What Size Solar Battery Do I Need in the UK? A Practical 2026 Guide
The right solar battery size for most UK homes is usually between 5kWh and 15kWh, but it is not determined by bedroom count alone. It depends on how much electricity you use after your panels stop generating, how much surplus solar can charge the battery, whether you plan to use a cheap overnight tariff, and whether you want backup power.
For many households, a 7–10kWh usable battery is a sensible starting point. Lower-use homes may need around 5kWh, while properties with a heat pump, electric heating or high evening demand may need 10–15kWh or a modular system.
Energy Saving Trust says a typical home battery system might be around 10kWh. Which? recommends matching storage to evening and night-time consumption rather than simply buying the largest unit available.
Quick answer
To estimate what size solar battery you need in the UK, start with your evening and overnight electricity use, not total annual consumption. Compare that figure with the surplus electricity your solar panels can realistically generate and store.
A low-use household may need around 5kWh, a typical family home often suits 7–10kWh, and a high-use home may require 10–15kWh or more.
Always compare usable capacity, not just headline capacity, and check output in kilowatts. Capacity determines how long the battery can run, while output determines how many appliances it can run at once. A larger battery is not automatically better if your panels rarely fill it.
Solar battery size guide for UK homes
| Household profile | Typical daily use | Suggested usable battery | Best suited to |
|---|---|---|---|
| Low-use flat or small home | 4–7kWh | 4–6kWh | Low evening demand and modest solar generation |
| Typical two- to four-person home | 7–12kWh | 7–10kWh | General household and evening use |
| High-use family home | 12–18kWh | 10–15kWh | Home working or a larger solar PV system |
| Heat pump or highly electrified home | 18kWh+ | 13.5–20kWh+ | Tariff charging or high winter demand |
These figures are starting points rather than fixed rules.
Which? reports that new lithium-ion home batteries commonly have capacities of around 5–15kWh. It recommends covering evening and night-time consumption while ensuring the solar panel system can generate enough surplus electricity to refill the battery.
How to calculate the right battery size
1. Find your real daily electricity usage
Take the electricity consumption shown on your last 12 months of bills and divide it by 365.
For example:
3,650kWh annual consumption ÷ 365 = 10kWh per day
That does not necessarily mean you need a 10kWh battery. Your solar panels may supply some electricity directly during daylight hours, leaving only 6–7kWh of evening and overnight demand for the battery to cover.
Smart-meter data is better because it shows when electricity is consumed across summer and winter.
2. Measure evening and overnight demand
Add the electricity used from late afternoon until the following morning. This is the demand that a solar-charged battery is most likely to serve.
If your household regularly uses 6.5kWh during this period, a battery providing approximately 7kWh of usable storage may be more appropriate than a 10kWh model.
Do not automatically include electric vehicle charging.
An EV can empty a domestic battery quickly, so many households charge the vehicle directly from surplus solar generation or a cheap overnight tariff. Include EV charging only when the battery, inverter and electricity tariff have been deliberately designed for it.
3. Check how much surplus solar is available
A battery can only store electricity that reaches it.
If someone is normally at home during the day and already uses most of the solar electricity as it is generated, a large battery may remain partly empty.
A household that is empty during daylight hours may export more surplus electricity and could benefit from greater storage capacity.
Ask your installer for a month-by-month generation and consumption model rather than a single annual estimate. UK winter solar generation is much lower than summer generation, so even a correctly sized battery may not refill from solar on darker days.
Home batteries can also be charged from the grid when used with a suitable time-of-use tariff.
4. Convert your energy requirement into battery capacity
Always calculate using usable capacity.
If your home needs 7kWh and a battery makes 90% of its nominal capacity available:
7kWh ÷ 0.90 = 7.8kWh nominal capacity
You should therefore look for a battery with at least 7kWh of usable capacity or approximately 7.8kWh of nominal capacity.
Check manufacturer information for usable energy, efficiency and warranty conditions.
Battery capacity is not the same as power output
Battery capacity is measured in kilowatt-hours, or kWh. It tells you how much energy the battery can store.
Battery and inverter output is measured in kilowatts, or kW. It tells you how quickly the stored energy can be delivered.
A large-capacity battery with limited output may run lighting, refrigeration and electronics for several hours but still import electricity from the grid when several high-power appliances operate together.
Check:
- Continuous output
- Peak output
- Single-phase or three-phase compatibility
- Maximum charging rate
- Supported backup circuits
- Inverter limitations
Backup power is not automatic. Some grid-connected batteries shut down during a power cut unless appropriate backup equipment and dedicated circuits have been installed.
Ask whether the proposed system will work during an outage, which appliances it will support and how long the available storage is likely to last.
Which battery size is best for your goal?
Maximum solar self-consumption
Choose a usable capacity close to the smaller of:
- Your normal evening and overnight consumption
- Your typical daily surplus solar generation
There is little financial benefit in buying 15kWh of storage if your panels normally produce only 5kWh of surplus electricity.
Cheap-rate tariff shifting
Size the battery around the electricity you want to avoid purchasing during expensive tariff periods.
A larger battery may make sense if it can charge cheaply overnight and power your home through the following peak-rate period.
