What decides a battery installation
Is a Home Battery Worth It? What the Independent Evidence Says
The honest starting point is not ours. The Energy Saving Trust, which has no battery to sell, puts it this way: battery storage savings "can be significant, but won’t always be enough on their own to justify the cost of the battery". It adds that a battery’s lifespan is shorter than solar panels’, that stored energy is used less efficiently than energy taken directly from your panels or the grid, and that the typical lifespan is about 10 to 12 years. Energy Saving Trust, "Battery storage" (page last updated 6 October 2026).
So whether a battery pays depends on what you charge it with and what you displace. Two numbers set that: the electricity price cap, 26.32p/kWh from 1 October to 31 December 2026, and the Outgoing Octopus export rate, 12p/kWh. Every unit of solar surplus you store instead of exporting is worth the gap between them, less what the battery loses. That gap is smaller than most sales pages imply.
A battery added to a solar home
Take a 4 kW south-facing array on the Hampshire coast and a medium-use household (Ofgem’s typical 2,500 kWh a year). We model it month by month from PVGIS yields, with bright and dull days, 90% battery round-trip efficiency and the 26.32p / 12p rates (the assumptions are printed under the tables). Adding a 5 kWh battery adds this much a year — and it depends mostly on how much of the day someone is home:
| When you are home | The 5 kWh battery adds, a year | Payback on Octopus’s £3,947 |
|---|---|---|
| Out all day (30% of use in solar hours) | £167 | 24 years |
| Part of the day at home (45%) | £133 | 30 years |
| Home most of the day (60%) | £94 | 42 years |
Model: monthly yields from PVGIS, half the days bright (160% of the monthly average) and half dull (40%), flat demand, no degradation or price changes. It still flatters the battery, because real weather is more variable than two day-types. Our solar panel calculator runs the same model on your figures.
For the home that is part of the day in, that is about £133 a year and a payback of roughly 30 years — far longer than the 10 to 12 years the Energy Saving Trust gives for a battery’s life. This is the Energy Saving Trust’s point in numbers: a battery that only shifts your own solar surplus rarely repays itself.
A battery charged at a cheap rate
The picture changes where you can charge from the grid at a low overnight rate, because the spread to the cap is far larger. The catch is that a battery can only save money on energy you actually use. A 10 kWh battery in a home that uses 6.8 kWh a day in total will never be fully emptied, however cheap the electricity going in. The table caps each battery at the energy the home uses outside solar hours, which we assume is 60% of its use (an assumption — yours may differ), and charges it at Octopus Go’s night rate, 8.21p, the rate Octopus publishes for region H on 7 October 2026. Octopus describes Go as an EV tariff, so check eligibility; the point is the shape of the result, not an offer.
| Household (Ofgem typical use) | Daily use | Used outside solar hours | 5 kWh battery: a year · payback | 10 kWh battery: a year · payback |
|---|---|---|---|---|
| Low (1,600 kWh a year) | 4.4 kWh | 2.6 kWh | £165 · 24 yrs | £165 · 32 yrs |
| Medium (2,500 kWh a year) | 6.8 kWh | 4.1 kWh | £258 · 15 yrs | £258 · 21 yrs |
| High (3,800 kWh a year) | 10.4 kWh | 6.2 kWh | £282 · 14 yrs | £392 · 14 yrs |
Daily use = annual kWh ÷ 365. Value = delivered kWh × (26.32p − 8.21p ÷ 0.9), 365 days, capped by use outside solar hours. Payback uses Octopus’s published battery-only prices of £3,947 (5 kWh) and £5,336 (10 kWh). No degradation, price changes, standing charges or export income are included. Ofgem typical domestic consumption values from 1 July 2026: 1,600 / 2,500 / 3,800 kWh.
