In short: to size depot charging, work out the energy each vehicle needs per day, divide it by the time it is parked, and compare the total with the power your site can spare. For vans parked overnight, the average power needed is often only a few kilowatts each, so one AC charger per van with load management usually works. Add a small number of DC chargers only for vehicles with short turnarounds.
Many depot projects start by asking “how many rapid chargers do we need?” The better question is how much energy has to reach each vehicle, and how long it has to get there. This article walks through the calculation with a worked example you can adapt.
What data do you need?
- Daily distance for each vehicle or route type, using a busy day rather than the average.
- Real-world energy use per mile for each vehicle model, from your own telematics or trial data if possible. Manufacturer figures are usually achieved in ideal conditions.
- Return and departure times, to give the charging window.
- Site headroom: your agreed supply capacity minus the building’s own load, for each half hour overnight.
Step 1: Energy per vehicle
Multiply daily distance by energy per mile, then add margins. Cold weather, heavy payloads and battery ageing all increase consumption, and some energy is lost in charging. The example below uses illustrative assumptions; replace them with your own figures.
| Illustrative example: 20 vans | Value |
|---|---|
| Busy-day distance | 80 miles |
| Energy use (assumed) | 0.35 kWh per mile |
| Energy to the battery | 28 kWh |
| Winter and ageing margin (assumed 20%) | 33.6 kWh |
| Allowance for charging losses (assumed 10%) | About 37 kWh from the grid per van |
Step 2: Power per vehicle
Divide the energy by the usable charging window. If the vans return at 7pm and leave at 6am, allow for late returns and early starts and use, say, 10 hours.
37 kWh over 10 hours is an average of about 3.7 kW per van. A standard 7 kW AC charger delivers that comfortably, with spare capacity for the occasional van that returns nearly empty.
Step 3: Check the site total
Twenty 7 kW chargers could draw 140 kW if every van started at full power at once. But the fleet only needs about 20 × 3.7 kW, roughly 75 kW, on average across the night. With load management sharing power between chargers, a site with around 100 kW of overnight headroom could serve this fleet without an upgrade. Base the connection request on figures like these, and remember that a budget estimate is indicative only; a formal offer is what you can rely on.
Load management is what makes this work. It caps the total, then shares the available power so every van is ready by its departure time. We explain the options in load management for depots.
Private depot chargers in Great Britain must also meet the Smart Charge Points Regulations, which require pre-set default charging hours outside the weekday peaks of 8am to 11am and 4pm to 10pm. The owner can change these, but for an overnight depot they usually suit you anyway, because off-peak electricity is cheaper.
Step 4: Vehicles that cannot wait
Now look for exceptions. Suppose five of the vans run a second shift with a 90-minute break at midday. If each needs 30 kWh in that break, that is 20 kW per van on average, beyond an AC charger. One or two DC chargers, shared between those vans on a rota, would cover it.
Keep DC charging for the vehicles that genuinely need it. DC chargers cost more to buy, install and maintain, and they need more of your site’s capacity. If the connection is the constraint, ask about a flexible connection, which can give a quicker power-on date where it avoids or defers reinforcement.
Step 5: Plan for growth
Fleets grow, routes change and heavier vehicles may follow. When the ground is open for the first chargers, install ducting and cabling for future bays. It costs far less than digging up the yard twice.
If the full fleet will need more than the site can supply, apply for the extra capacity now, even if you will not need it for years. Our article on what to do while you wait for a grid connection covers the bridges available in the meantime.
Summary of the example
| Need | Solution in the example |
|---|---|
| 20 vans parked overnight | 20 AC chargers at 7 kW, with load management |
| 5 vans with a midday top-up | 1 or 2 shared DC chargers |
| Site capacity | About 100 kW overnight headroom, no upgrade needed today |
| Growth | Ducting for future bays; early connection application |
For the bigger picture, from grid connection to procurement, read our guide to fleet depot charging, and use the EV charger requirements checklist when you choose hardware.
Frequently asked questions
Is one charger per van always necessary?
No, but it saves moving vehicles at night. If two vans can share a charger within their parking time, sharing can work, though it needs a reliable rota.
Why not install fast chargers so vans charge quicker?
Overnight, speed rarely matters. Faster chargers cost more, need more grid capacity and usually sit idle once the van is full.
How accurate does the energy estimate need to be?
Accurate enough to size the site with a sensible margin. Start with conservative figures, then refine them once vehicles are in service and you have real data.
Our solution recommendations service runs this analysis with your telematics and meter data. Send us your fleet details.
