Find out what size home battery you actually need. Upload your energy bill (or enter your consumption manually), and we’ll calculate the recommended battery size and show you realistic savings for Octopus Go and Economy 7 tariffs.
## How it works
Our calculator uses your daily electricity consumption to recommend a battery size that covers evening and night usage. We account for:
– **Peak consumption**: How much you use when the grid is most expensive (typically 5pm-7am)
– **Tariff cheap windows**: 5 hours for Octopus Go (00:30-05:30), 7 hours for Economy 7 (00:00-07:00)
– **Battery efficiency**: Round-trip losses when charging and discharging
– **Safety margin**: 15% headroom to handle usage spikes during cold weather or rainy days
We then show you annual savings for three scenarios:
1. **Your current flat rate** — what you pay now
2. **Time-of-use tariff alone** — the benefit of switching to Go or E7 (free)
3. **Time-of-use tariff + battery** — the extra savings from storing cheap-window energy
The payback period is calculated only on battery savings, not the tariff switch (because the tariff switch is free). This gives you an honest ROI.
## About the estimates
– Battery cost is estimated at £300/kWh (2026 UK market average for LFP batteries installed)
– Tariff rates are current as of Q2 2026. Rates change quarterly; your actual savings may vary
– Battery capacity degrades 1-2% per year. Estimates show year-1 performance
– Your actual savings depend on how consistently you shift usage into cheap windows
If you already have solar panels or an EV, your consumption patterns are different — the calculator will still work, but savings may be lower or higher depending on your situation.
## Next steps
1. **Browse batteries** in our [battery storage directory](https://www.solarenergyconcepts.co.uk/battery-storage-directory/) — compare prices, brands, and specs
2. **Get quotes** from your installer using your recommended size
3. **Check your actual tariff rates** — ask your supplier for your exact Economy 7 window or Octopus Go rates
4. **Read more** about [battery storage and returns](https://www.solarenergyconcepts.co.uk/post/battery-without-solar/)