Electric School Bus Depot Charging Scheduler

This electric school bus depot charging scheduler helps fleet managers, school districts, consultants, and utilities test whether a depot can reliably recharge buses between afternoon pull-in and morning rollout. By combining bus counts, battery sizes, charger power, time windows, and demand limits, it provides a quick feasibility check and an estimate of overnight energy costs.

How the depot charging scheduler works

The calculator uses a simplified energy and power model to approximate whether your current or planned depot design can fully recharge the fleet in the available overnight window. It focuses on four core ideas:

• Energy required per bus – how many kilowatt-hours (kWh) need to be added from arrival to departure.
• Available charging power – how much power (kW) your chargers can deliver at any instant.
• Available charging time – the number of hours between when buses can start charging and when they must be ready for morning dispatch.
• Site demand limit and tariffs – how your chosen kW cap and rate structure affect costs.

At a high level, the tool compares total energy needed with the maximum energy that can be delivered without exceeding your charger capacity or demand limit. It then estimates cost using off-peak and on-peak energy prices, plus an optional demand charge for power drawn above your chosen limit.

Key formulas behind the scheduler

The underlying calculations are intentionally simplified for planning purposes. Conceptually, the core quantities are:

• Energy needed per bus (kWh)

This depends on the difference between the state of charge (SoC) when buses return and the target SoC at departure, multiplied by battery capacity:

Where:

• B = battery capacity per bus (kWh)
• SoC_return = state of charge on return (%)
• SoC_target = target departure state of charge (%)

The calculator may also cross-check this against the daily route energy per bus input as a reasonableness check.

• Total fleet energy required (kWh)

If all buses are similar, the total energy is approximately:

Total fleet energy ≈ Number of buses × Energy needed per bus

• Maximum deliverable energy (kWh)

The maximum energy your depot can deliver within the charging window is limited by both the chargers and the site demand limit:

Charger-limited power (kW) = Number of active charger ports × Power per charger

Allowed site power (kW) = min(Charger-limited power, Site demand limit)

Maximum deliverable energy (kWh) = Allowed site power × Available charging window (hours)

• Cost estimation

Energy cost is broken into off-peak and on-peak based on how the schedule fits into your window. The tool multiplies kWh in each period by the respective rate and, if your simulated load exceeds the demand limit, adds a marginal demand charge above limit per kW above that cap.

How to use the Electric School Bus Depot Charging Scheduler

Use these inputs to describe your depot and routes:

• Number of Buses Returning to Depot – Count of buses that must be recharged overnight.
• Battery Capacity per Bus (kWh) – Typical usable battery capacity for each electric school bus.
• Daily Route Energy per Bus (kWh) – Approximate energy consumed in a typical day’s routes.
• State of Charge on Return (%) – Average SoC when buses get back to the depot in the afternoon.
• Target Departure State of Charge (%) – Desired SoC before leaving the depot in the morning.
• Number of Active Charger Ports – How many charge connectors can charge buses at the same time.
• Power per Charger (kW) – Nameplate power rating for each charger (for example, 60 kW DC fast chargers).
• Available Charging Window (hours) – Number of hours from the earliest start of charging to the latest departure.
• Site Demand Limit (kW) – Planning cap on total charging load, often based on a utility limit or internal constraint.
• Off-Peak and On-Peak Energy Rates ($/kWh) – Your tariff rates for energy in off-peak and on-peak periods.
• Demand Charge Above Limit ($/kW) – Marginal demand charge per kW for exceeding the chosen demand limit.
• Operational Buffer Before Morning Dispatch (%) – Extra margin on top of the target SoC to account for uncertainty.

After you enter values, run the calculation to see whether the fleet can be fully charged in time, what the approximate overnight energy use is, and how demand and energy rates affect cost.

Interpreting your charging plan results

The tool is designed to highlight whether your configuration is feasible and where bottlenecks appear. Typical outputs and how to interpret them include:

• Feasibility status – Indicates whether the depot can reach the target SoC (plus buffer) for all buses within the available window without violating your demand limit.
• Limiting factor – If the schedule is infeasible, the result usually points to one of three constraints: insufficient charger ports, too little time in the window, or a demand limit that is too low.
• Peak charging power – The highest instantaneous power draw implied by the schedule. Compare this to your demand limit and transformer capacity.
• Total overnight energy (kWh) – The amount of energy delivered to buses overnight. You can use this to cross-check against your route planning assumptions.
• Estimated cost – An indicative total cost for the overnight charging session, broken into off-peak, on-peak, and demand components.

