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A solar structure is the mounting system that holds PV modules at the designed angle and transfers every wind, snow and seismic load into the roof, the ground or a canopy.
It is a separate product from the module: the module is qualified under IEC 61215 and IEC 61730, while the structure is qualified under racking standards such as UL 2703, UL 3703 or IEC 62817. It is also part of the electrical system, because it carries the bonding path that protects module frames.
What you cannot do is specify it with adjectives. A usable solar structure specification states the design wind and snow load with its code edition, the module clamping zone and rated pressure, the coating thickness in micrometres, and the exact module models the system is listed with.
A solar structure — also called a PV mounting structure, racking system or solar bracket — is the load-bearing frame that fixes photovoltaic modules to a building surface or to the ground. It performs two jobs at once: it carries the mechanical loads without failing, and it gives every module frame a continuous, listed bonding path to earth.
The distinction matters because the structure is engineered, tested and certified as its own product. In the U.S. National Renewable Energy Laboratory guidebook on facility-scale solar, the frame that holds the modules is described as the mounting system, and it is treated as a design decision separate from the module and the inverter, with roof-mounted and ground-mounted systems as the two primary applications. So when a quotation refers to a solar structure, it refers to everything between the module and the building or the soil.
Carry the design loads. Uplift, downforce, sliding and seismic forces have to reach a structure that can resist them at every module position, not only at the centre of the array.
Hold the design tilt and orientation. Tilt governs yield and, on flat roofs, self-cleaning and drainage.
Keep the modules off the surface. Roof-mounted arrays need clearance so water drains and the modules stay ventilated.
Bond the module frames. Racking is listed for grounding and bonding continuity, not only for strength, because non-current-carrying metal parts must be bonded.
Survive the design life. The structure is expected to outlive the modules, so corrosion protection rather than initial strength usually decides the real service life.
Where the definition comes from
The mounting-system framing and the two application categories used here follow the Facility-Scale Solar PV Guidebook published by NREL and the U.S. Bureau of Reclamation, which is a primary technical reference rather than a vendor description.
A complete solar structure has four functional layers: the attachment or foundation, the supports, the horizontal members, and the clamps that grip the module frame. Bonding hardware, drainage details and cable management complete the assembly.
Part | Function | Typical material and note |
|---|---|---|
Roof attachment: L-feet, hanger bolts, standing-seam clamps | Connects the rail structure to the roof structure through or over the weatherproofing | Stainless or zinc-plated steel; must be flashed or clamped, never sealed and left exposed |
Ground foundation: ground screw, helix pile, concrete pier or ballast | Resists uplift and sliding in soil or on a membrane | Hot-dip galvanised steel or concrete; embedment and frost depth drive the design |
Post, pier or leg | Carries the substructure at the designed height and tilt | Extruded aluminium or rolled steel section |
Rail (main member) and purlin (cross member) | Spans between supports and provides the fixing line for clamps | Anodised aluminium profile or cold-formed galvanised section |
Mid clamp and end clamp | Grips the module frame and transfers load into the rail | Aluminium with stainless fasteners; the clamping zone is set by the module maker, not the racking maker |
Rail splice or connector | Joins rails into a continuous line and keeps the splice outside the high-bending zone | Same alloy as the rail; expansion joints become necessary on long continuous rows |
Bonding or grounding lug, EGC | Creates the fault-current path from module frames and the structure to earth | Listed bonding hardware; conductor sized to the overcurrent device |
Ballast blocks and wind deflectors | Replace penetration on flat roofs and reduce uplift at the array perimeter | Concrete blocks to a defined standard; ballast weight is a structural calculation, not a default |
Cable clips and management parts | Keep DC conductors off the roof surface and out of the drainage path | UV-stable polymer or metal, compatible with the roof membrane |
The four layers matter commercially because a weak link anywhere breaks the chain. A rail rated for a long span is worth nothing if the attachment to the rafter is under-torqued or if the clamp sits outside the zone the module manufacturer allows.
Wind uplift, not panel weight, usually governs the design. The structure must resist uplift, downforce and sliding at every module position, and two values decide whether it passes: the module's permitted clamping zone and the wind pressure calculated for that location.
The first value is specified by the module manufacturer. Module installation manuals publish clamping zones measured from the module edge, and each zone corresponds to a tested mechanical load, usually expressed in pascals. A representative example from a tier-one module manual applies a safety factor of 1.5 between the test load and the design load, so a 5,400 Pa test rating corresponds to 3,600 Pa in design. Move the clamp outside the permitted zone and the module is rated to the lower zone value only — a change that also affects the module warranty. The Q CELLS installation manual for the Q.PEAK DUO ML-G9.X series is a clear published example of this structure, including the maximum rail span that the rating assumes.
The second value is calculated for the site. Wind pressure depends on basic wind speed, terrain, height and the position of the array within the site, and edge and leading-row positions see materially higher uplift than the interior. ASCE 7-22 introduced a dedicated ground-mount calculation procedure with explicit geometric limits and an edge factor of 1.5 for panels close to an exposed array edge, which is why older open-monoslope tables are increasingly rejected by authorities having jurisdiction under the current building code cycle.
