Keep future grid capacity out of the current fleet plan
A fleet can grow before its planned electrical upgrade is ready. Run the next fleet phase against the supply available today before running an upgrade scenario. A purchase order or target completion date does not establish usable capacity.
Try these three fictional cases in the site-power planner. Keep 30 kWh of delivered DC energy per vehicle, a six-hour usable window, six simultaneous connectors, 60 kW existing peak demand and 20% service reserve. The planner also assumes 0.95 power factor, 92% conversion efficiency and a separate 20% charging-demand margin. These are desk-study assumptions, not a customer installation or equipment specification.
- Current fleet and supply: 10 vehicles require 300 kWh. The planning target is 300 ÷ 6 × 1.20 = 60 kW. A 200 kVA service gives (200 × 0.95 × 0.80 − 60) × 0.92 = 84.64 kW modeled DC output, displayed as 84.6 kW. This is a preliminary aggregate fit, not confirmation of a workable vehicle schedule.
- Expanded fleet before the upgrade: change only the vehicle count to 20. The 600 kWh requirement produces a 120 kW target against the same 84.64 kW output: a 35.36 kW screening gap, displayed as 35.4 kW. Future supply capacity must not hide this interim gap.
- Separate future scenario: keep 20 vehicles and change the assumed service to 400 kVA. Modeled AC headroom becomes 244 kW, giving 224.48 kW DC output, displayed as 224.5 kW. The arithmetic fits the 120 kW target, but this scenario is conditional on the actual upgrade and project review. The unchanged 60 kW building load is also an assumption to revisit.
Changing an input clears the old result. Recalculate each case and label any saved results with the fleet phase, supply status, load-data date and assumptions. The calculator does not store scenarios, check upgrade progress or verify that capacity is available. Its connector average is not a power-allocation instruction.
Before committing the larger fleet to the site, have the utility and qualified project team confirm the supply constraints, required approvals and actual available capacity. Review the interim vehicle schedule and any staged deployment with fleet operations. A proposed managed-charging system also needs its required capabilities and commissioned behavior checked against the operating objective. Do not solve the gap by increasing protective settings or assuming that additional plugs create additional supply.
DOE AFDC procurement guidance calls for utility coordination covering near- and long-term charging needs, upgrades, permits and inspections. DOE FEMP guidance distinguishes existing and planned fleet inventory and calls for capacity data and system commissioning. The three-case comparison is our original planning workflow, not a DOE sizing rule or a guarantee of fleet readiness.
BUYER PAIN POINT
Limited electrical capacity is one of the most common blockers for commercial sites, especially when existing building loads change throughout the day.
PROJECT RESPONSE
Build a load profile and charging-priority plan first; DLB and power allocation can then be evaluated against a real site-capacity assessment.
Start with the operating context.
A useful review identifies the site's available electrical capacity, other major loads, expected charging concurrency and whether specific vehicles, bays or operating periods need priority. These facts shape a realistic power-allocation strategy.
Good commercial charging decisions connect vehicle use, site conditions and the operator's intended service. The selected equipment can then be reviewed against the final technical, commercial and destination-market requirements.
Planning checklist.
- Available capacity and existing site electrical loads
- Charging concurrency at normal and peak periods
- Priority rules for fleet, public or managed charging sessions
- Required monitoring, control boundaries and final electrical design
Do not confuse service rating with charging headroom.
A transformer or service nameplate is not the amount available for EV charging. Start with verified service capacity and a representative load study that captures coincident building demand. Then reserve an agreed operating margin and assess the remaining input headroom. The local utility and a qualified electrical engineer must confirm interconnection limits, service equipment, protection, conductors, voltage drop, demand rules and the final design.
The updated site-power planner makes its simplified formula visible: service kVA × assumed power factor × (1 − reserve), minus existing peak demand; the remaining AC input headroom is then converted to a modeled DC output. This is a screening calculation, not a load calculation or installation approval.
Worked example: 20 fleet vehicles with an eight-hour window.
Assume 20 vehicles each need 40 kWh during an eight-hour charging window. That is 800 kWh per day and 100 kW average delivered DC power. The preliminary tool adds a visible 20% energy-throughput margin, producing a 120 kW planning target.
