Aluminum vs Steel
Solar Mounting: Full Comparison

Aluminum and steel are both structurally appropriate for solar mounting systems. The decision is not which material is "better" in absolute terms — it is which material is more cost-effective for a specific application, given the loading requirements, installation environment, roof type, and total landed cost including shipping.

Aluminum alloy 6005A-T5 has a density of 2.70 g/cm³ — approximately one-third that of steel (7.85 g/cm³). A standard aluminum rail section at 1.5 kg/m weighs roughly one-third as much as an equivalent steel C-section at 4.5 kg/m. For a 10 kW residential rooftop system requiring approximately 50 linear meters of rail, this translates to 75 kg of aluminum versus 225 kg of steel. That 150 kg difference is significant in two respects: it reduces the dead load on the roof structure, and it reduces the shipping cost for international freight.

Steel's advantage is structural capacity per unit cost. Q355B steel has a yield strength of 355 MPa versus 260 MPa for 6005A-T5 aluminum. For high-load applications — utility-scale ground mounting in high-wind zones, heavy snow load regions, or large commercial flat-roof ballast systems — steel sections can carry greater loads for less material cost, despite the weight and corrosion protection requirements.

For international solar mounting procurement from China, freight cost is a significant component of total landed cost. The relationship between material weight and freight cost differs depending on whether a container is loaded to weight limit (24 tonnes for a 20ft container) or volume limit (33 CBM for a 20ft container).

Aluminum mounting hardware is volumetrically bulky relative to its weight. A 20ft container loaded with aluminum roof mounting rail is typically limited by CBM (volume) before reaching the weight limit — meaning you are paying for the container volume, and lighter aluminum does not reduce the number of containers needed per MW. In this scenario, the weight advantage of aluminum translates primarily to reduced dead load on the roof structure, not to fewer containers.

Steel ground-mount structures — C-purlins, Z-sections, piles, and base plates — are denser and can be nested for packing efficiency. A well-packed steel ground-mount kit may fill a container to its weight limit before its volume limit, making the heavier-per-unit weight a real freight cost factor at scale. However, at 10 MW+ scale, the per-MW steel material cost saving (15–25%) typically outweighs the per-MW shipping premium.

Practical guideline: For residential and commercial rooftop projects up to 1 MW, aluminum roof mounting rail (mini-rail or standard rail) shipped in containers is typically more cost-effective on a total landed cost basis. For utility-scale ground mounting from 5 MW upward, steel C-section purlins and pile-driven foundations consistently win on cost per installed watt.

Aluminum: Bare 6005A-T5 aluminum extrusion is inherently corrosion-resistant in most outdoor environments due to the passive Al₂O₃ oxide layer. For solar mounting applications, anodised aluminum (minimum 10 µm coating for inland, 20 µm for coastal environments per AS 1231 or equivalent) provides additional protection and is specified by most quality manufacturers. Mill-finish (unanodised) aluminum is acceptable for inland dry climates but not recommended within 500m of the coast where salt spray is a factor.

Steel: Steel without corrosion protection will begin surface rusting within weeks of outdoor exposure in humid climates. Hot-dip galvanizing (HDG) is the standard protection method for solar mounting steel components. AS/NZS 4680 (Australia), EN ISO 1461 (Europe), and ASTM A123 (USA) specify minimum coating thickness. For solar mounting hardware, Z275 galvanising (275 g/m² zinc coating, approximately 38 µm per side) is the minimum acceptable specification. For coastal or tropical environments, ZM275 zinc-magnesium-aluminum coated steel (also written as ZMA275 or Magnelis) provides superior corrosion resistance with a thinner coating — the 5–11% aluminum content in the zinc-magnesium-aluminum alloy passivates cut edges, which is the most vulnerable point in galvanised sheet.

Fasteners: For both materials, specifying the correct fastener material is as important as the structural member material. SUS304 stainless steel (A2) is the minimum for general applications. SUS316 (A4) is required for tropical coastal environments. Carbon steel fasteners with zinc plating are not adequate for 25-year outdoor service — the coating delaminates within 5–10 years. OmniSol standard specifications use SUS304 for all fasteners in roof and ground-mount systems.

OmniSol manufactures both aluminum and steel solar mounting systems across all application categories. Aluminum roof mounting systems include the Universal Tile Hook System (6061-T6 stainless hook, 6005A-T5 anodised rail) and the Mini-Rail System (6005A-T5, split module design). Steel systems include the Carbon Steel Ballast Frame (Q235B, hot-dip galvanized) for flat roof applications, and the Ground Tripod System (Q355B, ZM275 coated) for utility-scale ground mounting.

For projects requiring a material specification recommendation, OmniSol's engineering team provides a written material recommendation with reference to the project application, wind region, snow load, and any applicable standards (AS/NZS 1170, ASCE 7, Eurocode) as part of the standard RFQ response. There is no charge for this service.