Do not apply one wind pressure to a whole array. Perimeter and leading-row positions carry the highest uplift, so a structure sized on interior pressure alone can fail at its own edge. The same caution applies to ballasted flat-roof systems, where full-scale testing has shown that peak array loads occur toward the roof centre rather than the edge, and that ballasted arrays can slide or lift below the nominal design wind speed.
Six structures cover almost every project: pitched-roof, flat-roof ballasted, ground-mount, carport or canopy, tracker, and building-integrated. The choice follows the mounting surface, the governing load case and how much annual yield the owner needs.
Type | Where it is used | What drives the design | Main constraint |
|---|---|---|---|
Pitched-roof structure | Residential and commercial roofs with rafters | Attachment to structural members and load distribution along the roof plane | Waterproofing at every penetration |
Flat-roof ballasted structure | Commercial roofs that must not be penetrated | Ballast weight, roof dead-load capacity and perimeter uplift | Roof load capacity; movement over single-ply membranes |
Farms, utility-scale plants, open land | Foundation type, frost depth, soil capacity and row spacing | Soil variability and self-shading between rows | |
Carport or canopy structure | Parking areas and public spaces | Combined structural duty: roof load plus vehicle clearance | Spans and lateral stability of an open structure |
Utility and large commercial projects | Drive and bearing design, wind stow strategy | Moving parts and control system maintenance | |
Building-integrated structure | Modules forming part of the building envelope | Building envelope performance and fire detailing | Roofing and module trades overlap |
Lowest part count and almost no maintenance.
Tilt chosen for annual yield, with row spacing set by the lowest winter sun angle to avoid self-shading.
Loading is simpler to verify because the geometry does not change.
Follow the sun to raise annual output; published figures put single-axis gains at up to about 25 percent and dual-axis at up to about 35 percent.
Design is governed by mechanical qualification of the complete tracker, not only by strength.
Control, drive and stow behaviour under high wind become part of the specification.
The gain figures above come from the same NREL and U.S. Bureau of Reclamation guidebook cited earlier. Tracker structures are also qualified differently from fixed structures: IEC 62817 defines the test procedure for tracker components and complete systems, while UL 3703 is the U.S. standard for solar trackers and references UL 2703 for the electrical mounting, bonding and grounding requirements.
Aluminium and hot-dip galvanised steel are the two standard material routes. The correct choice is the one whose coating thickness matches the corrosivity of the site, which is why a claim of corrosion resistance without a number in micrometres is not a specification.
Route | Typical use | Corrosion protection | What to ask for |
|---|---|---|---|
Extruded aluminium, 6005-T5 or 6063-T6 | Roof rails, purlins, clamps, carport frames | Anodising or powder coating over the extruded profile | Anodising thickness class to ISO 7599 and the coating system to a named specification |
Hot-dip galvanised steel | Ground posts, piers, cold-formed rails and purlins | Metallurgically bonded zinc coating after fabrication | Coating thickness or mass per unit area to ISO 1461 or ASTM A123, measured per batch |
Zinc-aluminium-magnesium coated steel | Rails and purlins where cut-edge protection matters | Alloy coating applied to coil before forming | Coating mass designation and independent salt-spray data |
Stainless or zinc-flake fasteners | All bolted connections | Grade-dependent | Fastener grade matched to the structural member to avoid galvanic corrosion |
Coating selection should start from the environment, not from the material. ISO 9223 classifies atmospheric corrosivity from C1, very low, to CX, extreme, based on measured first-year mass loss of reference steel specimens, and the category for a coastal or heavily polluted site can be two or three steps above an inland rural site in the same country. ISO 12944 then links durability expectations to that environment: a coating specified for high durability is intended for 15 to 25 years, and very high durability for more than 25 years — and the standard is explicit that durability is not a warranty period.
Once the category is known, the coating becomes a number. For hot-dip galvanised steel, ISO 1461 sets minimum mean coating thicknesses by steel thickness, at 85 micrometres for sections over 6 mm and 70 micrometres for sections between 3 mm and 6 mm, with lower permitted local minima; ASTM A123 uses the same values with a grade number equal to the mean thickness in micrometres. The ISO 1461 minimum thickness tables published by Zinc Info Benelux are a practical reference for checking a certificate. For anodised aluminium, ISO 7599 defines classes AA5 to AA25 where the number is the minimum average coating thickness in micrometres.
The mounting structure is part of the electrical system. Module frames and the structure have to be bonded so that fault current has a low-impedance path to earth, which is why racking is listed for bonding continuity as well as for mechanical strength.
