Why I switched to Octopus Agile (and how Predbat changed everything)
Standard tariffs made no sense once I had a battery. Agile + Predbat means the house charges when prices go negative and avoids every expensive peak.
When I got the Fox battery installed, I was still on a standard flat-rate tariff. The battery was useful — it stored solar and discharged in the evening — but I wasn’t getting anywhere near the most out of it.
The problem: a fixed tariff doesn’t reward when you use electricity. Charge the battery at 2pm or 2am, same price either way.
Enter Octopus Agile
Agile is a half-hourly tariff tied to the wholesale electricity market. Prices swing from negative (they pay you to use power) to 35p/kWh or more at winter teatime peaks.
With a 10.3kWh battery and Predbat making the charge/discharge decisions, the maths changed completely.
What Predbat actually does
Predbat runs inside Home Assistant and pulls:
- The next 24-48h of Agile prices
- A solar generation forecast from Solcast
- Your current battery state
It then plans out every half-hour slot. Charge cheap overnight. Let solar fill it during the day. Discharge during expensive evening peaks. Repeat.
On a good day the battery never touches expensive grid power at all.
Numbers so far
My average import rate has dropped from ~28p to closer to 12p when averaged over the month. On the best nights I’ve charged at negative rates — essentially getting paid to store electricity.
The payback tracker on this site is pulling real lifetime figures from Home Assistant. Watch it tick up.
Should you do it?
If you have a battery (or even just a storage heater or EV), Agile + Predbat is worth the setup effort. It took me an afternoon to get Predbat configured properly, but it’s been running hands-off ever since.
Switching to Octopus
If you’re not already with Octopus, you can join through my referral link below — we both get £50 credit. Once you’re a customer you can move onto Agile (or any of their smart tariffs) for free from your account.