Structure First Series — Solar Canopy Engineering (Article #3)
In the architectural landscape of a modern commercial property, the solar carport is often the most visible engineering feat. Yet, it is also the most frequently underestimated. While a ground-mounted solar farm is essentially a grid of low-profile racking pinned to a field, a solar carport is a high-clearance, elevated canopy—a "non-building structure" that must withstand the full spectrum of environmental forces while hovering over millions of dollars of vehicles and human traffic.
At Solaracks, our "Structure First" philosophy isn't just a marketing slogan; it is the fundamental principle that guides our R&D. When a structure sits 4 to 5 meters in the air, the physics of wind, snow, and seismic activity change dramatically compared to ground-level installations.
For structural engineers, EPC technical teams, and sophisticated buyers, understanding the load calculation checklist isn't just about code compliance—it's about ensuring a 25-year design life in an increasingly volatile climate. This article provides a deep dive into the seven critical load categories, referencing ASCE 7-16 and EN 1991 standards.
1. Dead Loads (DL): Calculating the Constant Gravity
The dead load is the weight of all permanent components. While it is the "static" part of the equation, the evolution of PV technology has made "standard" assumptions obsolete.
Material Selection and Self-Weight
The skeleton of the carport accounts for the majority of the dead load.
- Hot-Dip Galvanized Steel (Q235/Q355): Typically results in a structural self-weight of 15-30 kg/m². Steel provides the rigidity needed for long-span bays (7-10 meters), which minimizes the number of columns and maximizes parking space.
- Anodized Aluminum (6005-T5): Offers a lighter profile at 5-12 kg/m². Aluminum is increasingly popular for parking deck applications where the existing slab capacity is a hard constraint.
The PV Module Evolution
Modern bifacial modules have changed the weight profile of the canopy.
- Standard Monofacial Modules:
18-22 kg per panel (12-14 kg/m²). - Bifacial Glass-Glass Modules: With double-tempered glass, these can reach ~25 kg/m². At Solaracks, we always use the specific module SKU's weight plus a 5% margin for mounting hardware and clamps.
Ancillary Systems (The Forgotten Loads)
Engineers must account for "secondary" dead loads that accumulate:
- Cabling & Management: Heavy-duty DC cabling, cable trays, and conduit runs add 2-5 kg/m².
- Integrated Systems: Many high-end carports now feature integrated LED lighting, security cameras, and EV charging hardware. Mounting a Level 2 EV charger directly to a column introduces localized point loads and eccentric moments that must be modeled in the column's structural check.
2. Live Loads (LL): Designing for People, Not Cars
A common point of confusion is whether vehicle loads apply to the carport. Unless the canopy is a driving surface, vehicles stay below. However, the structure must be designed for maintenance access.
Per ASCE 7-16, a minimum live load of 1.0 kN/m² (approx. 20 psf) is standard for maintenance workers. This accounts for:
- Workers and their tools on the canopy for panel cleaning or inverter service.
- Concentrated loads of a worker leaning on a purlin or rail.
In our SAP 2000 models, we verify that these live loads do not cause excessive localized deflection (L/180 or L/240) which could stress the module glass or compromise the clamping system.
3. Wind Loads (WL): The Defining Design Challenge
For an open-canopy structure, wind is the governing load in over 90% of designs. Because air flows both over and under the canopy, the structure acts like an airfoil.
ASCE 7-16 and Open Canopies
We classify carports as "Open Structures" (all walls > 80% open). We use Chapter 27 for the Main Wind-Force Resisting System (MWFRS) and Chapter 30 for Components and Cladding (C&C).
The Math of Net Pressure (C_N)
Net pressure coefficients (C_N) from ASCE 7-16 Table 27.3-1 are derived from:
- Roof Angle (θ): A 10-degree tilt creates significantly more lift than a 5-degree tilt.
- Clearance Ratio (L/h): The ratio of horizontal canopy length to the mean roof height.
- Obstructed vs. Unobstructed Flow: Even if a carport is "open," if there are vehicles parked underneath, it can partially obstruct flow, leading to increased pressure.
Uplift: The "Wing" Effect
The most critical wind case for a carport is Uplift. When wind hits the tilted canopy from the low side, it creates a high-pressure zone underneath and a low-pressure zone above. This suction force is often 2-3 times greater than the dead weight of the structure. This is why carport foundations — whether piers or ballast — are often defined by their "pull-out" resistance, not their bearing capacity.
Height and Exposure Categories
- The Height Factor: Unlike ground mounts (0.5m-2m), carports sit at 3m-5m. Wind speed increases with height due to reduced ground friction. A structure at 5m height experiences ~15-20% more wind pressure than one at 2m in the same location.
- Exposure B (Suburban): Sheltered by trees and buildings.
- Exposure C (Open Terrain): Flat, open ground with scattered obstructions. This is our default baseline.
- Exposure D (Coastal/Waterfront): High wind pressure with no obstructions for miles. In Exposure D zones, we often upgrade the steel grade or increase column thickness to handle the base shear.
