Wind Load for Solar Purlins and Rafters in India: What EPCs Must Finalise Before Fabrication

Wind loading is one of the most important considerations in solar module mounting structure design. Unlike an ordinary stationary load, wind can act in different directions, creating pressure, uplift and forces that must be transferred safely through the solar mounting system.

For solar EPC companies, calculating the solar panel wind load is only one part of the process. The resulting engineering requirements must also be translated into accurate purlin dimensions, rafter specifications, material grades, connections and fabrication drawings.

A manufacturer cannot determine whether a particular C purlin or HAT purlin is suitable simply from the project’s location, installed capacity or a requested steel thickness. Those decisions depend on the approved structural design and the way loads move through the mounting structure.

This guide explains the basic wind-loading considerations for solar mounting structures in India, the relevance of IS 875 (Part 3), how wind forces affect purlins and rafters, and what EPC engineering and procurement teams must finalise before releasing steel components for fabrication.

What Is Wind Load on Solar Panels?

Wind load is the force or pressure generated when moving air interacts with a structure.

Solar panels present exposed surfaces to the wind. Depending on wind direction, panel inclination, mounting arrangement and surrounding conditions, aerodynamic effects can create forces acting towards or away from the panel surfaces.

These forces are transferred through the module mounting system and its connections into the supporting structure.

For structural design, the relevant considerations can include:

• Downward pressure: Wind effects that push towards the supporting structure.
• Uplift or suction: Wind effects that tend to lift modules or supporting components.
• Horizontal forces: Wind actions that contribute to lateral loads on the mounting system.
• Overturning effects: Moments that must be resisted by the overall structure and its supports.

The governing condition is not necessarily the same for every component. One load case may control a purlin, while another controls a connection, rafter or foundation.

This is why a single statement such as “the structure can withstand a particular wind speed” is not enough to define its structural performance.

Why Is Solar Panel Wind Uplift Important?

Solar panel wind uplift occurs when the net aerodynamic action on a module or array produces an upward force relative to the supporting system.

Wind can flow around the top, underside and edges of an inclined solar array. The resulting pressures depend on the geometry and wind conditions.

Uplift matters because the mounting system must resist forces acting in a direction that may differ from its ordinary gravity-loading condition.

The structural engineer must therefore consider how uplift is transferred through:

1. Solar modules and their approved fixing locations.
2. Module clamps, rails or other fixing components.
3. Supporting purlins.
4. Rafters or primary structural members.
5. Columns, posts, bracing and connections.
6. Foundations or other final structural supports.

If a connection is inadequately designed for the applicable forces, increasing the thickness of another steel member does not automatically resolve the problem.

The complete load path must be evaluated.

Wind Loads on Ground-Mounted Solar Panels

Wind loads on ground mounted solar panels are influenced by the geometry of the array and its exposure to the surrounding wind.

Important variables can include:

• Module inclination and orientation.
• Height of the modules above ground level.
• Length and width of individual module tables.
• Spacing between rows and tables.
• Location of modules within the array.
• Wind direction and site exposure.
• Whether the structure is fixed-tilt or uses a tracking arrangement.

Research on ground-mounted photovoltaic arrays shows that wind loading can differ between leading rows and other positions within an array. Panel inclination and wind direction can also affect the magnitude and distribution of aerodynamic forces.

However, these findings should not be converted into a universal rule that a particular row always needs a heavier purlin or that one module angle is safe for every site.

The responsible structural engineer must determine the applicable forces for the actual configuration.

Are Rooftop and Ground-Mounted Solar Wind Loads the Same?

No. Rooftop solar systems and ground-mounted systems have different supporting arrangements and surrounding aerodynamic conditions.

For a rooftop installation, the building geometry, roof position, mounting height and attachment to the existing structure may be important.

Ground-mounted systems instead require evaluation of the exposed array and the load transfer through its support structure and foundations.

