The single most useful question to ask before pricing solar is: are you going to be in this house for at least ten years?
If the answer's yes, the rest of the article is worth your time. A typical 4kW domestic system installed in the UK in 2026 costs £6,000-£10,000, generates somewhere between 2,800 and 3,800 kWh per year depending on roof orientation, and pays itself back in around 8-12 years. Beyond that point you're getting effectively-free electricity for another decade or more.
If the answer's no, the maths simply doesn't work. The payback window is the entire economic case. Skip to the bottom of this piece for the few exceptions.
What you'll actually pay
The cost ranges that hold up across MCS-certified installers I've seen in 2026:
| System size | Panels only | With battery |
|---|---|---|
| 3kW (small terrace, ~10 panels) | £4,500-£7,000 | £8,000-£11,000 |
| 4kW (typical 3-bed semi) | £6,000-£10,000 | £10,000-£16,000 |
| 6kW (larger detached, big roof) | £9,000-£14,000 | £14,000-£22,000 |
The 20-40% spread between installers is real. The same 4kW system genuinely quotes £6,500 from one company and £9,800 from another, with broadly similar panels and broadly similar workmanship. Get three quotes. Don't take the cheapest, don't take the most expensive, and don't trust the salesman who turned up in a van with a pre-printed quote sheet.
The variables that actually shift your number:
Roof complexity. Steeper than 45°, multiple aspects, dormers, awkward access — all add scaffolding time, which is the biggest line item after panels themselves. A simple 30° south-facing terrace roof installs in two days; a complicated four-aspect Edwardian semi can take four.
Inverter type. String inverters (cheaper, single point of failure) versus micro-inverters or optimisers (more expensive, better with shade, longer warranty). For unshaded roofs, string inverters are fine. For partial shade, the optimised systems pay back the extra £800-£1,500.
Panel brand. Tier 1 manufacturers (Jinko, Trina, JA Solar, Q Cells, LONGi) are basically interchangeable on quality at the domestic level. The cheap end of the market gets you Tier 2 or Tier 3 panels with shorter warranties and worse degradation curves. Worth paying the modest premium for Tier 1.
Generation and the savings maths
A south-facing roof in the south of England gets close to the textbook number: roughly 950 kWh per kW of installed capacity per year. So a 4kW system generates around 3,800 kWh annually.
Move the roof to east or west and you lose 15-25%. Move it to Scotland, you lose another 10-15%. North-facing roofs are not worth the conversation; the panels generate maybe a third of what a south-facing equivalent would, and the maths breaks down.
Now, the savings. UK domestic electricity in 2026 is running 27-32p/kWh on the standard tariff. Every kWh you generate and use yourself displaces a kWh you'd have bought, so it's worth the full retail price. Every kWh you export gets the Smart Export Guarantee rate, which is much smaller — Octopus Outgoing pays 15p, most other suppliers pay 4-8p.
The split between self-consumption and export depends entirely on when you're at home. A weekday-working couple who leave at 8 and get back at 6 will export 60-70% of their solar generation. A retired couple, working-from-home household, or family with a stay-at-home parent will self-consume 40-50%. The latter is much more economical because every self-consumed kWh is worth 3-6x what an exported kWh is.
For a typical 4kW system with average self-consumption: annual savings of £700-£1,200. On an £8,000 install that's an 8-12 year payback. After that, it's essentially free electricity until the panels degrade meaningfully (typically 20-25 years).
The battery question
This is where solar advice gets muddier and the salespeople get more confident.
A battery (typically 5-10 kWh, costing £4,000-£8,000 installed) lets you store daytime solar generation for evening use. For a household that's out during the day and home in the evening, this can flip your self-consumption from 30% to 70-80%. That's a meaningful improvement.
But the maths on the battery alone is harder than the maths on the panels alone. Battery payback is typically 8-12 years on its own merits, and the chemistry degrades faster than panels do. Most lithium home batteries are warrantied for 10 years and noticeably worse by year 8.
When the battery actually pays back:
- High evening electricity use (cooking, EV charging, electric heat)
- Time-of-use tariff like Octopus Flux or Cosy where you can charge the battery from cheap grid electricity at night and use it in expensive evening peaks
- A genuine want for some grid-failure resilience (most home batteries don't actually back up the home in a power cut without specific configuration; check before assuming)
When it doesn't:
- Daytime household where self-consumption is already high without storage
- Tight budget where the panel-only system is the financially sensible choice
- Short-term residence where the battery won't reach payback
Honest take: get the panels, see how your generation patterns work for a year, then add a battery as a separate decision if the use case actually emerges. Don't bundle them in the same purchase out of inertia.
