4kW Solar System With Battery: Price Guide
Adding a battery to a 4kW system is one of the most popular home solar setups. Here’s exactly what it costs, what the battery adds, and whether it’s worth it.
The short answer
A 4kW solar system with a battery typically costs £9,000–£12,000 installed in 2026. The panels alone are roughly £5,000–£7,000, and adding a battery (usually a 5kWh unit) adds about £3,500–£5,000. Both qualify for 0% VAT when installed together.
Is it worth it? For many homes, yes — the battery stores your daytime surplus so you use it in the evening rather than exporting it cheaply and buying it back dearer. It lengthens payback slightly (to around 8–12 years) but increases your savings and unlocks smart tariffs. A 4kW-plus-battery setup suits smaller-to-average homes especially well. Below, the full price breakdown and honest verdict.
What this guide covers
A 4kW system with a battery is one of the UK’s most popular home solar packages — big enough to cover a smaller-to-average home’s needs, with storage to make the most of what you generate. It’s also one of the most-asked-about on price, so let’s lay the numbers out plainly and honestly.
4kW system with battery: the full price breakdown
| Component | Typical cost (2026) |
|---|---|
| 4kW panels only | £5,000–£7,000 |
| Battery (~5kWh) | £3,500–£5,000 |
| 4kW + battery total | £9,000–£12,000 |
| VAT | 0% (residential) |
So £9,000–£12,000 covers most 4kW-plus-battery installs, with the spread driven mainly by battery size and brand, plus your roof and installer. Installing the panels and battery together is usually a little cheaper than doing them separately (shared scaffolding, one visit) and keeps the whole job on 0% VAT. For the panels-only picture, see our 4kW solar system guide; if you’re weighing a bigger system, the 5kW guide is the next step up.
What does the battery actually add?
The battery is the biggest variable in the price. A 5kWh battery — the typical pairing — adds roughly £3,500–£5,000 depending on brand and whether it’s AC or DC coupled. Popular choices include Fox ESS and SolaX, both of which offer good value modular storage. The battery’s job is simple but valuable: instead of your 4kW system exporting its midday surplus for a few pence, the battery stores it for your evening use, so you buy less from the grid at full price. That’s where the extra savings come from.
What size battery pairs with a 4kW system?
5kWh is the sweet spot
A 5kWh battery is the usual match for a 4kW system, and for good reason: a 4kW array generates roughly enough daytime surplus to fill about that much storage on an average day, and 5kWh comfortably covers a typical home’s evening and overnight use. Going much bigger can backfire — pair a large battery with a modest 4kW system and it may sit part-empty, because the panels can’t always generate enough surplus to fill it (unless you top up from a cheap off-peak tariff). If you’re genuinely unsure, our battery sizing guide walks through matching capacity to your actual usage — but for most 4kW homes, 5kWh is the honest sweet spot.
Is a battery worth it with a 4kW system?
The honest answer: for many homes, yes — but it depends on how and when you use electricity. A battery makes most sense if:
- You use most of your electricity in the evening, when your panels aren’t generating — the battery bridges that gap with stored solar.
- You’re on (or planning) a smart tariff — you can charge from cheap off-peak power and run the home through peak hours.
- You’re out during the day, so without a battery most of your generation would export cheaply rather than power your home.
It makes less sense if you already use most of your electricity during daylight (you’re self-consuming directly anyway) or you’re on the tightest budget and want the fastest payback. There’s no shame in starting with panels only and adding a battery later — it’s a common, sensible route.
Payback and savings
A 4kW system with a battery typically pays back in around 8–12 years — a little longer than panels alone (~7–10 years), because of the battery’s added cost. But the battery increases your total savings by raising how much of your own solar you use, and it keeps generating value for many years beyond payback (panels last 25+ years; quality batteries carry ~10-year warranties). Your exact payback depends on your usage, export rate, tariff and self-consumption. Getting paid for any remaining export via the Smart Export Guarantee (which needs a smart meter) improves the maths further.
Add the battery now or later?
| Approach | Pros | Cons |
|---|---|---|
| Battery now (with panels) | Cheaper combined install, 0% VAT, one visit | Higher upfront cost |
| Battery later (retrofit) | Spread the cost, decide once you see your usage | Second install cost; slightly dearer overall |
Both work. Adding the battery with the panels is usually a little cheaper overall and keeps everything on 0% VAT. But retrofitting later — easy with an AC-coupled battery — is a perfectly good way to spread the cost and decide once you’ve seen your real generation and usage. Neither is wrong; it comes down to budget and preference.
4kW + battery: pros & cons
✓ Pros
- Store daytime surplus for evening use
- Higher self-consumption, bigger bill savings
- Unlocks smart-tariff savings
- 0% VAT when installed together
- Suits smaller-to-average homes well
- Backup potential in some setups
✗ Cons / considerations
- Adds £3.5k–£5k upfront
- Lengthens payback (~8–12 yrs)
- Less benefit if you use power in daytime
- Don’t oversize the battery for 4kW
- Battery warranty ~10 yrs vs 25+ for panels
Frequently asked questions
How much does a 4kW system with a battery cost?
Around £9,000–£12,000 installed in 2026 — roughly £5,000–£7,000 for the 4kW panels plus £3,500–£5,000 for a 5kWh battery. Both get 0% VAT installed together. Price varies by battery size/brand, roof and installer.
Is a battery worth it with 4kW?
For many homes yes — it stores daytime surplus for evening use, cutting bills further, and suits evening-heavy usage or smart tariffs. Less so if you use most power in daylight or want the fastest payback. Starting panels-only and adding a battery later is a fine route.
What size battery pairs with 4kW?
Usually a 5kWh battery — a 4kW array generates roughly enough surplus to fill it, and it covers typical evening use. Bigger batteries can sit part-empty on a 4kW system. See our battery sizing guide to match your usage.
What’s the payback?
Around 8–12 years, a little longer than panels alone due to the battery cost — but the battery raises your savings and keeps generating value for years after. Depends on usage, tariff, export rate and self-consumption.
Can I add a battery later?
Yes — retrofitting is straightforward with an AC-coupled battery. Adding it with the panels is slightly cheaper and keeps 0% VAT, but retrofitting later lets you spread the cost — a common, workable option.
A popular, well-balanced home setup
The bottom line: A 4kW system with a 5kWh battery is a well-balanced, popular choice for smaller-to-average UK homes — £9,000–£12,000 buys a setup that covers your needs and stores your surplus for evening use. The battery lengthens payback a little but lifts your savings. If budget’s tight, panels-only now and a battery later is a sensible path.
See my price →The verdict
A 4kW solar system with a battery is one of the best-balanced home setups going — at £9,000–£12,000, it pairs enough generation for a smaller-to-average home with a 5kWh battery that stores your daytime surplus for the evening, lifting your bill savings well beyond panels alone. It suits 2-bed homes, modest family houses and bungalows particularly well.
The honest caveats: the battery adds £3,500–£5,000 and lengthens payback to 8–12 years, and it’s less essential if you use most of your power in daylight. But for evening-heavy homes or those on a smart tariff, it’s usually worth it — and if the upfront cost is a stretch, there’s nothing wrong with panels first, battery later. The best way to see your real numbers is a couple of free, no-obligation quotes.
Important
Going Solar UK is an introduction service, not an installer. We don’t design, supply, or fit solar systems ourselves. Prices, payback periods and figures here are indicative 2026 estimates and vary by home, battery, roof, usage, tariff and installer — always get a survey and quotes from MCS-certified installers before relying on them.
We may receive a commission when we introduce you to an installer, at no cost to you. Any contract for work is directly between you and the installer.