Octopus Agile Plunge Pricing, explained

Plunge Pricing is what Octopus calls it when Agile unit rates go unusually low, including below zero. In those half-hours the wholesale market is so long on power (often wind, sun, and low demand together) that you may be paid to import electricity.

It is not a separate product. It is just Agile doing what Agile does: 48 half-hourly prices, linked to wholesale, for the whole house. Official page: Octopus Agile.

Agile is day-ahead. Octopus says the next day’s 48 rates land in the afternoon, roughly 4–8pm, usually nearer 4pm. After that you (or software) can plan charging, immersion, and other flexible load into the cheapest stretch.

Until those rates publish, you do not know where tomorrow’s floor sits. That is why a fixed overnight tariff feels calmer, and why Agile rewards people who can wait for the 4pm drop and then act.

Plunge is the floor. The ceiling is Price Cap Protect: Octopus caps any Agile half-hour at 100p/kWh. High wholesale weeks can still hurt if you run the house through the evening peak, but you are not exposed to uncapped spikes.

The expensive habit on Agile is the same as on most ToU tariffs: plug the car in at 6pm because you just got home. Early evening is often one of the dear half-hours unless demand is soft.

Sunday 20 September 2026 in London (GSP C) is a clear illustration of plunge versus peak on the same day:

Overnight 00:00–05:00 on that London day was all negative (~-1.8p to -4.2p). The midday plunge (~11:00–15:30) went negative too. The 17:00–20:30 band sat roughly 38–50p. Intelligent Go’s overnight window would still have been a fixed 8p/kWh (8.4p until 1 Oct).

That shape is a good example day, not every day. Some Agile weeks look flatter. Some look worse than a fixed off-peak deal if wholesale is high and you do not shift. Full strip, region notes, and vs-Go caption: the worked example on the comparison page.