A Hat Purlin is one of the most important structural members in a Ground Mounted Solar Module Mounting Structure (MMS). It acts as the primary support for the solar PV modules and transfers all loads from the modules to the rafters. Although it is comparatively smaller than columns and rafters, the Hat Purlin plays a critical role in the overall stability and performance of the solar structure.
In this article, we will understand the function of a Hat Purlin, how it carries loads, the factors affecting its design, common installation mistakes and quality inspection points.
PROJECT DETAILS
- Project Type
- Ground Mounted Solar Power Plant
- Structure Type
- Fixed Tilt Solar MMS
- Module Configuration
- 2P × 28
- Total Modules
- 56 Nos
- Module Size
- 2382 × 1134 × 35 mm
- Tilt Angle
- 11°
WHAT IS A HAT PURLIN?
A Hat Purlin is a cold-formed galvanized steel member fixed over the rafters. It directly supports the solar PV modules and distributes the applied loads uniformly to the supporting rafters.
Because of its hat-shaped cross-section, it provides good stiffness while maintaining a relatively low self-weight, making it suitable for solar mounting structures.
FUNCTION OF A HAT PURLIN
The Hat Purlin performs several important functions in a Solar MMS.
- Supports the solar modules.
- Transfers dead load to the rafters.
- Transfers wind uplift to the rafters.
- Maintains the alignment of the solar module rows.
- Reduces local bending of the modules by providing continuous support.
- Improves the overall stiffness of the structure.
LOAD TRANSFER MECHANISM
The load transfer path in a Ground Mounted Solar MMS is as follows.
Solar Modules
↓
Hat Purlins
↓
Rafters
↓
Columns
↓
Foundation
Every load acting on the solar modules is first received by the Hat Purlins before it is transferred to the remaining structural members.
LOADS ACTING ON A HAT PURLIN
A Hat Purlin is subjected to multiple types of loading during the life of the structure.
Dead Load
The dead load includes the weight of the solar modules and the self-weight of the Hat Purlin.
Wind Pressure
When the wind acts downward on the solar modules, the Hat Purlin experiences downward bending.
Wind Uplift
When wind flows beneath the solar table, an upward force acts on the Hat Purlin. This condition is often more critical than downward loading.
Temperature Effects
Expansion and contraction caused by temperature variations may introduce additional stresses if adequate movement is not provided.
WHY HAT PURLINS ARE USED IN SOLAR STRUCTURES
Compared to conventional rolled steel sections, Hat Purlins offer several advantages.
- Lightweight construction.
- High strength-to-weight ratio.
- Easy transportation.
- Faster installation.
- Better corrosion resistance after galvanizing.
- Reduced overall steel consumption.
FACTORS THAT INFLUENCE HAT PURLIN DESIGN
The design of a Hat Purlin depends on several project-specific parameters.
- Module dimensions.
- Module weight.
- Module arrangement.
- Span between supporting rafters.
- Spacing between Hat Purlins.
- Wind speed at site.
- Terrain category.
- Tilt angle.
- Steel grade.
- Galvanizing specification.
A change in any one of these parameters can affect the required section size and structural performance.
COMMON FAILURE MODES
If a Hat Purlin is not properly selected or installed, the following problems may occur.
- Excessive bending.
- Excessive deflection.
- Local buckling.
- Twisting of the section.
- Connection loosening.
- Corrosion at damaged galvanized areas.
- Misalignment of solar modules.
QUALITY INSPECTION CHECKLIST
Before installing the solar modules, every Hat Purlin should be inspected for the following.
□ Correct section profile.
□ Correct member length.
□ No visible bends or twists.
□ Galvanized coating intact.
□ Proper bolt tightening.
□ Correct alignment with adjacent members.
□ Proper connection to rafters.
□ No sharp edges or burrs.
MAINTENANCE RECOMMENDATIONS
During plant maintenance, periodically inspect the Hat Purlins for the following.
- Corrosion.
- Loose fasteners.
- Permanent deformation.
- Cracks near bolt holes.
- Galvanizing damage.
- Water accumulation.
- Misalignment caused by foundation settlement.
COMMON INSTALLATION MISTAKES
- Installing the Hat Purlin in the wrong orientation.
- Improper alignment between adjacent members.
- Damaging the galvanized coating during handling.
- Over-tightening or under-tightening bolts.
- Using incorrect bolt grades.
- Leaving excessive gaps between connected members.
BEST PRACTICES
- Store members above ground level.
- Protect galvanized surfaces during transportation.
- Verify dimensions before installation.
- Tighten bolts using the recommended torque.
- Maintain uniform spacing throughout the structure.
- Inspect every connection before module installation.
CONCLUSION
The Hat Purlin is the first structural member that receives all loads from the solar modules. Although it appears to be a simple component, its performance directly influences the safety, durability and service life of the complete Solar Module Mounting Structure. Proper section selection, correct installation and regular inspection are essential to ensure long-term structural reliability.
In the next article, we will understand the role of the Solar MMS Rafter, how it receives loads from the Hat Purlins and transfers them safely to the supporting columns.