Octopus Flux + Battery: The Maths

Quick answer

A typical Scottish home with 6kWp solar + 10kWh battery on Octopus Flux earns £200–£400/year more than the same setup on a standard export tariff — paying off the battery 2–3 years faster.

What Octopus Flux actually pays

Octopus Flux is a domestic time-of-use tariff with three windows:

• Peak (16:00–19:00): Import 38p/kWh · Export 24p/kWh
• Off-peak (02:00–05:00): Import 15p/kWh · Export 15p/kWh
• Standard (rest of day): Import 30p/kWh · Export 15p/kWh

The trick: charge cheap (02:00–05:00 at 15p) and export expensive (16:00–19:00 at 24p). A 10kWh battery cycled through this window earns 10 × (24p − 15p) = 90p of arbitrage per cycle. Over 300 cycles a year that's £270.

The maths for a 6kWp + 10kWh setup

Annual solar generation (Scotland): 6kWp × 900 kWh/kWp = 5,400 kWh

Strategy: maximise self-consumption + arbitrage

• Self-consumed solar (battery-time-shifted, 75% capture): 4,050 kWh × 28p saved import = £1,134
• Exported peak solar (15% during 16:00–19:00 window): 810 kWh × 24p = £194
• Exported standard (10%): 540 kWh × 15p = £81
• Off-peak grid charge + peak export arbitrage (300 cycles × 10kWh): 3,000 kWh × 9p margin = £270
• Total annual benefit: £1,679

Compare to same setup on standard SEG (15p flat export):

• Self-consumed: £1,134
• Exported: 1,350 kWh × 15p = £203
• No arbitrage
• Total: £1,337

Flux uplift: £342/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.