Fleet Depot Energy and Power

grid feed · transformer · BESS · charger mix

A depot's energy need is set by the fleet's miles; its power need is set by how long the vehicles sit. Size the grid feed from dwell time and control first, and the charger count follows.

Worked example of peak grid draw for a depot of 50 trucks that need 25 MWh between them each night: about 2.7 MW if charging is managed across a 10-hour overnight dwell; about 6.8 MW if the same energy must be delivered in a 4-hour turn; and 17.5 MW if all 50 trucks plug into 350 kW chargers at once with no control. Below, the chain the grid feed buys, in order of lead time: medium-voltage feed, transformer, switchgear and chargers, with battery storage covering the gap while upgrades arrive and a microgrid controller that islands the site, black starts it and sets the charging order. PEAK DRAW FOR 50 TRUCKS NEEDING 25 MWH (WORKED EXAMPLE) Overnight, managed 2.7 MW 4-hour turn, managed 6.8 MW Unmanaged, 350 kW 17.5 MW Same energy every night; dwell time and control set the grid feed WHAT THE GRID FEED BUYS, IN ORDER OF LEAD TIME MV feed Transformer Switchgear Chargers Battery storage covers the gap while upgrades arrive Microgrid controller islands the site, black starts
Example energy
25 MWh/night
Managed peak
2.7 MW
Unmanaged peak
17.5 MW
Hub
Charging

Finding

The same fleet can need a 3 MW or an 18 MW grid connection, and the difference is dwell time and charge control, not vehicles

Fifty regional trucks covering 250 miles a day at 2 kWh per mile need 25 MWh between them every night. Spread across a 10-hour dwell with charger losses, that is about 2.7 MW. Squeeze it into a 4-hour turn and it is 6.8 MW. Let every truck plug into a 350 kW charger at once and the peak is 17.5 MW.

The grid feed is the expensive, slow part. A service above a few megawatts usually means a dedicated medium-voltage line, a pad-mount or substation transformer and switchgear, items that took 44-128 weeks to arrive in 2025. So the design order is fixed: measure duty cycles and dwell, set the managed peak, size the feed to that, then add a battery for the gap between today's feed and the full build. Chargers come last and are the easiest part to change. See Charging and Depot Supply Chain.

Grid-forming batteries and an on-site microgrid controller turn the depot from a load into a small power system: they cap peaks, keep critical charging running in an outage and let the site sell flexibility to the utility. The controller must run locally, because charging and protection loops cannot wait on a cloud connection. See Microgrid Controllers and Energy Orchestration.

Energy stack

Depot electrical stack, from utility to vehicle

Fleet depot energy stack
LayerComponentsSuppliersDesign note
Grid interconnectionUtility MV service (12.47-34.5 kV), protection relays, revenue meteringUtility; Schneider Electric, Siemens, Eaton, ABB, Hitachi EnergySets the import limit; 1-3 years to energize
Conversion and distributionPad-mount transformers, MV and LV switchgear, busway; DC bus or solid-state transformers at some sitesEaton, Siemens, ABB, Hitachi Energy, Hammond; Chinese makers TBEA, SieyuanTransformer is the longest lead item
StorageGrid-forming battery and bidirectional inverterTesla Megapack, Fluence, CATL, BYD, SungrowShaves peaks, opens site early, rides through outages
On-site generationSolar canopy, backup generators, fuel cellsFirst Solar, LONGi, JinkoSolar modules; Caterpillar, Bloom EnergyOffsets daytime load; backup runtime limited by fuel
Vehicle energy deliveryLevel 2, 150-400 kW DC, MCS, pantographs, robotic and wireless chargersTesla, ABB, Kempower, Alpitronic, Heliox, Siemens, InductEV, WiTricityPeripherals: the cheapest and fastest part to change
ControlMicrogrid controller, energy management, charger management (OCPP 2.0.1)Schneider EcoStruxure, Siemens, PowerSecure, Ampcontrol, The Mobility HouseRuns locally; the cloud cannot be in the control loop

Charging modes

Charging modes by fleet class

Depot charging modes
ModePowerBest forNotes
Depot AC (Level 2)11-19.2 kW (22 kW in Europe)Vans, pool cars, support vehiclesLowest cost and grid impact; needs 8+ hours of dwell
DC fast50-400 kWVans, box trucks, buses, robotaxis, drayage tractorsThe depot workhorse; supports shift changes and top-ups
Megawatt (MCS)750 kW-1.2 MW deployed; up to 3.75 MW in SAE J3271Class 8 tractors, mining and port equipmentDrives MV service and transformer size
Battery swapStation charges racks at a steady rateChinese heavy trucks (CATL Qiji), NIO cars, dronesFlattens the peak; needs standard packs
Robotic and wireless11-350 kW for cars and vans; higher for trucksRobotaxis, driverless delivery, automated yardsRemoves the person at the plug; Tesla wireless pads at its Austin lots

Voltage classes

Planning for mixed voltage classes

Plan for every class the depot will host, so chargers are not stranded when the fleet changes.

Vehicle voltage classes at depots
ClassTypical vehiclesPlanning note
400 V classOlder cars, many vans and robotsFine on AC and lower-power DC; cannot use full high-power output
800 V classNewer cars, Tesla Cybertruck and Semi, most new trucks and busesHigher DC power at the same current; check charger voltage range
MCS class (up to 1,250 V)Class 8 tractors, heavy site vehiclesLiquid-cooled cables, HV cabinets, thermal design at the pedestal

Sources

Sources and scope

Scope
Fleet Depot Energy and Power
Sources
ElectronsX worked example; Wood Mackenzie transformer and switchgear lead times (2025); SAE J3271; supplier disclosures
Updated
October 2026