Corrosion protection is one of the most important considerations in solar infrastructure. The Clean Energy Steel Construction Center (CES) emphasizes the need for proper characterization of the soil and an assessment of atmospheric corrosion rates to properly evaluate the various durability options currently used in solar projects. Piles, racking, and support structures must perform for decades under challenging soil and atmospheric conditions. CES encourages engineers to consider full soil characterization and established corrosion protection methods to ensure long service life in these applications. At the same time, it is important to understand how to evaluate the longevity of zinc coatings on a project-basis, and the strengths and limitations of alternative durability options.
Hot-Dip Galvanizing (HDG)- The Benchmark
What it is: A metallurgically bonded zinc coating applied after fabrication by immersing the finished steel in molten zinc.
- Why it matters:
- Applied After Manufacturing: Because the steel is galvanized after all fabrication, HDG ensures complete coverage of welds, edges, holes, threads, and inside corners.
- Strongest Bond: The metallurgical bond means the coating essentially becomes part of the steel itself, providing unmatched abrasion resistance during soil embedment and resisting underfilm corrosion.
- Longevity: HDG provides a thicker coating of zinc than possible through other protective coatings commonly used in solar, and the service life of metallic zinc coatings is directly proportional to zinc coating thickness.
- Proven Performance:
- Provides cathodic (sacrificial) protection to scratches or cut edges.
- Delivers 70–100+ years of service life in many soil and atmospheric environments.
- Metallurgical bond tested at 3,600 psi or greater, ensuring superior adhesion compared to paint or polymer coatings.
- Backed by extensive real-world soil and atmospheric corrosion data and experience across infrastructure markets including utility poles, guardrails, and bridges.
- Established guidance available from the American Galvanizers Association (AGA) to perform an accurate evaluation of soil and atmospheric corrosion rates.
Solar takeaway: HDG is the most reliable and field-proven solution for solar piles, posts, and racking systems, offering unmatched durability, coverage, and protection.
Bare Steel (Uncoated Carbon steel)
- Approach: Relies on corrosion allowance (extra thickness) rather than a protective coating.
- Limitations:
- Corrosion rate is unchanged by added thickness
- Pitting and localized loss can accelerate failure
- Models based only on soil resistivity or pH often underestimate corrosion
- Lifecycle:
- Bare steel posts usually cannot be reused due to advanced corrosion
- HDG-coated posts may be pulled and reused if coating remains intact
- Solar takeaway: Not recommended for long-term, maintenance-free solar installations where predictable service life is critical.
Continuous Sheet Galvanizing
What it is: A thin zinc coating applied on coil before fabrication (commonly used in cars, appliances, ductwork, roofing).
- Advantages: Uniform coating, precise thickness control.
- Limitations:
- Thinner coatings than batch HDG, resulting in shorter service life
- Fabrication after coating (cutting, punching, bending) exposes uncoated steel that must be touched up
- Only available for sheet products, not structural piles or racking shapes
- Solar takeaway: Suitable for thin sheet components, but not ideal for primary structural piles and posts.
Zinc-Aluminum-Magnesium (ZM) Coatings
- What it is: ZM coatings are a zinc-aluminum-magnesium alloy coating applied to steel sheet in a continuous coil line before fabrication. Typical compositions include about 90–96% zinc with small additions of aluminum and magnesium. ZM was developed as an alternative to continuous sheet galvanizing placed in aggressive environments to reduce coating thickness requirements while extending service life in thin sheet applications. This makes ZM particularly appealing in applications where weight savings or reduced coating consumption are priorities.
- Performance:
- Limited laboratory test data suggests comparable longevity to HDG. However, much of this data relies on accelerated corrosion testing proven to be unsuitable for comparing the performance of zinc coatings.
- Salt-spray tests do not replicate real-world conditions where natural wetting and drying cycles form a zinc patina that greatly slows atmospheric corrosion rates. See detailed information sheet developed by the European General Galvanizers Association (EGAA) and supported by the American Galvanizers Association (AGA) on salt spray testing and why it should not be used to compare different types of coatings: Information Sheet: Salt Spray Testing Limitations:
- Limited to sheet steel; no after-fabrication process for shapes or weldments.
- Many of the limitations are the same as continuous galvanizing, including thinner coatings, reliance on touch-up at cut edges, and less robust protection compared to batch HDG.
Solar takeaway: ZM coatings may be an option for secondary sheet components if cut edges are carefully detailed and touched up. For primary piles, posts, and racking, batch HDG after fabrication provides thicker zinc, full coverage, and lower lifecycle risk.
Polymer Coatings (Polyurethane, Epoxies, Paints)
- What they are: Liquid-applied protective coatings designed for steel piling embedment (example: Sherwin-Williams Poly-Cote 110).
- Advantages: Provide additional barrier protection, customizable finishes, can be applied over HDG for use in highly aggressive soils.
- Limitations:
- Does not provide sacrificial protection when applied over bare steel (still rust at small scratches)
- Susceptible to damage during pile driving or installation
- Requires strict surface prep and precise application
- Best Use: As part of a duplex system over HDG in highly corrosive environments, where the zinc provides sacrificial protection and the polymer adds barrier backup.
- Solar takeaway: Effective in aggressive soil conditions when combined with hot-dip galvanizing, but less reliable as a standalone solution.
Conclusion
Solar piles, racking, and frames face some of the harshest durability demands in the energy sector. Corrosivity of the environment and durability options in solar projects should be evaluated with care. Among available coatings, hot-dip galvanizing (HDG) remains the gold standard, with decades of real-world performance data in soils, water, and atmospheric conditions. Other options such as bare steel, continuous galvanizing, ZM coatings, and polymer systems may be suitable in certain cases, but they carry higher risks or shorter lifespans when used alone.
At CES, we promote clear, data-driven guidance to ensure solar infrastructure is built on steel and coatings that deliver the strength and protection needed for a sustainable future.
About the Clean Energy Steel Construction Center (CES)
The Clean Energy Steel Construction Center is an industry-led initiative focused on advancing the use of durable, cost-effective, and sustainable steel solutions in clean energy and utility infrastructure. CES works across transmission, distribution, solar, wind, and emerging energy markets through education, research, and collaboration to support long-life infrastructure solutions.
About the Author
Jeff Suda is an experienced trade association leader and utility industry professional with deep expertise in electric utility infrastructure, code standards, and clean energy deployment. He serves as a founding leader of CES and has led industry coalitions that bridge technical, regulatory, and commercial stakeholders to clarify and improve utility design and construction standards. Jeff’s work focuses on helping technical and non-technical audiences understand complex systems and how their application across distribution, transmission, and renewable energy infrastructure. He regularly writes and speaks on topics where materials performance, structural design, and electrical standards intersect in utility and clean energy projects.