If you’ve spent time comparing solar structure quotes, you’ve probably noticed that some suppliers mention “galvanised steel” and some mention “powder-coated steel” — and a few mention coating thicknesses in microns. Most buyers don’t know what these terms mean or whether they matter. They matter enormously.
The coating on your solar mounting structure is not cosmetic. It is the only barrier between the steel and the corrosive forces that begin working on it from the day of installation. The difference between the right coating and the wrong one is the difference between a structure that lasts 25 years and one that requires replacement in 8–10.
Why Steel Corrodes in the First Place
Steel corrodes because iron — its primary constituent — reacts with oxygen and moisture to form iron oxide (rust). This reaction is thermodynamically favourable, meaning it happens spontaneously and continuously wherever bare steel is exposed to an oxidising environment.
In India’s solar markets — outdoor, humid, UV-exposed, frequently wet from monsoon rain and dew, and in coastal areas laden with salt-bearing air — the conditions for steel corrosion are nearly ideal. An unprotected steel structure in coastal Andhra Pradesh begins showing visible corrosion within 12–18 months.
Every corrosion protection system works by creating a barrier between the steel surface and the oxidising environment. The differences between systems lie in the durability, adhesion, and self-healing capability of that barrier.
Hot-Dip Galvanisation: How It Works and Why It’s Different
Hot-dip galvanisation (HDG) is not a coating applied to steel’s surface. It is a metallurgical reaction that creates new alloy layers bonded to the steel at a molecular level.
The process: cleaned steel components are immersed in a bath of molten zinc at approximately 450°C. The zinc reacts with the iron in the steel to form a series of iron-zinc alloy layers, topped by a pure zinc outer layer. When the component is withdrawn, these layers are permanently part of the steel — not applied over it.
The result is a coating system with three distinct protective mechanisms:
Physical barrier: The zinc and iron-zinc alloy layers prevent oxygen and moisture from reaching the underlying steel.
Cathodic protection: Zinc is electrochemically more reactive than iron. Where the coating is scratched or damaged, the zinc sacrifices itself preferentially — corroding to protect the exposed steel. This self-healing mechanism is the fundamental advantage of galvanisation over paint-based systems.
Long service life: In moderate to severe industrial atmospheres — which outdoor solar installations qualify as — hot-dip galvanised coatings with 85 micron minimum thickness provide 40–70 years of effective corrosion protection in inland environments, and 25–40 years in coastal environments with salt-laden air.
The Indian standard for hot-dip galvanising on structural steel is IS 4759 (for fabricated articles) and IS 2629. The minimum acceptable coating thickness for structural outdoor applications in Indian conditions is 85 microns — this is the specification that matters when evaluating a solar structure.
Paint and Powder Coating: What They Can and Cannot Do
Paint and powder coating are surface-applied coatings. They create a physical barrier between steel and the environment, but they have critical limitations compared to HDG.
Adhesion is mechanical, not metallurgical. Paint bonds to steel through surface adhesion — it sits on top of the steel rather than being integrated with it. Any scratch, impact, or flexural crack in the paint creates a direct pathway for corrosion to begin underneath.
No cathodic protection. Paint has no sacrificial mechanism. When it fails at a point, it continues to fail outward as corrosion spreads under the coating — a process called undercutting. HDG’s cathodic protection stops this process at the damaged point.
Typical service life outdoors in Indian conditions: epoxy or polyurethane paint systems on steel exposed to tropical outdoor conditions show significant degradation in 5–8 years. Powder coating performs similarly. Both require periodic maintenance (repainting) to maintain effectiveness beyond this period.
Cold galvanising (zinc-rich paint) is a paint with zinc powder in it. It provides improved corrosion resistance over standard paint — including limited cathodic protection — but it is not a substitute for hot-dip galvanisation. The zinc is bound in a resin matrix rather than metallurgically integrated, resulting in significantly lower zinc density at the steel surface and shorter effective service life.
The Micron Number: What It Tells You
Coating thickness is measured in microns (µm) — millionths of a metre. The relationship between thickness and service life is direct: thicker coatings last longer.
For hot-dip galvanised solar structure steel:
Below 55 microns: inadequate for outdoor structural use in India
55–85 microns: minimum acceptable for inland, non-coastal sites
85 microns+: the appropriate standard for all solar structure applications in India
100+ microns: specified for coastal sites with high salt exposure
When a solar structure supplier quotes their structure as “galvanised” without specifying micron thickness, you are being told nothing meaningful. A 30-micron coating technically qualifies as galvanised. So does an 85-micron coating. The service life difference between them in coastal Andhra conditions is approximately 15 years.
Ask for the coating thickness. If you receive a specification, it tells you something. If you receive a blank look, it tells you something too.
Making the Right Choice
For any solar structure that you intend to install and leave in place for 20–25 years — which is the entire premise of a solar investment — the corrosion protection specification matters as much as the structural design.
The correct specification for India’s solar markets is IS 4923 structural steel with minimum 85-micron hot-dip galvanisation, with 100-micron minimum for coastal sites within 10 km of the sea or in high-humidity environments. All fasteners and connectors should be stainless steel grade 316 (for coastal sites) or 304 (for inland sites) — or hot-dip galvanised to the same minimum standard.
These specifications cost more than painted alternatives. The additional cost is roughly ₹3–6 per watt of system capacity at standard commercial scale. Over a 25-year system life, this translates to a protection cost of less than ₹0.01 per kWh generated — one of the cheapest insurance policies in engineering.
Vlux manufactures all solar mounting structures using IS 4923 steel with minimum 85-micron hot-dip galvanisation through a 7-stage process. We provide material test certificates and coating thickness documentation with every project delivery. If you’d like to understand the structural specifications of a system you’ve already quoted — or get a proposal on a new installation — contact our team.
