Solar Panel Payback UK 2026: Is a £7,000 4kW Array Worth It?

Published 13 May 2026 · 11 min read

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You've had two installer quotes. One is £6,800 for a 4 kW system with "10-year payback" stamped on the cover sheet. The other is £8,400 and the salesperson promised 7 years. The numbers don't match, the maths isn't shown, and you can't tell which one — if either — is real.

This guide does the arithmetic in front of you. Three worked household scenarios, real installed prices from May 2026, real PVGIS generation figures for your part of the UK, real current tariffs. By the end you'll know whether that £6,800 quote is honest, optimistic, or quietly fantasy.

TL;DR — three payback numbers

  • Scenario A — 4 kW, south-facing, no battery, standard household: ~£720/yr saved, 9.7-year payback on a £7,000 install.
  • Scenario B — 4 kW + 9.5 kWh battery, same house: ~£1,150/yr saved, 11.7-year payback on a £13,500 stack. (Full battery maths in the home battery payback guide.)
  • Scenario C — 6 kW + EV on Octopus Intelligent Go: ~£1,450/yr saved, 6.9-year payback on a £10,000 array. The EV does most of the heavy lifting.

If you only read this far: the £6,800 / 10-year quote is plausible for a sunny southern roof. It is not plausible in Manchester, and it is fantasy if your roof faces north.

What changed in 2026

Two things shifted the maths this year, and they pull in opposite directions.

Octopus Outgoing Fixed dropped from 15p to 12p on 1 March 2026. It had sat at 15p/kWh since September 2022. Wholesale prices have settled, and the export rate followed. Every other meaningful SEG offer in the UK is lower than Octopus, typically 3–7p/kWh from E.ON Next, British Gas, or EDF. So 12p is still the best mainstream export rate available — just less generous than it was.

0% VAT on solar PV and home batteries continues until 31 March 2027. After that it reverts to 5%. On a £7,000 install that's a £350 swing if you wait. The UK has never had a residential solar tax credit equivalent to the US ITC, but the 0% VAT does similar work while it's running.

The takeaway: exporting electricity pays 20% less than it did a year ago, but installing is still cheap. The lever has moved from "sell to the grid" toward "use it yourself" — which means smart hot water diversion, batteries, and EV charging windows matter more than they used to.

The three worked scenarios

Take a Birmingham semi-detached, south-facing main roof, four occupants, gas heating, ~3,800 kWh/year electricity consumption. Standard variable tariff at the April–June 2026 cap: 24.67p/kWh import.

Scenario A — 4 kW array, no battery

Installed cost: £7,000 (mid-range MCS quote, 0% VAT, basic scaffold, no diverter).

Generation: Midlands PVGIS figure is ~950 kWh per kWp installed per year for a south-facing 35° pitch. So:

4 kWp × 950 kWh/kWp = 3,800 kWh/year

Self-consumption: With no battery, no smart diverter, and a household that's empty 8am–6pm on weekdays, expect to use about 30% of what you generate in the moment. The rest gets exported.

Self-used:  3,800 × 0.30 = 1,140 kWh
Exported:   3,800 × 0.70 = 2,660 kWh

Savings:

Import avoided:  1,140 × 24.67p = £281
Export earned:   2,660 × 12p    = £319
Total:                            £600 / year

Payback: £7,000 ÷ £600 = 11.7 years.

Add a £400 Eddi-style hot water diverter and self-consumption climbs to ~50%. That moves more kWh from the 12p export bucket into the 24.67p saved-import bucket — worth about another £120/yr.

With diverter:
Self-used:  3,800 × 0.50 = 1,900 kWh × 24.67p = £469
Exported:   3,800 × 0.50 = 1,900 kWh × 12p    = £228
Total:                                          £697 / year

Payback with diverter: £7,400 ÷ £697 ≈ 10.6 years. Close to the installer's stamped figure, but only with the diverter included.

Scenario B — 4 kW + 9.5 kWh battery

Same Birmingham house, same array. Adding a 9.5 kWh battery (around £6,500 fitted in May 2026) does three things: stores the daytime surplus, lets you charge cheap off Octopus Go overnight, and pushes self-consumption from 30% to roughly 70%.