Operations and facilities teams can use these outputs to decide whether to adjust route blocks, add chargers, upgrade service, or negotiate different tariffs with the utility.

Worked example: 48-bus depot with 60 kW chargers

Consider a mid-size suburban depot similar to the default values:

• 48 buses returning to depot
• 210 kWh battery per bus
• Daily route energy per bus: 145 kWh
• State of charge on return: 35%
• Target departure state of charge: 90%
• 18 active charger ports at 60 kW each
• Available charging window: 12 hours
• Site demand limit: 900 kW
• Off-peak rate: $0.08/kWh; on-peak rate: $0.18/kWh
• Demand charge above limit: $12/kW
• Operational buffer: 10%

For each bus, the SoC increase from 35% to 90% is 55 percentage points. Applied to a 210 kWh battery, that is about 115.5 kWh per bus. For 48 buses, the total required energy is roughly 5,544 kWh, plus some margin from the operational buffer.

The charger-limited power is 18 × 60 kW = 1,080 kW. With a 900 kW demand limit, the tool will cap instantaneous power at 900 kW. Over a 12-hour window, the theoretical maximum deliverable energy at that cap is 10,800 kWh, which is well above the 5,544 kWh requirement. The scheduler therefore focuses on whether all buses can rotate through the available ports within 12 hours while respecting that 900 kW cap.

If the results show the plan is feasible, you can explore variations:

• Lower the number of charger ports to see when the solution becomes infeasible.
• Reduce the demand limit and note when peak load becomes the constraining factor.
• Test what happens if buses return with a lower SoC (for example, 25% instead of 35%).

Using the same structure, you can compare multiple investment options without building a full simulation model.

Comparing depot charging strategies

The table below illustrates how different depot configurations might behave in the scheduler. These are conceptual examples; use your own data for decisions.

Use these patterns as a starting point when running your own scenarios: for example, current depot vs. expanded charger count, or conservative vs. aggressive demand limits.

Assumptions and limitations

This scheduler is designed for early-stage planning and concept evaluation. It intentionally simplifies several real-world factors:

• Constant charger power – Charging is treated as if it occurs at a constant kW up to the target SoC. In reality, charging curves taper at high SoC.
• Uniform buses – All buses are assumed to have the same battery capacity, similar route energy use, and similar SoC on return.
• No mid-day or en-route charging – The tool only considers depot-based charging within the defined overnight window.
• Simplified demand charges – Demand charges are modeled as an incremental cost per kW above your chosen limit, not a full utility tariff.
• Static time-of-use structure – Only one off-peak and one on-peak rate are used; complex or seasonal TOU rate plans are not modeled.
• Idealized scheduling – The tool assumes buses can be rotated across chargers as needed and does not simulate detailed routing, blockage, or queueing.
• No equipment or grid constraints beyond the demand limit – Transformer, feeder, and switchgear limits are not modeled explicitly.
• No battery degradation or temperature effects – Long-term battery health, cold-weather derates, and auxiliary loads (HVAC, telematics) are not included.

Because of these assumptions, you should treat results as directional rather than definitive. For detailed engineering design, interconnection studies, or procurement decisions, always pair this tool with utility-side modeling, charger vendor input, and route-block level scheduling analysis.

When to adjust your depot design

If the results suggest your depot cannot fully charge the fleet within the available window or that demand charges become excessive, consider the following adjustments:

• Increase charger ports – Adding more ports, even at moderate power, can improve rotation flexibility.
• Increase charger power – Upgrading from Level 2 to DC fast charging can help depots with short overnight windows.
• Negotiate a different demand limit – Work with your utility to explore higher capacity or managed charging programs.
• Stagger routes and returns – Adjust schedules so that not all buses need maximum charging at the same time.
• Refine target SoC and buffers – In some cases, reducing target SoC or buffer (while staying safe) can relieve constraints.

By iterating a few scenarios in the scheduler and then validating promising options with your utility and vendors, you can design a depot that reliably supports full fleet electrification.