Smart Charging for Fleets

How reliability, operational efficiency, and cost control are created through smart charging and load management

When fleets talk about smart charging, load balancing, or load management, they’re really talking about one thing: controlling how much power the depot uses and how that power is shared across vehicles. This area can feel complicated, but understanding it is essential to running a reliable, cost-effective, and operationally efficient EV fleet.

Why Smart Charging Matters

1. Reliability (keep the depot online)

Smart charging stops the total site load from exceeding what the grid connection can handle. If it doesn’t, breakers trip, the depot goes dark, and nothing charges.

2. Operational efficiency & readiness (every vehicle ready for service)

A CMS ensures vehicles receive the right amount of energy, especially during overnight charging or tight dwell windows, so they’re ready for service each day.

3. Cost control (reduce the operating cost of energy)

Smart charging reduces exposure to expensive hours and can lower total site capacity requirements, reducing your energy bills today and your upgrade costs tomorrow.

The Smart-Charging Hierarchy

Smart charging becomes clearer when broken into three layers. Each layer answers a different operational question:

1. Can the site safely deliver power?
2. How should that power be shared across vehicles?
3. How should we charge to minimise cost?

This model helps fleets understand how decisions are made, and where the value comes from.

Layer 1: Load Management Across All Electrical Levels

(Make sure you don’t blow the fuse!)

EV charging power must be managed across every layer of the depot’s electrical system:

• Site limit
• Safe limit (headroom for background loads)
• Sub-board limit
• Feeder / circuit limit (internal site feeders)
• Group-level limit
• Charger-level limit

Static Load Limits

Fixed caps aligned to TOU periods or known constraints.

Purpose: avoid expensive tariff windows and demand charges.

Dynamic Load Limits

Real-time limits based on measured load at the site, sub-board, or feeder level.

Purpose: protect infrastructure and unlock more usable capacity.

Layer 1A: Managing Load Across Sub-Circuits, Panels & Feeder Groups

A depot does not have a single pool of power. Its electrical system is a hierarchy of constraints, some from the grid, others from the internal wiring.

Smart charging must respect all of them.

Key Reasons This Matters

• Prevents blowing fuses on sub-circuits
• Avoids panel overloads even when the site has headroom
• Enables electrification without expensive rewiring
• Maximises the number of chargers you can add
• Ensures power is distributed safely and fairly

The Site Hierarchy

Power needs to be controlled at various levels. On some sites, this is simple; on others, we have seen that an effective strategy requires control at multiple levels of the site.

• Site-level limit (grid connection) The maximum power the depot can draw from the utility, sometimes fed by multiple grid feeders, but treated as one top-level limit.
• Sub-board / distribution-board limits Breaker-rated boards feed different site areas.
• Internal feeder limits (site feeders) Cable runs from boards to groups of chargers. These are often the smallest limits, and where overloads happen most.
• Charger-group limits Shared limits for clusters of chargers fed from a common panel or transformer.
• Charger-level limits The output capacity of each individual EVSE.

Hint for those who do not have an electrical engineering background: Often you will hear “feeder and immediately think of the power coming into the site. The reality is there are two feeder levels – the site level and feeders within a site.

Simple Summary Of How Limits Work

Site → Sub-Board → Internal Feeder → Charger Group → Charger

None of these limits can be exceeded.

Layer 2: Charging Strategy & Load Balancing

(Make sure vehicles are ready!)

Once all limits are known, the CMS decides which vehicle gets power, when, and how much. There are several strategies – and many sites will just go with the strategy that is suggested by an installer or the default in the chargers. This can be leaving a lot of value on the table in terms of operational efficiencies.

Types of chargers

Before talking about charging strategies, you need to understand that there are two fundamental types of charging that will impact what you can do in terms of charging strategies

• Parallel – Multiple connectors output power at once (if hardware supports it). Useful for depots with many vehicles and limited charging windows.
• Sequential – One vehicle per charger receives full power at a time, even if a charger has multiple connectors. Useful when the infrastructure is simple and dwell times are long.

Core Charging Strategies

• Equal share or Needs-based – Power is shared evenly among vehicles.  Useful for simple depots, predictable dwell windows, and fairness-based operations.
• First-in/First-out (FIFO) – Vehicles charge in based on the order that they plug in – with the earliest to plug in charging first.   Useful for depots with low departure-time variability.
• Last-in/First Out (LIFO) – Vehicles are charged based on the order that they plug in, with the latest charging first. Good for constrained depots where there may be space constraints, where departures may involve vehicle blocking.
• Priority-based (efficiency sub-strategy) This is an efficiency sub-strategy that provides the user pre-configured granular control. Power is allocated based on operational rules:
  1. Priority connector
  2. Priority vehicle
  3. departure time
  4. SOC deficit
  5. urgency of next block
  6. route criticality
  7. emergency/utility response
  8. charger layout constraints

• Schedule-driven (based on duty cycles or dispatch schedules). A subtype of priority-based charging that uses timetables or duty cycles (GTFS/Hastus).

Efficiency Strategies

Load following – Real-time power reallocation based on how much each battery can accept. Prevents chargers being “wasted” on tapering vehicles.

• Bulk vs soak awareness – All EV batteries follow the same charging curve:

Bulk Phase (Constant Current)

• High power acceptance
• Fast charging
• Highest operational value

Soak Phase (Constant Voltage / Taper)

• Power acceptance drops
• Charging slows
• Charger becomes under-utilised
• Important for battery cell balancing

Load Following optimizes this by:

• reducing power to soak-phase vehicles
• reallocating unused capacity to those still in bulk
• improving total overnight throughput

Bulk/soak is the battery behaviour. Load following is the efficiency behaviour that makes use of it by allocating the amount being requested by the vehicle and giving capacity to other vehicles. .

Bulk and soak charging coupled with a FIFO strategy ensures vehicles are charged up to the point where charge rates slow as quickly as possible. Then those vehicles in soak phase enter a round-robin strategy, rotating power allocation until they reach full charge.

Layer 3: Energy Optimisation & Cost Control

(Charge at the lowest cost)

Smart charging isn’t just about how much and how,  it’s also about when. Energy costs vary widely across the day. Good smart charging systems lower and stabilise the cost of operating an EV fleet.

Time-of-Use (TOU) optimization

Shift flexible charging into low-cost windows while still meeting readiness.

Peak-Demand Management

Avoid high-demand spikes that increase monthly bills.

Utility Signals & Demand Response (DR)

Automatically reduce load during grid stress events without compromising readiness.

Why This Matters To Fleets

Managing energy has one of the most direct impacts on ROI:

• predictable monthly OPEX
• better budgeting for electrification
• lower lifetime cost of fleet EVs
• better use of renewable or low-cost periods
• stronger utility partnerships

Advanced energy management and microgrids

It is beyond the scope of this article; however, it is important to note that there are even higher-level capabilities available in energy management – vehicle to grid, local microgrid control of local generators and battery storage systems. These capabilities key lead to significant cost benefits as well as resilience benefits and will be addressed in a future article.

What Infrastructure Do You Need for These Strategies?