Both need project-specific wind-load assessment, but one system’s design assumptions should not automatically be applied to the other.

Wind Load Design in India: Understanding IS 875 (Part 3)

In India, IS 875 (Part 3):2015 is the Indian Standard covering wind loads for buildings and structures. The standard has published amendments that must also be considered when establishing the applicable design basis.

It provides a framework for determining wind-related design actions using relevant site and structural parameters.

For solar mounting structures, the engineering team should determine how the applicable Indian standards and project-specific requirements are to be used for the particular system.

What Wind-Design Inputs Matter?

Depending on the adopted design method, the engineer may need to establish:

• Site location: The location used to establish the basic wind-speed requirement.
• Design life and risk requirements: Relevant considerations under the applicable design basis.
• Terrain and exposure: The surrounding conditions affecting the wind environment.
• Height and topography: Parameters relevant to wind action at the structure.
• Array geometry: Module tilt, height, table dimensions and arrangement.
• Wind pressure coefficients: Appropriate aerodynamic values established using an accepted engineering method.
• Load combinations: The combinations of wind and other applicable actions used for structural checks.

Not every solar configuration can be assessed accurately by applying a generic pressure coefficient to the projected panel area.

Where the project configuration or contractual design basis requires additional aerodynamic assessment, the structural consultant must determine the appropriate method and supporting evidence.

Important: IS 875 (Part 3) provides wind-loading guidance; it does not replace the complete structural design of a solar mounting system. The relevant member-design standards, connection requirements and any project-specific requirements must also be considered.

How Does Wind Load Affect Solar Purlins?

In a solar module mounting structure, purlins commonly support the solar modules or their fixing system and transfer forces to rafters or other supporting members.

A wind load on a solar purlin can therefore create bending, shear and other effects that must be considered in its design.

For cold-formed steel sections, the engineer may also need to assess stability, local buckling, member restraint and the behaviour of the connected system.

1. Profile Geometry

C, Z and HAT sections have different cross-sectional geometries.

Web depth, flange dimensions, lips and other profile features influence the section’s properties and structural behaviour.

Two profiles made from steel of the same thickness are not necessarily equivalent under wind loading.

A project specifying a C purlin should therefore identify the complete approved cross-section rather than only its nominal depth.

2. Steel Grade and Thickness

Steel grade and thickness influence the section’s structural capacity.

However, selecting a higher-strength material or increasing thickness does not remove the need to check the full member and its connections.

The chosen material must also be suitable for the required fabrication process.

Any proposed change to an approved steel grade, thickness or profile should be referred to the responsible engineering team.

3. Purlin Span and Restraint

The distance between supports affects purlin behaviour under loading.

Restraint conditions also matter. Solar module connections should not automatically be assumed to provide the same lateral or rotational restraint as conventional roof sheeting.

The structural model must reflect the actual connections, supports and restraints available in the completed solar structure.

4. Wind Uplift and Load Reversal

Wind uplift can introduce loading conditions different from those created by downward gravity loads.

For some cold-formed members, the change in loading direction can affect which parts of the section experience compression and how member stability must be assessed.

The design should therefore address the applicable uplift and downward-load combinations rather than considering only one direction of loading.

How Does Wind Load Affect Solar Rafters?

Rafters form part of the supporting framework in many solar mounting systems.

Depending on the design, they receive forces from the purlins and transfer those forces to columns, posts or other primary supports.

The wind load on rafters depends on the forces delivered by the connected members and the structural arrangement.

The engineer must consider the applicable strength, deflection, stability and connection requirements.

Important fabrication-related details can include:

• Rafter cross-section and dimensions.
• Steel grade and material thickness.
• Member length and orientation.
• Connection plates or brackets, where specified.
• Hole positions and bolt arrangements.
• Required tolerances and fabrication details.

A fabrication drawing must reflect the approved structural design. The manufacturer should not independently reduce the member size or change its connection arrangement simply to reduce material usage.

