Carbon Steel Solar Ground Mount System - Inward-curved C-shaped steel

The inward-curved C-shaped steel is a core load-bearing component of a ground-mounted photovoltaic (PV) support system, belonging to the category of cold-formed thin-walled steel. Its cross-section is C-shaped, with inward-curving edges on both sides and reinforced ribs, hence it is also known as a "C-shaped PV purlin." This product is typically made from Q235B or Q345B hot-rolled steel plates or strips, processed by a continuous cold-bending forming unit, and then hot-dip galvanized or zinc-aluminum-magnesium galvanized surface treatment according to corrosion protection requirements.

As the longitudinal support structure of the PV array, it connects the pile foundation or helical piles to the upper PV modules, transferring external loads such as wind and snow to the ground. It is a key component ensuring the structural safety and stability of the power station.

Product Components

Advantage

▪ High structural strength and low steel consumption:

The unique rolled-edge reinforced section design significantly improves the bending, torsional, and buckling resistance of the components. Compared to ordinary C-shaped steel or open-section steel, it can save approximately 20%-30% of steel while maintaining the same strength, effectively reducing the cost of the support system.

▪ Excellent corrosion resistance:

Mainstream applications use hot-dip galvanizing (coating weight 275-600g/m²) or more advanced zinc-aluminum-magnesium (ZAM) coating processes. Zinc-aluminum-magnesium coating features self-healing cuts, scratch resistance, ammonia resistance, and resistance to sea salt spray corrosion, meeting the 25+ year service life requirements of photovoltaic power plants.

▪ Convenient installation and strong adaptability:

With dedicated connectors, spring nuts, and bolts, a fully bolted connection can be achieved, eliminating the need for on-site welding. Long mounting holes (or oblong holes) on the back allow for flexible length adjustment to accommodate uneven ground and installation errors.

▪ Easy transportation and stacking:

The steel sections can be stacked, occupying minimal space; the standard 6-meter length facilitates transportation by ordinary trucks, and proper cutting can reduce on-site secondary processing.

Parameters

Applicable Scenarios

▶ Large-scale centralized ground-mounted power stations:

Used as main load-bearing purlins and diagonal braces in open areas such as flat land, grasslands, deserts, and Gobi, forming single-column or double-column support systems.

▶ Commercial and residential ground-mounted photovoltaic systems:

Used as columns, diagonal beams, and horizontal braces in small to medium-sized ground-mounted projects such as factory areas, idle rural land, and around agricultural greenhouses.

▶ Concrete flat roofs (with additional supports):

Used in conjunction with ballast foundations as inclined or flat purlins supporting photovoltaic modules.

▶ Aquaculture-solar hybrid and agricultural-solar hybrid systems:

Used as the main load-bearing profile when the overhead height is high, effectively resisting wind loads and corrosion from long-term humid environments (requires galvanized aluminum-magnesium plating or reinforced anti-corrosion treatment).

▶ Mountainous and sloping terrain:

Adaptable to terrain slopes of 5-15° by adjusting the height difference between the front and rear columns and using the connecting elongated holes of inward-rolled C-shaped steel.

Applicable Soil Type

The inward-rolling C-shaped steel support system is suitable for almost all soil types because its load is transferred through the foundation. For foundation construction, the following soil types are ideal:

• Clay and silty clay: High bearing capacity, less prone to borehole collapse, suitable for bored piles or precast piles.
• Sand and gravelly sand: Good drainage, suitable for helical piles, rapid construction, and minimal disturbance.
• Compacted fill: For artificial foundations or old factory sites, precast piles or micro-hole bored piles can be used.
• Loess and red soil (non-collapseable): Conventional bored piles are sufficient; no special treatment is required for the C-shaped steel support.

Geological Limitations to Consider

Although C-shaped steel supports do not directly contact deep soil layers, the following geological conditions can affect foundation selection and cost, indirectly limiting their economic applicability:

▶ Rock or gravelly soil layers:

If moderately weathered rock or large gravel appears 0.5m below the surface, spiral piles cannot be driven in, and drilling and grouting piles become difficult and costly. In this case, concrete counterweight foundations (strip or independent foundations) must be considered, but this will increase excavation and concrete usage.

▶ Soft soil and silty soil:

These have extremely low bearing capacity (<60kPa) and are prone to settlement. Longer precast piles or deeper grouting piles are required, leading to a significant increase in pile foundation costs and potentially diminishing the advantages of lightweight C-shaped steel supports.

▶ Collapseable loess:

Significant additional settlement occurs upon contact with water. Waterproofing or foundation treatment measures (such as a lime-soil cushion layer or pre-soaking) are necessary; otherwise, uneven settlement of the support foundation will bend the C-shaped steel, causing microcracks in the photovoltaic modules.

▶ Frost-susceptible soils (silt, silty clay):

In cold regions, frost heave forces will lift the piles upwards. The pile foundation must be buried below the frost line, and the adjustment margin at the connection between the C-shaped steel and the pile top must be increased.

▶ High groundwater level or quicksand layers:

During drilling, borehole collapse and quicksand inflow are likely, affecting the quality of the cast-in-place piles. Steel spiral piles or driven precast piles can be used, but the C-shaped steel connection joints require special corrosion protection.

Summary

Inward-curved C-shaped steel, with its high strength-to-weight ratio, excellent corrosion resistance, and flexible installation adjustment capabilities, has become the most mainstream secondary and primary structural profile in ground-mounted photovoltaic (PV) support systems. Its cold-bent, rolled-edge cross-section design achieves a balance between reduced steel consumption and load-bearing capacity, making it suitable for most application scenarios, from plains to mountains, and from ordinary soil to mildly corrosive environments.

 

Key selection recommendations: In the early stages of a project, the cross-section and wall thickness of the C-shaped steel should first be determined through structural calculations based on local wind and snow loads. Secondly, a suitable coating should be selected based on the soil corrosivity level (hot-dip galvanizing is generally suitable for most inland sites; zinc-aluminum-magnesium coating is recommended for sites within 5km of the coastline or in heavy industrial areas). Finally, for special geological conditions such as rock, soft soil, and collapsible loess, separate foundation designs are required; relying solely on the universal joints of C-shaped steel is not advisable.

 

 

The future trend is the combination of high-strength steel (such as Q420 and Q460) and ultra-corrosion resistant coatings (zinc-aluminum-magnesium pre-coated plates), which aims to further reduce the total weight of the support structure and the total life cycle cost, while improving the power plant's ability to cope with extreme weather.

 

Solar First Project Reference

• 
• 

 

Related Knowledge Points

（1）Inward-Rolled C-Shaped Steel: Six Key Knowledge Points