Negative electricity prices: yes, they're real, and they happen often
On Octopus Agile, prices can go below zero. When that happens, your electricity meter runs backwards in terms of cost: every kilowatt hour you consume earns you money rather than costing you money. Your supplier credits your account for the electricity you use.
This sounds absurd. It is not. Negative prices occur on wholesale electricity markets around the world, and they have become more frequent as renewable energy penetration increases. They are a normal feature of a grid with significant wind and solar capacity, and they happen on the UK wholesale market several times a month.
For Agile customers, negative pricing events create a genuine earning opportunity. Running high-draw appliances during a plunge event does not just avoid cost. It generates actual credit. An EV charged at the Agile floor of -20p/kWh earns around £1.20-1.80 per charge session. An immersion heater running for 90 minutes earns around 90p. A washing machine earns 20-40p per cycle.
These figures are real. They appear as credits on Octopus Agile bills. Households who catch plunge events regularly save significantly more than the headline average of £440/year quoted by Octopus for typical Agile customers.
How negative prices happen: the physics and economics
Wind turbines generate electricity based on wind speed. They do not generate based on what the grid needs at any given moment. When wind is strong and demand is low, the UK grid faces a surplus problem: more electricity is being produced than is being consumed.
The grid cannot store surplus electricity directly. It must be consumed as it is generated, or it must be curtailed (generators are switched off or throttled). Curtailing a wind turbine is both wasteful and expensive. Wind farm operators pay to build and maintain their turbines. Stopping them unnecessarily destroys revenue and strains equipment.
So instead, generators do something counterintuitive: they bid negative prices. They effectively say, "I will pay you to consume my electricity." This is rational behaviour. Paying a small amount per kWh to keep the turbine running and maintain grid balance is cheaper than curtailment penalties and equipment wear.
The wholesale price signal flows through to Octopus Agile. On a half-hour when wholesale electricity is negative, Agile prices go negative too. Your bill reflects the market reality: the grid had surplus renewable energy, and you helped absorb it.
The UK national grid operates at a frequency of exactly 50Hz. Too much supply pushes frequency above 50Hz; too little supply pulls it below. Negative prices are the economic signal for "frequency is at risk of going high: please use electricity." Your appliances, running during a plunge event, are providing a balancing service to the grid.
The UK record: and what made it happen
Octopus Agile has recorded prices as low as -57p per kWh at wholesale level. The most extreme negative events share a common set of conditions:
- Strong, sustained wind across the UK and North Sea (high wind output)
- Mild temperatures (low heating demand, reducing grid draw)
- High solar output (spring or summer afternoon, adding to surplus)
- Low industrial demand (bank holiday or weekend, fewer factories running)
- High nuclear output (baseload cannot be quickly reduced)
When all these factors align simultaneously, the grid surplus can be extreme. Wind alone can cover 60-70% of UK demand on such days. Add nuclear baseload at 7GW, a sunny afternoon, and minimal industrial consumption, and the grid is overwhelmed with supply.
These events are most likely on spring bank holidays (low demand, windy, increasingly solar). They can last several consecutive half-hours, sometimes stretching across three to six hours. An alert household can earn £3-8 in a single event by running everything possible.
The Agile price cap, however, limits what you actually receive.
How often do Agile prices go negative? (with monthly data)
Negative Agile half-hours occur approximately 5-10 times per month on average, based on data from energy-stats.uk. The frequency varies significantly by season:
| Season | Typical plunge frequency | Reason |
|---|---|---|
| Spring (Mar-May) | High: 8-15 events/month | Mild demand + windy + solar growing |
| Summer (Jun-Aug) | Moderate: 5-10 events/month | Solar high, but wind variable |
| Autumn (Sep-Nov) | Moderate-high: 6-12 events/month | Wind picking up, demand still mild |
| Winter (Dec-Feb) | Lower: 2-6 events/month | High demand absorbs wind surplus |
The timing within a day follows a clear pattern. Overnight hours (midnight to 7am) produce the most negative and near-zero events. Wind does not switch off at night, but demand drops sharply as households sleep and businesses close. The mismatch between supply and demand is greatest at 3-5am on a windy night.
Midday hours in summer also see negative events when solar peaks and demand dips. These are harder to catch because they are less predictable and can be brief. The overnight window remains the most reliable opportunity.
The -20p floor: what Agile's cap means for you
Octopus Agile caps the negative price you receive at -20p per kWh. Even if wholesale electricity prices fall to -57p or lower, the most you earn on Agile is 20p per kWh consumed.
This cap protects Octopus's margin and limits the theoretical earning potential of extreme events. But -20p is still a significant rate. For comparison, peak Agile prices regularly reach 35-50p per kWh on winter evenings. The spread between the floor (-20p) and the peak (40p+) is 60p per kWh or more.
That spread is what makes home battery arbitrage so compelling, and it is also what makes plunge timing so valuable for high-draw appliances. Every kWh you shift from a peak half-hour to a negative half-hour saves you 60p or more, not just the cost of the peak unit.
