A solar battery stores surplus electricity generated by solar panels during daylight hours for use in the evening and overnight. Without a battery, approximately 50–60% of generated solar electricity is exported to the grid at rates far below what you pay to import it. With a battery, self-consumption rises to 70–80%, increasing annual savings by £300–£500 depending on system size and household usage patterns.
A 5kWh battery — the most common size for a UK 3-bedroom home — costs £3,000–£4,500 when installed alongside solar panels. A no upfront solar subscription includes battery storage in every plan at no additional cost, along with full replacement cover if the battery degrades below its rated capacity during the 25-year term.
What a Solar Battery Costs in the UK
Battery prices vary by capacity, chemistry, brand, and whether the battery is installed alongside new solar panels or retrofitted to an existing system. All prices below include installation, inverter, and 0% VAT (valid until March 2027).
| Battery Capacity | Installed With Solar Panels | Retrofitted to Existing System | Typical Home Size |
|---|---|---|---|
| 3kWh | £2,000–£3,000 | £2,800–£3,800 | 1–2 bed flat |
| 5kWh | £3,000–£4,500 | £4,000–£5,500 | 2–3 bed house |
| 10kWh | £4,500–£7,000 | £6,000–£8,500 | 4–5 bed house |
| 13kWh+ | £6,000–£10,000 | £7,500–£11,000 | Large detached / high consumption |
Retrofitting a battery to an existing solar system costs more because the installer must supply a new or upgraded inverter and rewire the connection to the consumer unit. Installing a battery at the same time as solar panels avoids this duplication.
Under a no upfront solar subscription, the battery is included in the monthly payment. There is no separate battery charge, no retrofit premium, and no additional cost when the battery needs replacing.
What Size Solar Battery You Need
Battery size should match your household's evening and overnight electricity consumption — the hours when solar panels produce little or no output.
How to Calculate Your Battery Size
The calculation uses 3 numbers: your daily electricity consumption in kWh, the percentage of consumption that falls outside daylight hours, and the battery's usable capacity (typically 90% of headline capacity due to depth of discharge).
A UK household consuming 10kWh per day, with 60% of that consumption occurring after 4pm, needs to cover approximately 6kWh of evening and overnight demand. A 5kWh usable-capacity battery covers most of this, while a 10kWh battery covers it entirely with headroom for cloudy days.
Battery Size by Property Type
| Property | Daily Consumption | Recommended Battery | Coverage |
|---|---|---|---|
| 2-bed flat / terrace | 6–8 kWh | 3–5 kWh | 50–70% of overnight demand |
| 3-bed semi-detached | 8–12 kWh | 5–7 kWh | 60–75% of overnight demand |
| 4-bed detached | 12–18 kWh | 10–13 kWh | 65–80% of overnight demand |
| High-consumption home (EV, heat pump) | 18–30 kWh | 13kWh+ | 50–70% of overnight demand |
Oversizing a battery wastes money if your solar panels do not generate enough surplus to fill it. Undersizing means exporting electricity during the day that could have been stored and used. The property survey conducted as part of a no upfront solar application designs the battery size to match your specific generation and consumption profile.
How a Solar Battery Increases Savings
A solar battery increases savings in 3 ways: it reduces the amount of electricity you import from the grid at full price, it enables you to charge from off-peak tariffs overnight, and it maximises the value of Smart Export Guarantee payments by giving you control over when you export.
Savings Without a Battery vs With a Battery
| Scenario | Self-Consumption Rate | Annual Bill Saving | SEG Export Income | Total Annual Return |
|---|---|---|---|---|
| 4kW panels, no battery | 40–50% | £500–£700 | £150–£250 | £650–£950 |
| 4kW panels + 5kWh battery | 70–80% | £900–£1,200 | £120–£180 | £1,020–£1,380 |
The battery adds £300–£450 in annual savings by shifting electricity consumption from imported grid power at 24.5p/kWh (Ofgem Q1 2026 rate) to stored solar power at £0/kWh. Export income drops slightly because less surplus is available for export, but the net gain is substantially higher.
Off-Peak Tariff Charging
Many UK energy tariffs now offer overnight rates as low as 7p per kWh for several hours. A battery allows homeowners to charge overnight at the cheapest rate and use that stored electricity during peak hours when rates exceed 24p/kWh. The price difference — roughly 17p per kWh — adds up to £200–£400 per year in additional savings for a typical household, on top of solar generation savings.