Read across the table. For a low-use home neither battery earns much; for a medium-use home the second 5 kWh adds nothing, because there is nothing left to displace; a 10 kWh battery only earns more than a 5 kWh one in a high-use home — or one with an electric car or a heat pump — and even there payback is about 14 years, the edge of the battery’s likely life. That is what “do not over-battery” means with numbers attached. And how sensitive is it to the cheap rate? For a medium-use home and a 5 kWh battery:
| Cheap overnight rate | Value a year | Payback on £3,947 |
|---|---|---|
| 5.00p — illustrative, below any current Octopus tariff | £311 | 13 years |
| 8.21p — Octopus Go night rate | £258 | 15 years |
| 12.49p — Cosy Octopus cheap windows | £187 | 21 years |
| 14.61p — Octopus Flux off-peak | £151 | 26 years |
Same assumptions as above. Octopus rates are region H, including VAT, read 7 October 2026 from Octopus’s public product API; they change, and each tariff has its own eligibility. A battery that cannot get a rate well below the cap saves little.
On a smart time-of-use tariff, with an electric car or a heat pump, or where a power-cut backup is worth paying for. Where none of those apply, the Energy Saving Trust’s caution is the right one — and we would rather tell you that at the survey than after the scaffold is down. Our solar and battery storage page covers buying both together.
How a Battery Storage Installation Runs
Survey and sizing
We look at your consumer unit, the location, any solar system and inverter already installed (make, age, whether you receive Feed-in Tariff payments) and a year of usage. The size is set from the evening and overnight energy you actually use — not from the roof.
Choose the route
Retrofit on the AC side, hybrid-inverter swap, or a new combined install — compared in the section below. The cheapest route is not always the right one.
Network paperwork
Up to 16 amps per phase (3.68 kW single-phase) is notified under G98; anything larger needs G99 approval from the network operator before installation. We prepare both. SSEN is the network operator across most of our area, and we confirm yours from your meter number.
Installation
The supply is isolated, the battery mounted, the circuits wired and labelled, and the installation tested to BS 7671 before it is energised.
Commissioning and app
Charge and discharge windows, export limit and backup mode are set to the way your home uses electricity, and the monitoring is registered.
Handover and warranty
You receive the electrical certificate and the commissioning record. The manufacturer warranty is registered through the installer — Fox ESS’s UK policy, for example, says only the installer and Fox-authorised staff can make a claim.
Adding a Battery to Solar You Already Have — or Fitting Both Together
The route matters more than the brand, and it changes the price. There are three:
- AC-coupled retrofit. Your panels and inverter stay exactly as they are; the battery brings its own inverter and connects on the AC side. Nothing on the roof is touched and no scaffold is needed. It adds a second inverter, which is why it can cost more per kWh stored than a combined install. If you receive Feed-in Tariff payments, tell us first so the metering is checked before anything is quoted.
- Hybrid-inverter swap. If your existing inverter is close to the end of its life, replacing it with a hybrid inverter and connecting the battery on the DC side gives you one modern unit instead of two. It is a bigger job and often the better value if a replacement was coming anyway.
- New combined install. Panels and battery on one hybrid inverter, in one visit, with one set of electrical work and one commissioning. It is normally the most efficient way to buy both.
Compatibility is a real constraint rather than a sales line: not every battery pairs with every existing inverter, and we check this before recommending anything. We also work on systems that other installers fitted, including ones whose installer has stopped trading. Our guide to adding a battery to existing solar walks through the decision.
Fox ESS, SigEnergy and GoodWe: What the Manufacturers’ Own Documents Say
We fit Fox ESS, SigEnergy and GoodWe. We no longer fit GivEnergy: the company went into administration on 9 April 2026, and a warranty is only as good as the company behind it. The table is built from the manufacturers’ own datasheets and warranty documents, not from marketing pages — and where their documents disagree with each other, it says so.
