Solar Carports vs Rooftop Solar: Which Is Right?

Once an organisation accepts that on-site solar pays, the next question is where to put it: on the roof, or on a steel canopy over the car park. They are not interchangeable. Rooftop solar reuses a surface you already own, so it is cheaper and faster to pay back. Solar carports build the surface first, which costs more, but they do jobs a roof simply cannot, sheltering vehicles, carrying EV charging, and turning dead tarmac into generation. This guide compares the two honestly on the terms that decide it, and sets out a framework for choosing the right one, or the right mix, for your site.

The two options in plain terms

Rooftop solar. Panels mounted on an existing building roof, flat or pitched. The roof already bears load and already exists, so you pay for panels, inverters, mounting and labour, and little else structurally. It is the default first move because it reuses an asset you have.

Solar carports. A ground-mounted steel canopy built over the bays of a car park, engineered to stand over live parking and carry wind and snow load to Eurocode standards, with panels on top. It is not a roof array, it is a structure you build, and then put solar on. That structural difference drives the cost, the planning route, and most of the extra value.

Putting the options side by side

The key factors separate cleanly across the two routes:

Factor	Solar carports	Rooftop solar
Cost per kWp installed	£1,200 to £3,000	£600 to £1,000
Structure	New steel canopy, around 45% of project cost	Reuses existing roof, no structural build
Payback (panels only)	8 to 10 years	5 to 7 years
EV-charging synergy	Carries chargers, cable routes, behind-meter supply	None, separate project
Planning route (England)	Class OA prior approval, 56 days	Usually permitted development
Lead time	4 to 9 months	Shorter, no canopy build
Best fit	No suitable roof, large car park, EV demand	Empty, sound, well-oriented roof going spare

The headline trade is cost versus capability. Rooftop wins on price and speed because it skips the structural spend. A carport costs roughly two to three times as much per kWp, but it shelters vehicles, it provides the backbone and feed for EV chargepoints you very likely have to install regardless, and it is a visible, customer-facing decarbonisation statement that an invisible roof array never delivers.

Why carports cost more: the steel

The single most important number in this comparison is that the steel structure, columns, beams, purlins and the canopy frame, accounts for roughly 45% of total carport project cost. Rooftop solar avoids that entirely because the roof is already there. That is the whole reason a carport sits at £1,200 to £3,000 per kWp against £600 to £1,000 for a roof.

That fixed structural overhead is also why carports become far more cost-effective at scale. The steel cost is broadly fixed per bay, so a 50-bay scheme spreads it across far more generating capacity than a 10-bay scheme. A small carport is poor value, a large one is genuinely competitive once you count everything it returns. Rooftop economics, by contrast, scale more gently because there is no big fixed structure to dilute.

Generation and orientation

On a per-kWp basis the two generate similarly: UK yields run around 850 to 1,000 kWh per kWp per year for both. The difference is orientation and how much capacity you can fit.

A carport sizes from the parking footprint. Plan around 1.5 to 2.0 kWp per standard bay, roughly four to six panels across about 12 square metres of canopy, generating around 1,200 to 1,300 kWh per bay each year. A 100-bay car park therefore carries roughly 150 to 200 kWp and generates around 120,000 to 130,000 kWh annually. Canopy tilt is set by design, so a well-laid-out carport can achieve a near-optimal pitch regardless of how the car park is oriented.

A roof gives you whatever the roof gives you. A large, south-facing, unshaded flat roof is excellent and beats a carport on cost every time. A small, north-pitched, plant-cluttered or shaded roof is not, and on many commercial buildings the usable roof is far smaller than it looks once rooflights, plant, walkways and structural limits are deducted. This is why so many sites end up at the car park: the roof was either full, unsuitable, or simply too small for the load.

EV charging: where carports pull ahead

This is the argument that tips most decisions, and it is the one rooftop cannot answer. Retail, employer, healthcare, leisure and education car parks face growing pressure to provide EV charging for customers, staff and fleets, and that infrastructure has to be funded regardless of where the solar goes.

