If you’ve started collecting quotes for solar panels in 2026, you’ve probably noticed installers quoting in different units — some give you a total price, some quote per kWp, and a few will happily talk in cost-per-watt. Cost per watt (£/W) is the cleanest way to strip out system size and compare quotes on a level footing, but it means something quite different depending on whether you’re pricing a 4kW roof in Surrey or a 250kW rooftop array on a Doncaster warehouse. This piece sets out what’s actually normal for £/W in the UK right now, why the number falls so sharply with scale, and how to use it to sanity-check a quote without getting misled by a headline figure.
What “cost per watt” actually measures
Cost per watt is simply the all-in installed price divided by the system’s rated capacity in watts (or, more commonly quoted, £ per kWp — thousands of watts). A £7,000 system rated at 4kWp works out at £1.75/W. It’s a useful normaliser because a 3kW system and a 10kW system will never have comparable total prices, but their £/W figures should sit in a similar band if the market is behaving efficiently — and mostly it does, with one big exception: fixed costs don’t shrink with system size, so small systems always look more expensive per watt than large ones.
For a full breakdown of what makes up that installed price — panels, inverter, mounting, scaffolding, labour, DNO notification — The Cost of Solar’s guide to UK solar panel costs goes through the line items in detail.
Residential £/W in 2026: what’s normal
For a typical UK home installation in 2026, expect these bands (installed, including VAT — though see the VAT note below):
| System size | Typical installed cost | Approx £/W |
|---|---|---|
| 3kW | £5,000 | ~£1.67/W |
| 4kW | £6,000–£8,000 | ~£1.50–£2.00/W |
| 10kW | £13,000–£17,000 | ~£1.30–£1.70/W |
The pattern is obvious: £/W falls as system size rises. A 3kW system carries almost the same scaffolding, inverter commissioning, DNO paperwork and site-visit overhead as a 10kW system, so those fixed costs are spread across far fewer watts. If your quote for a small 3-4kW system comes back above £2.00/W, that’s not necessarily a rip-off — small systems on complex roofs (multiple pitches, slate re-hangs, tricky access) genuinely cost more per watt to install — but it’s worth asking the installer to itemise where the premium sits.
One thing that helps residential economics right now: 0% VAT applies to solar panels and battery storage installed in Great Britain until 31 March 2027, after which it’s scheduled to revert to 5%. That’s a real, time-limited saving baked into today’s pricing — it isn’t a discount the installer is giving you, it’s the government’s, and it’s worth checking your quote explicitly states VAT-inclusive pricing at 0% rather than showing a phantom 20% baked in.
For a rough return-on-investment check to sit alongside the £/W figure, The Cost of Solar’s payback period calculator and solar panel calculator both let you plug in your own quote and estimated yield.
Commercial £/W: a different game entirely
Commercial and industrial rooftop solar is priced on a completely different curve, and this is where cost-per-watt really earns its keep as a comparison tool. Expect roughly £900–£1,200 per kWp for commercial installations in the UK in 2026 — that’s £0.90–£1.20/W, often a third to half the per-watt cost of a small domestic system.
Why the gap is so wide:
- Fixed costs are diluted over a much bigger array. A single access scaffold or crane hire covers 200kWp instead of 4kWp.
- Panel and inverter unit pricing improves with bulk procurement. Installers buying pallets rather than a handful of panels get meaningfully better trade pricing.
- Design and labour efficiency per watt improves. Racking a flat commercial roof in long, uninterrupted rows is faster per kWp than working around dormers, chimneys and multiple roof pitches on a house.
- Grid connection and export infrastructure costs, spread over more capacity, shrink per watt even though the absolute DNO application and switchgear costs are higher in cash terms.
This is the number to use when benchmarking quotes for warehouses, factories, schools, care homes or offices — if a commercial quote is coming in north of £1.50/W for a straightforward flat-roof array over 100kWp, that’s worth querying against a second or third quote. Commercial Solar Panels Installation is a useful reference point for what a properly scoped commercial quote should include, and both Solar Panels for Warehouses and Solar Panels for Factories set out the specific roof-loading, planning and grid-connection considerations that push large flat-roof projects toward the lower end of that £/W band. For businesses trying to size the investment case rather than just the unit price, Commercial Solar Finance and Solar Panel Grants for Businesses cover the financing routes and the (limited, sector-specific) grant landscape that sits alongside a commercial quote.
It’s worth being precise here on grants, because this is one of the most commonly garbled figures in UK solar content: there is no blanket small-business or commercial solar grant at 40%. The scheme that actually exists for farms is the Improving Farm Productivity grant in England, which funds roughly 25% of eligible costs — rates and schemes differ by nation, and Scotland, Wales and Northern Ireland run separate agricultural support routes. If you’re in the farm sector specifically, Solar Panels for Farms and Solar Panels for Barns go through what current eligible-cost percentages actually look like rather than repeating outdated headline figures still circulating from earlier scheme iterations.
