Key facts
- Energy (kWh) and power (kW) are distinct measurements.
- Theoretical average power equals energy divided by charging hours before losses or power constraints.
- An electrical site survey is necessary before any charger procurement or installation decision.
Quick answer: A fleet should start depot electrification with daily energy demand and actual parking hours, not a shopping list of charging stations. Peak electrical demand depends on the number of simultaneous vehicles, charging limits, building loads and power-sharing strategy.
Step 1: record the vehicles, not an assumed charger count
For each fleet vehicle, record daily travel, measured efficiency, arriving battery percentage, target departure percentage and parking schedule. Use observed operation where possible. A 12-hour parked window is not a 12-hour charging opportunity if the driver needs the vehicle for several hours in between.
Step 2: calculate the energy budget
Here is a fully hypothetical depot of six vans, each requiring 24 kWh added to its battery overnight. Total battery energy is 6 × 24 = 144 kWh. At a hypothetical 90% wall-to-battery charging efficiency, the supply must provide 144 ÷ 0.90 = 160 kWh. The efficiency value is illustrative, not a fleet or charger specification.
Step 3: estimate theoretical average site power
| Available charging window | Illustrative wall energy | Average supply power |
|---|---|---|
| 8 hours | 160 kWh | 20 kW |
| 10 hours | 160 kWh | 16 kW |
| 12 hours | 160 kWh | 13.3 kW |
These figures are only average power. They do not prove that a real site’s electrical service can deliver the charge or that vehicles can accept it throughout the window. Loads are not perfectly uniform.
Step 4: find the constraint that matters
- Building’s measured baseline and peak loads.
- Utility import capacity and local transformer constraints.
- Parking positions and cable reach.
- Charging windows for individual vehicles.
- Vehicle AC/DC charging limits.
- Maintenance and reserve-vehicle scheduling.
- Charge management, demand charges and tariff structure.
- Local permit, fire-safety and accessibility requirements.
Why six high-power chargers can be the wrong first purchase
Six ports with high advertised kW do not create more site electrical capacity. Dynamic load sharing can adjust charging rates, provided the control design and individual departure deadlines are suitable. Conversely, undersized equipment may miss early departures even if the average energy calculation looks adequate. Procurement requires a proper engineering design.
Use a two-day operating scenario
Test a normal day and a peak-duty day with different return times and energy requirements. If one vehicle returns at midnight and departs at 05:00, its window is five hours regardless of whether the rest of the fleet parks from 18:00 to 08:00. Plan around this narrow window instead of averaging it away. The load-sharing explainer and our energy-unit converter provide supporting definitions.
Frequently asked questions
Does kWh divided by time equal the required installed charger power?
It gives a theoretical average, not a final installation specification. Losses, charging curves, simultaneous vehicle needs and grid constraints all matter.
Can I skip the utility assessment if the chargers have load balancing?
No. Electrical supply, protection and site permission still require qualified assessment.
Worked values are hypothetical. For deployment, consult a qualified electrical engineer and the utility.
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