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Solar battery storage: how it works and when it pays
How home solar batteries work in the UK, what time-of-use tariffs add, worked examples with losses and export given up, and what to check before you buy.
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Fox ESS batteries and inverters in the UK
Fox ESS sells all-in-one batteries, hybrid inverters and stackable battery modules in the UK. The model family decides usable capacity, backup and how long the warranty lasts.
China
2,000+ employees
Founded 2019
Fox ESS is worth shortlisting if you want a battery and hybrid inverter from one manufacturer with a UK office and a UK-specific warranty. Its UK range runs from the EVO all-in-one unit (inverter and 10.24 kWh battery in one case) to H1-G2 hybrid inverters paired with EP or EQ battery modules. Fox's UK warranty gives 10 or 12 years depending on the product, but the inverter cover drops to 5 years if the system isn't connected to Fox Cloud within 120 days of installation. Before comparing prices, find out which Fox family you are being quoted and what its usable capacity is.
Fox ESS UK is based in Coventry, sells through UK distributors including Segen, UK Greentech and CEF, and runs a UK service email. On 23 September 2026, Octopus Energy's installation packages page listed Fox EVO batteries in its 5 kWh and 10 kWh solar-and-battery packages; see our Octopus solar review.
The Fox ESS families you'll see on a UK quote
Fox model names describe different products, and specifications from one family don't carry over to another. These are the residential families on Fox's UK site:
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| Family | What it is | Typical use |
|---|---|---|
| EVO (EVO 5, EVO 10) | All-in-one: hybrid inverter and battery in one wall or floor unit | New solar and battery systems with fewer boxes |
| PowerQ | All-in-one with stackable battery modules, 9.84 to 29.52 kWh | Larger storage in one stack |
| H1-G2 / AC1-G2 | Single-phase hybrid (H1) or AC-coupled (AC1) inverter, 3 to 6 kW | H1 for new systems; AC1 to add a battery to existing panels |
| KH / KA | Single-phase hybrid (KH) or AC-coupled (KA) inverters, 7 to 10 kW | Larger single-phase arrays |
| H3 Smart, Plus, Pro | Three-phase hybrid inverters | Homes with a three-phase supply |
| EP6, EP12 | High-voltage battery modules, floor or wall | Pair with a Fox hybrid inverter |
| EQ2900, EQ4300, EQ4800, EQ5000 | Stackable floor-standing battery modules | Pair with a Fox hybrid inverter |
| CQ7 | High-voltage modules, 7.02 kWh each | Larger modular storage |
If you already have an ECS2900 battery, it is an older Fox family. It wasn't on Fox's UK residential range page when we checked (23 September 2026), or in the product list of the UK battery warranty we checked (version 4.5), so keep the warranty document that came with your system.
Fox also sells MiniQube, a compact plug-in storage unit. This page covers installed systems. If you are looking at plug-in solar, note that the rules for plug-in solar in Great Britain, in force since August 2026, exclude batteries; see our plug-in solar guide.
Usable capacity: nominal kWh is not what you get
Fox quotes a battery's nominal energy, then a depth of discharge (DoD): the share of that energy the system lets you use.
| Battery | Nominal energy | Depth of discharge | Usable (nominal × DoD) |
|---|---|---|---|
| EVO 10 | 10.24 kWh | 95% | about 9.7 kWh |
| EP6 | 5.76 kWh | 90% | about 5.2 kWh |
| EP12 | 11.52 kWh | 90% | about 10.4 kWh |
| ECS2900 H4 (older) | 11.52 kWh | 90% | about 10.4 kWh |
The last column is arithmetic on the datasheet figures, measured at the battery. What reaches your appliances is a little lower after conversion losses and any backup reserve. When one quote says "10 kWh" and another says "10.24 kWh", ask each installer for the usable figure so you compare like with like.
Example (illustrative): your smart meter shows about 7 kWh used between evening and morning. An EP12 (about 10.4 kWh usable) leaves room for a reserve and higher winter use; an EP6 (about 5.2 kWh) would run out before morning on those days. But if your panels only leave 5 kWh of surplus on a typical day, the bigger battery won't fill from solar alone unless you also charge it on a cheap overnight rate. Ask for a month-by-month estimate, not one summer day multiplied by 365.
Power: set by the inverter, and by the grid rules
kWh is how much a battery stores; kW is how much power the system can deliver at once. In a Fox system the inverter sets the power. The H1-G2 datasheet we checked (V2.0, December 2025) lists 3.0, 3.7, 4.6, 5.0 and 6.0 kW versions. Fox's UK EVO page lists 5, 8 and 10 kW versions, with a 3.7 kW G98 version, paired with the 5 kWh battery, "available shortly"; the newer EVO 10E datasheet we checked (V1.1, July 2026) lists 2.5 to 10 kW.
The rating also decides the grid paperwork. On a single-phase supply, the G98 connect-and-notify route covers up to 16 A per phase in total, which is 3.68 kW, and a battery inverter counts towards that total. Fox builds for this: the H1-G2 datasheet limits the H1-3.7 to 3,680 W for G98, and Fox's EVO datasheets include a 3.7 kW version rated at 3,680 W, which its UK page pairs with the 5 kWh EVO. A bigger inverter, or a Fox AC1 battery inverter added alongside your existing solar inverter, means your installer applies to the network operator under G99 and gets approval before connecting.
New system or battery for existing panels
On a new installation, an EVO or an H1-G2 hybrid with EP or EQ batteries lets the installer design panels, battery and metering together. An EVO saves wall space; separate modules give more choice of capacity.