Self-used:  3,800 × 0.70 = 2,660 kWh × 24.67p = £656
Exported:   3,800 × 0.30 = 1,140 kWh × 12p    = £137
Plus off-peak arbitrage on import (~£350/yr — see battery guide)
Total:                                          £1,143 / year

Stack cost: £7,000 (array) + £6,500 (battery) = £13,500.

Payback: £13,500 ÷ £1,143 ≈ 11.8 years. Slightly worse on payback than solar alone, but much higher absolute savings and far better grid-outage resilience.

The full battery-only analysis — including degradation, depth-of-discharge assumptions, and whether to retrofit a battery to existing solar — lives in the home battery payback guide.

Scenario C — 6 kW array + EV + Octopus Intelligent Go

Same house, but now there's an EV in the driveway doing ~9,000 miles a year (≈ 2,500 kWh of charging). The roof had spare space, so the installer fitted a 6 kW array for £10,000.

Generation:

6 kWp × 950 kWh/kWp = 5,700 kWh/year

Self-consumption pattern: Octopus Intelligent Go gives a flat 7p/kWh off-peak slot from 23:30–05:30 for the whole house, not just the car. Daytime solar covers about 35% of the household baseline plus opportunistic EV top-ups when the car is home in daylight. Roughly:

Self-used by house:       1,800 kWh × 24.67p saved = £444
Self-used by EV (day):      600 kWh × 24.67p saved = £148
Exported:                 3,300 kWh × 12p          = £396
EV night charging (2,500 kWh × 7p) = £175 vs £617 on cap = £442 saved
Total:                                               £1,430 / year

Payback: £10,000 ÷ £1,430 ≈ 6.9 years.

This is the strongest payback in the guide, and it isn't because the panels are doing anything clever. It's because Intelligent Go costs 7p/kWh and the household cap costs 24.67p/kWh — a 17.7p gap on every off-peak kWh. The solar is bonus. The tariff is the engine.

If you have an EV, you should be on a smart tariff whether or not you install solar. Solar just makes the rest of the day cheaper too.

Generation by region

PVGIS figures for a well-installed south-facing 35° pitch array, no significant shading:

RegionkWh per kWp per year4 kW array6 kW array
Southern England (Cornwall, Sussex)~1,0504,200 kWh6,300 kWh
Midlands (Birmingham)~9503,800 kWh5,700 kWh
Northern England (Manchester, Leeds)~8803,500 kWh5,300 kWh
Scotland (Edinburgh, Glasgow)~8303,300 kWh5,000 kWh

East- or west-facing arrays produce about 85–90% of the south-facing figure. North-facing drops to roughly 65% — usually not worth the kit and scaffolding, but on a big enough north pitch it can still clear payback in 15 years if the rest of the install is cheap.

A 5% generation difference on a 4 kW array is worth about £30/year. So the difference between Cornwall and Glasgow on the same kit is roughly £130/year — meaningful, but it does not by itself make solar pointless in Scotland.

Why self-consumption is the lever, not export

The 2026 export rate is 12p/kWh. The 2026 import rate is 24.67p/kWh. Every kWh you use yourself is worth 2x what you export.

That gap is the whole story. It means:

  • A pound spent improving self-consumption beats a pound spent adding more panels, once you've sized for your daytime load
  • Smart hot water diversion (Eddi, iBoost) is the cheapest self-consumption upgrade — ~£400 fitted, typically £120/year payoff
  • A battery is the most expensive self-consumption upgrade but it works at all hours
  • An EV on a smart tariff is effectively a 40+ kWh battery that someone else paid for

Home Assistant ties these together — diverter, battery, EV charger, all on one dashboard reading the same solar production signal. That's the topic of the solar + Home Assistant guide.

