Design Guide
Solar Canopy Design: How It Works
Every commercial solar canopy starts as a blank car park. Turning it into a generating asset takes five interlocking design stages — structural engineering, panel layout, electrical design, planning drawings and grid connection. This page sets out what each stage involves and what to ask an installer for.
In short: Solar canopy design runs feasibility → structural scheme → yield model → DNO application; every design is engineered to BS EN 1990/1991/1993 and signed off by a chartered structural engineer.
Five stages of solar canopy design
A complete solar canopy design package covers structural engineering, yield modelling, electrical design, and all drawings required for planning, building regulations, and DNO grid connection.
- Aerial imagery analysis and measurement of car park bays
- Existing underground services survey (BT Openreach, water, gas, electrical)
- Obstruction mapping: trees, lamp posts, service bays, fire hydrants
- Access route assessment for piling rig and crane
- Preliminary panel count and yield calculation (PVSyst P50)
- Grid connection desk study: DNO capacity, connection point, G98/G99 route
- Indicative structural scheme and foundation type assessment
- Wind loading calculation to BS EN 1991-1-4 (Eurocode 1) for site location and exposure
- Snow loading to BS EN 1991-1-3 for geographic zone
- Column, rafter, and purlin design to BS EN 1993 (Eurocode 3)
- Connection design: base plates, bolted rafter connections, purlin cleats
- Foundation design: pile capacity, ground investigation data, pile schedule
- Hot-dip galvanising specification to BS EN ISO 1461
- Structural engineer certification and PE stamp on all calculation packages
- Detailed panel layout in AutoCAD: bay dimensions, panel positions, row spacing
- PVSyst full yield simulation: P50 and P90 annual output, monthly generation profile
- Shading analysis: near-shading from trees, buildings, adjacent structures
- String configuration: series string length, parallel string count, MPPT allocation
- Bifacial gain modelling: albedo measurement or standard assumption with sensitivity analysis
- Performance ratio calculation: system losses, degradation, inverter efficiency
- Export vs self-consumption profile (against site half-hourly meter data)
- Single-line diagram: DC strings → combiner boxes → string inverters → AC DB → metering → grid
- DC cable sizing: voltage drop, short-circuit current, temperature derating
- AC cable sizing from inverter to distribution board
- Earthing design and lightning protection to BS EN 62305
- Inverter selection and technical specification
- Revenue grade metering: generation meter, export meter, DNO metering where required
- Protection relay design for G99 systems
- Site location plan (1:2500)
- Site plan showing canopy footprint, existing car park layout (1:500)
- Structural elevations: all four sides with dimensions and eaves heights (1:200)
- Panel layout plan view (1:200)
- Cross-section through structure showing column, rafter, purlin, and panel (1:50)
- Foundation detail drawing with pile positions and base plate details (1:20)
- Materials and finishes schedule
Design standards and certifications
Eurocode structural design
All structural design is completed to BS EN 1991 (actions), BS EN 1993 (steel structures), and BS EN 1997 (geotechnics). Wind and snow loads are calculated for the specific site from the UK National Annex maps to BS EN 1991-1-4 and BS EN 1991-1-3. The structural calculations should be certified by a chartered structural engineer (MIStructE or MICE).
yield modelling
Annual energy yield is modelled in PVSyst using TMY (Typical Meteorological Year) climate data for the site location. A yield study should give P50 (median) and P90 (90th percentile) estimates. The P90 figure is used for financial modelling — a conservative estimate that excludes the 10% of years with worst irradiance.
Electrical design to BS 7671
All electrical design is completed to BS 7671:2018 (IET Wiring Regulations, 18th Edition) with Amendment 2. DC system design follows IEC 62548. The electrical design should be reviewed and signed off by a suitably qualified electrical engineer before installation begins.
Planning drawings to standard
Planning drawings are prepared to the standard required by the local planning authority — typically 1:2500 location plan, 1:500 site plan, and 1:200 elevations and floor plans. Depending on the site, the council may also ask for a design and access statement, a heritage impact assessment and an ecology summary; the planning page sets out when a canopy needs prior approval and when it needs a full application.
DNO technical submission
Grid connection technical design is prepared to the requirements of EREC G98 (very small systems, up to 16 A per phase) or EREC G99 (larger systems, including every commercial canopy). G99 submissions include the complete engineering study package: protection relay settings, power quality assessment, and single-line diagram to DNO standard.
Building Regulations compliance
Free-standing solar canopy structures require Building Regulations Part A (structural) compliance. The installer’s structural engineer should certify Part A compliance as part of the structural design package. This is separate from the planning permission and must be completed before installation begins.
Key solar canopy design decisions
For a fixed-tilt canopy in the UK, the optimum pitch angle for maximum annual energy yield is 35 degrees. However, most car park canopies are designed at 8-12 degrees for three practical reasons: lower wind loading (reducing structural steel weight and foundation cost), better car park aesthetics, and lower eaves-to-ridge height differential (easier to achieve planning consent). The yield difference between 8 and 35 degrees in the UK is approximately 5-8% — small relative to the structural cost saving from a shallow pitch.
A south-facing mono-pitch canopy maximises yield. However, many car parks are not oriented north-south. A T-frame canopy covers east-west oriented car park rows from a central column row, with slopes facing east and west — achieving 92-95% of south-facing yield while covering the actual car park layout. Model both options and choose based on the specific site geometry and yield priority.
Column spacing is determined by the rafter span, which is limited by the steel section depth required to span the car park aisle width. Typical column spacing: 5.0-6.0m for a standard single-row mono-pitch. T-frame canopies have columns at 5.0-6.0m centres along the central aisle, with rafters spanning 5-6m to each side. Longer spans require heavier steel sections and deeper foundations — there is a cost trade-off between fewer columns (less disruption to car park surface) and heavier structure (higher steel cost).
Standard car park clearance: 2.4m minimum (passenger vehicles). Accessible car parks, service vehicles: 3.0m. Vans and high-roof vehicles: 3.5m. HGV delivery access: 4.5-5.5m. The required eaves height significantly affects the structural design — higher eaves means taller columns with greater bending moment under wind loading, requiring heavier base plates and larger foundations.
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