When is electricity cheapest in the UK?
On a half-hourly tariff like Octopus Agile, UK electricity is usually cheapest overnight, most often in the small hours between about 02:00 and 05:00, and is occasionally free or negative when the grid has surplus wind or solar.
The short answer
Demand falls overnight while wind generation often keeps blowing, so the cheapest half-hours of the day usually land in the early morning. On a typical day the lowest slot sits well under the daytime price, and the peak arrives in the early evening as the country gets home and switches things on.
That pattern is a tendency, not a timetable. The exact cheapest half-hour moves every day and differs between the 14 UK regions, so the only dependable way to know tonight's cheapest slot is to look at the actual published prices for where you live.
When prices go negative
Sometimes the price drops below zero, which Octopus calls a plunge, and during one you are effectively paid to use electricity. Plunges happen when supply runs ahead of demand: windy nights, and mild, sunny weekend afternoons when solar is high and the country is quiet. They are occasional rather than daily, and whether one lands depends on the weather and your region.
Why it changes day to day
Agile prices follow half-hourly wholesale costs, which rise and fall with demand and with how much wind and solar the grid has at that moment. A calm, cold night can keep overnight prices high; a blustery afternoon can make the middle of the day the cheapest part of it. Tomorrow's prices publish each afternoon, usually around 16:00 London time, so the cheapest slot for tomorrow simply isn't known earlier in the day.
negawatt won't tell you to run your dishwasher at 2am. It just shows you the prices, clearly, on one fixed scale, so you can decide for yourself.
Common questions
What time is electricity cheapest in the UK?
On the Octopus Agile tariff, the cheapest half-hours are usually overnight, most often between about 02:00 and 05:00, when demand is low. The exact cheapest slot changes every day and differs by region, so the only reliable way to know is to look at the published prices.
Is electricity cheaper at night on Octopus Agile?
Usually, yes. Overnight half-hours tend to be the cheapest of the day because demand drops while wind generation often stays high. But it is not guaranteed: a calm, cold night can keep overnight prices up, and a windy afternoon can make the middle of the day cheaper instead.
When is electricity free or negative ("plunge") in the UK?
"Plunge" is Octopus's term for half-hours when the Agile price goes below zero and you are effectively paid to use electricity. It happens when supply outstrips demand, typically windy nights and sunny, mild weekend afternoons. Plunges are occasional, not daily, and vary by region.
When does Octopus publish the next day's Agile prices?
Tomorrow's half-hourly Agile prices are published each afternoon, usually around 16:00 London time. Until then only today's prices are final, so the cheapest slot for tomorrow is not known earlier in the day.
Why does the cheapest time change every day?
Agile prices track half-hourly wholesale electricity costs, which depend on demand and on how much wind and solar the grid has at that moment. Both shift daily and by region, so the cheapest window moves around rather than sitting at a fixed time.
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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.