The plunge pricing window: how long does it last?
Plunge pricing events on Octopus Agile typically last between one and four hours. The most common window is 11pm to 5am, when grid demand is low and wind generation often peaks. Some events last as little as 30 minutes; others extend through the entire night.
The value of an event scales with its duration. A four-hour event at -14p on a 10 kWh battery creates two separate income streams:
- Credit earned from negative rate: 10 kWh x 14p x 4 hours of supply = £5.60 in bill credits (Octopus pays you for what you import at negative rates)
- Stored energy value: 10 kWh of fully charged battery discharged the next day at 35p avoided peak import = £3.50
Total value from one four-hour plunge event: approximately £9.10. Over a month with six to eight such events, the battery earns £30-50 from plunge charging alone. AgileAlert shows the full tomorrow price schedule, including any negative slots, from around 4pm each day.
The shorter events are harder to capture manually. A 30-minute window at -20p at 3:15am is worth catching, but only automation makes it reliable.
Manual approach: checking AgileAlert and charging manually
Before setting up automation, the manual approach captures the majority of value with zero cost:
- Open AgileAlert at 9-10pm and check tomorrow's price schedule
- If negative or sub-2p prices are visible overnight, set the battery to force-charge from the grid
- Run all large appliances immediately if prices are already negative
- Plug in the EV and set it to charge at the cheapest window
This approach captures large, predictable overnight events reliably. It misses short events that occur while you sleep, and it requires remembering to check every evening. For households new to Agile, the manual check is the right starting point. It costs nothing and builds intuition about when events typically occur.
Automated approach 1: GivEnergy with Agile integration
GivEnergy inverters, widely used in the UK with batteries such as the GivEnergy 9.5 kWh and 13.5 kWh systems, support direct Octopus Agile API integration through the GivEnergy portal.
Setup steps:
- Log in to the GivEnergy customer portal at givenergy.cloud
- Navigate to your inverter settings and find the Smart Tariff or Agile Scheduling section
- Enter your Octopus API key (found in your Octopus account settings under Developer API)
- Select your DNO region
- Set your charge threshold, for example "charge when price is below 5p" or "charge when price is below 0p"
- The system automatically schedules battery charging for the next day based on the Agile half-hourly prices
No coding is required. This is the simplest complete automation available for GivEnergy users. The portal updates its schedule each afternoon when Octopus publishes the next day's prices.
Automated approach 2: Home Assistant plus Octopus API
Home Assistant is a free, open-source home automation platform that runs on a Raspberry Pi, a NUC mini-PC, or even a spare old laptop. The Octopus Energy integration for Home Assistant provides live half-hourly prices, consumption data, and Demand Flexibility Service signals.
A basic automation for battery plunge charging in Home Assistant works like this in plain English:
- Trigger: When the Octopus Agile current price sensor drops below 0
- Condition: Battery state of charge is below 90%
- Action: Send force-charge command to battery inverter (via Modbus, GivEnergy, SolarEdge, or Solax integration)
The community at home-assistant.io has published ready-made blueprint automations for Agile price response. Search "Octopus Agile battery automation blueprint" on the Home Assistant community forum to find working templates for GivEnergy, Solax, SolarEdge, and Solis inverters. These typically require no coding, just import the blueprint and configure your thresholds.
The setup investment is one weekend. The ongoing maintenance is minimal. Once running, the system responds to prices within seconds of a new half-hour slot beginning.
Automated approach 3: third-party tools
For households who want Agile-responsive automation but do not want to invest in Home Assistant, several third-party services offer battery scheduling without requiring any self-hosted infrastructure:
- Geeve.energy: A UK startup providing Agile-aware battery scheduling. Connect your inverter and your Octopus account; the service handles scheduling automatically. Subscription-based; minimal setup required.
- HomeEnergyBot: A Telegram bot that sends Agile price notifications and supports some automation triggers. Free to use; community-maintained. Good for notifications; limited direct battery control.
- Octopus Energy app (Power-Ups and Demand Flexibility): Octopus occasionally runs demand flexibility events where they pay you to shift consumption. Opt in through the Octopus app to participate automatically.
The third-party tool landscape is growing rapidly in 2026. Check AgileAlert's guides section for updated recommendations as new services emerge.
Earnings potential: one month of automated plunge charging
A realistic estimate for a 10 kWh battery using automated plunge charge capture in a typical UK month:
| Metric | Value |
|---|---|
| Plunge pricing events per month | 6 events |
| Average negative price during event | -12p/kWh |
| Average event duration | 2 hours |
| Battery capacity charged per event | 10 kWh |
| Credit earned from negative rates | £7.20/month |
| Stored energy value (at 35p avoided peak) | £21.00/month |
| Monthly total from plunge events | £28.20/month |
| Annualised (assuming consistent pattern) | ~£338/year |
This is on top of the regular overnight arbitrage value from non-plunge charging sessions. Combined, a fully automated 10 kWh battery on Agile can deliver £600-900 in annual electricity cost reduction. The automation investment, whether a GivEnergy portal setting or a Home Assistant weekend project, pays back within the first month of operation.
Check AgileAlert tonight to see whether there are any negative slots in tomorrow's schedule. If there are, your battery should be ready to charge.