Anodised aluminium or galvanised steel: which material for a solar structure
Technical comparison anodised aluminium 6063-T5 vs galvanised steel Z275 for solar carports, canopies and ground mounts: density, corrosion, price per kg, aesthetics, coastal lifespan. Verdict per use case.
Once you have chosen metal (over wood) for your solar mounting structure, a second question arises: anodised aluminium or galvanised steel? The answer is not binary. Aluminium 6063-T5 anodised and galvanised steel Z275 have very different property profiles: density, corrosion resistance, price per kg, aesthetics, fatigue behaviour. Depending on your site (coastal UK, Highland Scotland, inland England) and use case (residential vs commercial), one material dominates over the other.
This article compares both materials by 8 quantified criteria and gives a verdict for 5 typical UK use cases.
The two materials in brief
Aluminium 6063-T5 anodised
Magnesium-silicon alloy, most used in construction. T5 temper: press quenched + artificially aged. 15 µm anodising: electrochemically grown oxide layer, protects against corrosion, gives matt satin finish, allows colouring (bronze, black, anthracite).
- Density: 2.70 g/cm³ (1/3 of steel)
- Young’s modulus: 70 GPa
- Yield strength: 170 MPa
- Thermal expansion: 23 × 10⁻⁶ /K
- Extruded profile price: £18-22/kg
Galvanised steel Z275
S235JR or S275JR construction steel coated with 275 g/m² zinc on both faces (BS EN 10346). Standard for outdoor use in non-aggressive environments.
- Density: 7.85 g/cm³ (3× aluminium)
- Young’s modulus: 210 GPa (3× aluminium)
- Yield strength: 235-275 MPa
- Galvanised tube/profile price: £8-14/kg
Comparison across 8 criteria
1. Strength-to-weight ratio
| Material | Re/ρ |
|---|---|
| Aluminium 6063-T5 | 63 |
| Steel S275 galvanised | 35 |
Aluminium is 80% more efficient per kg for strength.
2. Stiffness
Steel is 3× stiffer than aluminium (Young’s modulus). Compensated with wider profiles in aluminium designs.
3. Corrosion resistance
| Environment | Anodised aluminium | Galvanised steel Z275 |
|---|---|---|
| Indoor dry | Excellent > 50 years | Excellent > 50 years |
| Outdoor temperate (inland England, Wales) | Excellent 30-40 years | Very good 25-35 years |
| Urban polluted (London, Manchester) | Very good 25-35 years | Good 20-30 years |
| UK coastal (Brighton, Cornwall, Scottish coast) | Good 20-30 years | Poor 10-15 years |
| Industrial (S²O, NH₃) | Very good with adapted finish | Poor |
Aluminium dominates UK coastal applications. Galvanised steel Z275 alone is not viable for coastal installations — needs duplex epoxy coating.
4. Material cost per kg
Steel is 2-3× cheaper per kg in raw material. But aluminium weighs 3× less, balancing total cost.
5. Total 2-car carport cost
For 6 × 5.5 m to BS EN 1991 Manchester area:
| Item | Aluminium | Galvanised steel |
|---|---|---|
| Profiles + accessories | £1,700 | £1,250 |
| Stainless A2 fasteners | £160 | £160 |
| Foundations | £310 | £400 |
| Transport | £250 | £315 |
| Installation | £760 | £850 |
| Total ex VAT | £3,180 | £2,975 |
Final difference marginal — about 6-7% in favour of steel for inland UK standard carports.
6. Aesthetics
Anodised aluminium has a “premium” satin matt look for modern architecture. Galvanised steel raw has industrial-functional appearance. Powder-coated steel RAL (+£3-4/kg) bridges the gap.
7. Recyclability and embodied carbon
| Criterion | Aluminium | Galvanised steel |
|---|---|---|
| Recycling rate | 95% | 90% |
| Recycling energy vs primary | 5% | 25% |
| Primary CO₂ | 8-15 kg CO₂/kg | 2-3 kg CO₂/kg |
| Recycled CO₂ | 0.5-1 kg CO₂/kg | 0.5-1 kg CO₂/kg |
Aluminium has higher primary footprint, better recycling loop. Sunrak uses 35-65% recycled aluminium content.
8. Fatigue performance
Galvanised steel has 2-3× higher fatigue strength than aluminium. Important for canopies exposed to recurring high winds (Hebrides, Outer Hebrides, west coast Scotland).
Verdict by use case
| Use case | Recommendation |
|---|---|
| Residential carport, temperate inland UK | Anodised aluminium 6063-T5 |
| Residential carport coastal (UK / Ireland) | Anodised aluminium 6063-T5 |
| Agricultural structure (livestock NH₃) | Aluminium |
| Commercial car park canopy inland | Powder-coated galvanised steel Z275 |
| Coastal or high-wind exposed car park | Mixed: steel posts + aluminium rafters |
| Large solar farm ground mounting | Galvanised steel Z275 |
| Listed-building-adjacent visible structure | Powder-coated aluminium specific RAL |
FAQ
Does aluminium resist UK coastal salt air?
Yes, when anodised. 15 µm anodised aluminium lasts 20-30 years in UK coastal environments. Untreated aluminium oxidises in 5-10 years. Galvanised steel only lasts 10-15 years in these conditions.
Is there a more corrosion-resistant galvanised option than Z275?
Yes. Z350 (350 g/m²), Z450 (450 g/m²), or hot-dip galvanising (80-100 µm thicker). Also "duplex": galvanising + epoxy coating. Cost +30-50% over Z275 standard.
What is the Sunrak warranty for each material?
20-year structural warranty (corrosion, deformation, integrity) for anodised aluminium 6063-T5 and galvanised steel Z275 in inland environments. 15 years in direct coastal exposure.
Is mixing aluminium and steel feasible?
Yes, often optimal for exposed canopies: steel posts (fatigue) + aluminium rafters (lightness). Galvanic isolation required at contact (plastic washer or insulating paint) to prevent corrosion.
Which material best integrates an EV charger?
Aluminium — our extruded profiles include a cable channel in the section core for invisible wiring. Steel requires drilling and a weatherproof cable gland.
Galvanised steel in agricultural / livestock buildings?
Not recommended. NH₃ from livestock and humid environments attack zinc rapidly. For agricultural use with animals, opt for anodised aluminium or 316 stainless steel.
What if I am in Highland Scotland with extreme wind exposure?
For Highland Scotland or Outer Hebrides with vb,map of 28-32 m/s and frequent gusts > 40 m/s, our recommendation is a hybrid structure: galvanised steel S275 for primary posts (better fatigue) + anodised aluminium for rafters. Foundations sized for uplift resistance.
Further reading: