Calculate your savings
Assumes one full charge/discharge cycle per day at 90% round-trip efficiency. Actual savings depend on usage patterns.
How the savings calculation works
The savings from a home battery come from the tariff spread – the difference between what you pay during cheap off-peak hours and what you'd pay during expensive peak hours. Here's the formula:
Usable capacity = battery capacity × 0.9 (efficiency)
Example (10kWh on Octopus Go):
(29p − 7p) × 9kWh × 365 = 72,270p = £723/year
Savings comparison by tariff
| Tariff | Off-peak | Peak | Spread | Annual (10kWh) |
|---|---|---|---|---|
| Intelligent Octopus Go | 7p | 29p | 22p | ~£803 |
| Octopus Go | 7.5p | 28p | 20.5p | ~£748 |
| Economy 7 | 12p | 28p | 16p | ~£584 |
What about payback?
Your payback period is simply the cost of your battery system divided by your annual savings. For a 10kWh Habo bundle:
| Tariff | Annual saving | Payback (£5,500 system) | Net saving over 12 years |
|---|---|---|---|
| Intelligent Octopus Go | £803 | ~3.4 years | ~£4,136 |
| Octopus Go | £748 | ~3.7 years | ~£3,476 |
| Economy 7 | £584 | ~4.7 years | ~£1,508 |
Factors that affect your savings
Your tariff spread is the biggest factor. A bigger gap between off-peak and peak rates means more savings. On a flat-rate tariff with no off-peak period, a standalone battery saves nothing.
Battery size determines how much energy you can shift per day. A 10kWh battery shifts roughly twice as much as a 5kWh – and saves roughly twice as much.
Your actual usage matters too. If you use less electricity during peak hours than your battery can supply, the excess capacity goes unused. A battery matched to your peak-hour consumption delivers the best returns.
Round-trip efficiency – the energy lost during charging and discharging – is typically 88-92% for modern LiFePO4 batteries. Our calculator uses 90% as a conservative estimate.
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