Carport

Step 1: single bay, double bay and span

The bay is the unit of a carport. A bay shelters one vehicle, and the frame is extended by repeating bays along a common beam. Span, the clear distance between posts, is what drives the steel section and therefore the cost.

• Single bay: roughly 2.7 to 3.0 m clear width per car, typically carrying six to ten modules depending on module size and layout. The simplest structure, usually four posts and a single beam pair.
• Double bay: around 5.5 to 6.0 m clear width. A cantilever design with posts on one side only gives clear access from both sides but needs deeper foundations to resist the overturning moment.
• Rows and commercial arrays: repeated bays share posts, so cost per kWp falls quickly. Plan an aisle and door-opening clearance between rows, not just the vehicle footprint.
• Headroom: 2.2 to 2.5 m at the low edge suits cars and vans. Check the lowest point of the sloped roof and any gutter, not the ridge, and allow for roof boxes and cyclists where relevant.

Step 2: foundations and soil

Everything the carport carries ends up in the ground. Wind uplift is the critical case, because it loads the foundation in tension and overturning rather than compression, and a footing sized only for the weight of the structure will not hold it down.

• Ground screws: galvanised screw piles driven by machine, typically 1.5 to 2.0 m deep. No concrete, no curing time, installable in a day and removable at end of life. Best in cohesive and sandy soils, poor where rock or heavy rubble is near the surface.
• Concrete footings: cast pads or piers with anchor bolts or a cast-in post shoe. The universal answer where soil is weak, made ground, or where uplift and overturning are high. They need excavation, curing time and accurate setting out.
• Soil investigation: a pull-out test for screws or a simple trial pit for footings. Made ground, high water table, frost depth and buried services all change the design, and guessing here is the one shortcut that cannot be corrected later.
• Existing hardstanding: an existing slab is rarely adequate on its own. It has to be cored and the foundation taken to competent ground below, unless a structural engineer confirms otherwise.

Step 3: tilt, orientation and yield

A carport is free of any existing roof geometry, so tilt and azimuth can be chosen for the production profile you want rather than for what the building dictates. Shallower angles are usual because of headroom, drainage and wind attack area.

• Typical tilt: 5 to 15 degrees. Enough for water and dirt to run off and for wind uplift to stay manageable, and it keeps the high edge from towering over the drive.
• Single slope or duo pitch: a mono-pitch roof drains to one side and is simplest to gutter. A duo-pitch or butterfly layout puts modules on two orientations and flattens the daily curve, which suits daytime EV charging.
• Orientation: south facing gives the highest annual total. East and west facing produces less in total but more in the morning and evening, which usually matches self-consumption and charging better.
• Below 10 degrees: self-cleaning by rain gets weak, so expect soiling at the lower edge and plan occasional cleaning, especially under trees.

Step 4: drainage, gutters and a watertight roof

Decide early whether the carport must keep the vehicle dry. It changes the module clamping method, the frame and the price, and it cannot be added afterwards.

• Open clamped roof: standard mid and end clamps with gaps between modules. Cheapest and lightest, provides shade and hail protection, but water runs through the joints. Acceptable for many private drives.
• Watertight roof: modules are set into drainage profiles with EPDM seals so each joint becomes a channel feeding a collector at the low edge. This needs a purpose-built system and modules whose dimensions match the profile grid.
• Gutter and downpipe: route the downpipe inside or beside a post, and take the discharge to a soakaway or drain. A carport roof sheds the whole plan area at once, so a single undersized downpipe floods the parking bay in a storm.
• Ice and snow shedding: a smooth low-tilt roof sheds snow in a slab. Consider snow guards or the position of the low edge where people walk or where a neighbouring boundary is close.

Step 5: bifacial gain under a carport

A carport is one of the best places for bifacial modules. Rear gain needs three conditions, and a carport satisfies all of them: clear height behind the module, an open unobstructed rear face, and a reflective surface below.

• Ground reflectance drives it: light concrete or pale paving reflects far more than dark asphalt or grass. The surface under the carport is a design choice, so choose the light one.
• Keep the rear clear: purlins, cable trays and conduit crossing behind the cells cut into the gain, so route cabling along the beams rather than across the module backs.
• Frameless or dual-glass: dual-glass modules suit an exposed structure well, but they need clamps rated for glass-glass laminates and the correct clamping zone.
• Parked vehicles: cars under the array shade part of the reflecting surface, so treat any published rear-gain figure as an upper bound, not a planning value.

Step 6: wallbox, cable routing and electrical integration

Charging under the array is the point of a solar carport, and it is mostly a cabling exercise done in the right order.

• Mount the charger on a post: a wallbox at 0.9 to 1.2 m on the post nearest the vehicle inlet keeps the cable off the ground. Outdoor units need an adequate IP and impact rating and, in practice, some shading from direct sun.
• Keep DC and AC apart: string cabling runs in the beams to the inverter position, AC runs in its own duct to the distribution board. Separate the routes and keep DC runs short and UV-protected.
• Protection: the charging circuit needs its own overcurrent protection and residual current protection to the local wiring rules, plus DC fault detection appropriate to the charger.
• Surge and earthing: a free-standing structure in an open yard is exposed, so bond the frame into the equipotential system and fit surge protection on both the DC and AC sides.
• Solar-led charging: with an energy meter and a compatible charger the vehicle can be set to charge from surplus generation, which is where a carport array and an EV pay off together.

Step 7: planning permission and static documentation

A carport is a permanent structure with foundations, so it is treated as building work in most European jurisdictions, unlike modules laid on an existing roof. Confirm the local position before ordering.

• Permit thresholds: rules commonly turn on roofed area, height, and distance to the boundary and to the road. Small single carports may fall under a simplified notification, larger and commercial ones generally do not.
• Static documentation: the supplier's structural calculation for the frame, plus a foundation design for the actual soil, signed by a qualified engineer where required.
• Grid documentation: the array is a generating installation like any other, so the connection application, protection settings and commissioning records still apply.
• Insurance and neighbours: check that boundary distances, rainwater discharge and snow shedding do not fall onto adjacent land. These are the objections that hold up an otherwise finished project.

Carport options compared

Swipe the table to the left