Energy Systems Catapult published analysis on 25 June 2025 showing that time of use tariffs, which incentivise overnight electric vehicle charging, could create a new overnight demand peak as EV adoption rises. The finding comes from smart meter data collected across 854 homes in the Catapult's Living Lab during a typical week in November 20241.
The sample split into 446 homes with no EV or charger and 408 homes, about 48% of the total, whose occupants reported owning an EV and a home charger. The homes without EVs followed the familiar pattern, with a clear peak between 17:00 and 17:30 and low overnight use rising from about 05:30 to 06:00. In homes with an EV, the largest daily spike fell in the middle of the night rather than the early evening. At around 50% EV uptake, that overnight peak was twice the size of the early evening peak1.
The analysis attributes the timing to tariff design as well as convenience. A notable spike appears at 00:30, when Octopus Go's cheaper overnight rate begins, followed by a significant drop-off at 05:30 when the discounted period ends. The Catapult states that the number of UK homes with an EV charger is currently around 3%, and describes the Living Lab homes as an indication of what future demand could look like1.
"as more consumers switch to EVs, herding behaviours could create a dramatic new overnight peak in electricity demand"
The Catapult notes the sample may not represent maximum potential demand, since EV owners typically charge at home two to three times per week, suggesting the figures could represent only a third to half of peak consumption. Among groups of homes that all have EVs, including those in flexibility trials using the Catapult's WESA facility, pre-trial smart meter data showed an overnight demand peak around four times the early evening peak1.
| Measure | Homes without EVs | Homes with EVs |
|---|---|---|
| Homes in sample | 446 | 408 (about 48%) |
| Largest daily demand spike | 17:00 to 17:30 | Middle of the night |
| Overnight peak versus early evening peak | Not applicable | Twice the size at around 50% uptake |
The November week was chosen because no demand-side response trials were running, so consumption reflected natural behaviour, and the weather was typical for the season1.
Why it matters for households
The analysis concerns the shape of national demand rather than any individual bill, but the mechanism runs through household charging behaviour. Tariffs that make overnight charging cheaper are the same tariffs many EV owners use, and the Catapult's data shows charging clustering around the start and end of the discounted window. For a household, that clustering is largely invisible: the car charges while the occupants sleep. Its effect is on the wider system, where a concentration of charging in fixed hours can raise demand at the very time it was meant to be low.
For a home weighing EV charging and household energy independence, the finding points to the difference between shifting load off the evening peak and shifting it into a new peak. The Catapult states that conventional time of use tariffs will eventually reach a critical mass at which herding creates problematic new peaks, and that charging systems will then be needed that smooth demand across the day rather than crowding it into fixed, cheap periods that are the same for everyone. It suggests this might involve smart and bidirectional charging responding to real-time grid conditions, potentially with incentives based on local as well as national conditions, and more dynamic tariff structures that vary the cheapest times from home to home1.
What happens next
The Catapult states that while 48% EV ownership may seem distant, growth in EV sales suggests the scenario could become reality within the next few years, and that adoption is rising faster in some areas than others, so it could arrive quickly in some locations. It says understanding these patterns gives time to develop solutions before they become critical problems, and that success will require technology and market innovations as well as new types of tariffs1. No dates for specific tariff or market changes are given in the analysis.
Sources1 cited
- The emerging EV overnight demand peak - Claire Rowland - Energy Systems Catapult, es.catapult.org.uk