Ground-mounted solar Module Mounting Structure (MMS) design always starts with Dead Load calculation.
Dead Load (DL) is the permanent load acting on the structure due to the self-weight of all structural members and solar PV modules.
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(# How to Calculate Dead Load of a Solar MMS Structure (Step-by-Step Manual Calculation)
Ground-mounted solar Module Mounting Structure (MMS) design always starts with Dead Load calculation. Dead Load (DL) is the permanent load acting on the structure due to the self-weight of all structural members and solar PV modules. It is the first load considered before wind load, seismic load, and load combinations.
In this article, we will calculate the Dead Load of a 2P × 28 Ground Mounted Solar MMS supporting 56 Goldi 620 Wp modules. The procedure explained here can be applied to any fixed-tilt solar mounting structure by replacing the member dimensions and weights with project-specific values.
Project Details
- Project Type
- Ground Mounted Solar Power Plant
- Structure Type
- Fixed Tilt MMS
- Module Configuration
- 2P × 28
- Total Modules
- 56 Nos
- Module Size
- 2382 × 1134 × 35 mm
- Module Rating
- 620 Wp
- Tilt Angle
- 11°
- Steel Grade
- G350 HDG
- Design Method
- Manual Calculation
What Is Dead Load?
Dead Load is the weight of all permanent components that remain fixed throughout the life of the structure.
For a typical Solar MMS, the dead load consists of:
- Solar PV Modules
- Hat Purlins
- Rafters
- Columns
- Front Bracings
- Rear Bracings
- Wind Bracings
- Cleats
- Bolts, Nuts and Washers
Dead Load always acts vertically downward due to gravity.
Step 1 – Calculate Solar Module Dead Load
The solar module contributes the largest portion of the total dead load.
Given
Weight of One Module = 35.0 kg
Total Modules = 56 Nos
Convert kg into kN
Step 2 – Calculate Hat Purlin Dead Load
The Hat Purlin supports the solar modules and transfers the load to the rafters.
To calculate its dead load, first determine:
- Number of Hat Purlins
- Length of each Hat Purlin
- Unit Weight (kg/m)
Formula
Example
If
Total Hat Purlin Length = Lp
Then
Step 3 – Calculate Rafter Dead Load
The rafters transfer the load from the purlins to the columns.
Required Data
- Number of Rafters
- Length of each Rafter
- Unit Weight
Formula
Step 4 – Calculate Column Dead Load
Columns transfer the structural load safely into the foundation.
Required Data
- Number of Columns
- Length of each Column
- Unit Weight
Formula
Step 5 – Calculate Front Bracing Dead Load
Front Bracing improves structural stability and resists horizontal movement.
Formula
Step 6 – Calculate Rear Bracing Dead Load
The calculation procedure is exactly the same as the front bracing.
Formula
Step 7 – Calculate Wind Bracing Dead Load
Wind bracing increases lateral stiffness of the complete structure.
Formula
Step 8 – Calculate Cleat Dead Load
Cleats are used to connect purlins, rafters and bracing members.
Formula
Step 9 – Calculate Bolt Dead Load
Although bolts contribute only a small percentage of the total dead load, they should not be ignored in detailed structural calculations.
Formula
Step 10 – Total Dead Load
The total dead load acting on the Solar MMS is obtained by adding the dead load of every permanent component.
Formula
+ Hat Purlin Dead Load
+ Rafter Dead Load
+ Column Dead Load
+ Front Bracing Dead Load
+ Rear Bracing Dead Load
+ Wind Bracing Dead Load
+ Cleat Dead Load
+ Bolt Dead Load
Load Transfer Path
The dead load travels through the structure in the following sequence.
Solar Modules
↓
Hat Purlins
↓
Rafters
↓
Columns
↓
Foundation
Every member should be capable of safely transferring the load to the next structural member without exceeding the allowable stress limits.
Important Design Notes
1. Dead Load is always a permanent load.
2. Dead Load always acts vertically downward.
3. Dead Load must include the self-weight of every structural member.
4. Structural member weights should be calculated using the manufacturer's published unit weight or calculated from the cross-sectional area and steel density.
5. All calculations should be converted into kN before performing structural analysis.
Common Mistakes
- Ignoring the self-weight of steel members.
- Excluding bolts, cleats and connection plates.
- Mixing kg and kN without proper conversion.
- Using estimated member weights instead of actual section weights.
- Forgetting to include all permanent structural components.
Conclusion
Dead Load is the first structural load calculated during the design of a Ground Mounted Solar MMS. Once the dead load has been determined, the next step is to calculate the wind load acting on the structure as per IS 875 (Part 3). The combined effect of dead load and wind load will then be used for the manual design of hat purlins, rafters, columns and bracing members.
In the next article, we will learn how to calculate Wind Load on a Ground Mounted Solar MMS using IS 875 (Part 3) step by step.)