You can monitor approaching negative periods in real time on AgileAlert's live dashboard, which shows tomorrow's prices as soon as Octopus publishes them each afternoon.
What to run during a plunge pricing event
The priority order for a plunge event is simple: maximise kilowatt hours consumed. Higher draw appliances earn more. Here is the priority order:
- EV charging (7kW home charger or higher). An EV charging at 7kW for a 2-hour plunge event earns 14 kWh x 20p = £2.80 credit. This is the highest single-appliance earner in most households.
- Immersion heater (2.5-3kW element). Running for 90 minutes heats a full 150-litre tank and earns approximately £0.68-0.90 credit. Hot water stored in a well-insulated cylinder keeps for 24 hours.
- Home battery charging (if fitted). Charge at -20p, discharge at peak. See the battery section below for the full maths.
- Washing machine (0.8-1.5kW average draw). A full cycle earns £0.15-0.25 credit. Smaller than an EV but completely passive: start it and walk away.
- Dishwasher (1-1.5kW). Similar to washing machine: £0.10-0.20 credit per cycle.
- Tumble dryer (2-2.5kW). Earns £0.20-0.30 per cycle. Higher draw than washing machine but shorter cycle.
Do not run appliances with no flexible load: lights, phone chargers, and standby devices draw tiny amounts and are not worth worrying about. Focus entirely on appliances with large motors or heating elements.
Setting up alerts so you never miss them
Agile prices are published by Octopus at approximately 4-5pm each afternoon for the following day. This means you have from late afternoon to midnight to plan your usage around any negative windows overnight.
There are three main ways to receive alerts:
- AgileAlert dashboard: Check your region's prices each afternoon. Negative half-hours appear clearly highlighted. Takes 30 seconds to review and plan.
- Octopus Energy app: Octopus sends push notifications for plunge pricing events. Enable notifications in the app settings. You will receive an alert when a negative period is imminent.
- Third-party tools: Octograph and similar apps provide email or push alerts when prices in your region drop below a threshold you set.
The most reliable approach combines a daily afternoon check of AgileAlert with Octopus app notifications as a backup. This takes less than a minute per day and ensures you catch the majority of negative events even when they occur at unusual times.
You can also automate some responses. Smart EV chargers like Zappi, Ohme, and the Octopus app itself allow you to set minimum and maximum price thresholds for charging. If you set your EV to charge automatically whenever prices go below 5p, it will capture most plunge events without any manual intervention.
Plunge pricing and home batteries: the money-earning strategy
If you have a home battery, negative pricing events move from a savings opportunity to a genuine revenue source. The maths are straightforward.
Charge a 10kWh battery at -20p/kWh during a plunge event: the credit for charging is 10 x 20p = £2.00. Discharge that battery the following evening at a peak rate of 35p/kWh: the saving from not importing peak electricity is 10 x 35p = £3.50. Total benefit per full cycle: £5.50.
In practice, battery round-trip efficiency is around 85-90%, so the actual dischargeable energy from a 10kWh charge is 8.5-9kWh. The realistic figure per plunge cycle is closer to £4.70-5.20, still highly significant.
With 5-10 plunge events per month, a household with a well-configured home battery could earn £23-52 per month from plunge arbitrage alone, before accounting for broader time-shifting benefits. Annual battery benefits on Agile for an active user can reach £300-600/year.
Popular home battery systems compatible with Agile optimisation include the Tesla Powerwall, GivEnergy, Solis, and Fox ESS. Smart inverter software such as GivTCP, Solax, or the Octopus app allows automatic scheduling to align charging with Agile's cheapest half-hours.
The environmental win-win: why negative prices are good for the planet
Negative electricity prices are not a market dysfunction. They are a direct signal that the UK has more renewable energy than it currently knows what to do with. When you consume electricity during a plunge event, you are absorbing wind power that would otherwise be curtailed. You are letting turbines keep spinning. You are preventing the waste of clean energy.
The carbon intensity of electricity during a negative price event is as low as it gets on the UK grid. Wind-dominant surplus periods typically run at 20-50g CO2 per kWh, compared to 200-250g at peak demand on a winter evening. Consuming electricity during a plunge event is ten times cleaner than consuming it at peak.
This is the extraordinary double win that the cheap electricity and green electricity connection creates. You are not choosing between saving money and helping the environment. You are doing both simultaneously, and the two goals are perfectly aligned.
At scale, demand flexibility during plunge events reduces the need for curtailment payments to wind farms, improves the economics of renewable generation, and makes the UK's clean power targets more achievable. Millions of households responding to negative price signals collectively absorb gigawatts of surplus renewable energy that would otherwise be wasted.
You are not just saving £440 a year. You are showing the grid that demand can move. You are making renewable energy economically viable. You are part of the solution, and your electricity bill reflects that in real time.
Check the live AgileAlert dashboard this evening to see whether your region has any low or negative half-hours tonight, and plan your appliances accordingly.