Paid to charge: Octopus Agile’s negative prices, explained
August 2026
A few times a month in Britain, electricity costs less than nothing. Here’s why that happens, and what a Powerwall should do about it.
Why a price goes negative
Wholesale electricity is auctioned every half hour, and supply has to match demand in real time. On a windy night or a bright, mild Sunday, Britain’s wind and solar can produce more than the country wants — and because large generators can’t always shut off cheaply, they’ll pay someone to take the surplus rather than curtail. Most tariffs hide this from you behind a flat rate. Octopus Agile passes it through: when the wholesale price plunges below zero, so does your import price. For those half-hours, consuming electricity earns you money.
What a battery does with that
A Powerwall is the perfect plunge customer. It can absorb 5 kW on command, hold 13.5 kWh, and spend it later when prices recover — which they always do, usually by dinner. The play: charge hard through the negative window (get paid), then discharge through the evening peak (avoid 25–40p imports). One good plunge event can be worth a couple of pounds on its own; the habit of catching them, compounded over a year, is real money. If you have an EV, the same logic applies with a bigger tank.
The honest caveats
Plunge events are weather-driven — some months bring several, some bring none, and they often land at inconvenient hours, which is exactly why this belongs to automation rather than to you watching an app at 3 AM. The daily standing charge applies regardless. And negative half-hours are outnumbered by ordinary cheap ones — the boring 8p overnights fund most of the savings; plunges are the bonus round.
Automating it
In SolDial, Agile is a native plan: pick it on the Hourly tab and your automations trigger on the live half-hour price. The plunge rule is one automation: when the import price drops below 0p, enable grid charging and fill the battery — negative thresholds are fully supported. Pair it with a peak rule that spends the stored energy when the price crosses back above your line, and an alert that confirms the charge actually happened. The dashboard shows tomorrow’s prices from about 4 PM, so you’ll see the plunge coming a day ahead.
Read the full Agile Powerwall playbook, or start the free trial and let it run.