Why £/W falls with scale — the mechanics in more detail
It’s worth unpacking why the curve bends the way it does, because it directly tells you where a quote should and shouldn’t be negotiable:
- Soft costs are near-fixed regardless of size. Site survey, structural assessment, DNO (G98/G99) application, scaffolding mobilisation, and commissioning paperwork cost roughly the same whether you’re fitting 10 panels or 400.
- Inverter cost bands step, not scale linearly. A single string inverter might cover anything from 3kW to 10kW at a similar unit price; above that, systems typically need multiple inverters or a hybrid/three-phase unit, so the £/W curve has visible “steps” at common inverter capacity thresholds rather than a smooth line.
- Panel wholesale pricing has volume tiers. Installers buying at pallet or container volume access materially better ex-works pricing than those buying in small batches for single domestic jobs.
- Labour productivity per kWp rises with array size. A team can rack and wire a large, unobstructed commercial roof faster per kWp than a fragmented, multi-pitch domestic roof with chimneys, vents and valleys to work around.
- Overheads and margin get spread thinner across a bigger contract value, so the same absolute profit represents a smaller percentage — and a smaller £/W addition.
None of this means a domestic installer is overcharging you at £1.70/W — it means the comparison only works if you’re comparing like-for-like scale, roof complexity and equipment tier.
How to benchmark a quote properly
A raw £/W number in isolation can mislead as easily as it can inform. Before you compare quotes on cost-per-watt alone, check:
- Panel technology and tier. Modern N-type panels (TOPCon, HJT or the emerging back-contact ABC designs) degrade more slowly — typically around 0.4% per year — and are commonly warrantied for 25-30 years, but they usually cost more per watt than older P-type panels. A cheaper £/W quote using an older panel tier isn’t automatically the better deal once you price in 25 years of generation.
- Inverter brand and warranty length. String inverters typically last 10-15 years and cost roughly £500-£1,000 to replace — factor that mid-life replacement into any long-term comparison, especially if one quote is markedly cheaper because it’s specified a shorter-warranty inverter.
- Whether scaffolding, DNO fees and making-good are included, or quoted as extras that will land later.
- MCS certification. Confirm the installer and the specific installation will be MCS-certified — it’s a requirement for Smart Export Guarantee eligibility, and increasingly for home insurance and future property sales. 2025 was a record year for UK solar with 257,397 MCS-certified installations (up 32% on the previous year) and roughly 21.6GW of cumulative deployed capacity, so certified installers are not in short supply — there’s no reason to accept an uncertified quote.
- Whether the export tariff assumption in any savings projection is realistic. Smart Export Guarantee rates vary by supplier and currently run up to roughly 12-20p/kWh at the top end — they are not a single fixed national rate, and a projection using an unusually high assumed export rate will flatter the payback figures.
- Battery pricing separately, since it’s usually quoted alongside solar but priced on its own £/kWh curve — typically £400-£700 per kWh installed, with a Tesla Powerwall 3 (13.5kWh) running around £8,500-£10,500. Don’t let a blended £/W figure hide an expensive battery attachment. The Cost of Solar’s battery storage cost guide breaks that out separately.
Regional installers are generally comfortable itemising all of this on request — worth asking ElectriFusion Solutions in South Yorkshire, Ecoaim in Livingston, or FLD Electrical in Swansea for a line-by-line breakdown rather than a single headline number, since a transparent quote should survive that scrutiny without the total price moving. For larger commercial or farm-scale arrays, EC Eco Energy in Essex and Greenlinc Renewables in Lincolnshire both work regularly across the domestic/commercial size boundary where £/W drops fastest, so they’re a useful comparison point if you’re straddling that line — a 15-20kWp array on a large house or smallholding, for instance.
The bottom line on £/W
Use cost-per-watt as a scale-normalised sanity check, not a single deciding number. Roughly £1.50-£2.00/W is normal for a small-to-mid domestic system in 2026, falling toward £1.30-£1.70/W for larger 10kW+ homes, and dropping again to roughly £0.90-£1.20/W once you’re in commercial territory above 50-100kWp. Anything wildly outside those bands — in either direction — deserves a second look: too high, ask what’s driving it (roof complexity, premium panel tier, scaffolding); too low, check panel tier, inverter warranty and whether MCS certification and DNO fees are actually included. A good quote should hold up in both directions once you interrogate it.
If you’re weighing up the industry backdrop behind these prices — installer volumes, supply chain trends, where 2026 pricing is heading next — Solar Weekly’s UK solar industry overview tracks the trade-side data that ultimately feeds into what installers can quote.