For illustration only, a 500 kVA service at the tool's fixed 0.95 power-factor assumption produces 475 kW modeled input capacity. After a 20% operating reserve, the modeled ceiling is 380 kW. Subtracting a verified 200 kW existing peak leaves 180 kW AC input headroom; at the fixed 92% conversion assumption, modeled usable DC output is 165.6 kW. The result suggests enough preliminary headroom for the 120 kW target, but it does not select a charger, breaker, transformer or cable.
Use vehicle schedules before buying maximum nameplate power.
DOE fleet guidance recommends using vehicle battery needs, operating schedules and dwell periods when defining charging requirements. If only part of the fleet overlaps, staggered charging or managed charging may keep the site below an agreed ceiling. Longer-dwell vehicles may also be candidates for lower-power AC charging, while time-critical routes receive priority DC capacity.
Plan expansion paths early, but stage equipment purchases against verified fleet growth. Managed charging can reduce coincidence with building peaks; it cannot create energy, remove utility constraints or replace engineering review.
The service is unchanged. Why did charging headroom shrink?
A facilities team adds cooling or production equipment while its vehicle schedule stays the same. The transformer label has not changed, but an earlier charging estimate may no longer represent the site. Compare credible building-load scenarios before ordering more charging points. Do not use a quiet-day reading as proof of year-round spare capacity.
This original desk-based example uses 12 vehicles needing 30 kWh each during a six-hour window, two simultaneous connectors and a 250 kVA service. The tool assumes 0.95 power factor, 20% service reserve, 92% conversion efficiency and a separate 20% charging-demand margin. These are screening assumptions, not measured product specifications or electrical design rules.
- Demand: 12 × 30 = 360 kWh; 360 ÷ 6 = 60 kW average DC output; with the illustrative margin, the planning target is 72 kW.
- Earlier load scenario, 80 kW: 250 × 0.95 × 0.80 − 80 = 110 kW modeled AC headroom; 110 × 0.92 = 101.2 kW modeled usable DC output. That is 29.2 kW above the screening target, not installation approval.
- Changed load scenario, 140 kW: the same calculation leaves 50 kW AC headroom and 46 kW DC output. The screening shortfall is 26 kW even though vehicle demand and the service rating are unchanged.
- More plugs, same budget: changing two simultaneous connectors to four changes average planning load per connector from 36 kW to 18 kW. It does not increase the 46 kW modeled site output or remove the shortfall. Neither number predicts an individual vehicle's charging curve.
Enter both cases in the site-power planner. Leaving an unknown existing peak blank now blocks calculation instead of treating it as zero. Enter zero only when supported by the relevant site assessment; the tool cannot verify your load data. Counts of vehicles and connectors must be whole numbers.
Next, ask the utility and qualified engineer for a representative coincident load profile covering the relevant operating and seasonal conditions. Review feasible charging schedules and a staged equipment plan before committing capital. Any managed-charging proposal needs project-specific capabilities, integration and commissioned control behavior; it is not a substitute for capacity, protection or interconnection review. There is no promised cost saving or guaranteed departure state of charge.
Parked for eight hours does not always mean eight charging hours.
Original fictional planning example: 18 vehicles each need 24 kWh, with six simultaneous connector positions. The vehicles are on site for eight hours, but the operating plan leaves only six usable hours after time reserved for unloading, moving vehicles and dispatch preparation. These two hours are an illustrative schedule assumption, not a standard allowance.
- Same energy: 18 × 24 = 432 kWh.
- Eight usable hours: 432 ÷ 8 = 54 kW average DC; the tool's separate 20% demand margin gives 64.8 kW.
- Six usable hours: 432 ÷ 6 = 72 kW average DC; with the same margin, the target becomes 86.4 kW—one third higher.
- Unchanged capacity model: a 200 kVA service, assumed 0.95 power factor, 20% service reserve and 60 kW existing peak leave 92 kW modeled AC headroom. At assumed 92% conversion efficiency, modeled DC output is 84.64 kW (displayed as 84.6 kW).
- Changed screening outcome: the eight-hour case has 19.84 kW modeled headroom; the six-hour case has a 1.76 kW modeled shortfall (displayed as 1.8 kW). That small arithmetic gap is not a precision claim or a final equipment-sizing decision.
Run both windows in the site-power planner, keeping the other inputs unchanged. Changing any input now removes the old result; submit again after reviewing the new assumptions. The formulas are unchanged. The tool does not infer a usable window from a timetable or simulate bay turnover, individual vehicle charging curves, late arrivals or missed departures.
