20kW Solar System UK: Cost, Output & Payback (2026)
Quick Answer
A 20kW solar system in the UK costs £22,000–£28,000 installed in 2026, including 0% VAT for residential properties. It uses 40–74 panels, needs 65–121 m² of roof space, generates around 18,537 kWh/year, and pays back in 5–7 years.
Prices verified April 2026. Actual quotes vary with installer, brand and site conditions.
This guide covers everything that figure buys you — panels, roof space, annual output, payback and who this size actually suits.
20kW System at a Glance
| Typical cost | £22,000–£28,000 installed |
| Panels | 40–74 (depends on panel wattage) |
| Roof space | 65–121 m² |
| Annual output | ~18,537 kWh |
| Annual savings (self-use) | ~£2,836 |
| SEG export income | ~£1,529/yr |
| 25-year savings | ~£78,634 |
| Payback period | 5–7 years |
| Battery add-on | £15,000–£25,000 |
Who a 20kW System Suits
Small commercial properties, farms, workshops, and large estates. Typically three-phase. 0% VAT does not apply to commercial — reclaim VAT where eligible.
Cost Breakdown
The headline £25,000 price for a 20kW system covers:
- Panels: 40–74 modules from a tier-1 manufacturer
- Inverter: string or hybrid inverter matched to system size
- Mounting & cabling: roof hooks, rails, DC/AC cabling, isolators
- Installation labour: typically 1–3 days for residential, longer for larger commercial
- DNO application: G98 notification or G99 approval — see below
- Commissioning & MCS certificate: required for SEG registration and 0% VAT
See our solar battery cost guide if you are considering adding storage. For a 20kW system, expect £15,000–£25,000 for a matched battery.
How Much Electricity Will It Produce?
A 20kW system in the UK produces around 18,537 kWh per year. Daily and monthly output varies with season — roughly 70% of generation arrives between April and September. Regional variation is significant:
- Southern England: upper end of the range (18,537 kWh)
- Midlands & Wales: ~90–95% of that figure
- Northern England: ~85–90%
- Scotland & Northern Ireland: ~80–85%
For context, the UK average household uses around 2,900 kWh per year — so a 20kW system produces 6.4× the typical home's electricity needs.
Savings & Payback
Savings come from two sources:
- Self-consumption: ~£2,836/year avoiding imported electricity at ~24–25p/kWh
- SEG export income: ~£1,529/year from surplus sold back to the grid
Over 25 years — the typical panel warranty — total savings reach roughly £78,634. That gives a payback period of 5–7 years at current prices. Electricity prices have risen faster than inflation historically, so real-world payback is often shorter than the modelled figure.
Pairing the system with a time-of-use tariff like Octopus Flux can lift export earnings significantly — see our best Octopus tariffs for solar guide.
DNO Approval (G98 vs G99)
G99 approval required. Export limits common on smaller local networks.
For full detail on the application process, timelines, and the nine UK DNO regions, see our DNO application guide.
Common Mistakes at This Size
- Not filing for Annual Investment Allowance — missing 100% first-year capital relief is the most common commercial solar mistake
- Assuming residential 0% VAT applies — commercial solar is 20% VAT, reclaimable for VAT-registered businesses only
- Budgeting the headline £ figure without a structural survey — older commercial roofs frequently need strengthening
- Ignoring export caps — at 20kW+ in congested areas, the DNO may require an export limit that changes payback materially
Frequently Asked Questions
How much does a 20kW solar system cost in the UK?
A 20kW solar system costs £22,000–£28,000 installed in the UK in 2026, typically around £25,000. Prices include 0% VAT for residential installations and cover panels, inverter, mounting, labour, and DNO paperwork.
How many solar panels in a 20kW system?
A 20kW system uses 40–74 panels, depending on panel wattage (modern panels range from 300W to 500W each). Higher-wattage panels reduce the count and the roof space needed.
How much roof space does a 20kW system need?
A 20kW array needs 65–121 m² of unshaded roof space. Each panel covers roughly 1.6 m². South-facing pitched roofs between 30° and 45° deliver the best output in the UK.
How much electricity does a 20kW system produce per year?
A 20kW solar system in the UK generates around 18,537 kWh per year. Southern UK averages the high end; Scotland and Northern Ireland sit 10–15% lower. Actual output depends on orientation, shading, and panel quality.
What is the payback period for a 20kW system?
Typical payback for a 20kW system is 5–7 years, assuming current electricity prices around 24–25p/kWh and a fair SEG export rate. Battery pairing and time-of-use tariffs (e.g. Octopus Flux) can shorten payback further.
Compare Other System Sizes
| Size | Typical cost | Annual output | Payback | |
|---|---|---|---|---|
| 4kW | £5,500–£7,000 | ~3,800 kWh | 7–9 yrs | View → |
| 7kW | £8,500–£10,500 | ~6,488 kWh | 6–8 yrs | View → |
| 12kW | £12,000–£15,000 | ~11,122 kWh | 6–8 yrs | View → |
| 15kW | £17,000–£20,000 | ~13,903 kWh | 6–8 yrs | View → |
| 50kW | £55,000–£70,000 | ~46,343 kWh | 5–7 yrs | View → |
Get a Real Quote for Your Home
The easiest way to benchmark a 20kW system for your property is to compare quotes from two or three MCS-certified installers in your area. Pricing varies with roof complexity, panel brand, and whether you need scaffolding.
Sources
John Rooney is the founder of Solar Info and has been covering the UK solar energy market since 2023. He fact-checks all content against official MCS and Ofgem data and maintains relationships with MCS-certified installers across the UK.