Tariff Arbitrage Calculator
Calculate savings from charging your battery on cheap off-peak rates
Tariff arbitrage calculator
Charge your battery at off-peak rates, use it during expensive peak hours. Pick a tariff to auto-fill the rates.
4.5 hour overnight window, standard daytime rate
10 kWh
10 kWh/day
24-hour rate — off-peak window 00:00 to 05:00 (5h)
Daily saving
£1.34
Annual saving
£489
Usable capacity
9 kWh
Actually displaced
7.9 kWh
limited by peak-hour usage
Your 10 kWh/day usage is spread across 24 hours. Roughly 7.9 kWh of it falls in the 19-hour peak window (everything outside the 5-hour off-peak window). The battery can only save you money on the peak-hour portion — the rest is already being imported during the cheap window, so there is nothing to arbitrage. This is why a 32 kWh battery with 30 kWh of daily usage shows 7.9 kWh displaced: you are only using 7.9 kWh during expensive hours in the first place. 90% usable capacity accounts for battery health reserve.
How this works
Smart tariffs like Octopus Go, Flux, and Agile offer cheap overnight rates — often 7-10p/kWh compared to the 24.5p daytime standard rate. A battery lets you charge up during those cheap hours and use that electricity during expensive peak times.
The savings per cycle equals your battery usable capacity (90% of nameplate) multiplied by the difference between peak and off-peak rates. A 10 kWh battery moving 9 kWh per day from 7.5p to 24.5p saves roughly £1.53/day or £559/year — before any solar involvement.
The calculator caps savings by your actual daily usage, because you only benefit on kWh you would otherwise have imported at peak rate.
Things to consider
- •Requires a smart meter and a compatible tariff — your installer will need to confirm your inverter supports scheduled charging.
- •Some tariffs require a hybrid inverter that can charge the battery from the grid. String inverters cannot do this.
- •Octopus Flux has export bonuses on top of the cheap import rate, which stack with tariff arbitrage.
- •Winter savings are higher because solar self-consumption drops — the battery picks up the slack.
Dig deeper
Octopus Flux Tariff: The Best Tariff for Solar + Battery?
How Octopus Flux works for UK solar and battery owners — import/export rates, daily schedule, real savings calculations, and whether it beats Agile.
Octopus Go and Intelligent Go Explained
How Octopus Go and Intelligent Octopus Go work for UK households with EVs and solar panels — rates, eligibility, and real-world savings in 2026.
Octopus Agile Tariff: Is It Worth It with Solar?
A detailed look at the Octopus Agile tariff for UK solar households — how half-hourly pricing works, real savings potential, and who should avoid it.
Tariff Stacking: Combining Solar, Battery, and Smart Tariffs
How to stack solar self-consumption, battery arbitrage, export tariffs, and smart import tariffs for maximum savings. A UK guide to tariff optimisation.
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