In the U.S. installation standard NFPA 70, non-current-carrying metal parts — module frames, mounting structures, equipment enclosures and conduit — must be grounded, and DC grounding is made at a single point on the PV output circuit. UL 2703 is the listing standard that tests this property for racking: its scope covers rack mounting systems, grounding and bonding devices and clamping devices for specific module models, and is limited to the ground and bonding path, mechanical strength, fire classification and suitability of materials. A racking cut sheet marked compliant is therefore not enough on its own — the listing is module-specific and should be verified against the exact module model in the bill of materials.
Confirm that the racking and the module combination appears in the listing, not just the racking product family.
Check that bonding is achieved by a listed device or an integrated bonding clamp, rather than by a star washer or a self-tapping screw added on site.
Size the equipment grounding conductor to the overcurrent protective device, not to the assumed fault current.
Keep the DC grounding connection at a single point on the PV output circuit.
Record the measured continuity value at commissioning, together with the torque used on every bonding terminal.
Why the listing is separated into attributes
The standard page for UL 2703 on the UL standards store states the scope limits directly: bonding and grounding paths, mechanical strength, fire classification and material suitability. Structural code compliance remains a separate exercise, because it requires load combinations built from dead, snow, wind and seismic forces.
Read a solar structure offer as a set of verified numbers: design wind and snow loads with the code edition, the module clamping zone and rated pressure, coating thickness, the scope of each certificate, and the module models the system is listed with.
Most failed comparisons happen because two suppliers are answering different questions. One quotes a wind speed, the other quotes a pressure; one cites a certificate number, the other cites a test report; one gives a rail span, the other gives a rail profile. Normalising those six items takes one email and removes most of the risk from the decision.
Loads with a code edition. Ask for the wind and snow loads used, the basic wind speed, the exposure or terrain category, and whether edge and leading-row zones were treated separately.
Clamping zone and rated pressure. State the module model and ask which zone the drawing uses, and what the module is rated to in that zone.
Coating as a number. Request mean and local coating thickness, the anodising class or galvanising standard, and the batch inspection record.
Certificate scope. Confirm which standard, which notified body, which product family, and whether the certificate covers the specific configuration quoted.
Foundation or attachment calculation. For ground screws, ask for the design torque and embedment; for roof attachments, ask for the rafter fixing detail and the flashing method.
Bill of materials completeness. Confirm that clamps, splices, bonding hardware and cable management are included rather than sold separately.
Drawings and load tables. Ask for the general arrangement drawing and the span table for the rail section quoted.
Next step: compare solar structure types, materials and rail configurations side by side before you commit to a design.
Compare solar structure specifications
A solar structure is the engineered interface between a photovoltaic module and the surface it sits on. Its structural job is to move wind, snow and seismic loads into a foundation or a roof structure that can take them. Its electrical job is to bond module frames and carry fault current safely. Its commercial job is to still be doing both of those things after twenty-five years of weather.
That is why the useful questions about a solar structure are numeric. What wind and snow load, under which code edition? Which clamping zone, and what pressure does the module carry there? Which material, with what coating thickness in micrometres? Which certificate, covering which configuration? Answer those four and the type selection usually follows on its own.
The panel, or module, converts sunlight into electricity and is qualified under the IEC 61215 and IEC 61730 series. The solar structure is the mechanical system that holds the modules in position and carries the loads into the building or the ground. They are separate products with separate standards, warranties and suppliers.
No. In astronomy, the phrase describes the Sun's internal layers, the core, radiative zone and convection zone, and its atmospheric layers, the photosphere, chromosphere, transition region and corona. In the solar industry, a solar structure is the mounting system that holds PV modules. The two meanings share the word "solar" but nothing else, which is why the search results for the bare phrase can be entirely astronomical.
In practice, service life is decided by corrosion protection and by the durability class chosen for the site, not by the initial strength of the steel or aluminium. ISO 12944 defines high durability as 15 to 25 years and very high durability as more than 25 years, and states clearly that durability is not a warranty period, so the coating thickness record is the best available evidence.
Neither is universally better. Extruded aluminium suits roof rails, clamps and carport frames where weight and profile accuracy matter, and it is protected by anodising or powder coating. Hot-dip galvanised steel suits ground posts, piers and cold-formed sections where stiffness and cost per tonne matter. The deciding factor is the corrosivity category of the site and the coating thickness that follows from it.
An anchored roof structure adds the weight of rails, clamps and attachments, which is modest compared with the modules themselves. A ballasted flat-roof structure is a different case: the ballast is the load path, so the array can add several times more weight than the modules alone. Because the ballast weight is a structural calculation, the roof's dead-load capacity must be verified before the system is selected, not after.
In most jurisdictions the answer is yes for anything beyond a small residential array, because the installer must confirm that the roof structure, rafters and connections can carry the code-level loads. The relevant loads are snow, wind, exposure and topographic factors, and they should be confirmed with the building official or a licensed structural engineer rather than assumed from the module count.
The structure should be designed for the code-level basic wind speed of the site rather than a vendor's headline figure, because the resulting pressure also depends on terrain, height and the position of each array within the site. Edge and leading-row panels experience noticeably higher uplift than interior panels, so the design has to be evaluated zone by zone.
