust resistance.

Best for: Clean inland areas with no heavy industrial pollution. Examples include inland mountains, commercial and industrial rooftops, and solar farms far from the coast. Low humidity, no heavy salt spray.

Advantages: Good balance of cost and performance. Strong atmospheric corrosion resistance. Good workability.

316 Stainless Steel Solar Nuts

Composition: Contains roughly 16% to 18% chromium, 10% to 14% nickel, and 2% to 3% molybdenum. Maximum carbon content 0.08%. The added molybdenum dramatically improves resistance to chlorides and salt spray. Much better resistance to pitting and crevice corrosion compared to 304.

Best for: Coastal tidal flat solar farms, near-shore rooftops, chemical industrial parks, high-humidity fish pond solar installations, and other highly corrosive environments.

Advantages: Excellent resistance to chloride corrosion. Very good pitting resistance. More stable mechanical properties at high temperatures.

Procurement and Installation

Procurement Tips to Avoid Problems

• Reject low-cost, substandard, off-spec stainless steel. Ask the manufacturer to provide material test reports. Verify that chromium, nickel, and molybdenum content meet required standards.

• Choose factory passivated products whenever possible. Passivation removes iron particles and contaminants left behind from manufacturing. This helps prevent surface rust from forming later.

• For coastal projects, buy 316 stainless steel directly. For standard inland projects, use certified 304 stainless steel that meets specifications.

Installation Guidelines

• Clean dust, carbon steel particles, and debris off rails and bolts before installation. Foreign metal dust on the surface can cause localized surface rust.

• Control tightening torque to standard values. Do not overtighten. Excessive torque can scratch or damage the passive film on the stainless steel surface.

• In highly corrosive areas, add insulating washers. These further block moisture and corrosive media, extending the service life of the fasteners.

• Keep nuts, bolts, and flat washers all made of the same material. Mixing different metals outdoors can cause galvanic corrosion due to different electrical potentials, which accelerates damage to the parts.