What the spreadsheet doesn't capture

  • Feel-good factor. Watching the inverter app on a sunny April afternoon is genuinely pleasant. Not worth £7,000 by itself, but it's a real thing.
  • Modest home-value uplift. Estate agents talk up "energy-efficient features" but the data on actual sale-price premiums is thin. Don't bank on it.
  • Grid resilience. Standard grid-tied solar shuts down during a power cut for safety. Only batteries with islanding and a backup circuit give you any outage cover. If resilience matters, that's a battery decision, not a solar decision.
  • Tariff eligibility. Smart-meter plus half-hourly export readings unlock Octopus Outgoing, Intelligent Go, and Cosy. Without solar you'd still want a smart meter for these, but solar tends to be the trigger that finally gets one installed.

What kills payback

The four common ways a quote turns from "10 years" into "20 years":

  1. North-facing roof. Loses 35% of generation versus south. Drops Scenario A from a 11.7-year payback to closer to 18.
  2. Heavy tree shading. Even partial shade on one panel can pull a whole string's output down sharply. String inverters punish shade harder than microinverters or optimisers — worth asking which you're being quoted.
  3. Undersized inverter. If the installer fits a 3.6 kW inverter on a 4 kW array to dodge a DNO application, you'll clip on the brightest summer days. Modest loss, but it's a real number — typically 2–5% of annual generation.
  4. Oversized array on a low-consumption household. Putting 8 kW on a pensioner couple's roof generates a lot of 12p export and very little 24.67p saved import. You'd pay back, but slowly. Size to your load, then add a battery if you want to use more of what you generate.

Verdict

UK solar PV genuinely pays back. 8–12 years is the honest range for a south-facing 4 kW install in 2026, depending on region, occupancy pattern, and whether you bolt on a hot water diverter. Push to 6–8 years if you've got an EV and a smart tariff. Stretch to 12–15 years on a shaded or east/west site without a battery.

What the 2026 export-rate cut changed: self-consumption is now the win, not export. The installs that pay back fastest are the ones that use what they generate — diverter to the hot water tank, EV charging in daylight, battery to time-shift the evening, all coordinated. Selling to the grid at 12p is the consolation prize for the kWh you couldn't use yourself.

That orchestration layer is exactly where Home Assistant earns its keep, and it's exactly the layer that's a chore to set up and maintain. If you'd rather not learn YAML, run your own backups, or read inverter modbus registers at 11pm to figure out why the battery isn't charging — that's what habbb is for.

We keep what you have working. The boiler-service analogy holds: adding the solar is a separate job, but once it's in, the maintenance contract is what stops it quietly degrading into "the panels are up there but nothing's automated any more". See the managed Home Assistant service.

FAQs

Is solar still worth it in the UK in 2026 after the export rate cut? Yes, on a south- or east/west-facing roof. The cut from 15p to 12p adds roughly one year to a typical payback — Scenario A moved from about 10.5 to 11.7 years without a diverter. It didn't break the maths, it just tilted it further toward self-consumption.

How long do solar panels last? Most reputable panels carry a 25-year performance warranty guaranteeing ~85% of original output at year 25. Inverters are the weak link — expect to replace once in the lifetime of the panels, typically at year 10–15, budget £900–£1,400.

Do I need a battery to make solar pay back? No. Scenario A pays back without one. A battery improves absolute savings and resilience, but its own payback is slower than the panels'. Add solar first, live with it for a year, then decide on a battery once you can see your actual self-consumption pattern.

What if my roof faces east-west, not south? Expect ~85–90% of south-facing generation. Often actually a better fit for a working household: more morning and evening output, less midday peak you'd have exported cheaply. Payback typically only 6–12 months worse than a south install.

Does 0% VAT apply to repairs and add-ons? It applies to new installs of solar PV and batteries through an MCS-registered installer until 31 March 2027. Standalone battery retrofits also qualify (since February 2024). Spare-part repairs are usually charged at standard VAT.

Should I wait for prices to fall further? Installed prices have been broadly flat for two years. Panel costs keep dropping, but scaffolding, labour, and DNO admin don't. Waiting for the 0% VAT to expire in March 2027 is the more likely outcome than a meaningful price drop — and that's a 5% swing against you.