Expert electrical advice from our NICEIC registered team
Written by Tim, NICEIC registered with 18+ years experience in Poole & Dorset · 5-star Google reviews · Same-day fixed quote, no obligation.
Cost to add a battery to existing solar panels in 2026: from £2,500 installed for a GivEnergy 5.2kWh unit, with 0% VAT on domestic battery storage. A retrofit is typically completed in half a day, and on a smart tariff the combined savings reach £400–500 a year. We fit GivEnergy and Fox ESS batteries across Poole, Bournemouth and Dorset — solar & battery service page here. Below is how a retrofit works, what it costs, and which battery suits your system.
If you already have solar panels on your roof, you’re generating free electricity — but you’re probably exporting half of it to the grid for a fraction of what you pay to buy it back in the evening. Adding a battery changes that equation completely. Instead of selling your surplus at 4–15p/kWh and buying it back at 24p, you store it and use it when you need it.
We retrofit batteries to existing solar systems across Poole, Bournemouth, and Dorset every week. Here’s how it works, what it costs, and which battery is right for your setup.
Three reasons are driving the current wave of battery retrofits:
Without a battery, a typical 4kWp solar system in Dorset uses about 50% of its generation directly and exports the rest. With a battery, self-consumption jumps to 80%+.
| Scenario | Self-Use | Export | Annual Saving | Annual Export Income | Total Benefit |
|---|---|---|---|---|---|
| Solar only (4kWp) | 1,800 kWh | 1,800 kWh | £432 | £135 | £567 |
| Solar + 5.2kWh battery | 2,880 kWh | 720 kWh | £691 | £54 | £745 |
| Battery adds | +£259 | -£81 | +£178/year |
That’s an extra £178 per year from a battery — but it gets better. If you’re on a smart tariff like Octopus Go, you can also charge the battery overnight at 7.5p/kWh and discharge it during peak hours at 24p. That adds another £250–300 per year, bringing your total battery savings to £400–500 annually. For the full savings picture across solar, battery and smart tariffs — including what a whole new system saves — see our solar and battery savings guide.
Want to know what a battery would save you? Message Tim on WhatsApp with your current system details and he’ll model the savings for your setup. Free, no obligation.
When you retrofit a battery to an existing solar system, the battery connects via AC coupling. This is the standard approach for retrofits and it’s straightforward:
DC coupling is when the solar panels and battery share a single hybrid inverter. This is only possible with a new installation or if you’re replacing your existing inverter. It’s slightly more efficient but not necessary — AC coupling loses only 2–3% compared to DC, and the flexibility of keeping your existing setup makes it the sensible choice for most retrofits.
These are the two batteries we install most for retrofits. Both are excellent — the right choice depends on your priorities.
| GivEnergy 5.2kWh | GivEnergy 9.5kWh | Fox ESS ECS 5.2kWh | Fox ESS ECS 10.4kWh | |
|---|---|---|---|---|
| Price installed | From £2,500 | From £3,800 | From £2,300 | From £3,500 |
| Usable capacity | 5.2 kWh | 9.5 kWh | 5.2 kWh | 10.4 kWh |
| Warranty | 12 years | 12 years | 10 years | 10 years |
| Cycles | 6,000 | 6,000 | 6,000 | 6,000 |
| Smart tariff | Yes (app) | Yes (app) | Yes (app) | Yes (app) |
| Expandable | Yes (stack up to 3) | Yes (stack up to 3) | Yes (stack up to 4) | Yes (stack up to 4) |
| Monitoring | Excellent app | Excellent app | Good app | Good app |
| Best for | Most homes | Higher consumption | Budget-conscious | Larger systems |
GivEnergy is a UK-based manufacturer with an outstanding app and monitoring platform. The real-time dashboard shows exactly where every watt is going — generation, battery charge/discharge, grid import/export, house load. It’s genuinely useful, not just a novelty.
The 5.2kWh unit suits most 3–4 bed homes. If you have an EV, higher consumption, or want to maximise smart tariff arbitrage, the 9.5kWh gives you more capacity to play with. Both units are expandable — you can add a second battery later if your needs change.
Fox ESS batteries are well-engineered and come in at a lower price point. The 5.2kWh unit starts from £2,300 installed — the most affordable retrofit option we offer. The warranty is 10 years vs GivEnergy’s 12, but 10 years is still substantial and the cycle rating is identical.
The monitoring app is good but not quite at GivEnergy’s level. If the app experience matters to you, GivEnergy wins. If you want the most storage per pound, Fox ESS is the better value.
Tim’s take: For most customers I recommend GivEnergy. The app is best-in-class, the warranty is longer, and we’ve installed hundreds of them without issues. But if budget is the priority and you want to keep costs as low as possible, Fox ESS is a solid choice — I wouldn’t hesitate to install one in my own home.
An honest answer most installers skip: not by default. A standard grid-tied battery shuts down the moment the grid goes off. That’s not a fault — it’s a safety requirement called anti-islanding (part of the G98/G99 grid connection rules) that stops your system back-feeding a line an SSEN engineer is working on.
If riding out power cuts matters to you, the battery needs an EPS (Emergency Power Supply) output or a backup gateway specified at the outset, wired to the circuits you want to keep alive — typically lighting, the fridge and the broadband router, not the whole house. It’s a design decision at survey stage, not a setting you can switch on later, so tell us up front if outage cover is part of why you want a battery.
Almost certainly yes. Battery retrofits work with virtually all existing solar systems, regardless of:
The only thing we check during the survey is your consumer unit — it needs a spare way for the battery circuit. If it doesn’t, a small upgrade may be needed, which we include in the quote.
A battery retrofit is a straightforward job — typically completed in half a day:
The first step is a quick survey to check your existing setup and model the savings. Tim will tell you exactly what a battery would save you — with real numbers based on your system, not manufacturer estimates.
Ready? Message Tim on WhatsApp or call 07809 680068. Free survey, fixed pricing, 0% VAT. We cover all of Poole, Bournemouth, Wimborne, and East Dorset.
From £2,300 installed for a Fox ESS 5.2kWh, from £2,500 for a GivEnergy 5.2kWh, up to £3,500–£3,800 for 9.5–10.4kWh units — all at 0% VAT and typically fitted in half a day via AC coupling, keeping your existing inverter.
Almost certainly. AC-coupled retrofits work with virtually any existing setup — any panel age, any inverter brand (SolarEdge, SMA, Solis, Fronius), string or micro-inverters, 3kWp to 15kWp. The only check is a spare way in your consumer unit.
Not by default. Standard grid-tied batteries shut down in a power cut (a safety requirement called anti-islanding under G98/G99) so they can't back-feed the grid. Keeping essential circuits live needs an EPS (Emergency Power Supply) or backup gateway specified at the outset — ask at the survey if outage cover matters to you.
For most 3–4 bed homes, yes — it lifts self-consumption of a 4kWp system from about 50% to 80%+. If you have an EV, high evening usage, or want to maximise cheap-overnight-tariff charging, the 9.5–10.4kWh units give more headroom, and both brands stack extra units later.
The current zero rate on domestic battery storage runs until 31 March 2027. Fitting before that deadline locks in the saving on the full installed price.
Tim and his team are happy to answer questions or provide a free, no-obligation quote. 5-star Google reviews and counting.
Tim and his NICEIC-registered team are here to help. Message us on WhatsApp or call 07809 680068 for a free, no-obligation quote.