The Smart Export Guarantee, and why your supplier matters
SEG is the legal requirement that energy suppliers buy your exported solar. The rates differ wildly:
- Octopus Outgoing: 15p/kWh
- E.ON Next Export: 4-5p/kWh
- OVO: 4-5p/kWh
- British Gas Export & Earn Plus: variable, typically 6-10p/kWh
- Most other suppliers: 4-8p/kWh
Octopus is the obvious choice for solar exporters and has been for years. The 15p rate is roughly 2-4x what most competitors pay. Switch to them on the day your system is commissioned, not later.
The catch worth knowing: Octopus Outgoing is the standalone export tariff. If you want their imports tariff too (Octopus Tracker, Cosy, Go), you sign up for those separately and they go on the same account. Most solar exporters benefit from being on Octopus for both sides of the meter.
Choosing an installer without getting screwed
Solar in the UK has a long history of dodgy door-to-door sales, and the industry's still not free of it. The pattern: someone knocks at your door, says they're "in the area" doing free assessments, and produces a quote that's £4,000 above the market for a system that's actually undersized for your usage.
The defences:
MCS certification is non-negotiable. Without it, you can't claim Smart Export Guarantee. The MCS database is searchable online; verify any installer who quotes you.
RECC or HIES membership adds consumer protection on top of MCS. Both are voluntary trade bodies with codes of conduct and complaints processes.
A track record of 10+ years operating in your region. Local installers tend to do better installations because they care about local reputation. Big national installers can be excellent or terrible.
Three quotes from companies you found independently (not from the door-knocker). Compare line by line: panel make and model, inverter make and model, battery if applicable, scaffolding, electrical work, monitoring. The honest installers will itemise. The dodgy ones will give you a single number with no breakdown.
What I'd specifically reject:
- Anyone who turned up at your door uninvited
- "Free solar panels" or "rent your roof" schemes (the math benefits the company, not you)
- Quotes that pressure you to sign within 24 hours
- Anyone whose quote is dramatically lower than the others without explaining why
- Installers who claim "government grants" exist for domestic solar in 2026 (they basically don't, outside very specific local authority schemes)
When solar doesn't work
A non-exhaustive list of houses where I'd tell a friend not to bother:
- North-facing roof with no other suitable aspect
- Heavy shade from trees or neighbouring buildings most of the day
- Listed building or conservation area where consent is uncertain
- Slate roof in poor condition (you should probably reroof first; solar adds load)
- Plans to move within 5 years
- Renting (this is your landlord's investment, not yours)
- Off-grid property without grid connection (different conversation; smaller systems plus battery + generator backup makes sense, but the simple maths above doesn't apply)
What to do this week if you're solar-curious
Three things, in this order:
Spend twenty minutes on the MCS Solar Calculator at energysavingtrust.org.uk. It'll give you a rough generation estimate and payback figure based on your postcode and roof orientation. The numbers won't be perfect but they'll tell you whether the conversation is worth continuing.
Get three quotes from MCS installers. The local-search-then-Trustpilot route works fine. If the quotes come back at wildly different sizing recommendations (3kW vs 6kW for the same roof), that's a sign one of them isn't paying attention. The right size is driven by your annual electricity usage and your roof area, not by what the salesman wants to upsell you on.
Talk to your neighbours who already have solar. They'll tell you which installer was good and which wasn't, what their actual generation has been versus what they were promised, and whether the system needed any callbacks. This is more useful than reading reviews.
The order that's worth keeping in mind: if your home has poor insulation, fix that first — it's almost always a cheaper payback than solar. Solar makes the most sense on top of a reasonably well-insulated home with a heat pump and ideally an EV, where the daytime electricity demand soaks up the daytime generation. If you're at the start of that journey, the smart thermostat guide is a smaller and faster move to make first.
This article is general consumer information about UK home solar, not regulated advice. UK solar pricing and incentives change; verify current quotes before committing. Solar installation is a meaningful capital decision, consult MCS-certified UK installers and a UK financial adviser if relevant.
Affiliate disclosure: Morningfold has affiliate partnerships with several UK solar installers and energy brands. See editorial standards.