Find out how much a home battery could save you each year — and how quickly it pays for itself — based on your solar setup, tariff type and daily electricity use.
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EcoHome UK supplies and installs home battery systems — standalone or combined with solar PV. We'll survey your property and find the right size for your usage.
Get a free quote →How is this calculated? (Methodology & sources)
This calculator uses conservative UK-specific figures for battery round-trip efficiency, tariff rates and cycling frequency. Three distinct scenarios apply depending on your inputs:
Scenario A — Solar PV + battery (any tariff)
The battery stores surplus solar generation that would otherwise be exported at the low Smart Export Guarantee (SEG) rate. That stored energy is used in the evening instead of buying from the grid. Saving per kWh cycled = import price − SEG export rate = ~25p − 5p = ~20p/kWh. On a time-of-use tariff an additional overnight grid-charge top-up is also applied (saving ~17p/kWh on remaining usable capacity).
Scenario B — No solar, time-of-use tariff
The battery charges from the grid at a cheap overnight rate (~7–8p/kWh, e.g. Octopus Go) and discharges during peak periods (~24–25p/kWh). Saving per kWh cycled ≈ ~17p/kWh after round-trip losses.
Scenario C — No solar, flat-rate tariff
Without solar or a cheap off-peak rate, there is no price arbitrage. A battery in this scenario provides resilience/backup but minimal financial return. This calculator shows a minimal estimated saving (<£30/yr) and honestly flags that payback is unlikely within the warranty period.
Assumptions used in all scenarios:
| Parameter | Value used | Source / basis |
|---|---|---|
| Import (peak) rate | 25p/kWh | Ofgem price cap Q2 2024 default tariff |
| SEG export rate | 5p/kWh | Typical SEG rates, Ofgem SEG data 2024 |
| Time-of-use cheap rate | 8p/kWh | Octopus Go / Intelligent overnight rate |
| Round-trip efficiency | 90% | Typical Li-ion home battery (e.g. Tesla Powerwall, GivEnergy) |
| Usable capacity | 90% of nameplate | Manufacturer DoD specifications |
| Useful cycles per year | 350 | Conservative — allows for low-generation winter days |
| Battery VAT rate | 0% | Gov.uk — Energy Saving Materials relief (to at least 2027) |
Cost estimates (indicative, fitted inc. 0% VAT):
| Battery size | Usable capacity | Indicative installed cost |
|---|---|---|
| 5 kWh | ~4.5 kWh | ~£3,500 |
| 10 kWh | ~9 kWh | ~£5,000 |
| 13.5 kWh | ~12 kWh | ~£6,500 |
Daily kWh cycled calculation: usable capacity is capped at the lesser of the battery's usable kWh, the available solar surplus or shiftable demand (estimated as 60% of daily use for solar scenarios, 70% for TOU scenarios), and what the household can actually absorb in the evening. The annual cycled kWh = daily cycled kWh × 350 cycles, × 90% efficiency.
Sources: Ofgem energy price cap · Ofgem Smart Export Guarantee · Gov.uk — 0% VAT on energy saving materials · Gov.uk energy price guarantee
All figures are estimates. Actual savings depend on your specific tariff, usage patterns, solar array size, battery model and installer pricing. Request a free survey for a tailored assessment.
Which battery size is right for me?
5 kWh suits smaller households (1–2 people) on a time-of-use tariff or with a small solar array (2–3 kWp). It can typically cover evening usage for a typical night.
10 kWh is the most popular choice for average UK households (2–4 people). It captures most of a 3–4 kWp solar array's surplus and provides meaningful overnight resilience.
13.5 kWh suits larger homes, high usage (EV, heat pump), or larger solar arrays (4 kWp+). Some households with a 13.5 kWh battery and good solar generation run virtually self-sufficient from April to September.
EcoHome UK will survey your property, review your bills and solar generation data (if available), and recommend the optimum size for your situation.