Can You Add Solar Panels to an Existing Carport or Car Park Shelter?

What decides whether an existing structure can take panels

The shelter was designed to keep rain off cars, not to carry an array in the wind. Ten things decide whether it can change role. An engineer can answer most from drawings and a visit; two or three can end the idea outright.

1. Roof covering and fixing type

The covering sets how modules attach. Profiled sheet is commonly clamped or through-fixed, depending on profile and condition. Standing seam can often take seam clamps without holes, but only clamps made for that profile. Glazed roofs (polycarbonate or glass) are generally not a place to fix PV, so the roof would be replaced. Fabric or membrane shelters are tensioned structures, not a surface to fix modules to. Ask the covering’s manufacturer what is acceptable.

2. Purlin spacing and condition

A typical module is about 2.3 × 1.1 m, and its rails must land on purlins or other members at spacings the module manufacturer allows. Purlins that are too far apart, too light or corroded cannot be relied on, and adding secondary members adds work and load.

3. Structural capacity

The engineer compares the original design loads with what the array adds: dead load from modules and rails (a module is commonly in the region of 25-35 kg, but the chosen module’s datasheet gives the real figure) and wind uplift on a larger, more exposed surface. As the weight guide explains, wind and ground usually govern, not the panels. Loads follow BS EN 1991 for the site, and connections and foundations are checked as well as members.

4. Age and corrosion

The structure has to stay sound as long as the panels do. Look at galvanising or paint, column bases, connections and impact damage. If the roof covering will need replacing before the panels reach the end of their life, the array has to come off and go back on.

5. Drainage

Gutters and downpipes were sized for the old roof. Modules change where water runs, so check the discharge point and any drainage conditions on the site.

6. Shading and orientation

An existing roof has a fixed pitch and direction, and trees, buildings or lighting columns may shade it. In the PVGIS runs on the tilt and orientation page, an east-west plane at 10 degrees yields roughly 8-9% less per year than a south-facing plane at the same tilt. Model the actual roof before assuming a figure.

7. Cable routes to the main board

DC cables run from the array to inverters and AC cables on to the main distribution board. The route, inverter location and isolation points must be planned, and trenching through tarmac needs a utilities survey. A long run from a remote shelter can decide the scheme.

8. Fire, inspection and access

Modules need safe access for inspection and cleaning, clear labelling and isolation points responders can find. A fragile roof needs access arrangements before anyone walks on it. Agree these with the site’s insurer and fire risk assessor.

9. Warranty on the existing roof

Fixing to a roof can affect its own warranty. Ask the roof supplier or installer in writing whether the proposed fixings are acceptable, before ordering anything.

10. Grid connection

The G98 route stops at 16 A per phase, about 3.68 kW per phase, so any car park array is a G99 application to the DNO. The response can carry a cost, a condition or a queue position, and it can end a scheme, so start early. The G99 application guide sets out the steps.

Retrofit or replace with a purpose-built solar carport?

A retrofit is worth pursuing when the frame is sound, the covering can be fixed to, the pitch and orientation are reasonable and the shelter covers the bays you want to generate over. It stops making sense when strengthening cost and disruption approach the cost of starting again.

Signs that point to replacement: a frame that is old, light or corroded; a glazed, fabric or end-of-life roof; a poor orientation or pitch; columns in the wrong place for the bay layout; or a shelter over a walkway rather than parking. A purpose-built frame is designed for the array, with loads, clearance and column grid set together. As a planning figure, a single-deck solar carport is sized at about 1.5 kWp per bay, and an existing shelter covering fewer bays gives less. The solar carports guide covers the purpose-built route, the costs page shows how a scheme is built up, and the terms and structure types guide helps you describe the structure you would commission.