Using Octopus Flux with Solar Panels and a Battery: The Cornwall Strategy

What is Octopus Flux

Octopus Flux is a time-of-use electricity tariff from Octopus Energy that pays different rates depending on time of day. In 2026, the headline rates are approximately:

• Off-peak (02:00–05:00) — import rate around 7p/kWh
• Standard (06:00–16:00 and 19:00–01:00) — import rate around 24p/kWh
• Peak (16:00–19:00) — import rate around 38p/kWh; export rate around 25p/kWh
• Off-peak export (02:00–05:00) — export rate around 14p/kWh

The spread between the 7p import rate and the 25p export rate creates an arbitrage opportunity if you have a battery — buy cheap, sell during peak, repeat daily.

The basic arbitrage

A battery-only household on Octopus Flux (no solar) can profit from the tariff by charging at 7p in the small hours and exporting at 25p during the 16:00–19:00 peak window. On a 10kWh battery fully cycled each day, this generates roughly £(0.25 – 0.07) × 10 = £1.80 per cycle, or around £650 per year before degradation. Battery degradation and cycle limits reduce this, but the core economics are sound for modern LFP chemistry batteries (Foxstar, GivEnergy, SIG Energy).

How solar changes the equation

Solar generation in Cornwall peaks from 09:00–15:00, which overlaps significantly with the standard-rate import window. Solar reduces your grid imports during the day, saving 24p/kWh instead of 7p (the off-peak rate) — so solar is actually worth more per kWh avoided on a time-of-use tariff than on a flat-rate tariff.

Summer solar surplus can be exported at 24p during the day (standard rate) or 25p during the evening peak window (if you can time the export). A battery enables the latter — charge the battery from solar during the day, discharge it during the 16:00–19:00 peak window for maximum export rate.

Adding battery storage

With solar and a battery, the optimal day looks like this:

• 02:00–05:00: Charge battery from grid at 7p to provide overnight resilience or top up for the evening export.
• 07:00–15:00: Solar charges battery and covers house consumption. Grid imports minimal.
• 15:00–16:00: Solar still generating; battery approaching full charge.
• 16:00–19:00: Export battery to grid at 25p (peak export window). Also export any surplus solar at 25p.
• 19:00–02:00: Draw from residual battery for house consumption at standard rate.

This strategy uses the battery twice — once to capture cheap grid electricity in the night, and once to shift solar generation into the peak export window. A 10kWh battery is sufficient for most Cornwall households to execute this strategy.

Optimal control strategy

Manual scheduling is tedious. Most modern inverters (Foxstar, GivEnergy, SIG Energy, Victron) have Octopus Agile/Flux integration built in or available via third-party apps (Solax cloud, Home Assistant, Givenergy app). Set a charge target of 90–100% by 05:00 and a discharge target of 10–20% by 19:00. Let the inverter handle the rest based on solar forecast data.

Annual savings estimate for Cornwall

A typical Cornwall household with a 6kWp solar array, 10kWh battery, and a heat pump on Octopus Flux can expect:

• Solar self-consumption savings: ~£700/year (at 24p average avoided rate)
• Peak export income: ~£350/year (600–700 kWh exported at 25p)
• Off-peak grid charging arbitrage: ~£400/year (net of import cost vs export value)
• Total annual benefit: ~£1,400–£1,700/year compared to a flat-rate tariff with no solar

Figures vary by consumption, battery usage pattern, and actual tariff rates. The strategy is most effective in spring and autumn when Cornwall irradiance is strong but not overwhelming.

Explore our solar panel installation service, battery storage, or contact us for a free system design consultation.