Fleet Operating Data Before EV Charging-Site Sizing: An Owner’s Input Pack

Executive answer: do not size a fleet charging site from vehicle count or charger nameplate power. Start with time-stamped operating data: when each vehicle returns, when it must leave, distance or energy used, arrival state of charge, usable dwell time, vehicle charging acceptance, parking constraints and the site’s non-EV demand. Convert those records into energy-by-deadline and concurrent-power scenarios, then test them against the electrical connection and operating workflow.

This guide is for an FDI owner, fleet operator and electrical project team preparing an EV charging RFQ in Vietnam. It does not recommend a charger brand, tariff, fleet size or universal design margin. The numerical example is hypothetical. Final design must use the selected vehicles’ and chargers’ verified data, the approved electrical study, site conditions and the requirements in force for the project.

1. Frame the operating promise before the equipment list

The useful requirement is not “install 20 chargers”. It is “have the named vehicles ready for their next routes, with agreed exceptions, while staying inside the site demand limit and safe operating rules”. That sentence identifies four decisions:

• which vehicles are operationally critical;
• how much energy each needs by a stated departure time;
• which parking bay and connector can serve it; and
• what electrical power may be allocated without disrupting the factory or depot.

The corporate EV depot electrical brief explains the wider power, controls and contractual interfaces. This article goes deeper into the operating dataset that should exist before power and port counts are frozen.

2. Collect a representative fleet dataset

Use vehicle-level records for at least one representative operating cycle, and preferably enough history to capture weekday, shift, seasonal, production and exception patterns. A 30–60 day sample may support an early screen, but the owner should justify whether it includes peak routes and abnormal days. Do not treat missing telematics as zero use.

Keep raw observations separate from corrected data. Every correction should identify the reason, method and reviewer. A fleet-average kilometre figure can hide the early-departure vehicles that determine the design.

3. Build an energy-by-deadline table

For each arrival, calculate the energy required at the vehicle and the grid energy required at the agreed meter. One screening relationship is:

E_grid = E_vehicle / eta_path

where eta_path is an explicit assumed charging-path efficiency for the scenario. It is not a permanent vehicle or charger guarantee. If SOC data are reliable, another check is:

E_vehicle = C_usable × (SOC_target − SOC_arrival)

Compare this with distance-based energy. A large disagreement may reveal bad telemetry, exceptional auxiliary consumption, an incomplete route or an incorrect usable-capacity assumption.

Assign every energy requirement a deadline. Aggregate daily kWh alone cannot show whether a group that leaves at 05:30 is ready.

4. A bounded worked example

Assume a hypothetical fleet of 40 vans. Each travels 110 km per operating day and consumes 0.24 kWh/km at the battery for the modeled route. The energy to replace is:

40 × 110 × 0.24 = 1,056 kWh/day

If the screening model assumes 90% energy transfer efficiency from the site meter to stored vehicle energy, grid energy is:

1,056 / 0.90 = 1,173.3 kWh/day

Fifteen vans have a six-hour connection opportunity before an early departure. Their grid energy is:

15 × 110 × 0.24 / 0.90 = 440.0 kWh

The ideal average power is 440 / 6 = 73.3 kW. Applying a hypothetical 1.20 planning factor for arrival scatter, reconnection and data uncertainty gives 88.0 kW. This factor is not a standard value; replace it with scenario evidence.

The other 25 vans require 733.3 kWh from the grid. Over nine usable hours, their ideal average is 81.5 kW. Because their window overlaps the early group, adding the two averages without a time-step model could overstate or understate the peak. A 15-minute simulation should place every arrival, deadline and charging constraint on one timeline.

5. Test the site headroom at the same interval

Use measured base-load data at the intended control boundary. State meter ID, interval, period, shutdowns and known future loads. The factory metering-boundary guide explains why data from different meters cannot be mixed without reconciliation.