4. Snow Loads (SL): Managing Gravity and Drifts
Snow load calculations follow EN 1991-1-3 and ASCE 7-16 Chapter 7. For open structures, snow doesn't just sit flat; it moves.
Conversion Factors
The ground snow load (p_g) is modified by several factors:
- Exposure Factor (C_e): Wind can blow snow off the canopy, but in many carport layouts, the adjacent units shield each other, preventing this "scouring" effect.
- Thermal Factor (C_t): Carports are unheated. Per code, we use C_t = 1.2. Because the structure doesn't radiate heat like a building, snow persists longer and can freeze into ice.
Unbalanced Snow on Mono-slopes
Most carports are mono-slope. Wind often deposits snow disproportionately on the lower side of the slope. This Unbalanced Snow Load creates a non-uniform pressure on the purlins, which can lead to torsional stress in the main rafter beams if not accounted for.
The Drift Load Risk
If a carport is built within two heights (2H) of a taller building, Drift Loads must be calculated. Snow can blow off the roof of the adjacent building and pile up on the carport. We've seen projects where the drift load on the canopy was 300% higher than the local ground snow load.
5. Seismic Loads (E): Inertia and Lateral Force
While carports are light compared to buildings, they have a "top-heavy" mass distribution. In a seismic event, the lateral acceleration of the PV modules and rafters creates a significant moment at the base of the columns.
Per ASCE 7-16 Chapter 12 (Non-building Structures):
- We calculate the Base Shear (V) based on the Response Modification Coefficient (R) — typically 1.5 to 2.5 for these cantilevered structures.
- In high-seismic regions like Japan or Chile, the seismic load often dictates the size of the foundation piers and the reinforcement of the column-to-foundation connection.
6. Special Loads: The "Real-World" Engineering Buffer
A code-compliant structure is a starting point. A reliable structure accounts for the environment.
Vehicle Collision and Impact
Columns in parking lots are targets. We design with a two-tier strategy:
- Passive Protection: Independent steel bollards.
- Structural Redundancy: We check that the failure of a secondary purlin or a minor connection doesn't lead to a "zipper effect" collapse of the entire row.
Thermal Expansion and Contraction
For carport runs exceeding 30 meters, thermal expansion is non-negligible. Aluminum expands about 2.5 times more than steel. If your mounting rails are rigidly attached over a long span without expansion joints, the thermal cycle will shear bolts or crack the module glass. Solaracks systems utilize slotted holes and thermal breaks to accommodate this movement.
Drainage and Ponding
A 5-degree slope is great for solar, but poor for drainage if gutters are blocked. Ponding Loads occur when water weight causes a purlin to deflect, creating a "pool" that invites more water. We calculate the stiffness of our long-span members to ensure ponding is physically impossible under standard rainfall rates.
Hail Impact
In regions like the US Midwest or South Africa, hail is a major factor. While this is primarily a module durability issue, we ensure our clamping systems don't create "stress points" on the glass that would make panels more susceptible to hail damage.
SAP 2000 Workflow Callout
At Solaracks, we believe in the "Digital Twin" approach. We run every structural analysis through SAP 2000 for projects requiring specific load verification. Our model includes:
- Member-by-Member Stress Checks: Every beam, column, and rail is checked against AISC 360 or Eurocode standards.
- Deflection Analysis: Ensuring that the structure doesn't "feel" flimsy to the client and doesn't stress the panels.
- Connection Design: Finite element analysis on the critical column-to-rafter connections.
We deliver this as a complete engineering package — professional, stamped, and ready for your AHJ.
7. Load Combinations: How Everything Acts Together
An engineer doesn't just add all the loads together — that would lead to an over-designed, expensive structure. We use ASCE 7-16 Section 2.3 (LRFD) to find the most likely worst-case scenarios.
Critical LRFD Combinations for Carports:
- 1.2D + 1.6L + 0.5(Lr or S): The primary gravity check.
- 1.2D + 1.0W + L + 0.5(Lr or S): The combined storm check (Dead + Wind + Live + half Snow).
- 0.9D + 1.0W: The Uplift Case. This is the most critical for carports. By reducing the dead load to 0.9D (to account for the lightest possible panel weight) and applying full wind (1.0W), we ensure the foundations won't lift.
Structure Check — Load Calculation Completeness
Before moving from design to fabrication, use this checklist to verify your structural integrity:
- Load Identification: Have all seven load types (Dead, Live, Wind, Snow, Seismic, Impact, Thermal) been quantified?
- Height Correction: Is the wind load adjusted for the 3m-5m canopy height, not ground level?
- Directional Wind: Have both uplift (suction) and downforce cases been modeled?
- Unbalanced Snow: Does the model account for snow accumulation on the low side of the mono-slope?
- Future-Proofing: Does the Dead Load include weight for EV chargers, lighting, and heavy bifacial modules?
- Code Compliance: Are the load combinations calculated per ASCE 7-16 Section 2.3 or EN 1990?
At Solaracks, we don't just provide the steel; we provide the certainty. Our SAP 2000 modeling, load calculations, and engineering reports are provided with every quote — often within 24 hours.
Solaracks. Be Supported.
Structure First Series — Solar Canopy Engineering