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BatteriesWhat size battery does your home actually need?
The right battery size is a function of how your household uses electricity, not how big your roof is. It takes one number off your annual statement to work out, and we do it with you on the call.
Updated 4 August 2026 · from the OVO Solar & Battery team
Start with one number
Find the annual kWh total on your electricity statement or in your smart meter app, then divide it by 365. That gives your average daily consumption, and everything about battery sizing follows from it.
For reference, Ofgem's typical consumption values for 2026 put a low use home at 1,600 kWh a year, a medium home at 2,500 and a high use home at 3,800. That works out at roughly 4.4, 6.8 and 10.4 kWh a day. Homes with electric heating, an EV or a heat pump sit well above the top of that range.
The number you want is your evening, not your day
A battery is not there to cover every unit you use in 24 hours. It is there to cover the block your solar cannot reach, which for most households is the run from late afternoon through to the following morning. Sizing to the whole day buys capacity that never gets used.
What most UK homes land on
Across the market, most homes end up somewhere between 5 and 10 kWh of storage. A typical three bedroom house getting through around 10 kWh a day is often pointed at 10 to 12 kWh of capacity if the aim is maximum self sufficiency, while homes with electric heating or unusually high consumption are steered towards 10 to 15 kWh.
Our own standard specification is 5.2 kWh usable, which is sized to carry a normal household through the expensive evening peak rather than to cover an entire day off grid. On the design call your local OVO expert looks at your real consumption pattern and tells you straight whether that is the right shape for your home.
| Household | Annual use | Daily average | Where sizing usually starts |
|---|---|---|---|
| Low use, one or two people | 1,600 kWh | 4.4 kWh | Around 5 kWh usable |
| Medium use, typical family | 2,500 kWh | 6.8 kWh | 5 to 10 kWh usable |
| High use, larger household | 3,800 kWh | 10.4 kWh | 10 kWh usable and up |
| Electric heating, EV or heat pump | Above 3,800 kWh | Above 10.4 kWh | 10 to 15 kWh usable |
Consumption bands are Ofgem's 2026 typical domestic consumption values. Sizing bands are the ranges reported across the UK installer market, not a quote. Your own figure comes from your actual meter data on the design call.
Why oversizing quietly costs you money
A battery earns per cycle. If you fit 15 kWh and only ever put 6 kWh through it, you have paid for capacity that sits idle, and the payback on the whole system stretches out accordingly. Right sizing beats oversizing, and it is one of the few places in this industry where buying less is the better decision.
The counterweight is worth knowing too. A slightly larger battery than the solar array alone would justify can still make sense, because it keeps earning through winter on off peak charging when the roof has almost nothing to give. The deciding factor is whether you can realistically fill and empty it most days.
The quick test
Could you fill this battery every night at the off peak rate and empty it again by the following evening? If yes, it is working for its living. If the honest answer is only on a good day in June, it is too big.
Bring your last annual statement to the free 45 minute design call and we will size it against your actual usage, on screen, before you commit to anything.
Get your free quote →Four things that change the answer
- When you are home. A household that is out all day exports most of its solar and leans harder on stored off peak electricity in the evening, which pushes sizing up. A household home all day self consumes more directly.
- Your tariff. If you are on an off peak plan with a decent overnight window, the battery can be filled from the grid every night regardless of weather, so capacity gets used year round.
- An EV or a heat pump. Both add substantial load, and both are usually better served by charging in the same cheap window rather than by drawing the house battery flat.
- Your export rate. At OVO's SEG Install Exclusive rate of 20p per kWh, exporting surplus solar is close to as valuable as storing it, which changes what the battery is for. That logic is set out on the strategy page.
Size the inverter, not just the battery
There is a second number that catches people out. Your Distribution Network Operator assesses your connection on inverter rating, not on battery capacity. Up to 16A per phase, which is 3.68 kW on a single phase supply, the system can be installed and then notified under G98. Above that you need G99 approval before the work happens, and the network operator has up to 45 working days to respond.
The assessment is cumulative, so a battery inverter added alongside an existing solar inverter is counted together with it. Two 3.5 kW inverters on one property put the site into G99 territory. Your regional partner handles that application as part of the job, but it is a reason to plan the full system in one go rather than in pieces.
What it costs at each size
Installed prices across the UK market run at roughly £400 to £900 per kWh, and published ranges by size overlap heavily, so treat any figure as a band rather than a price. Our own battery pricing is fixed and published: £2,444 for 5.2 kWh usable, about £470 per usable kWh, flat across every system size we fit. The full breakdown is on the costs page.
Whatever size you land on, the install is carried out by the regional partner business holding the exclusive OVO partnership for your area, and covered by the OVO guaranteed 10 year workmanship warranty. Put your postcode into the coverage page to see who that is.
Battery storage in a Great Britain home currently attracts 0% VAT, scheduled to run until 31 March 2027. More on how sizing interacts with the rest of the system in how a home battery actually works.
Sizing questions, answered
How do I find my annual electricity use?
It is printed on your annual statement, and it is usually in your supplier's app under usage or consumption. Take the kWh figure for electricity only, leave gas out of it, and divide by 365 for your daily baseline. If you have moved in recently and do not have a full year, your local OVO expert can work from a shorter period and adjust.
Is a 5 kWh battery big enough?
For a great many households, yes. Around 5 kWh of usable capacity covers the evening peak in a typical home, which is where the expensive units are. It becomes tight if you have electric heating, an EV charging off the house battery, or a household that is home and drawing power all day. That is exactly what the design call checks.
Should I buy bigger now in case I get an EV or heat pump?
Sometimes, but not automatically. Most batteries in the current market are modular, so capacity can be added later. Weigh the cost of unused capacity today against the cost of a second visit tomorrow. Where a heat pump or EV is a firm plan rather than a maybe, sizing up at the start is usually the better call.
Does a bigger battery get me a better export rate?
No. OVO's SEG Install Exclusive rate of 20p per kWh depends on OVO having installed both your solar panels and your battery, and on you being an OVO energy customer, not on the size of the battery. Eligibility criteria including system size limits apply, and rates were correct at July 2026. See the export rates page.
Can I add more capacity later?
Usually. Most current home batteries are modular, built from stackable units, so extra capacity can be added to an existing stack. Two things to check before assuming it: whether the inverter has headroom, and whether adding capacity pushes your connection over the G98 threshold and into a fresh G99 application.
What if my usage is about to change?
Tell us. A new baby, someone moving in, retirement, an EV on order or a heat pump quote in the drawer all move the number materially. We would rather size against the household you are about to be than the one on last year's bill.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- Ofgem typical domestic consumption values 2026, low, medium and high electricity bands kindenergy.co.uk
- Sizing method, annual kWh divided by 365 for a daily baseline iheat.co.uk
- Most UK homes need 5 to 10 kWh of storage, driven by daily use rather than roof size sunsave.energy
- Sizing guidance for a typical three bedroom home and for high consumption households haboenergy.co.uk
- The case against oversizing, unused capacity extends payback spectrumenergysystems.co.uk
- G98 and G99 thresholds, cumulative inverter assessment and DNO response times capture.energy
- Installed cost per kWh benchmarks for UK home battery storage, 2026 kilowatts.uk
- OVO Solar and Battery published battery pricing and SEG Install Exclusive rates ovosolarandbattery.co.uk
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