Why Connection Details Matter as Much as Member Sizes

When reviewing solar panel wind load, it is easy to focus on the size of steel purlins and rafters while overlooking their connections.

But the mounting system must transfer forces between components safely.

Relevant interfaces include:

• Module-to-purlin or module-to-rail connections.
• Purlin-to-rafter connections.
• Rafter-to-post connections.
• Bracing and other specified structural connections.
• Connections to the foundation system.

Each connection must follow the approved design requirements.

For example, a change in hole diameter, slot length or bolt position can affect more than assembly convenience. It may alter the intended connection behaviour or available edge distances.

Similarly, a substitution from one purlin profile to another may require a different connection detail even if the alternative appears to have a similar size.

For manufacturing purposes, the correct hole pattern and connection drawing are therefore essential.

What Must EPCs Finalise Before Solar Purlin and Rafter Fabrication?

The most useful outcome of the wind-design process is a coordinated, approved set of manufacturing requirements.

Before releasing drawings to the manufacturer, the EPC should confirm that the engineering team has finalised the relevant structural decisions.

Wind-Design and Fabrication Handover Checklist

Requirement	What Must Be Confirmed	Responsible Function
Wind-design basis	Applicable standards, editions, amendments and project design criteria	Structural engineering
Site inputs	Location, terrain, exposure, height and relevant topographic conditions	Structural engineering
Module arrangement	Approved table layout, inclination, module dimensions and relevant support geometry	Project engineering
Design actions	Wind pressure, uplift and other applicable load cases and combinations	Structural engineering
Purlin schedule	Profile type, dimensions, grade, thickness, length and identification	Structural engineering / detailing
Rafter schedule	Member dimensions, material specifications and lengths	Structural engineering / detailing
Connections	Approved fixing locations, holes, slots, brackets and fastener requirements	Structural engineering / detailing
Fabrication documents	Final drawing numbers, revisions, quantities and tolerances	Engineering / procurement
Release approval	Formal confirmation that the relevant documents are approved for manufacturing	Authorised project team

The manufacturer does not necessarily need every structural calculation sheet to fabricate an approved component. However, the responsible EPC and engineering teams must ensure that the drawings and specifications being issued correctly reflect the completed design.

If the manufacturer identifies conflicting or missing details, the relevant documents should be clarified before production.

What Should the Final Fabrication Drawing Include?

For a project-specific solar purlin or rafter, the fabrication drawing should provide sufficient information to manufacture and inspect the correct component.

This may include:

1. Unique part number: Identifies the member in the approved material schedule.
2. Cross-section: Defines the complete section geometry.
3. Member length: Specifies the required finished length.
4. Steel specification: Identifies the grade and thickness.
5. Hole and slot details: Defines positions, sizes and relevant tolerances.
6. Connection references: Links the component to its approved connection details.
7. Coating specification: States the required protective finish where applicable.
8. Drawing revision: Establishes the approved version to be manufactured.
9. Quantity or schedule reference: Connects the drawing to the production requirement.

A fabrication team should not need to infer critical dimensions from a general arrangement image or an outdated drawing.

Common Mistakes EPCs Should Avoid Before Fabrication

1. Selecting Purlin Thickness from Wind Speed Alone

Wind speed is not a direct substitute for the completed structural design.

Member sizing depends on the calculated forces, geometry, span, restraint, material properties and connection requirements.

2. Using One Wind Requirement for Every Solar Site

Different locations and array arrangements can require different design assessments.

A previous project’s design should not be reused without checking its applicability.

3. Treating Panel Wind Rating as Complete MMS Certification

A module’s stated mechanical-load capacity does not automatically verify the capacity of the entire mounting structure.

The clamps, purlins, rafters, other supporting members, connections and foundations must also meet their respective design requirements.

4. Changing Sections After Engineering Approval

Replacing a C purlin with another profile or changing steel thickness can alter the member properties and connections.