Backup power
Calculate the electricity used by your essential appliances and multiply it by the number of backup hours required.
Whole-home backup normally requires greater storage and output than a system designed to keep only lighting, refrigeration and broadband running.
Future electrification
Consider a modular battery if you expect to install a heat pump, switch to induction cooking, work from home more frequently or increase household occupancy.
Check how many additional modules can be added and whether expansion would require a different inverter or updated network approval.
Seven steps for choosing a solar battery
- Collect 12 months of data. Separate normal household consumption from EV charging and unusual loads.
- Identify when electricity is used. Focus on evening, overnight and peak-tariff periods.
- Model monthly solar surplus. Do not base the calculation on annual solar generation alone.
- Compare capacity and output. Check usable kWh, continuous kW and system efficiency.
- Choose a control strategy. Decide whether the battery will prioritise solar storage, cheap grid charging, exporting or backup.
- Review the warranty. Compare warranty length, cycle limits, retained capacity, throughput limits and labour cover.
- Assess the installation location. Consider temperature, access, ventilation, manufacturer requirements and fire safety. PAS 63100:2024 covers fire-safety requirements for small-scale domestic battery installations.
Typical UK solar battery costs
| Battery requirement | Indicative installed budget | Typical buyer | Key consideration |
|---|---|---|---|
| Around 5kWh | Approximately £4,000–£5,500 | Low-use home | May cover basic evening demand |
| Around 8–10kWh | Approximately £5,500–£8,000 | Typical family home | Often the practical middle ground |
| Around 13.5–15kWh | Approximately £7,000–£10,000+ | High-use home | Confirm solar surplus and inverter output |
| Solar and battery package | Often £9,000–£12,000 overall | New combined installation | Roof, scaffolding and solar array size affect cost |
Energy Saving Trust gives a broad battery-system cost range of £1,500–£10,000 and estimates approximately £4,600 for a 5kWh system.
Which? also reports prices ranging from below £2,000 to £10,000. A January 2026 UK Government announcement described £9,000–£12,000 as the current average cost of a combined solar and battery installation. These figures are guides rather than quotations.
A property survey is required for an accurate price. Retrofit work, backup equipment, inverter replacement, cable routes and consumer-unit upgrades can all affect the final cost.
At the time of writing in August 2026, qualifying residential battery installations are zero-rated for VAT until 31 March 2027. Supplying a battery without installation can remain standard-rated.
Will a bigger battery save more money?
Not necessarily.
Savings depend on:
- How often the battery charges and discharges
- Your import electricity rate
- Your export tariff
- Charging and discharging losses
- Battery degradation
- Installation cost
- The effectiveness of the control software
- How your electricity consumption changes
Exported solar electricity may earn payments through the Smart Export Guarantee. Suppliers set their own rates and contract terms, so storing every spare unit of solar electricity is not always the most valuable strategy.
A proper financial assessment should compare:
- Solar panels without a battery
- Solar panels with the proposed battery
- A larger battery combined with a time-of-use tariff
Replacement costs should also be considered. Energy Saving Trust gives a typical battery lifespan of around 10–12 years, while Which? notes that many systems have a 10-year warranty.
Why the installer matters
A competent installer should model your electricity demand and solar generation, confirm system compatibility, assess the proposed location and explain how the battery will be controlled.
Poor design can leave you with a battery that:
- Rarely becomes fully charged
- Empties too early in the evening
- Cannot support important appliances
- Conflicts with your existing inverter
- Produces disappointing savings
- Cannot provide the expected backup
- Creates warranty or safety concerns
Obtain itemised quotations and ask each installer to show the assumptions behind projected savings.
Energy Saving Trust recommends getting at least three quotations from MCS-certified installers. Which? also advises checking MCS certification and membership of an appropriate consumer protection code.
Frequently asked questions (FAQs)
Clear answers about choosing a solar-battery size, 5kWh and 10kWh systems, oversized batteries, winter charging, time-of-use tariffs, modular expansion, retrofits and backup power. Speak to Simple Green Energy .
Unsure what battery size suits your home?
Speak with Simple Green Energy about your solar generation, evening usage, tariff, inverter, future expansion, retrofit options and whether backup power should be included.
Check my battery optionsFinal recommendation
For most UK homeowners, start by testing a 7–10kWh usable battery against real smart-meter data.
Move towards 5kWh if your evening consumption and solar surplus are low. Consider 10–15kWh if your non-EV demand is high, you have a heat pump or you intend to charge the battery using a cheap overnight tariff.
Prioritise:
- Usable capacity
- Continuous power output
- Inverter compatibility
- Warranty protection
- Control software
- Expansion options
- Installation quality
A properly sized battery should be used regularly, refill often enough to be useful and support a clear financial or resilience goal.
Book a free home survey with Simple Green Energy for a property-specific battery recommendation based on your electricity consumption, solar potential, tariff and future energy plans.
5kWp, while EV, heat-pump and high-use households may benefit from a larger design. Start with actual annual consumption, then test the recommendation against roof space, shading, usage times and future plans.
Compare at least two modelled designs, challenge generic savings claims and prioritise installation quality. A professional survey is the only reliable way to turn an online estimate into an accurate system size and quotation.