| Fox ESS | SigEnergy SigenStor | GoodWe Lynx Home F / F PLUS+ | |
|---|---|---|---|
| Units (manufacturer documents) | EP5 (5.18 kWh), EP11 (10.36 kWh nominal, scalable to 41.6 kWh); EVO5 and EVO10 all-in-one | BAT 5.0: 5.38 kWh total, 5.2 kWh usable. BAT 8.0: 8.06 kWh total, 7.8 kWh usable | LX F 6.6 / 9.8 / 13.1 / 16.4: 6.55 / 9.83 / 13.1 / 16.38 kWh usable; up to eight towers in parallel (131 kWh) |
| Ingress protection | EP11: IP65 | IP66 | IP55 for indoor and outdoor installation |
| Performance warranty | EP series 10 years; EVO and EQ series 12 years. At least 70% of nominal energy, or a throughput cap, whichever comes first (EP5 19.42 MWh, EP11 38.85 MWh, EVO5 23.99 MWh, EVO10 47.88 MWh) | 10 years: 70% of usable energy or a throughput floor, whichever first (EU warranty); extension to 15 years at 60%. A 2025 Europe revision we found states 60% at ten years — ask for the current document | 10 years: 70% of usable energy or a minimum throughput (LX F 9.8-H: 25.16 MWh; 13.1-H: 33.54 MWh) |
| Product (defect) warranty | See the UK & Ireland policy (V4.4) | 10 years on battery and energy controller; 5 years gateway; 2 years power sensor and comms | 5 years on electronics and enclosure (global LX F document) |
| Who can claim | The installer and Fox-authorised staff; the end user claims through the installer | See the claim process in the current document | Skilled or third-party installer; proof of purchase; installed within six months of production |
| Programme extras | — | Warranty extension option to 15 years | PLUS+ programme extends the HYBRID INVERTER warranty to 10 years, for PLUS+ installers, where the battery is first operated by 31 December 2026 |
Sources: Fox ESS Battery Warranty Policy, UK & Ireland (V4.4); Fox ESS EP11 datasheet V1.4; Sigenergy SigenStor warranty (EU); Sigen Battery datasheet; GoodWe Lynx Home F PLUS+ product page; GoodWe, warranty extension for hybrid inverters in 2026. Fox ESS and GoodWe terms are read from their warranty PDFs; Sigenergy’s server blocks automated downloads, so its terms are taken from extracts of its documents — confirm them against the current PDF. Warranty terms change between revisions and regions; read the current document for the exact model and firmware before you buy.
Two points the headline "10-year warranty" hides. First, every one of these guarantees is capacity retained to 70% (Sigenergy’s extension: 60%) or a throughput limit, whichever comes first — a battery that has delivered its rated energy can fall out of warranty before the calendar does. Second, the claim runs through the installer, so who installed it matters. For a head-to-head on these three, see our best solar battery comparison and Fox ESS vs GoodWe.
Claims that a particular battery is “MCS approved” cannot be checked: the MCS product directory has no battery category. What can be checked is compliance per model and firmware version on the ENA type-test register, which is what the network operator relies on for the connection paperwork.
Where a Home Battery Can Go, and What the Regulations Require
The best place for a home battery is outside the living space. PAS 63100:2024 is BSI’s fire-safety specification for batteries in dwellings, and since BS 7671:2018+A4:2026 (published 15 April 2026), regulation 570.6.7.203 requires batteries in dwellings to be installed in line with it. In summary it says a battery should not go:
- in a room where people are intended to sleep;
- on an escape route that is not a protected route — landings, staircases and corridors — or in the corridors, shafts, stairs or lobbies of a protected one;
- in a void, roof space or loft;
- within 2 metres of stored flammable materials;
- in a cellar or basement with no access to the outside.
An outdoor battery should not be within 1 metre of an escape route, a door, a window or a ventilation opening. The usual answers are a garage, a utility room, a plant space, an outbuilding or an external wall — the same places the Energy Saving Trust names. The specification has limits, too: BSI excludes, among other cases, dwellings over 200 m² and batteries fitted before the meter. BSI PAS 63100:2024 section 6, as summarised in Tesla's compliance library; BS 7671:2018+A4:2026 (published 15 April 2026), regulation 570.6.7.203.
On chemistry: the lithium iron phosphate (LFP) cells these batteries use are more thermally stable than other lithium chemistries, as GoodWe says of its own range. More stable is not the same as incapable of failing, which is why the siting rules above exist and why we do not describe any battery as risk-free.
