Free electricity, explained
Prices on Octopus Energy’s Agile tariff rise and fall with the wholesale price of electricity. Some days prices drop below zero, and customers are paid to use electricity. It sounds too good to be true, but it isn’t. Here’s why.
Agile follows the wholesale price
Energy companies buy electricity in bulk from power stations and wind farms on the wholesale market. Prices change through the day. Most tariffs smooth those swings into one steady price. Agile passes them on to you.1 When wholesale prices drop, so does Agile, sometimes below zero.2
Prices can rise too. In the last 5 years, Agile went above 50p per kWh about 4% of the time.7 It’s capped at £1 per kWh.2
Tomorrow's prices are out by 4pm.6
Balancing the grid
The National Energy System Operator (NESO) runs Britain’s grid: the network of power lines carrying electricity from power stations and wind farms to homes and businesses. Every second, it must match the power made with the power used. The electricity alternates 50 times a second, a frequency of 50Hz. Too much power raises the frequency; too little lowers it. NESO must keep it within 0.5Hz of 50Hz and aims to stay within 0.2Hz.3
A normal day
Level, so the price is normal
A windy, quiet night
Too much power, so the price falls below 0p
Too much power, not enough demand
When demand is lower than usual, the grid can have too much power. To stay balanced, it sometimes pays energy suppliers, the companies that sell you electricity, to use more, or power stations to make less. That’s when prices go negative.1
It usually happens in the early hours of windy nights, when few people use energy. On Sunday 5 April 2020, lockdown had cut demand and a sunny, windy weekend brought record renewable power: 40% from wind and almost 20% from solar. Agile customers were paid to use power from 10.30am to 4pm.1
Where power is made matters too. Britain’s cables can’t always carry wind power from the north to where it’s needed in the south. Then NESO pays wind farms to switch off and other power stations, usually in the south, to turn on.4
Where the money comes from
When prices fall below zero, suppliers are paid to take electricity off the grid.2 Agile passes that on, so you’re paid for what you use in those half-hours.1
It helps the grid too. Octopus says using more power when it’s plentiful means fewer renewable plants sit idle.1 In 2014, Ofgem, the energy regulator, said tariffs charging less when electricity is cheaper to produce, such as when more renewable power is available, could bring big savings for people who can be flexible.5
Making the most of it
Move flexible jobs to the free half-hours, such as running the washing machine, dishwasher or tumble dryer, or charging an electric car. See when the next free hours are.
Sources
- Octopus Energy, Social distancing plus sunny, windy weather means AgileOctopus prices plunge, 8 April 2020.
- Octopus Energy, Agile Octopus (checked 25 October 2026).
- NESO, What is frequency? (checked 25 October 2026).
- NESO, Energy explained: the costs of balancing Britain's electricity system, 30 April 2026.
- Ofgem, Ofgem launches project to pave the way for cheaper off-peak electricity, 4 April 2014.
- This site's own checks: since 23 September 2026, the next day's prices have been out every day by 4pm UK time, when we first look. Octopus itself says “between 4pm and 8pm”.2
- This site's stored Agile prices for the South East (region J), from 25 October 2021 to 24 October 2026: above 50p for 1,890 of 43,824 hours (4.3%).