What negative electricity prices actually are
A negative electricity price means the wholesale market is paying buyers to consume power. Instead of paying for the electricity you use, your supplier charges a negative amount, and that credit flows to you. On Octopus Agile, this passes through directly. If the rate is -10p/kWh and you use 5kWh, your bill is -50p. Octopus credits 50p to your account.
This sounds impossible. Energy companies charging you money to use electricity? But it is not a promotional trick or a loss leader. It reflects a genuine physical reality in the electricity grid. At certain moments, the system has more power than it can use, and paying consumers to absorb that surplus is cheaper than the alternatives.
The minimum negative price on Octopus Agile is -20p per kWh. This floor exists because further negative prices, while they do occur in the wholesale market, are not passed through beyond this point. In practice, most plunge pricing events sit between -5p and -15p per kWh.
Why the grid pays you to use electricity
The UK electricity grid must balance supply and demand continuously. At 50Hz precisely. When supply exceeds demand, frequency rises above 50Hz and the system faces stability risks. To prevent this, excess generation must either be curtailed, stored, exported via interconnectors, or absorbed by additional consumption.
Curtailment costs money. Wind farm operators are typically paid constraint payments to switch off turbines when the grid cannot absorb their output. These payments come from all electricity consumers through network charges. It is genuinely cheaper to pay households to use electricity than to pay wind farms to stop generating.
Storage is limited. Battery storage capacity across the UK is growing but remains insufficient to absorb large surpluses from very high wind events. Interconnector export to France, Norway, and Belgium helps but has physical capacity limits.
The result is that at peak renewable generation periods, especially breezy nights and mild weekends, the system faces surplus power with nowhere obvious to send it. Negative prices are the market's mechanism for solving this problem. They signal to any flexible consumer: use electricity now, we will pay you, and help us balance the grid.
UK renewables generated 50.8% of UK electricity in 2024, according to Ember. Wind alone provided around 30% of UK electricity in 2025. As this share grows, the frequency and depth of negative price events increases. What was rare a decade ago is now a routine feature of the Agile tariff.
How often do plunge pricing events happen? Real data.
Plunge pricing events, defined as periods where Agile prices drop to -20p or below, occur approximately 5 to 10 times per month on average. This figure varies significantly by season.
Winter months with strong offshore winds produce more events, often concentrated between 11pm and 6am when demand is lowest. Spring and autumn offer a mix, with some events driven by mild weather reducing heating demand while wind remains strong. Summer events are typically fewer but can be dramatic: high solar output coinciding with low overnight demand creates conditions for very low or negative prices.
It is important to distinguish between full plunge events at -20p and the broader category of very cheap prices. Slots at 1p to 5p per kWh occur on most days. Slots between 0p and -5p per kWh occur several times per week in windier seasons. The -20p floor is reached less frequently but often enough to reward customers who are watching.
Over a full year, an engaged Agile customer who responds to every plunge pricing event might capture 50 to 100 of these windows. Each window typically covers 2 to 6 half-hour slots. Running a 2kW appliance for 3 hours during a -10p event saves 60p compared to not running it, and saves £1.08 compared to running it at the price cap rate. Multiply that across dozens of events per year and the contribution to annual savings is meaningful.
The AgileAlert live dashboard publishes each day's prices as soon as Octopus releases them, typically around 4pm. Negative slots are clearly highlighted. You can see exactly when tonight's cheap window opens before you go to bed.
How low can prices go? The -20p/kWh minimum explained.
The -20p per kWh figure is Octopus Agile's contracted floor. Wholesale EPEX prices sometimes clear more negative than this, but Octopus does not pass the additional benefit below -20p through to customers. The floor is stated in the Agile tariff terms.
In the wholesale market, prices can occasionally fall further. During extreme wind events or periods of very low demand combined with high renewable output, day-ahead prices in Europe have cleared below -50p per kWh equivalent in some half-hour periods. UK prices are coupled to these European markets through interconnectors.
For most practical purposes, -20p is the number to plan around. A household that uses 3kWh during a -20p event receives 60p in credit. An EV owner charging at 7kW for three hours during such an event receives £4.20 in credit and gains a meaningful portion of their weekly driving range for free.
Beyond the direct financial benefit, the -20p floor means there is genuinely no cost to running every energy-intensive appliance you own during these windows. The more you use, the more you earn. The limiting factor is your appliances' physical capacity and your smart home setup's ability to respond quickly enough.
How to get notified and what to do
The most important habit for capturing plunge pricing is checking prices each afternoon. Octopus publishes tomorrow's Agile prices at around 4pm every day. Negative slots for the following night are visible from this moment. You have hours to prepare before they begin.
Check the AgileAlert dashboard after 4pm each day. Negative or near-zero slots will be visible in the price chart. Note the start and end times. Set your appliances accordingly. Most modern dishwashers, washing machines, and tumble dryers have delay-start functions. Set them to begin at the cheapest slot and run through any negative window.
For EV owners, most charge management apps allow you to schedule charging by time. Set a charging window that overlaps with the negative period. Even if you only partially charge during the window, you capture some of the benefit.
Smart home platforms including Home Assistant, Octopus Home Mini, and various third-party integrations can automate this entirely. Connected devices respond to the published price schedule without any manual input. You wake up in the morning, your home has heated, your car has charged, your dishwasher has run, and your bill is lower than it would have been with no action.
The appliances to prioritise during plunge pricing
Not every appliance is worth running during a 30-minute negative window. Prioritise appliances with high wattage and the ability to run independently for the duration of the cheap period.
EV charging tops the list. A 7kW home charger running for three hours at -10p generates 21kWh of charge and earns £2.10 in credit while adding roughly 80 miles of range. The combination of credit earned and expensive peak charging avoided makes EV charging the single biggest plunge pricing opportunity.
Immersion heaters and heat pumps can draw 3-4kW and run for hours. If your hot water cylinder is set to heat during cheap overnight periods, scheduling this to coincide with negative slots earns money while building a thermal reserve. A 4kW immersion running for two hours at -15p earns £1.20 in credit.
Washing machines and tumble dryers typically draw 2-3kW. A full wash and dry cycle during a negative window earns 30-60p in credit and avoids 60-80p of cost compared to daytime running. Set the delay-start function before bed.
Dishwashers draw 1.5-2kW and fit neatly into overnight windows. Again, delay-start is the tool. Set it to begin during the negative period and let it run unattended.
The bigger picture: what plunge pricing means for the planet
Plunge pricing is not just a personal finance opportunity. It is a mechanism that connects household behaviour to the health of the electricity grid and the economics of renewable energy.
When consumers respond to negative prices by using more electricity, they absorb surplus renewable generation that would otherwise be curtailed. Curtailed wind energy is wasted clean power. Every kilowatt hour a household consumes during a plunge event is one less kilowatt hour that a wind farm operator is paid to not generate.
This flexibility also makes the economics of new renewable investment more favourable. Developers and investors price curtailment risk when deciding whether to build new wind or solar capacity. A more responsive consumer base that absorbs surplus generation reduces this risk, lowers the cost of capital, and supports more renewable investment. Your tumble dryer at 2am is, in a meaningful sense, part of the clean energy transition.
The UK generated 50.8% of its electricity from renewables in 2024. That proportion will only grow. Plunge pricing events will become more frequent, not less. The households positioned to respond to them are already building habits and infrastructure that will pay dividends for years. The households on flat tariffs are missing every single one.