Octopus plunge pricing: when electricity goes free or negative
A plunge is when the Octopus Agile price drops below zero and you are effectively paid to use electricity. It happens when the grid has more power than it needs, usually windy nights and mild, sunny weekends, and it is occasional rather than daily.
What "plunge" actually means
On the Agile tariff the price changes every half-hour and follows wholesale electricity costs. When those costs fall far enough the price can reach zero, making electricity free, or drop below zero, which Octopus calls a plunge. During a plunge the rate is negative, so rather than paying for a unit you are credited for it.
Why prices go negative
It comes down to surplus. When wind and solar are generating more than the country is using, the wholesale price falls, and sometimes it falls below zero. The two reliable patterns are blustery overnight hours, when demand is low and the wind keeps blowing, and mild, sunny weekend afternoons, when solar is high and offices are closed. Whether a plunge lands depends on the weather and on your region, so it is a tendency rather than a timetable.
How to catch one
Plunges are easy to miss because they are announced only when the next day's prices publish, usually around 16:00 London time. negawatt can email you a calm heads-up when a plunge is coming in your region, so you do not have to watch a chart all afternoon.
negawatt won't tell you to run your dishwasher during the plunge. It just shows you when the cheap and negative half-hours are, clearly, on one fixed scale, so you can decide for yourself.
Common questions
What is a "plunge" on Octopus Agile?
"Plunge" is Octopus's own term for half-hours when the Agile price falls below zero. During a plunge you are effectively paid to use electricity, because the price per kilowatt-hour is negative rather than something you pay.
Is electricity ever actually free on Octopus Agile?
Yes. When wholesale prices fall far enough, Agile half-hours can reach zero or go negative. At zero the electricity is free; below zero it is a plunge and you are credited for using it. Both are occasional, not daily, and depend on the weather and your region.
When do plunge prices usually happen?
Plunges happen when supply runs ahead of demand. The common patterns are windy overnight hours, when wind generation is high and demand is low, and mild, sunny weekend afternoons, when solar is high and the country is quiet. They are weather-driven, so there is no fixed schedule.
How do I get a plunge or free-electricity alert?
negawatt can email you when a plunge is coming in your region. You pick your region, choose a plunge alert, and get a calm heads-up when the next negative half-hour is published. No dashboard to watch, and no appliance instructions, just the prices.
Does every region get the same plunge at the same time?
No. Agile prices differ across the 14 UK regions, so a plunge in one region need not appear in another, and the timing can differ even when it does. The only reliable way to know your region is to look at its published prices.
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negawatt is a trading name of BN3 Consulting Limited (Company No. 12848799, Horsham, UK). negawatt is not affiliated with Octopus Energy; it consumes their public Agile tariff API.