If you already have panels, check the label on your inverter. A standard solar inverter doesn't gain battery control because it's the same brand. The usual Fox route is an AC1-G2 or KA inverter that charges the battery from the AC side and leaves your existing inverter in place. That keeps a working inverter but adds a second one, which normally means a G99 application. The alternative is to replace your inverter with a hybrid. Ask for both options priced, with the same battery.
At handover, ask for access to Fox Cloud and check it shows production, home use, export and battery charging. You also need the system connected to Fox Cloud to keep the full inverter warranty.
Backup in a power cut
A Fox battery doesn't automatically keep your home running in a power cut. Two levels are available:
- Backup circuits. Fox hybrids have an EPS (emergency power supply) output. On an H1-G2 it is limited to the inverter's rating, 3.68 kVA on the 3.7 kW version, and the H1-G2 datasheet gives a switch time under 10 ms. The installer wires chosen circuits, such as lights, the fridge and your router, to that output.
- Whole-home backup. Fox's EPS-BOX-SP is a single-phase whole-home backup gateway rated for a 100 A supply. Fox says it changes over in about 2 to 3 seconds and works with Fox's single-phase H1-G2/AC1-G2, KH/KA, EVO and PowerQ systems. Whole-home still means what the battery and inverter can supply: an electric shower or oven may be too much.
Ask which of the two your quote includes, which circuits are covered and to see a changeover test at handover.
The UK warranty: 10 or 12 years, with conditions
Fox publishes separate UK and Ireland warranty policies for batteries (version 4.5, 11 September 2025) and for inverters (version 2.3, 29 October 2025).
| Product | Warranty | Battery capacity guarantee |
|---|---|---|
| EVO 5, EVO 10, EQ batteries | 12 years | 70% of nominal energy for 12 years, or a throughput limit (EVO 10: 47.88 MWh) |
| EP5, EP6, EP11, EP12, CQ6, CQ16 | 10 years | 70% of nominal energy for 10 years, or a throughput limit (EP12: 43.19 MWh) |
| Hybrid, AC-coupled and three-phase inverters (including H1-G2, AC1-G2, H3) | 10 years | — |
| EVO and PowerQ inverter sections | 12 years | — |
| EPS-BOX-SP backup gateway | 5 years | — |
CQ7 isn't in the product list of battery policy version 4.5; ask the installer for its warranty terms in writing.
Periods run from installation, with a cap from the date of manufacture. Three conditions matter:
- Fox Cloud. If the inverter isn't connected to Fox Cloud within 120 days of installation, and kept connected, its warranty falls from 10 or 12 years to 5 years. Keep the system on your home internet.
- Claims go through the installer. Fox's policy names the installer as the party who claims. If your installer has gone into administration or is insolvent, you can appoint another local installer to act for you, at your own expense. While your installer is trading, a faulty battery or poor fitting is also covered by your rights under the Consumer Rights Act 2015 against them; Fox's warranty adds to those rights, it doesn't replace them.
- Throughput. The EVO 10's 47.88 MWh is about 4,700 full cycles of its 10.24 kWh (47,880 ÷ 10.24 = 4,676), roughly one a day over 12 years. Charging from solar and again from a cheap overnight rate uses that allowance faster.
Fox's UK warranties also exclude faults from installation by a "non-accredited Installer" without defining the term, so ask the installer to confirm in writing that their installation is covered.
Checking a Fox ESS quote
A quote you can compare should give:
- the exact inverter or all-in-one model and its kW rating;
- each battery module by name, with nominal and usable kWh;
- EPS circuits or the EPS-BOX-SP, or a clear statement that there is no backup;
- the G98 notification or G99 application, and who makes it;
- the 300 mm clearance Fox's battery warranty requires around the battery, and how the chosen spot meets PAS 63100:2024, the BSI fire-safety specification for home batteries;
- connection to Fox Cloud within 120 days of installation.
VAT depends on how you buy. Bought from an installer and fitted in your home, an EVO or EP battery has 0% VAT until 31 March 2027, then 5% from 1 April 2027 unless the relief is extended; a MiniQube or other unit bought without installation is charged at 20%. For typical installed prices, see our solar battery cost guide.
MCS's product directory doesn't list batteries or inverters, so check the installer's MCS certificate number. Fox runs its own accredited installer programme, which it says is recommended but not required to install its products. Fox accreditation and MCS certification are both separate from consumer-code membership: under MCS's redeveloped installer scheme a code is no longer required, so if you want RECC or HIES deposit and complaint protection, check the installer on that code's own register. Our guide to comparing solar quotes covers the rest.
Our view: Fox ESS makes sense when the quote names the family, shows usable kWh and backup clearly, and the installer connects the system to Fox Cloud. Compare it on usable capacity, inverter rating and warranty terms with other options in our best solar batteries guide, and read solar battery storage if you're still deciding on a battery at all.
Fox ESS FAQs
How long is the Fox ESS warranty in the UK?
12 years for EVO and EQ batteries and the EVO and PowerQ inverters, 10 years for EP batteries and Fox's other hybrid, AC-coupled and three-phase inverters, and 5 years for the EPS-BOX-SP. Inverter cover falls to 5 years if the system isn't on Fox Cloud within 120 days of installation.
Is the EVO 10 really 10 kWh?
Its nominal energy is 10.24 kWh, with a 95% depth of discharge, so about 9.7 kWh is usable at the battery before conversion losses.
Can I add a Fox battery to my existing solar panels?
Yes, usually with an AC-coupled AC1-G2 or KA inverter that leaves your existing inverter in place. The combined inverter power normally needs a G99 application to your network operator first.
Who do I contact if my Fox battery develops a fault?
Your installer: Fox's UK policy has the installer make the claim. If the installer has gone into administration or is insolvent, you can appoint another installer to claim for you.