Octopus Flux + Battery: The Maths

Quick answer

A typical Scottish home with 6kWp solar + 10kWh battery on Octopus Flux earns about £250/year more than the same setup on a flat 12p export tariff, in our worked example at Octopus's published South Scotland rates for 16 September 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 16 September 2026 (import rates include 5% VAT, which comes off household electricity from 1 October 2026):

• Peak (16:00–19:00): Import 34.94p/kWh · Export 27.19p/kWh
• Off-peak (02:00–05:00): Import 14.98p/kWh · Export 4.42p/kWh
• Standard (rest of day): Import 24.96p/kWh · Export 9.55p/kWh

The trick: charge cheap (02:00–05:00 at 14.98p) and export expensive (16:00–19:00 at 27.19p). A 10kWh battery cycled through this window clears 10 × (27.19p − 14.98p) = about £1.22 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 × 24.96p saved import = £966
• Exported peak solar (15% during 16:00–19:00 window): 774 kWh × 27.19p = £210
• Exported standard (10%): 516 kWh × 9.55p = £49
• Off-peak grid charge + peak export, about 150 winter cycles × 10kWh: 1,500 kWh × 12.21p margin = £183
• Total annual benefit: £1,408

Compare to the same setup on Flexible Octopus (25.85p/kWh import, Direct Debit, July–September 2026) with Outgoing Octopus at 12p/kWh:

• Self-consumed: 3,870 kWh × 25.85p = £1,000
• Exported: 1,290 kWh × 12p = £155
• No arbitrage
• Total: £1,155

Flux uplift: about £253/year

Battery sizing for Flux strategy

The bigger your battery, the more arbitrage opportunity — but with diminishing returns. 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 38p peak import; battery should be charged off-peak in advance

Bottom line

On Octopus Flux, a battery isn't just for resilience or evening solar — it's an active revenue tool. The right setup typically returns £200–£400/year more than non-Flux operation, which is enough to shorten battery payback from 11 years to 8–9.

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