Overnight fleet charging is the process of charging a fleet of electric vehicles (EVs)—such as vans, service vehicles, buses, or company cars—primarily during nighttime hours when vehicles are parked at a depot or secure yard. It typically relies on AC charging (and sometimes mixed AC/DC) to restore vehicles to the required state of charge (SoC) before the next day’s routes.
Why Overnight Fleet Charging Matters
Overnight fleet charging is one of the most cost-effective and operationally stable ways to electrify fleets because it matches fleet dwell time with charging time. It helps fleets:
– Ensure predictable vehicle readiness for morning dispatch
– Reduce charging costs by using time-of-use (TOU) or off-peak tariffs
– Minimize reliance on public infrastructure and DC fast charging
– Avoid depot overload through load management and staged charging
– Scale EV adoption without immediate large grid upgrades
How Overnight Fleet Charging Works
A depot charging system is designed to charge multiple vehicles safely within a defined window (e.g., 8–12 hours):
– Vehicles plug in after returning from routes
– A charge management system schedules and prioritizes charging
– Power is distributed across chargers based on site limits (main fuse, transformer)
– Vehicles reach target SoC by a set deadline (e.g., 06:00)
– Reporting and alerts track charger status, energy use, and exceptions
Charging Strategies Used in Depots
Overnight fleet charging often combines several control methods:
– Staggered start times to prevent simultaneous peak demand
– Priority-based charging (vehicles with early departures first)
– Power sharing / load balancing across multiple charge points
– Minimum SoC guarantees for critical vehicles
– Charge window scheduling aligned to TOU pricing
– Fallback modes for outages or charger faults (reassignment to spare bays)
Typical Power Levels and Infrastructure
Most overnight depots use AC power levels that match long dwell times:
– 7.4 kW – Light-duty fleets or limited electrical capacity
– 11 kW – Common depot baseline for vans and mixed fleets
– 22 kW – Faster recovery for high-mileage vehicles or shorter windows
Some depots include a small number of DC chargers for exceptions:
– Rapid top-ups for late arrivals, unexpected routes, or operational disruptions
Site Design Considerations
A reliable overnight fleet setup depends on planning beyond chargers:
– Grid connection capacity and import limits
– Electrical distribution (switchboards, cable routing, protection devices)
– Bay layout and cable management for quick plug-in routines
– Access control and user permissions (drivers, supervisors, contractors)
– Energy metering per vehicle, per charger, or per cost center
– Redundancy planning (spare chargers, spare bays, service SLAs)
Key Benefits of Overnight Fleet Charging
– Lowest-cost energy delivery when paired with TOU tariffs
– High operational predictability and centralized control
– Reduced downtime and less dependence on public charging
– Scalable rollout: expand bays and chargers as fleet grows
– Supports sustainability targets with measurable energy and CO₂ reporting
Limitations and Risks to Manage
– Site power constraints can limit fleet growth without smart controls
– High simultaneous load if unmanaged (demand charges, fuse trips)
– Requires disciplined operational processes (parking, plugging in, bay allocation)
– Single-point failures at depots can disrupt readiness without redundancy
– Billing complexity for mixed-use depots (employee cars + fleet vehicles)
Related Glossary Terms
Depot Charging
Fleet Depot Charging
Fleet Charging Schedules
Smart Charging
Load Management
Load Balancing
Power Sharing
Demand Charges
Time-of-Use (TOU) Tariffs
Charge Management System
OCPP
MID Metering