Planning permission
Work that only affects the inside of a building is not development, so a battery fitted inside a garage or utility room does not need planning permission (Town and Country Planning Act 1990, s55(2)(a)). A battery in an outdoor cabinet is operational development, and the permitted-development rights for solar (Part 14 of the General Permitted Development Order, as amended to 27 August 2026) contain no battery class. Listed buildings need listed building consent for works affecting their character, interior included. If your plan is an outside unit, ask your council — or request a lawful development certificate — before ordering.
Network approval: G98 and G99
A single-phase system up to 16 amps per phase (3.68 kW) is connected under G98: you notify the network operator before commissioning or within 28 days of it. Larger systems — including many battery installs — need G99 approval before installation. SSEN’s small-generation fast track aims to respond within 10 working days; we submit the application as part of the job. ENA Engineering Recommendations G98 Issue 2 and G99; SSEN fast-track pages.
Battery Storage Costs: What Published Prices Show
Prices vary with the battery, the route and the job, so a figure from a sales page tells you little. These are published by sources with no reason to flatter an installer, with dates.
Energy Saving Trust, "Battery storage" (page last updated 6 October 2026); Octopus Energy, battery-only installation (April 2026 prices, read 7 October 2026); HMRC VAT Notice 708/6, energy-saving materials and heating equipment. Octopus adds a £500 non-refundable advance payment and, for solar installed by someone else, an MCS certificate and inverter details. Zero-rate VAT applies to a battery installed on its own since 1 February 2024. Our quote follows a survey, because the roof, the inverter you have and the cable runs move the price.
Grants and Loans for Home Batteries
There is no general grant for a home battery. Two government schemes can help, and both are narrower than headlines suggest.
- Warm Homes: Local Grant (England). For privately owned homes with an EPC of D to G, with eligibility by income band, means-tested benefit or household income of £36,000 or less, delivered through your council. Batteries are funded only where they complement solar PV, and the installer must be MCS-certified to MIS 3012. The cost caps are averages across a council’s project, not an entitlement. DESNZ Warm Homes: Local Grant policy guidance (July 2026).
- Warm Homes Loan Scheme. A lender’s loan, not a grant, with no income threshold; the battery loan cap is £15,000. Government pays lenders up to 20% of the loan, which must be passed on as a lower interest rate — lower, not guaranteed zero. Launch is phased from September 2026. DESNZ Warm Homes Loan Scheme rules (September 2026).
The Energy Saving Trust notes that there is also 0% VAT on installation until 31 March 2027. If a scheme matters to you, check eligibility with your council or lender before you commit; we cannot apply for it on your behalf.
Battery Storage Installation FAQs
The questions we are asked most, answered against published sources.
Published figures: the Energy Saving Trust puts a 5 kWh system at around £4,600 within a £1,500–£10,000 range, and Octopus lists battery-only installation at £3,947 for 5 kWh and £5,336 for 10 kWh (April 2026 prices). There is 0% VAT on installation until 31 March 2027 and 5% after that. The price of your job depends on the route, the inverter you already have and the cable runs, so ours follows a survey.
Sometimes. The Energy Saving Trust says savings “won’t always be enough on their own to justify the cost”. Shifting solar surplus alone adds about £133 a year to a 4 kW home that is part of the day in, with a 5 kWh battery at today’s cap and export rate. A cheap overnight tariff, an electric car, a heat pump or a power-cut backup need changes that — see the worked tables above.
Size it to the energy your home uses outside solar hours, not to the roof. A typical home system might be 10 kWh, but Ofgem’s medium household uses about 6.8 kWh a day in total, so a 10 kWh battery there is never fully used. The Energy Saving Trust says there is no exact formula and your installer should advise from your circumstances.
Yes. An AC-coupled retrofit leaves your panels and inverter untouched and adds a battery with its own inverter; a hybrid-inverter swap replaces the old inverter with one that handles both. Compatibility varies by inverter, and if you receive Feed-in Tariff payments the metering should be checked first.
In a garage, utility room, plant space, outbuilding or on an external wall. PAS 63100:2024 says not in a room where people sleep, on an unprotected escape route, in a loft or roof space, or within 2 metres of stored flammable materials; an outdoor battery should be at least 1 metre from an escape route, door, window or ventilation opening.