Battery Chemistry — What Is Installed in a No Upfront Solar Plan
Two lithium-ion chemistries dominate the UK residential battery market.
Lithium Iron Phosphate (LiFePO4)
LiFePO4 batteries are the current standard for premium residential installations. They are chemically stable, virtually eliminate the risk of thermal runaway, and are rated for 6,000–10,000 charge-discharge cycles. At one cycle per day, this translates to a functional lifespan of 16–27 years. LiFePO4 is the chemistry used in no upfront solar subscriptions because its longevity aligns with the 25-year plan term and reduces the likelihood of mid-term replacement.
Nickel Manganese Cobalt (NMC)
NMC batteries offer slightly higher energy density, meaning they are physically smaller for the same capacity. However, they are rated for 3,000–5,000 cycles — a functional lifespan of 8–14 years — and carry a marginally higher thermal risk. NMC batteries are more likely to need replacement within a 25-year period.
Why Chemistry Matters for No Upfront Solar
Under a no upfront solar subscription, battery replacement is included at no cost regardless of chemistry. However, providers select LiFePO4 batteries by default because fewer replacements mean lower long-term service costs and more consistent performance for the homeowner. Cash buyers should factor battery replacement into their total cost of ownership — a single replacement at year 10–12 costs £3,000–£5,000 at current prices.
Battery Degradation — The Hidden Cost Cash Buyers Face
All batteries lose capacity over time. A well-maintained lithium battery retains approximately 80% of its original capacity after 10 years and 60–70% after 15 years. Once usable capacity drops below a practical threshold, the battery requires replacement.
What Replacement Costs
| Replacement Scenario | Estimated Cost (2026 Prices) |
|---|---|
| 5kWh battery replacement (year 10–12) | £3,000–£4,500 |
| 10kWh battery replacement (year 10–12) | £4,500–£7,000 |
| Inverter replacement (year 10–12) | £700–£1,400 |
| Combined battery + inverter replacement | £3,700–£8,400 |
Cash buyers must budget for at least one battery replacement and one inverter replacement within a 25-year ownership period. These costs are rarely factored into advertised payback calculations.
Under a no upfront solar subscription, both replacements are included. The provider monitors battery health through 24/7 performance tracking and schedules replacement proactively when degradation reaches the warranty threshold. The homeowner receives no unexpected bills.
Battery Storage and the Smart Export Guarantee
A battery changes your relationship with the Smart Export Guarantee. Without a battery, all surplus solar electricity is exported immediately at whatever rate your SEG tariff pays. With a battery, you choose when to export — allowing you to take advantage of time-of-use export tariffs that pay higher rates during peak grid demand.
Current SEG rates in the UK range from 3p to 15p per kWh. Some flexible tariffs pay 15p+ during peak evening hours and as little as 1p during midday surplus periods. A battery enables homeowners to store midday surplus and export it during the evening peak, maximising export income by 30–50% compared to immediate daytime export.
Over 25 years, the difference between optimised and unoptimised export timing is worth approximately £1,000–£3,000 in additional income.
Can You Add a Battery to Existing Solar Panels
Yes. A battery can be retrofitted to any existing solar panel system. The retrofit requires a compatible hybrid inverter and a qualified electrician. Costs are 15–25% higher than installing a battery alongside new panels because of the additional inverter and wiring work.
Retrofitting is not available under a no upfront solar subscription, which covers new complete system installations only. Homeowners with existing panels who want battery storage without upfront cost should explore solar finance options or contact their original installer for retrofit pricing.
Solar Battery Storage With No Upfront Cost
Every no upfront solar subscription includes battery storage sized to match the property. The battery, inverter, panels, installation, insurance, monitoring, and all maintenance are bundled into one fixed monthly payment starting from £69.
The subscription eliminates the 3 highest-risk costs of battery ownership: the £3,000–£5,000 upfront purchase, the £3,000–£5,000 mid-term replacement, and the ongoing uncertainty of managing degradation and performance issues independently.
Homeowners in England and Wales who own their property and pass a soft credit check can check eligibility in 2 minutes.