Octopus Flux + Battery: The Maths

Quick answer

A Scottish home with 6kWp solar + 10kWh battery that uses about 4,500 kWh of electricity a year earns about £350/year more on Octopus Flux than the same setup on a flat 12p export tariff, in our worked example at Octopus's published South Scotland rates for 6 November 2026.

What Octopus Flux actually pays

Octopus Flux is a domestic time-of-use tariff with three windows. Octopus paused it to new customers in March 2026; as of 16 September 2026 its Flux page is taking sign-ups again (you need solar, a home battery, a smart meter and an Octopus account). Octopus's published South Scotland rates for 6 November 2026 (no VAT on household electricity from 1 October 2026 to 31 March 2027):

• Peak (16:00–19:00): Import 36.70p/kWh · Export 29.75p/kWh
• Off-peak (02:00–05:00): Import 15.87p/kWh · Export 4.63p/kWh
• Standard (rest of day): Import 26.28p/kWh · Export 10.91p/kWh

The trick: charge cheap (02:00–05:00 at 15.87p) and export expensive (16:00–19:00 at 29.75p). A 10kWh battery cycled through this window clears 10 × (29.75p − 15.87p) = about £1.39 per cycle before round-trip losses. The catch in Scotland is that a battery your panels have already filled has nothing spare to cycle, so most grid-charged cycles fall between November and February.

The maths for a 6kWp + 10kWh setup

Annual solar generation (Livingston, PVGIS v5.3, 35° south-facing, 14% losses): 6kWp × 860 kWh/kWp = 5,160 kWh

Strategy: maximise self-consumption + winter arbitrage

• Self-consumed solar (battery-time-shifted, 75% capture): 3,870 kWh × 26.28p saved import = £1,017
• Exported peak solar (15% during 16:00–19:00 window): 774 kWh × 29.75p = £230
• Exported standard (10%): 516 kWh × 10.91p = £56
• Off-peak grid charge + peak export, about 150 winter cycles × 10kWh: 1,500 kWh × 13.89p margin = £208
• Total annual benefit: £1,511

Compare to the same setup on Flexible Octopus (26.11p/kWh import, Direct Debit, from 1 October 2026, no VAT) with Outgoing Octopus at 12p/kWh:

• Self-consumed: 3,870 kWh × 26.11p = £1,010
• Exported: 1,290 kWh × 12p = £155
• No arbitrage
• Total: £1,165

Flux uplift: about £346/year

These are year-one figures for one household: one using about 4,500 kWh of electricity a year (a larger home, or one with an EV or heat pump), so the 3,870 kWh of solar it uses itself stays under 90% of its annual use. They use Octopus's rates for 6 November 2026, which Octopus changes from time to time, and they leave out battery and panel degradation, round-trip losses, price changes and maintenance. Your own figures depend on your usage, your battery and the rates on the day you sign up.

Battery sizing for Flux strategy

The bigger your battery, the more arbitrage opportunity — but each extra kWh adds less than the last. Our rule of thumb:

• 5kWh: good for self-consumption only, limited arbitrage
• 10kWh: sweet spot for typical 3–4 bed home; ~300 full cycles/year possible
• 13.5kWh (Powerwall): maximum arbitrage if you've got >6kWp solar
• 20kWh+: only justifies if you have EV charging or heat pump loads

What you need

• MCS-certified solar (required to register for SEG/Flux)
• Smart meter (essential — Flux requires half-hourly data)
• Octopus account with Flux tariff enabled
• Battery with Modbus/API control — GivEnergy excellent, Tesla Powerwall good, EcoFlow PowerOcean adequate

Setup steps

1. Confirm your battery supports time-of-use scheduling

2. Apply for Flux via Octopus website (existing customers only, must have solar registered)

3. Schedule battery charge: 02:00–05:00 off-peak slot

4. Schedule battery discharge: 16:00–19:00 peak export

5. Monitor first month, tune dispatch logic

We provide a Flux dispatch profile as part of every battery commissioning where the customer is on or moving to Flux.

Things that break the maths

• EV charging during peak — defeats your peak-export strategy
• Heat pumps cycling during peak — same problem
• Cold spells with no solar — you're paying the peak import rate (36.70p/kWh on 6 November 2026); battery should be charged off-peak in advance

Bottom line

On Octopus Flux, a battery isn't just for resilience or evening solar — it can earn from the gap between cheap and peak prices. In our worked example the right setup earned about £350 a year more than non-Flux operation; yours depends on your usage, your battery size and the rates at the time.

We model Flux vs non-Flux economics at every battery quote. Call 03330 384 380 or use our online form.