Not for an installation inside the building, which is not development. An outdoor cabinet is operational development, and the solar permitted-development rights in Part 14 of the General Permitted Development Order contain no battery class, so ask your council first. Listed buildings need listed building consent.
Always some paperwork. A system up to 16 amps per phase (3.68 kW single-phase) is notified under G98, before commissioning or within 28 days. Larger systems need G99 approval before installation. We prepare and submit it.
The Energy Saving Trust gives a typical lifespan of 10 to 12 years. Manufacturers’ warranties run 10 or 12 years, but they guarantee 70% of capacity or a throughput cap, whichever comes first, so they are not a promise that it will last that long at full capacity.
Not by default: a grid-tied battery shuts down in an outage for safety unless the system includes backup hardware, such as an emergency power supply circuit or a backup gateway, specified at design stage. Whole-home or essential-circuits-only backup is a design choice.
Yes. Under HMRC VAT Notice 708/6 the zero rate applies to installing a battery in residential accommodation, including on its own from 1 February 2024, until 31 March 2027. From 1 April 2027 the reduced rate of 5% applies.
Where these figures come from
Every figure above comes from a published source or from arithmetic on one. Read 7 October 2026. Where a source updates, the page should be re-read before a figure is reused.
- Energy Saving Trust, "Battery storage" (page last updated 6 October 2026) — typical lifespan 10 to 12 years; 5 kWh around £4,600, range £1,500 to £10,000; typical system 10 kWh; savings "won't always be enough on their own to justify the cost"; stored energy is less efficient than direct use
- Octopus Energy, battery-only installation (April 2026 prices, read 7 October 2026) — 5 kWh £3,947; 10 kWh £5,336; Tesla Powerwall 3 £7,999; £500 non-refundable advance payment
- Fox ESS Battery Warranty Policy, UK & Ireland (V4.4) — EP5 and EP11 10 years, EVO 12 years; at least 70% of nominal energy or a throughput cap, whichever comes first; EP11 10.36 kWh nominal, 38.85 MWh cap (about 3,750 full cycles)
- Sigenergy SigenStor warranty (EU) — 10-year battery warranty; 70% of usable energy at 10 years or a throughput floor, whichever first; extension to 15 years at 60%
- GoodWe Lynx Home F PLUS+ product page — usable energy 6.55 / 9.83 / 13.1 / 16.38 kWh; LFP; IP55; up to eight towers in parallel (131 kWh)
- GoodWe, warranty extension for hybrid inverters in 2026 — Lynx F / F PLUS+ batteries carry a 10-year product and performance warranty; the PLUS+ programme extends the HYBRID INVERTER warranty to 10 years when installed by a GoodWe PLUS+ installer and the battery is first operated between 15 May 2023 and 31 December 2026
- HMRC VAT Notice 708/6, energy-saving materials and heating equipment — zero rate for installation to 31 March 2027, 5% from 1 April 2027; batteries qualify on their own from 1 February 2024
- BSI PAS 63100:2024 section 6, as summarised in Tesla's compliance library — not in rooms where people sleep, unprotected escape routes, voids/roof spaces/lofts, within 2 m of stored flammables; outdoors not within 1 m of an escape route, door, window or ventilation opening
- BS 7671:2018+A4:2026 (published 15 April 2026), regulation 570.6.7.203 — requires batteries in dwellings to be installed in line with PAS 63100
- ENA Engineering Recommendations G98 Issue 2 and G99; SSEN fast-track pages — G98 up to 16 A per phase (3.68 kW single phase), notify before or within 28 days of commissioning; larger needs G99 approval
- Ofgem energy price cap, 1 October to 31 December 2026 — electricity 26.32p/kWh (Direct Debit)
- Octopus Outgoing, region H (OUTGOING-VAR-24-10-26, from 1 March 2026) — export 12.0p/kWh
- DESNZ Warm Homes: Local Grant policy guidance (July 2026) — batteries only where they complement solar PV; MCS installer to MIS 3012
- DESNZ Warm Homes Loan Scheme rules (September 2026) — battery loan cap £15,000; government pays lenders up to 20% of the loan, to be passed on as a lower interest rate
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