Solar and batteries
How big should your solar and battery system be?
How to size solar panels and a home battery for your usage, the battery sizes Octopus installs, and how sizing affects which tariff pays best.
Edited by Rob Gibbs. Published: . Guidance reviewed: .
Short answer
Size the battery to your evening and overnight use, not to the roof. Octopus recommends matching battery size to your home’s consumption. It installs 5kWh and 10kWh batteries, and its most popular system in April 2026 was 12 panels with a 10kWh battery for £11,115. A bigger battery only pays if you can use or sell the extra energy, for example on Intelligent Flux.
Panels: start from the roof and your use
More panels mean more generation, but in summer much of it is exported at a lower price than you pay for imports. Your installer’s quote should show expected yearly generation. Compare it with your yearly use from your bills.
Batteries: match the gap you need to fill
A rough way to size a battery:
- Find how much you use between late afternoon and the next cheap window. Your half-hourly data shows this.
- A 5kWh battery suits small to medium homes. Octopus pairs 10kWh with larger systems of 10 to 20 panels.
- Allow for an EV or heat pump you plan to add, which raises evening and overnight demand.
Sizing and tariffs go together
A battery that fills overnight on a cheap rate and empties at the evening peak earns the gap between the two. Flux and Intelligent Flux reward exporting at the peak, so a larger battery can earn more there than on a flat export tariff.
Questions people ask
Is a 10kWh battery worth it over 5kWh?
Only if you regularly use or export more than 5kWh at peak times. Check your half-hourly data first.
Can I add a battery later?
Usually, yes. Octopus also offers battery-only installations without solar.
Tariffs in this guide
Related guides
- A home battery without solar on Octopus: does it pay?How a home battery without solar panels can save money on Octopus by charging cheaply overnight, and what to check first.
- Solar panels with Octopus Energy: getting the most from themHow to set up solar panels with Octopus: getting paid for export, choosing an import tariff, and when a battery or EV changes the answer.
- Octopus export tariffs explained: Outgoing, Agile, Flux and SEGHow Octopus pays you for solar electricity you send to the grid, how the export tariffs differ, and which import tariff each one needs.
- Import, export and generation meters (and MPANs) explainedThe difference between import, export and generation readings for solar homes, why export needs its own MPAN, and what each one is used for.
- Octopus Charge Pack: the home battery add-on explainedWhat Octopus Charge Pack does with your home battery, which tariffs and batteries it works with, what you earn and who should skip it.
- EV chargepoint grants: who can still claimThe government EV chargepoint grant for renters and flat owners: how much it pays, who qualifies and how it changed on 1 April 2026.
Primary sources
- Solar and battery options — Octopus Energy; checked 2026-10-30. Octopus battery sizes and its most popular system and price (April 2026).
- Introducing battery-only installation with Octopus — Octopus Energy; checked 2026-10-30. Matching battery size to home consumption.