The design of a Ground Mounted Solar Module Mounting Structure (MMS) is not a single activity. It is a complete engineering workflow that begins at the site and ends only after the structure is erected, inspected and handed over to the client.
This article brings the complete series together into one practical workflow so that an engineer can follow the same sequence on any ground mounted solar project.
Project Details
- Project Type
- Ground Mounted Solar Power Plant
- Structure Type
- Fixed Tilt Solar MMS
- Module Configuration
- 2P × 28
- Total Modules
- 56 Nos
- Design Life
- 25 Years
Step 1 – Site Reconnaissance
The first step is the physical site visit. During this visit the following information is collected:
Site location and coordinates
Approach road and material access
Existing ground profile and slope
Vegetation, water bodies and obstructions
Nearest weather station data
Local wind and seismic zone
This information decides the structure type, foundation type and the erection methodology.
Step 2 – Topographical Survey
A topographical survey is carried out to prepare the contour plan of the plant area. The contour plan is used to fix the table layout, row spacing and the finished ground level of each table.
Where the ground slope is high, the table positions are adjusted so that the column lengths remain within the fabrication limits.
Step 3 – Geotechnical Investigation
The soil investigation report provides the design inputs for the foundation:
Safe Bearing Capacity of soil
Soil type and layer thickness
Water table level
Chemical properties such as pH, chlorides and sulphates
Recommended foundation type
For pile foundations, the pull out test and lateral load test results are also required.
Step 4 – Module and Layout Selection
The solar module datasheet is collected and the following values are recorded:
Module length and width
Module weight
Module thickness
Mounting hole locations
Maximum allowable load on the module frame
Based on the module dimensions, the table configuration is fixed as 2P × 28 and the overall table dimensions are calculated.
Step 5 – Dead Load Calculation
The dead load of the structure is calculated by adding the weight of the modules and the self weight of all structural members such as purlins, rafters, columns and bracings.
Step 6 – Wind Load Calculation
The wind load is calculated as per IS 875 Part 3 using the basic wind speed of the site.
The wind force on the module surface is calculated using the net pressure coefficient for the applicable tilt angle.
Step 7 – Load Combinations
All the calculated loads are combined as per IS 800 for the limit state design:
1.5 (DL + LL)
1.2 (DL + LL + WL)
0.9 DL + 1.5 WL
1.5 (DL + WL)
The most critical combination is used for the member design.
Step 8 – Structural Member Design
Each member is designed in the following sequence because the reaction of one member becomes the load of the next member:
Purlin design
Rafter design
Column design
Bracing design
Cleats and connection plates
Bolts, nuts and washers
Foundation design
For every member the bending stress, shear stress, deflection and slenderness ratio are checked against the permissible values.
Step 9 – Foundation Design
The foundation is designed for the column reactions obtained from the structural analysis. The following checks are carried out:
Bearing pressure check
Overturning check
Sliding check
Uplift check
Reinforcement design for pedestal and footing
Step 10 – Material Selection and Corrosion Protection
The steel grade, section type and the corrosion protection system are finalised based on the site environment. Hot Dip Galvanising as per IS 4759 is normally specified for ground mounted solar structures.
Step 11 – Drawings and Bill of Materials
The following documents are prepared and issued for construction:
General Arrangement Drawing
Table Assembly Drawing
Member Fabrication Drawings
Connection Details
Foundation Drawings
Bill of Materials
Step 12 – Fabrication and Inspection
The members are fabricated as per the approved drawings. During fabrication the dimensional accuracy, hole positions, welding quality and galvanising thickness are inspected.
Step 13 – Erection and Alignment
The erection is carried out in the following sequence:
Marking and excavation
Foundation casting or pile driving
Column erection and alignment
Rafter fixing
Purlin fixing
Bracing fixing
Torque tightening of all bolts
The tilt angle, row spacing and the table level are checked after erection.
Step 14 – Quality Control
The quality control checks include:
Verticality of columns
Tilt angle of rafters
Galvanising thickness measurement
Bolt torque verification
Touch up painting at damaged areas
Step 15 – Commissioning and Handover
After the module mounting is completed, the final inspection is carried out and the following documents are handed over to the client:
Design calculation report
Approved drawings
Material test certificates
Inspection reports
Torque records
Preventive maintenance schedule
Conclusion
The Solar MMS design workflow is a step by step engineering process where every stage depends on the output of the previous stage. When the sequence is followed correctly, the structure remains safe, economical and serviceable for the complete design life of the solar power plant.