What Moves Commercial Solar Prices — The Nine Factors
Two identical-capacity systems can be priced £30,000 apart for legitimate reasons. These are the nine variables that do it, with the numbers attached, so you can read any quote like an engineer rather than a hopeful buyer.
1. System size — the dominant factor
Per-kWp pricing falls roughly 30% between 30kW and 500kW because design, mobilisation, scaffolding and grid application costs are largely fixed. In 2026: £900–£1,100/kWp at 30kW, £800–£950 at 100kW, £650–£800 at 500kW. If your roof and load can justify the next size up, the marginal capacity is the cheapest electricity you will ever buy.
2. Roof construction
Trapezoidal steel sheeting is the baseline — fast clamp-fit mounting, minimal penetrations. Standing seam costs slightly more but clamps cleanly. Flat membrane roofs need ballasted or hybrid systems and wind-load calculations, adding 5–15%. Fibre cement and asbestos roofs are the expensive end: fragile-roof working, netting, sometimes full replacement before solar is viable. A roof survey photo set is the first thing any serious estimator asks for.
3. Roof condition and remaining life
Panels last 25+ years; putting them on a roof with 8 years of life left is a false economy, because removal and reinstatement for re-roofing costs £40–£70 per panel. Where a roof is marginal, pricing the re-roof and solar together (often with integrated mounting) is frequently cheaper over 10 years than solar now and a crane-off later.
4. Access and logistics
Scaffolding and powered access run £2,500 on an easy single-storey unit to £30,000+ on a tall, tight urban site. Drivers: eaves height, perimeter access for MEWPs, hardstanding, distance from panel laydown area to roof, and whether public footways need licences. Sites that can take a telehandler and scissor lift price meaningfully better than those needing full scaffold wraps.
5. The DNO: application, limitation, reinforcement
Every system above 16A per phase needs a G99 application. The application itself is cheap; what it reveals is not always. Outcomes range from clean approval, through export limitation (a device capping grid export, modest cost, small revenue impact), to reinforcement quotations that can reach five or six figures on constrained networks. Rule of thumb: the bigger the system and the more rural the network, the earlier you want the DNO's answer. We cover this at length in the 250kW and 500kW guides.
6. Existing electrical infrastructure
A modern LV panel with spare ways absorbs solar cheaply. A 1980s board at capacity means switchgear upgrades — £2,000 to £15,000 depending on scale. Long cable runs between the array and the connection point add copper and trenching costs; a roof 150 metres from the switch room is a different project from one directly above it.
7. Hardware selection
Panel tier moves price less than people expect; inverter architecture moves it more. String inverters are the commercial default. Microinverter or optimiser systems add 8–15% and earn it only on complex, shaded roofs. Batteries are the big swing: £350–£550 per kWh installed at commercial scale, justified by export share and tariff structure, not by enthusiasm.
8. Labour conditions and programme
Can installers work normal hours with free roof access? Or is it a live food factory requiring out-of-hours work, permits, and hygiene controls? Night and weekend working adds 10–25% to labour lines. Similarly, winter programmes carry weather risk that estimators price in; spring and summer slots are cheaper and book out first.
9. Scope completeness — the silent differentiator
The cheapest quote is usually the least complete. Check whether each bid includes: scaffolding, G99 application and witnessing, structural engineer sign-off, export limitation device (if required), monitoring with export metering, O&M documentation, and making good penetrations. Anything "by others" lands back on your budget later. It is also worth asking who actually services the system after handover — plenty of installers subcontract this to maintenance specialists such as Solar Maintenance Solutions, which works fine provided response times are written into the contract. A fixed price against a written scope is the only number worth comparing.
Putting it together
Size sets the band; the other eight factors place you within it — or occasionally outside it. This is why we model from your actual meter data and roof drawings before quoting, and why the first output is an honest indicative band rather than a suspiciously precise figure. When the band looks good, a survey turns it into a fixed price. See how typical projects land by sector in the sector guide, or how funding choice changes the cash flow in finance vs purchase.
Price factor questions
Why are two quotes for the same roof thousands of pounds apart?
Almost always scope, not margin. Common differences: one quote excludes scaffolding or the G99 application; one uses 410W panels where the other uses 460W; one includes an export limitation device and structural sign-off, the other lists them as "by others". Line the scopes up item by item before comparing totals.
Does panel brand really matter to price?
Less than it used to. The spread between reputable tier-1 manufacturers is now pennies per watt; what matters more is the warranty counterparty still existing in year 20. The meaningful price gaps come from inverter choice, mounting quality, and labour — not the panel badge.
When does a commercial install need planning permission?
Most rooftop commercial solar in England proceeds under permitted development, with conditions on how far panels protrude and exclusions for listed buildings and some conservation areas. Ground-mount arrays and installations on protected buildings need consent. Your installer should confirm the position in writing as part of feasibility.