Powerwall on Octopus Agile: A UK Guide to Smart Tariffs

Octopus publishes tomorrow's Agile prices at about 4pm every day: 48 half-hour slots, each one different. For most households that's a bit stressful. For a Powerwall owner, that daily spread is exactly what a battery is for. Your battery can move kilowatt-hours from cheap half-hours to expensive ones, and on Agile the gap between them changes every day.

It's also a tariff that needs more rules than any other. A schedule that looked right in October will be wrong by November, and the Powerwall's built-in modes have no way of knowing.

If you want the broader picture of how dynamic pricing works with batteries in different countries, start with our guide to dynamic electricity pricing for batteries. This post is about Agile and the UK.

Why half-hourly pricing suits a battery

Most rate plans give you two or three prices that stay the same for months. Your battery learns the shape once and repeats it. Agile gives you 48 prices a day, tied to the wholesale market, published the afternoon before.

That works out well for a battery for two reasons.

First, the gap between cheap and expensive is real and you can see it in advance. Take Friday 2 October 2026, using the national average Agile figures from Energy Stats UK:

• Cheapest slot: 23.0p at 13:30
• Most expensive slot: 48.7p at 18:30
• 4pm–7pm average: 46.3p
• Whole-day average excluding peak: 29.9p

Second, a Powerwall 3 holds 13.5 kWh usable, which is more than most UK homes use between 4pm and 7pm. You can cover the whole peak from the battery and still have plenty left over.

Here's the maths on that 2 October day. Say your house uses 4 kWh between 4pm and 7pm. Covering that from the grid costs 4 × 46.3p = £1.85. With roughly 90% round-trip efficiency, you need about 4.45 kWh from the grid to deliver 4 kWh out of the battery. A Powerwall 3 grid-charges at up to 5 kW, so that charge takes about an hour, spread over two or three of the cheapest early-afternoon slots. The low that day was 23.0p; assume you pay around 25p on average across those slots and the charge costs about £1.11. You save roughly 74p, on a fairly unremarkable October day with no solar involved. If every day had a similar spread, that's around £22 a month. Some days will be flatter and some much wider, and that's before counting any cheaper overnight slots or plunge days.

The 4–7pm peak premium

Agile isn't purely the wholesale price. Octopus's formula adds a peak premium between 4pm and 7pm, and it depends on your region. According to Octopus's own figures (before VAT), it's lowest in Yorkshire at 12.32p/kWh and highest in the South East at 23.5p/kWh, with London in between at 15.16p.

So if you're in the South East or South West, 4–7pm carries a premium of 20p or more on top of the wholesale price every day, whatever the market is doing. That's the one fixed part of Agile, and it's where a battery earns most of its money.

Octopus has also announced it's lowering Agile's price cap from 100p to 70p/kWh including VAT. Don't treat 70p as a hard ceiling yet, though: published Agile prices went above it in August, September and October, with one September evening in the East of England at 91.65p.

What matters for your settings: the peak is predictable, but your house's evening load isn't, and neither is the state of charge your battery reaches at 4pm. In October you might arrive at peak at 90% after a sunny afternoon. In late November, with sunset before 4:30pm and the heating running, you might arrive at 40%.

Plunge days: getting paid to charge

When the wind is strong and demand is low, wholesale prices can go below zero. Agile passes that on, so Octopus pays you to use electricity. These are called plunge prices, and they're the most fun part of owning a battery in the UK.

On a plunge day you want to:

• Turn on grid charging during the negative slots and fill the battery to 100%
• Push big loads into those slots too (EV, immersion heater, washing machine, dishwasher)
• Keep that charge until the evening peak instead of letting it drain by mid-afternoon

They don't happen every week. They cluster on windy, mild days, often weekends and holidays, and the timing varies by region. You find out at about 4pm the day before, when the prices come out.

That's the problem. A plunge day needs your battery to do something different from what it did yesterday, for one day only, at times you couldn't have known 24 hours earlier.

Why a static schedule can't track Agile

The Powerwall's Time-Based Control works from the tariff set in the Tesla app. Unless your app pulls in Agile's half-hourly prices (check yours, because Tesla keeps adding UK tariff support), that means fixed periods and fixed prices, and on Agile every number you enter is an approximation. Even with live prices, Time-Based Control still doesn't know how much solar you'll get this afternoon. You might set 4–7pm as peak and a cheap overnight window, and that's roughly right on most days.