A solar carport carries the structure, the cable routes and a behind-the-meter solar supply for those chargepoints. Deliver the two together and you dig the car park once, not twice, and daytime solar feeds the chargers at your generation cost rather than full grid retail. The EV sockets can also be part-funded by the Workplace Charging Scheme through an OZEV-authorised installer (see gov.uk for the current rate, per-socket cap and closing date). Rooftop solar offers none of this synergy: the panels and the chargers stay two unrelated projects.

Planning: different routes, both manageable

Rooftop commercial solar is usually permitted development, the simplest route. A carport sits under Class OA of the General Permitted Development Order (England, since December 2023), which allows solar canopies on non-domestic, off-street car parks under a lighter-touch prior-approval process: a 56-day determination on siting, design, glare and drainage, rather than full planning.

There are limits worth knowing. The canopy must be no higher than 4m and not within 10m of a residential boundary, and the right excludes listed buildings, scheduled monuments and conservation areas, which still need full planning. Class OA does not currently extend to Wales or Northern Ireland. Two technical conditions catch people out on carports specifically: glare onto neighbouring premises, the highway or a flight path is the most common prior-approval condition, handled with a glare and glint study, and a new canopy over open tarmac is a new impermeable surface, so a SuDS drainage strategy is required. Both are routine for a competent installer, but they are real, and rooftop solar avoids them.

When carports make sense, and when the roof wins

A few questions sort it quickly.

The roof wins when:

• You have a large, suitable, structurally sound roof going spare, especially south-facing and unshaded. Fill it first, it pays back faster.
• The car park is small, so the fixed steel cost cannot be spread across enough capacity.
• You have no EV-charging requirement and no need for a visible sustainability statement.

A carport makes sense when:

• The roof is already full, unsuitable, shaded, or too small for your load, and the car park is the only solar surface left.
• The car park is large, 50 bays and up, so the steel cost spreads across real capacity.
• You need EV charging anyway, so the canopy funds infrastructure you were going to build regardless.
• The site has strong daytime electricity demand, so most generation is self-consumed at full retail rate rather than exported cheaply.
• A visible, customer-facing decarbonisation statement carries commercial weight for the brand.

For many commercial sites the honest answer is both: fill the roof first for the cheapest kilowatt-hours, then add a carport over the car park for the capacity the roof cannot hold, the EV charging you have to provide, and the visibility the roof lacks. The two are complementary, not rival, and where a car park shares a grid connection with an existing rooftop array, the only extra step is confirming spare DNO capacity before sizing the canopy.

An illustrative worked example

It helps to ground this in an illustrative case. A regional supermarket has a 160-bay surface car park and an earlier rooftop solar array that already fills the store roof, leaving no further roof space. With the roof committed, the only remaining solar surface is the car park. A roughly 240 kWp canopy over 130 bays generates around 216,000 kWh a year, almost all of it self-consumed into refrigeration and lighting during trading hours, with 20 EV sockets beneath it part-funded by the Workplace Charging Scheme and the PV plant written off under the 100% Annual Investment Allowance. Payback on the canopy lands around 8 to 9 years, longer than the roof array, but the roof was full and could not have carried this capacity, and the sheltered EV charging now draws footfall. Had the roof still been empty, the right move would have been to fill it first. The figures are illustrative and depend entirely on your site, bay count, load profile, tariff and roof condition.

How to choose

The decision tree is short. If you have a suitable, sound, well-oriented roof going spare, put solar on the roof first, it is cheaper per kWp and pays back faster. If the roof is full, unusable or too small, and you have a large car park, especially with EV charging to deliver and strong daytime demand, build a carport. If you have a partial roof and a big car park, do both, roof for the cheapest capacity, carport for the rest plus the EV charging and the visible statement.

The right answer is specific to your roof, your car park, your load and your EV plans, so the sensible next step is to model both against your real numbers. Read the full cost and payback breakdown for the underlying figures, check the grants and funding you can stack on a carport, and run a first estimate in our savings calculator. For the wider case on whether a canopy earns its place at all, see are solar car parks worth it. When you want a straight answer for your own site, request a free feasibility and we will model the roof against the car park for you.