Guides

Plunge pricing: the days electricity goes negative

Last updated: 10 August 2026

A few times a year, something happens on the Agile tariff that sounds like a mistake: the price per kWh drops below zero, and for a half hour or several, you are paid to use electricity. It isn't a glitch or a promotion. It's the wholesale market working exactly as designed — and if you're set up for it, it's the cheapest laundry day of the year.

Why would anyone pay you to use electricity?

Electricity supply and demand have to balance second by second — the grid can't put surplus power on a shelf. Most of the time the balance is kept by turning generators up and down. But some generators are expensive or slow to switch off: a nuclear plant doesn't want to stop for one breezy afternoon, and some renewable generation earns support payments that make producing worthwhile even at a small negative price.

So when a windy night or a bright, blustery spring day produces more cheap power than the country can use, the day-ahead wholesale auction can settle below zero: generators effectively pay to keep exporting rather than shut down. Agile passes wholesale prices through to households, so those negative half hours land on your smart meter as negative unit rates. Use a kWh in that window and it's credited, not charged.

When plunges tend to happen

• Windy nights — high wind output meets the overnight demand trough. The small hours are the classic slot.
• Storms — named-storm weekends have produced some of the deepest negative pricing on record.
• Sunny, breezy spring and early-summer afternoons — solar output peaks while heating is off and demand is mild, most often on weekends and bank holidays when workplaces are quiet.

They're not schedulable — plunge days follow the weather, not the calendar. What you can rely on is the publication rhythm: tomorrow's prices appear at around 4pm today, so a negative window always comes with several hours' notice, and often a full evening's worth.

Making the most of a plunge

The honest arithmetic first: a negative price of, say, −5p/kWh on a 1 kWh wash earns you 5p. Nobody is retiring on plunge pricing. The real win is that everything energy-hungry you'd been putting off becomes free-or-better at once:

• The tumble dryer — normally the appliance you time most carefully, because it's often the biggest single-cycle energy user in the house. In a negative window it's the top of the list. See our tumble dryer guide.
• Washing machine and dishwasher — run full loads, back to back if the window is long enough.
• EV, home battery, immersion heater — anything that stores energy turns a plunge into value that outlasts the window.

One caution: don't invent demand. Running a heater into an open window to "earn" 3p is the energy equivalent of buying things in a sale you'd never have bought at full price. Shift real usage into the window; don't create fake usage for it.

Catching plunges without watching charts

The practical problem with plunge pricing is simply noticing it. The people who catch negative windows are either the ones refreshing a price chart every afternoon — or the ones whose tools check for them. Cheap Hours scores your appliances against every published half hour, so when a negative window exists within your appliance's timer range, the recommendation lands on it automatically and the saving figure shows just how good a run it is. The price chart highlights negative slots too, so a plunge is hard to miss.

Keep reading

• Octopus Agile explained — the tariff behind the plunges
• How much can you actually save? — the everyday savings between plunges
• The fourteen Agile regions — why a plunge can be deeper next door