GI Steel vs Aluminium Mounting Structures
Verdict
Verdict: Hot-dip galvanised steel is the cost-effective default for most Indian rooftops and ground mounts, provided the coating is genuinely 80+ microns per IS 4759. Aluminium costs more but wins decisively in coastal and high-humidity environments, and where structure weight is constrained by the roof.
Side-by-Side Comparison
| Criterion | Hot-Dip Galvanised Steel | Aluminium |
|---|---|---|
| Material cost | Lower | 30–60% higher |
| Structural strength | Higher per section | Lower (needs larger sections) |
| Corrosion resistance | Good if coating intact | Excellent (self-passivating) |
| Coastal / saline suitability | Risk at cut edges & damage | Preferred choice |
| Weight on roof | Heavy | Light |
| Site modification | Cutting exposes bare steel | Cuts remain corrosion-safe |
| Typical service life | 20–25 yr with proper coating | 25+ years |
| Availability in India | Very wide | Wide, more fabricator-dependent |
Bold green marks the stronger option on that criterion. Figures are typical Indian market values as of 2026 and vary by brand, site, and supplier.
Choose Hot-Dip Galvanised Steel If…
- Inland rooftops and ground mounts in normal (non-saline) environments
- Cost-driven projects where structure is a significant budget line
- Ground-mount tables where strength per rupee dominates
- Provided you verify galvanising thickness — this is where cheap quotes cut corners
Choose Aluminium If…
- Coastal sites, high-humidity regions, or industrial areas with corrosive air
- Roofs with load limits where structure weight genuinely matters
- Elevated architectural installations where appearance and finish matter
- Projects prioritising 25-year maintenance-free life over upfront cost
Coating Thickness Is the Whole Argument
GI steel’s corrosion resistance lives entirely in its zinc coating. IS 4759 practice for solar structures calls for around 80 microns of hot-dip galvanising; cheap structures often carry 40–50 microns, or worse, are pre-galvanised sheet folded after coating, leaving bare steel at every bend and cut.
Ask for the galvanising test certificate with measured microns. This single document separates a 25-year structure from one that will show rust before its first five monsoons.
What Both Must Prove
Material is secondary to engineering. Whatever the metal, the structure must be designed for the site’s basic wind speed per IS 875 Part 3, with anchoring specified accordingly. India’s coastal and cyclone-prone zones see 150+ km/h design speeds, and underweight structures with inadequate anchoring are a leading cause of catastrophic rooftop failures.
Insist on the wind-load design calculation and the anchoring detail. A fabricator who cannot produce them is selling metal, not a structure.
Frequently Asked Questions
- Which structure is better for coastal solar installations?
- Aluminium, generally — it resists saline corrosion inherently, including at cut edges where galvanised steel is vulnerable. Marine-grade alloys with stainless fasteners are standard near the coast.
- How thick should galvanising be on a solar structure?
- Around 80 microns of hot-dip galvanising is the practice for solar structures under IS 4759. Ask for the measured test certificate — thin coating is a common cost-cutting shortcut.
- Does structure choice affect my generation?
- Indirectly but meaningfully — through tilt accuracy, elevation (ventilation and bifacial rear gain), and row spacing. A structure that shifts or corrodes also risks module damage and downtime.