Such changes require appropriate design review and approval before manufacturing.

5. Sending Drawings with Unresolved Connection Details

Incorrect or incomplete hole patterns can affect assembly and the intended structural connection.

All critical fabrication details should be finalized before release.

6. Mixing Drawing Revisions

If the bill of materials, member schedule and fabrication drawings reference different revisions, there is a risk of manufacturing components that do not match.

A controlled drawing release helps avoid this problem.

How Shree Deepak Industries Supports Solar Structure Fabrication Requirements

Shree Deepak Industries, based in Jaipur, Rajasthan, manufactures galvanized steel profiles for solar module mounting structures and industrial structural applications.

The company’s product range includes C purlins and HAT purlins, with profile dimensions, thicknesses, lengths and finishes varying according to the selected product and project requirements.

For solar structure procurement, EPC companies can share their approved fabrication drawings, steel grades, member dimensions, coating requirements, quantities and delivery location.

The manufacturing enquiry can then be reviewed against the requested product scope and available fabrication capabilities.

Shree Deepak Industries’ role as a steel profile manufacturer should not be confused with responsibility for independent wind-load calculations or approval of the complete solar plant structure unless such services are separately established and agreed.

Need solar purlins or structural profiles manufactured to your project drawings? Contact Shree Deepak Industries with your approved member schedule, drawings, steel specifications, quantity and delivery details to discuss your requirements and request a quotation.

Frequently Asked Questions

What is solar panel wind load?

Solar panel wind load refers to the forces and pressures generated when wind interacts with solar modules and their mounting arrangement. These actions can include uplift, downward pressure and horizontal forces that must be transferred through the supporting structure.

Which Indian standard is used for wind-load design?

IS 875 (Part 3):2015, together with its applicable amendments, is an important Indian Standard for wind loads on buildings and structures. The responsible engineer must determine how the relevant standards and project requirements apply to the particular solar mounting system.

How is wind load on a solar mounting structure calculated?

A structural engineer establishes the design wind conditions, relevant aerodynamic effects, array geometry and applicable load combinations. These are used to determine actions on the mounting structure and verify its members and connections. A complete calculation must follow the adopted engineering method and project requirements.

Do ground-mounted solar panels experience wind uplift?

Yes. Ground-mounted arrays can experience uplift as well as other aerodynamic forces. The magnitude and distribution depend on the site’s wind conditions, array arrangement, module geometry and other design factors.

Can the same C purlin be used for every solar project?

No. The required C purlin depends on the approved structural design, including member dimensions, grade, thickness, span, load effects, restraint and connections. A profile suitable for one project is not automatically suitable for another.

Does increasing purlin thickness always solve wind-load problems?

No. Increasing thickness may change a member’s structural capacity, but the adequacy of the complete mounting system also depends on geometry, connections, restraints and other components. Modifications require engineering assessment.

Why are hole patterns important for solar structure wind loads?

Hole positions, sizes and connection details influence how components are assembled and how forces are transferred between members. The manufactured hole pattern must match the approved structural connection drawings.

What should EPCs send a purlin manufacturer after wind-load design is finalized?

EPCs should provide the approved fabrication drawings, member schedule, complete profile dimensions, steel grade, thickness, coating, hole patterns, quantities and delivery requirements. Any unresolved technical details should be clarified before manufacturing.

Conclusion

Solar panel wind load is an important input to the structural design of module mounting systems in India, but the engineering assessment must extend beyond the panels themselves.

Wind pressure and uplift create forces that pass through module connections, purlins, rafters, other supporting members and ultimately the foundations. Each component and connection must be assessed according to the approved structural design.

For solar EPC and procurement teams, the critical step before fabrication is to ensure that the wind-design requirements have been translated into accurate member schedules, material specifications, connection details and approved drawings.

Clear coordination between engineering, procurement and manufacturing helps ensure that the supplied steel profiles match the intended design and reduces avoidable revisions during production and installation.