Around £710 a year in our EP6 simulation

For a home using about 3,600kWh a year, with no solar, our model combines a battery, the move from a standard tariff to Octopus Agile, and Axle export rewards.

After the £15/month membership, that is £529 a year, before battery wear and installation costs.

The first figure includes the cost of charging for Axle events. Adding these two figures gives the total saving; Axle rewards are counted once.

EP6 and EP12

Annual savings from a battery and switching to Agile, keeping any existing solar in the comparison. These figures include Axle rewards and are before membership and wear.

Both batteries use a 5kW inverter and an 88% round-trip efficiency assumption. EP6 has 5.76kWh nominal capacity; EP12 has 11.52kWh. The simulated charge range is 10–100%.

What solar contributes

The solar example uses an effective 2kW array with York weather, generating 2,130kWh over the year. Panels alone save £379 on the standard tariff, through direct use and surplus exports.

Adding a battery and switching to Agile brings the combined saving to £1,003 with EP6 or £1,096 with EP12. Subtract the panels’ existing saving to get the additional battery figures in the table.

A battery can earn more from tariff differences in a home without panels because solar already covers some expensive daytime demand. Your roof and usage pattern matter.

Axle assumptions

We model 84 export events totalling 70 hours: 30 half-hour events, 53 one-hour events and one two-hour event. The long events retain their existing 3–6 monthly distribution, with more in winter; two or three short events are added each month. Exported energy earns an extra £1/kWh. Event windows are sampled towards high Octopus import prices.

This is a synthetic schedule based on Axle’s published guidance and a reported longer event. The additional 30 half-hour events model an opted-in household: Axle describes occasional short-notice events but does not publish their frequency. Thirty is our assumption. This is not a replay of Axle history. Actual events can be regional; frequency, eligibility and battery charge affect earnings. The model includes no paid import events or monthly minimum-payment top-ups.

How we calculated it

• 3 July 2025–2 July 2026: a full year of Octopus Agile import and export prices, region C.
• The same synthetic 3,606kWh household in every case.
• A standard import baseline of 26.11p/kWh; the same export rates for the solar-only comparison.
• The Brain’s rolling planner, recalculating every minute using past usage, solar forecasts and published prices.
• Independent standard, solar-only and battery bills, including charging losses and export income.

The planner allows 2p per kWh discharged for battery wear. Deducting that allowance from the no-solar saving leaves £661 for EP6 or £736 for EP12, before membership.

Simulation results, not a guarantee. Unless stated otherwise, savings exclude membership (£180/year), battery wear, purchase and installation, finance and standing charges. Changes in standing charges between tariffs are not modelled.

Updated 7 September 2026. Full results and reproduction instructions · Download the figures.