Use operating records to establish realistic arrival, plug-in and departure windows, and check individual vehicle deadlines separately. Six connector positions do not prove that all 18 vehicles can rotate through in time. Ask the fleet and facilities teams to review a feasible schedule, representative building loads and qualified electrical design. Do not solve a scheduling gap by changing protective settings or assuming more plugs create more power. No saving, departure readiness or installation approval is guaranteed.
Enough site power does not prove every vehicle is ready
A site-level energy total can fit the modeled supply while one vehicle still misses its energy target. The site-power planner divides aggregate demand by a common window. It does not know each vehicle's charging curve, actual connection times or power limit. Its per-connector figure is an arithmetic average, not a command sent to equipment.
Consider six fictional vehicles, each needing 30 kWh of delivered DC energy, with six simultaneous connection positions and a six-hour usable window. Enter 200 kVA service capacity, 60 kW existing peak and 20% service reserve. These are desk-study inputs, not measurements of a customer site.
- Aggregate demand: 6 × 30 = 180 kWh; over six hours this is 30 kW average output. The planner's separate 20% demand margin gives a 36 kW target, or 6 kW average planning load per simultaneous connector.
- Modeled capacity: 200 × 0.95 × 0.80 − 60 = 92 kW AC headroom; at the assumed 92% conversion efficiency, this becomes 84.64 kW modeled DC output, displayed as 84.6 kW. The site-level screen therefore shows a preliminary fit.
- One constrained vehicle: separately assume its delivered DC power can never exceed 4 kW during that window. Even with uninterrupted charging at that upper bound, it could receive at most 4 × 6 = 24 kWh, below its 30 kWh need. The 4 kW limit is hypothetical, not a rating for any vehicle or Xiaochong product.
- Time lower bound: 30 ÷ 4 = 7.5 hours would be the ideal minimum at constant 4 kW. Tapering, interruptions or a lower actual rate could require longer. This calculation does not establish a feasible charging schedule.
Extra aggregate headroom cannot make that vehicle exceed its assumed limit. Nor does dividing 36 kW by six prove six vehicles will each receive 6 kW. A charger nameplate, allocated ceiling and accepted vehicle power are different quantities; changing the service rating alone does not resolve this hypothetical constraint.
For an actual fleet, review each vehicle's energy need, arrival and departure times, compatible charging mode and documented capability with the fleet and equipment teams. Keep AC-side input and delivered DC quantities separate. Use representative charging records and the exact vehicle and equipment documentation to assess achievable energy, then review the combined schedule and electrical design. Do not alter vehicle or equipment protections to make a target fit.
DOE AFDC charging-equipment guidance explains that charging time depends on vehicle, battery and equipment factors. DOE FEMP guidance calls for vehicle schedules, energy requirements and commissioning against fleet objectives. The arithmetic above is our illustrative screening example, not a DOE sizing rule, actual vehicle-performance prediction or readiness guarantee.
How this applies to a commercial charging project.
DLB and power allocation can be discussed with Xiaochong during commercial project review. The final design is based on the selected product, local electrical requirements and the site engineer's completed assessment.
Images and portfolio references are a useful starting point, but final technical data, dimensions, protection rating, certification, payment integration and delivery terms should be confirmed for the selected model and destination market.
Common buyer questions.
Can a transformer nameplate be treated as spare charging capacity?
No. Existing coincident demand, operating limits, service equipment and utility constraints must be reviewed before estimating charging headroom.
Can DLB replace an electrical capacity assessment?
No. It supports a planned operational strategy but does not remove the need for appropriate electrical design, interconnection review and local compliance approval.
What fleet data is needed first?
Provide energy needed by vehicle, return and departure times, dwell windows, required departure state of charge, expected simultaneous sessions and a representative building load profile.
Official planning sources.
AFDC procurement/installation and FEMP smart charge management pages rechecked October 24, 2026. The AFDC charging-equipment page retains its October 15 review; the fleet overview is retained background from September 13. These sources support utility coordination, load/schedule data and commissioning; the calculation in this guide is our illustrative screening model, not a DOE formula or endorsement. Local utility requirements and project-specific engineering control the final design.
PROJECT REVIEW
Turn this planning guide into a project brief.
Send the country, site type, required power, connector, quantity and operating needs. Xiaochong Energy will help identify the relevant product and technical questions for your project.