Comparison And Selection Of Steel And Aluminum For Photovoltaic Brackets

1. Material strength

Generally, for photovoltaic brackets, steel is better than aluminum alloy profiles in strong wind areas and large spans.

2. Deflection deformation

The deflection deformation of the structure is related to the shape and size of the profile and the elastic modulus (a parameter inherent in the material). It has no direct relationship with the strength of the material.

Under the same conditions, the deformation of aluminum alloy profiles is 2.9 times that of steel, and the weight is 35% of steel's. Regarding cost, aluminum is 3 times that of steel at the same weight. Therefore, steel is generally better than aluminum alloy profiles in strong wind areas, large spans, and cost.

3. Corrosion resistance

Currently, the main anti-corrosion method for brackets is hot-dip galvanizing 55-80μm for steel and anodizing 5-10μm for aluminum alloy.

Aluminum alloy is in the passivation zone under the atmospheric environment. A dense oxide film is formed on its surface, which prevents the active aluminum matrix from contacting the surrounding atmosphere. Therefore, it has very good corrosion resistance, and the corrosion rate decreases with time.

Under normal conditions (C1-C4 environment), 80μm galvanized steel can be used for more than 20 years, but in high-humidity industrial areas high-salinity seashores, or even temperate seawater, the corrosion rate is accelerated. The galvanizing amount needs to be 100μm or more and regular maintenance is required yearly.

In terms of corrosion resistance, aluminum alloy is far superior to steel.

4. Comparison of other aspects of corrosion

(1) Appearance:

Aluminum alloy profiles have many surface treatment methods, such as anodizing, chemical polishing, fluorocarbon spraying, electrophoretic painting, etc. The appearance is beautiful and can adapt to various highly corrosive environments.

Steel is generally treated by hot-dip galvanizing, surface spraying, paint coating, etc. The appearance is worse than aluminum alloy profiles. It is also worse than aluminum profiles in terms of corrosion resistance.

(2) Diversity of cross-sections

The general processing methods for aluminum alloy profiles include extrusion, casting, bending, stamping, etc. Extrusion production is the current mainstream production method. Opening an extrusion die can produce any cross-section profile, and the production speed is relatively fast.

Steel is generally produced by rolling, casting, bending, stamping, etc. Rolling is currently the mainstream production method for cold-bent steel. The cross-section needs to be adjusted by a rolling wheelset, but generally, the machine can only produce the same product after the finalization, the size can be adjusted, and the cross-section shape cannot be changed, such as C-shaped steel, Z-shaped steel, and other cross-sections. The rolling production method is relatively fixed and the production speed is relatively fast.

5. Material recycling

The maintenance cost of steel structures increases by 3% each year. In contrast, the brackets of aluminum structures require almost no maintenance and maintenance, and aluminum still has a 65% recycling rate after 30 years. The price of aluminum is expected to increase by 3% each year. After 30 years, the steel structure is a pile of scrap iron with no recycling value.

6. Comprehensive performance comparison

(1) Aluminum alloy profiles are light in weight, beautiful in appearance, and have excellent corrosion resistance. They are generally used in household rooftop power stations with load-bearing requirements and in highly corrosive environments.

(2) Steel has high strength and small deflection when bearing loads. It is generally used in ordinary power stations or for components with relatively large forces.

(3) Cost: Under normal circumstances, when the basic wind pressure is 0.6kN/m2 and the span is less than 2m, the cost of aluminum alloy brackets is 1.3-1.5 times that of steel structure brackets. In small-span systems (such as color steel plate roofs), the cost difference between aluminum alloy brackets and steel structure brackets is relatively small, and aluminum alloy brackets are much lighter than steel brackets in terms of weight, so they are very suitable for household rooftop power stations.