Roughly right goes wrong in a couple of predictable ways.

The seasons change, and modes can't follow

A schedule you set in October assumes October's solar. Once the clocks go back (25 October this year), the afternoon solar that used to top up the battery before 4pm mostly disappears. If your grid charging is set for "overnight only, solar does the rest", you'll start reaching the peak half-full, and the app won't tell you.

The underlying issue is that Self-Powered, Time-Based Control and Backup are modes, and a mode is one fixed behaviour. What you actually want on Agile is a set of conditions: "if it's after 1pm, before 4pm, and I'm below 70%, charge from the grid." No mode in the Tesla app can say that, so nothing adjusts when the season does.

Intelligent Octopus Go: cheap, but Octopus drives

Intelligent Octopus Go is the other popular choice: a cheap overnight rate of 7.6p/kWh from 23:30 to 05:30, with Octopus controlling the Powerwall. It works well for a lot of people, especially EV drivers. The catch is that while Octopus is managing the battery, your own control over settings like the backup reserve and operating mode is limited. On Intelligent Octopus Flux, for example, Octopus says it manages all the Powerwall's control settings and fixes the reserve at 20%. Check what your tariff allows before you sign up. That's a fair trade if you want a fixed cheap window. It isn't Agile.

Your rules, checked all day

Grid Getter works differently. You write rules, and they're checked against what your Powerwall is actually doing: time-based rules every minute, battery rules every few minutes.

For an Agile household, it looks like this:

• A time-based rule for the peak (Scheduled plan). At 4pm on weekdays (and weekends, since Agile's peak runs every day), switch to Self-Powered with a low reserve so the battery covers the evening. At 7pm, raise the reserve again. You can limit it to certain months, so your winter rules and summer rules can differ.
• A battery threshold rule before the peak. Watch the state of charge during a window you choose, say 12:00–15:30. If it drops below your threshold, charge from the grid up to a target, then stop. This is what fixes the November problem: the rule checks the battery, not the calendar. The free plan includes one of these.
• Coming soon: Pre-Peak Charge (Adaptive plan). If you have solar, this uses your site's solar history, today's conditions and the weather forecast to predict whether the panels will fill the battery to your target before your 4pm peak rule kicks in. It only charges from the grid if they won't. On a bright day it does nothing; on a grey one it tops up early.

On the Scheduled and Adaptive plans you can have as many automations as you like, so a winter set and a plunge-day set can sit alongside your everyday rules and only run when they should.

To be clear about what it doesn't do: Grid Getter doesn't read Octopus's half-hourly prices. You still look at the 4pm price release. On a plunge day, though, you turn on a rule you've already written (grid-charge to 100% between these times) instead of digging through the Tesla app's tariff screen and remembering to undo it tomorrow.

Could you script all this yourself with Home Assistant and the Octopus API? Yes, and plenty of people do. Grid Getter is for people who want the same result without maintaining a script.

Start with what your battery is doing now

Before you change any settings, look at what actually happened at 4pm yesterday. What state of charge did your battery have at peak start, and did it last until 7pm? The free Live Monitor in Grid Getter shows exactly that. Start free here or get the app.

One thing to check today: look at your Agile tariff code in your Octopus account (something like E-1R-AGILE-24-10-01-C). The last letter is your region. Find it below, then multiply the premium by what you use between 4pm and 7pm. That's roughly how much the evening peak adds each day before the wholesale price is even counted, and it tells you how much your battery should be covering.

Add 5% VAT to get what you actually pay. For example, 4 kWh in the South East is 4 × 23.5p × 1.05, about 99p a day from the premium alone.

Sources

• Octopus: Agile pricing explained
• Energy Stats UK, Agile prices on 2 October 2026
• Energy Stats UK: how Agile works
• Octopus: Intelligent Octopus Go
• Octopus: Intelligent Octopus Flux Powerwall FAQ
• Tesla: Powerwall 3 datasheet (UK)
• Octopus integrates with Tesla Powerwall
• Solar Power Portal: Octopus plunge pricing
• Coolcuration: Agile vs Tracker