Plenty of commercial sites have both: a car park that needs resurfacing one day, and a corner of land doing nothing. The instinct is to compare the two options on cost per kilowatt installed, at which point the car park loses — and that comparison is the wrong one often enough to be worth unpicking.
This is the companion piece to our solar carport page, which covers capacity per bay, the published cost appraisal and the consent route. Here we deal only with the choice between structures.
Why ground-mount wins on cost per kWp
A ground-mounted array needs frames, foundations and cabling. A carport needs all of that plus enough structure to span parking bays at a height vehicles can drive under, on foundations that resist wind uplift on a large exposed deck, through a surface you then have to reinstate. The extra steel is not marginal — it is the defining cost of the structure.
Ground-mount also lets you choose the pitch. A canopy sits at a shallow angle, typically around 10 degrees, because a steeper deck over bays needs more height and more steel; a ground-mounted array can take the optimum tilt for the latitude and gain several percent of annual yield for nothing. On top of that, ground-mount can be oriented freely, built in rows with maintenance access designed in, and extended later without touching anything operational.
So if the only question is pounds per kWp, spare land wins. The reason sites still build carports is that the question is usually not that.
Four things that put the carport ahead
1. The land has a higher use, or a planning history. Open land on a commercial site is often the expansion plot, the future yard, or the bit the local plan has an opinion about. Covering it in a 25-year array forecloses that. Bays, by contrast, keep working as bays. If the land has any realistic alternative use, the carport is competing against zero land-take rather than against cheap steel.
2. The consent routes are different, and in England the canopy one is easier. Since December 2023 a canopy above off-street non-domestic parking in England has had its own permitted development right — Class OA, introduced by S.I. 2023/1279 — subject to prior approval, with the authority given 56 days to determine, a glare assessment in every case, a 4 m height cap and a 10 m separation from the curtilage of a dwellinghouse. A ground-mounted array has no equivalent right at that scale, so it is usually a full planning application. On a constrained site, the difference between prior approval and a full application can be the difference between a scheme and no scheme. The conditions are on our solar carport planning permission page — and note that Scotland’s Class 9M and Wales’s position differ, with solar canopies in Wales needing a full application regardless.
3. Proximity to the load. Self-consumption is where the value is, and the connection point matters. A car park is usually right beside the building, so cable runs are short and the generation lands on the site’s own supply. A field at the back of the plot may need a long cable route, a second connection point, or export arrangements that change the economics. This is a site-specific question worth answering early, because the cable can quietly cost more than the structural saving.
4. The secondary outputs. A carport produces covered parking, a mounting platform for EV charging with shared groundworks and switchgear, and lighting support — none of which a field produces. Whether those are worth the premium depends on the site, but they are real outputs rather than soft benefits. If EV charging is on the roadmap at all, building the infrastructure once is materially cheaper than retrofitting it; see EV charging under a solar canopy.
What is the same either way
Four things do not change with the choice, and they are worth stating because they are often presented as carport-specific problems:
- The grid connection. Both are G99 applications. G98 stops at 16 A per phase — about 3.68 kW single-phase and 11.04 kW three-phase — so no commercial array of either type falls inside the connect-and-notify route. The application is free to submit and is usually the longest item in the programme, which is the argument for lodging it before you have settled the structure.
- The tax treatment. Solar panels are special rate expenditure under the Capital Allowances Act 2001 s.104A(1)(g), so full expensing does not apply to either option: the Annual Investment Allowance covers the first £1 million of qualifying spend, then a 50% first-year allowance.
- The rating position. Qualifying on-site renewable generation plant is excepted from rating valuations until 31 March 2035 in both cases, with the land and settings remaining rateable.
- The ground investigation. Both need it, and in both cases the foundation type that comes out of it is the largest cost variable. A fixed foundation price offered before anyone has looked is a provisional sum in either structure.
A reasonable way to decide
- Price the land properly. Not at book value — at what it would be worth to the business in five years if it were still available. If that number is not zero, put it in the comparison.
- Check the consent route for each, on the actual site, including any designation or Article 4 direction. In England this often favours the canopy.
- Cost the cable run for the field option at the same level of detail as the structure. It is the line most often left out.
- Decide whether EV charging is coming. If it is, the carport absorbs that cost far more cheaply than a retrofit will.
- Then compare cost per kWp — and expect the field to win that single metric while possibly losing the decision.
There is also a legitimate answer of “both”: a ground-mounted array sized for base load and a modest canopy over the bays nearest the building, sharing one connection. On sites with the space, that often prices better than either at full size.
If you want the comparison run for a specific site, get an instant estimate — it returns indicative capacity for the car park, a modelled generation figure for your location, the consent route and the grid connection position by email.