Suppose the site’s permitted or contractual demand is 900 kW, the representative 15-minute non-EV peak is 720 kW, and the owner retains a 50 kW operating reserve. The screening EV headroom is:

900 − 720 − 50 = 130 kW

The owner may install charger nameplate capacity above 130 kW, but a supervisory system would have to constrain coincident input to the approved limit. Two 120 kW chargers cannot both be assumed to deliver full output at that moment. The design must also verify transformer, switchgear, cable, protection, voltage-drop, power-quality and thermal constraints; a contractual demand figure does not prove equipment capacity.

6. Distinguish four power limits

IEC 61851-1:2017 covers general requirements for conductive EV supply equipment within its stated voltage scope. IEC 60364-7-722:2018 applies to circuits intended to supply EVs and circuits intended for feeding energy back. These scopes guide the electrical specification; neither provides the project’s fleet duty cycle or a universal charger count.

7. Convert parking behaviour into port demand

A vehicle can be on site without being connected. Record queue time, bay entry, plug-in, energy transfer, plug-out and bay exit. If 40 vehicles each occupy a port for three hours, they require 120 port-hours. If a port provides nine productive hours in the relevant window, the arithmetic minimum is:

120 / 9 = 13.3, therefore at least 14 ports.

Fourteen is not a recommended design. It assumes perfect sequencing, compatible connectors, no failed ports, no blocked bays and no priority conflict. The discrete event model should add real arrival clustering, movement rules, maintenance and the agreed resilience case. A smaller number of higher-power chargers may fail if vehicles cannot be moved; more low-power ports may fail if early vehicles need faster replenishment.

8. Use percentile scenarios without hiding outliers

Report medians and upper percentiles for daily distance, energy, arrival lateness and required turnaround, but keep safety-critical or business-critical outliers visible. A P90 route can be a sensible planning input only when the owner defines what happens to the remaining 10%: opportunity charge, spare vehicle, route reassignment, delayed departure or approved exception.

At minimum model:

• a normal representative day;
• a high-energy route day;
• late simultaneous arrivals;
• one charger or one control-communication path unavailable;
• reduced site headroom during a factory peak;
• planned maintenance and a power-restoration sequence; and
• fleet growth or route change stated separately from the base case.

Do not add every worst case simultaneously unless that combined event is an actual contractual requirement. Show which scenarios are independent and which can coincide.

9. Define smart-charging inputs and authority

A controller needs vehicle identity or class, energy target, departure deadline, available connector, present power, site import, charge limits and priority. Define the source, timestamp, update rate and unavailable-data rule for each value. IEC 63110-1:2022 describes definitions, use cases and architecture for managing charging and discharging infrastructures, including session, energy, grid and metering data flows. It does not prove that any two selected products interoperate.

ISO 15118-20:2022 specifies communication messages and sequences between EV and EVSE for power transfer, including bidirectional functions within its scope. Do not write a project requirement that assumes every fleet vehicle exposes the same data or implements the same feature. Confirm the actual vehicle, EVSE and backend combination.

Set one dispatch hierarchy. The site controller, charger cloud, building system and fleet platform must not issue conflicting limits. Document who can change the site cap, how changes are logged and what safe fallback applies after loss of the site meter, local controller, WAN, charger communications or time synchronization.

10. Protect production and essential loads

A factory-connected depot should treat production demand as a constraint, not a forecast that can be ignored. Include approved future machines, motor starting where relevant, HVAC peaks, standby generation, PV/BESS operation and planned outages. If charging is shed, define which vehicles lose power first and whether a minimum operational fleet must be protected.

Use the factory electrical interface register to assign the PCC meter, MV/LV supply, charger feeder, communications, earthing, civil and test responsibilities. The controller’s commercial limit is not a substitute for protective devices or approved electrical interlocks.

11. Turn the dataset into an RFQ package

Issue bidders the same controlled information:

• an anonymized vehicle and route dataset with a data dictionary;
• arrival, departure and energy-by-deadline scenarios;
• verified vehicle acceptance and connector schedule;
• representative site demand at the agreed meter interval;
• current SLD, equipment schedule and known future loads;
• bay plan, circulation, queuing and vehicle-movement rules;
• site demand cap, operating reserve and load-priority logic;
• communications architecture, data ownership and cybersecurity boundaries;
• availability, growth and resilience scenarios; and
• required simulation files, assumptions, deviations and acceptance evidence.

