Selecting Solar Mounting Profiles: Criteria for C, U, Sigma and W Piles, Purlins and Rails

The steel structure that carries the modules of a ground-mount solar plant consists of four member groups: piles driven into the ground, chords and rafters that set the tilt, purlins and rails that carry the modules, and the connections that tie them together. All of them work outdoors for a 25–30-year design life under wind, snow and corrosion. An undersized section creates structural risk; an oversized one adds tonnage and cost.

This guide covers profile selection in the engineering sequence we follow on a project. For technical ranges and section tables see our solar steel profiles page.

Profile selection starts from site data, not from a catalogue. The required inputs: wind (basic wind speed and terrain category; EN 1991-1-4 / Eurocode 1 or ASCE 7), snow (ground snow load; EN 1991-1-3), seismic (TBDY 2018 in Türkiye, Eurocode 8 or the local code elsewhere), soil (geotechnical survey: soil class, stones, groundwater, corrosivity) and the corrosion environment (ISO 9223 atmospheric corrosivity category and soil corrosivity).

Wind does not only press on tilted modules: suction on their back tries to pull the pile out of the ground. On most sites that uplift sets pile depth, and the higher wind pressures at array edges set the sections of edge and corner tables.

Table layout is the design decision that affects profile demand most. 1V tables (one row of portrait modules) are low and load each pile lightly, but need more piles per MW. 2V tables (two rows) carry more power on fewer piles, at the cost of a larger moment per pile and taller rear piles. Landscape layouts are assessed the same way.

Tilt changes the loads too: a steeper angle means more exposed area and taller rear piles. Pre-sizing 1V and 2V for the same site and comparing total tonnage usually identifies the most economical solution — see our guide on steel tonnage per MW.

The aim is to achieve the required bending and uplift capacity with the least steel weight. Section details: C-pile, U-pile, sigma pile, W-beam pile.

Adding gauge to the same section adds capacity but increases tonnage in direct proportion. Raising the steel grade is often the more efficient route: with S420GD or S450GD instead of S350GD (all EN 10346 grades) the same load is carried at a thinner gauge. Cold-formed profiles are designed to EN 1993-1-3, where local buckling means effective section properties, rather than the gross section, are used.

Capacity is not the only driver of gauge: the pile tip must withstand driving into hard ground, and some projects add a corrosion allowance for soil corrosion (the EN 1993-5 approach).

The part of a pile above ground faces the atmosphere and the embedded part faces the soil; corrosion is usually heaviest just below the ground surface, in the transition zone where moisture and oxygen conditions vary. The coating class is therefore chosen from soil corrosivity as well as the atmospheric corrosivity category (ISO 9223).

Zn-Al-Mg (ZM) is widely used on solar profiles because it self-heals at cut and punched edges and outlasts galvanizing at the same coating mass. Coating classes, corrosion rates and a preliminary life estimate are covered in our Zn-Al-Mg guide.

Purlin and rail sections follow the module size, the clamping zones permitted by the module manufacturer and the span. C purlins are simple and common; Z purlins lap over supports and act as continuous beams along long rows, reducing tonnage; omega rails, being symmetric, give module clamps a wide mounting face. Details: purlins and rails.

Drilling, cutting and welding on site add labour and damage the coating, so every connection hole and adjustment slot should be punched in production on the roll-forming line. Slot lengths must be designed to absorb pile-driving tolerances — verticality, level and row alignment — otherwise individual piles need correcting on site. Fabrication is carried out under EN 1090.

Applying one section to the whole site. Edge and corner tables see higher wind loads than interior ones; zoned sizing reduces tonnage.

Setting pile depth without tests. A depth chosen without pull-out tests is either inadequate or longer than necessary — see pile driving and pull-out testing.

Selecting the coating for atmospheric conditions only. Below ground, soil corrosivity governs.

Leaving holes to the site. Every field-drilled hole costs time and coating integrity.

Preparing the length list independently of shipping. Truck and container dimensions shape the length list; plan packing at design stage.

For an accurate, fast quotation the data below is required. With it we size sections and tonnage together; we supply projects across Türkiye and in Europe, the Middle East and the USA (through our Mona Steel branch). Upload your files through our quote form.