A solar mounting structure is the least glamorous component of a PV project and the one most likely to fail first. Panels and inverters come with performance warranties backed by large manufacturers. The galvanized steel or aluminium frame that holds those panels at the right tilt angle in cyclone-rated wind for 25 years usually comes from a fabricator with a two-page datasheet and no wind load calculation in the documentation pack. By the time a site audit or insurance inspection asks for the structural calculation, the EPC's original supplier has moved on.
Ground mount or rooftop: the structural logic is different
A ground mount structure sits on driven piles or concrete footings, carries the full wind uplift and in-plane shear load through the racking system to the ground, and must not impose moment loads that cause piles to walk over 25 years of thermal cycling. A rooftop structure transfers loads into a building roof that has its own structural capacity limit, the EPC must know the roof's allowable distributed load, the purlin spacing and the roofing sheet type before specifying ballasted or penetrating fixings. Getting this wrong does not cause an immediate collapse; it causes cumulative fatigue at the fixing point that shows up as a leak or a loose panel in year seven.
Wind load: the calculation that most suppliers skip
Solar structures are classified as open structures under IS 875 Part 3 (India's wind load code) or ASCE 7 (USA/Middle East), AS 1170.2 (Australia), or BS EN 1991-1-4 (UK/Europe). The design wind pressure depends on the basic wind speed at the site (in m/s), the terrain category, the height above ground, and the shape coefficient for the panel array. A 40 m/s basic wind speed site in coastal Kerala or coastal Queensland produces roughly twice the wind pressure of a 28 m/s inland site. If the structural drawing from the manufacturer does not show the design wind speed, terrain category and code reference, it has not been designed for your site.
Material: galvanized steel vs aluminium, when each is right
- Hot-dip galvanized steel (IS 2629 / IS 4759): higher load capacity per section, lower cost per tonne for ground mount arrays. HDG life in rural inland climate is 25+ years. For coastal sites within 2 km of the sea, the minimum coating is 85 µm (610 g/m² per IS 4759), verify by XRF on delivery.
- Aluminium sections (6005A-T5 or 6061-T6): standard for rooftop residential and small commercial arrays. Lower weight, naturally corrosion-resistant, no coating maintenance. More expensive per tonne but faster to install due to lighter components.
- Pre-galvanized (GI sheet, Z180 or Z275 coating): common in low-cost residential rooftop racking. Not appropriate for industrial ground mount or coastal EPC projects, the coating is thin (18–27 µm) and cannot be repaired after fabrication.
Tilt angle and module compatibility
Ground mount structures for fixed-tilt systems are typically supplied at 10°, 15°, 20° or 25° tilt (adjustable at the leg during installation). The optimal tilt for maximum annual yield is roughly equal to the site latitude, about 25° for most of India's north, 12° for the equatorial belt. Structures designed for India at 20° work well for GCC export. The key compatibility check is panel frame width, most ground mount racking is designed for 1000–1134 mm wide panels (standard 72-cell landscape) and may not accept 1303 mm wide panels (some high-power 132-cell modules) without a structure modification.
Earthing the mounting structure: IS 3043 and IEC 62446
A solar farm earthing system must bond all metallic mounting structures to a common earthing grid and provide a path to earth for DC fault current from the array. IS 3043 requires a maximum earth resistance of 1 Ω for generating installations. IEC 62446-1 (commissioning and testing) requires documented earth resistance measurement for every string combiner and inverter. The mounting structure itself is not a substitute for a dedicated earthing conductor, the GI or aluminium structure provides a mechanical path but not a reliably sized earthing path. A dedicated GI strip or copper conductor sized to the array fault current must run along the structure and connect to the earthing grid at defined intervals.
Documentation the EPC needs before installation
- Structural drawing with design wind speed, terrain category, code reference (IS 875 / AS 1170.2 / ASCE 7), member sizes and connection details.
- EN 10204 Type 3.1 material test certificate for the steel sections or aluminium extrusions, confirming grade, chemical composition and mechanical properties.
- HDG inspection report with XRF coating thickness readings per IS 4759 / ASTM A123, per batch.
- Bill of materials with part numbers, so site teams can identify missing or damaged components for replacement.
- Certificate of Origin for import duty purposes, with HS code declaration (typically HS 7308.90 or 7610.90 for aluminium).
The wind load calculation and the coating inspection report are the two documents most missing from solar structure imports. Both are easy to produce if the manufacturer actually does the engineering. If they cannot produce them, they did not.
Vajra International fabricates HDG steel and aluminium solar mounting structures at Howrah, India. All ground mount systems are supplied with IS 875 structural calculations, EN 10204 Type 3.1 MTC, XRF coating report and EEPC India Certificate of Origin.