Require each bidder to return the time-step model, charger/port schedule, coincident site-load result, feeder demand, losses, unserved-departure events and a deviation register. The electrical EPC tender-boundary guide helps normalize civil, electrical, controls and handover scope before price comparison.

12. Build a priceable BOQ without inventing capacity

Keep provisional quantities visible. Do not hide a route length, road crossing, transformer upgrade or software subscription inside “complete system”.

13. Put data and model checks into the ITP

The electrical ITP should provide a wider structure for hold points and traceable records. Project tests must state instruments, accuracy, preconditions, tolerances, invalid-test rules and retest responsibility.

14. Keep HSE and vehicle movement separate from optimization

Charging optimization does not authorize electrical work or vehicle movement. The site plan should address traffic segregation, wheel stops or bollards, cable trip/damage risk, weather exposure, emergency access, impact protection, lighting, drainage and accessible emergency controls. Electrical installation and maintenance require approved isolation, lockout/tagout, stored-energy verification and competent authorized personnel.

Define normal stop, remote stop, emergency isolation and maintenance isolation separately. An application command is not proof of electrical isolation. Vehicle batteries and EVSE remain subject to manufacturer instructions and the approved emergency plan.

15. Govern privacy and operational data

Collect only fields needed for design and operation. Replace driver names with pseudonymous IDs in engineering files, restrict access, define retention and record who can export or correct data. Separate driver-performance management from electrical sizing. A route exception should be technically explainable without exposing unnecessary personal information.

At handover, provide the owner with a data dictionary, meter map, time-synchronization method, model version, controller settings, user roles, audit logs, API/export arrangements and an exit plan from hosted services. Contractual access should survive personnel and service-provider changes.

16. Decision table before concept freeze

17. Questions fleet owners should answer

1. Which departures are mandatory, and what is the permitted exception process?
2. What energy, not merely SOC percentage, must each vehicle receive by that deadline?
3. Which records prove the vehicle and charger power limits?
4. How much connected time is lost to parking, queuing or labour?
5. At which meter and interval is the non-EV peak measured?
6. What reserve protects production and essential loads?
7. What happens when one charger, meter or communication path is unavailable?
8. Who may change dispatch priorities and the site power cap?
9. Which model and field records will prove the system before acceptance?

FAQ

Can daily fleet energy determine transformer size?

No. Daily kWh is only one input. Transformer and electrical design also depend on coincident kW/kVA, existing demand, power factor, harmonics, voltage drop, protection, thermal conditions, growth and operating scenarios.

Is the fastest available charger always the safest design choice?

No. The vehicle may accept less power; the site may have less headroom; the parking workflow may favour more ports; and faster equipment may add cost or interface requirements. Compare complete operating scenarios.

Can smart charging compensate for an undersized connection?

It can allocate an approved power limit, but it cannot create energy or time. If the required energy-by-deadline exceeds the feasible window, the owner must change routes, dwell, port/vehicle mix, charging opportunities or electrical capacity.

Should every vehicle receive equal power?

Not necessarily. Deadline-aware control can prioritize vehicles by required departure, energy deficit and operational criticality. The rule must be transparent, testable and subject to authorized overrides.

Does ISO 15118 guarantee fleet-backend interoperability?

No. Its scope concerns EV–EVSE communication. Confirm the exact vehicle, EVSE, controller and backend functions, versions and conformance evidence required by the project.

Owner takeaway

A dependable fleet charging site begins as an operating-data project. Give every kWh a vehicle, deadline and evidence source; give every kW a meter boundary and electrical constraint; give every port a parking workflow; and give every control decision an owner and fallback. Then bidders can price the same problem and commissioning can test the promise that actually matters: vehicles ready for duty without compromising the site.

For an owner-side review of fleet data, electrical headroom, RFQ boundaries and acceptance records, contact QuangAnhcons with the available route dataset, SLD, interval demand and vehicle schedule. The review should confirm assumptions and missing evidence before equipment selection.

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