Solar Carport Structure Design — Wind Load Engineering per Thai DPT / AS/NZS 1170

Solar carports — car parks roofed with PV panels — are gaining popularity across Thai malls, factories and EV charging hubs because they put parking land to double use: shade for vehicles + power generation.

But what decides success isn't the "panels" — panels are commodity, anyone can buy them — it's a structure that genuinely resists wind and passes Thai building code. This article focuses on the part most often gotten wrong.

1. Why a Carport Is Harder Than a Rooftop

Mounting solar on a factory roof = adding weight to an existing structure. But a carport is a brand-new, free-standing outdoor structure with people and vehicles beneath it → it must be designed as a full "building."

The key difference: the critical load is wind uplift, not downward weight.

flowchart TD
    W["Wind under tilted panels"] --> U["Net uplift
pulls structure up"]
    U --> M["Overturning moment"]
    M --> F["Foundation + columns
must resist pull-out + overturning"]
    DL["Self-weight (panels+steel)"] -.minor downforce.-> F
    F --> OK["Stable when
resistance > uplift × safety factor"]

Tilted panels on an open site act like a sail — wind creates net uplift trying to lift and overturn the whole frame. The foundation must resist pull-out + overturning moment, not merely carry downward load.

2. Wind — The Standards to Cite

What must be computed:

• Basic wind speed — ~25-30 m/s in Thailand by zone (มยผ. 1311 has a map)
• Terrain/exposure category — open/coastal sites catch more wind than urban
• Pressure coefficient (Cp) for a tilted canopy — top vs underside differ → net uplift
• Importance + safety factors by occupancy (people/vehicles beneath = important)

3. Tilt Angle — Energy vs Wind Balance

Thailand's low latitude puts peak energy at about 10-15°, near horizontal — a carport advantage:

Lower angle = less wind-exposed area = lower uplift = smaller steel and foundations. But keep enough slope for rain drainage + dust runoff (otherwise soiling builds up and cuts output).

4. Components You Must Design Fully

flowchart LR
    A["Tilt/geometry
(single/double slope)"] --> B["Clearance
≥2.2-2.5m (trucks higher)"]
    B --> C["Steel frame
hot-dip galvanized"]
    C --> D["Foundation
resist pull-out + overturning"]
    D --> E["EV charger + DC/AC runs
+ drainage"]

• Clearance: tall enough for vehicles — cars ≥2.2-2.5 m; if serving trucks/vans, higher
• Steel: hot-dip galvanized (ISO 1461/12944) for long-term outdoor corrosion resistance — critical in high-chloride coastal areas; panel rails are usually anodized aluminum
• Galvanic corrosion: at steel-aluminum joints use stainless fasteners + isolate surfaces to prevent dissimilar-metal corrosion
• Foundation: designed to resist pull-out + overturning from wind — often larger concrete footings than expected
• Drainage + DC/AC runs + EV charger — planned from the start, not retrofitted

5. Permit + Engineer Sign-Off (Don't Skip)

A solar carport is a structure with people/vehicles beneath it — safety is a legal matter:

• It generally requires a building permit (Aor.1) under the Building Control Act once it exceeds size/area thresholds
• A licensed civil engineer (Associate Engineer level or above) must stamp the drawings and calculations — especially the wind-load analysis
• Check with the local municipality before starting, as thresholds vary
• Electrical: a grid-tie system needs MEA/PEA interconnection + an inverter passing anti-islanding (IEC 62116) and array design per IEC 62548

6. Choosing the Structural Configuration

flowchart TD
    Q1{Number of bays
+ area?} -->|Single row| S1["Single-slope / cantilever
(open on one side)"]
    Q1 -->|Two rows back-to-back| S2["Double-slope / T-config
(shared center column, economical)"]
    S1 --> R1["Good: easy access
Watch: cantilever catches more wind"]
    S2 --> R2["Good: saves columns/footings
per bay"]

• Single-slope / cantilever — open on one side, easy access, but a long cantilever takes large wind moment, needing bigger columns/footings
• Double-slope / T-configuration — two rows sharing a center column, saving columns and footings per bay, ideal for large lots
• Choose by bay count, under-structure traffic and foundation budget

Conclusion

In a solar carport, panels are the easy part; the structure is the hard part — the critical load is wind uplift, not downward weight. Design per มยผ. 1311 / AS/NZS 1170.2, choose a low tilt (5-10°) to balance energy against wind, use hot-dip galvanized steel against corrosion, design foundations to resist pull-out and overturning, and obtain a licensed-engineer sign-off + Aor.1 permit.

Done right from the start = a structure that stays safe for the panels' 25-year life + double-use of parking land + readiness for EV chargers.

Sahawatthanakit (1988) handles survey, design and installation of Solar systems together with steel mounting structures for factories, warehouses and car parks — our engineering team assesses wind, structure and ROI from your actual site.