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A fleet depot is the best case for solar and storage in transport: the vehicles are in the same place every night or every day, the duty cycle is knowable, and the electricity bill is large enough to matter. It is also the case where the grid connection, not the array, is usually the constraint.
This page is for fleet operators, depot managers and the EPCs designing for them. It covers the sequence that avoids the two classic mistakes: ordering chargers before checking the connection, and sizing the array to the charging load rather than to the available area.
Start with the duty cycle, not the charger count
What matters is how far each vehicle must travel, how long it is parked, and when it must be ready. Those three numbers decide charging power per bay. For a van with a long overnight dwell, compare the energy that must be replenished with the vehicle’s accepted charging power and available charging time; AC charging may meet the duty without fast charging. A distribution truck that turns around in two hours needs something very different.
This is where most depot budgets are won or lost. Specifying DC fast charging across a depot that does not need it multiplies the connection size, the distribution equipment and the demand charges, and the vehicles will never use the capability.
Check the grid connection before choosing chargers
The existing supply is the hard constraint. Adding charging capacity that exceeds it triggers an upgrade, and an upgrade has both a cost and a lead time that can be longer than the vehicle procurement. Establishing the available capacity first is what tells you whether the project is a charger installation or a connection project with chargers attached.
Where an upgrade is unavoidable, storage changes the arithmetic. A battery can cover the peak charging window so the connection only has to carry the average, which is often the difference between a manageable upgrade and a major one. That is usually the strongest financial argument for storage on a depot.
Demand charges are often bigger than the energy cost
On commercial tariffs the charge for the highest fifteen-minute demand in the month can exceed the cost of the energy itself, and a depot where every vehicle plugs in on arrival creates exactly the sharp peak that tariff penalises. Two things fix it: staggering the charging, which charge management software does well, and discharging a battery across the peak.
Modelling this properly needs the tariff as well as the load. Bring both and the storage size falls out of the calculation rather than being guessed.
Size the array to the area you have, not to the load
On most depots the roof and the parking area generate less than the fleet consumes, and that is fine. The array is there to reduce the daytime import and to charge the battery, not to cover the whole duty. Trying to close the gap with more modules usually means structural work on a roof that was not designed for it, at a cost per kilowatt-hour well above the saving.
The carport is often the better surface: it adds area without touching the building, it shades the fleet, and the column layout can be set to the bays. Where a depot has both, the roof is usually cheaper per kilowatt and the carport is where the chargers already need to go.
Storage does three separate jobs here
It is worth being clear which of them you are buying, because they size the battery differently:
- Peak shaving — discharge across the charging peak to cut demand charges. Sized in kilowatts and minutes.
- Energy shifting — charge from solar during the day, discharge into the evening charging window. Sized in kilowatt-hours.
- Backup — keep the depot operating through an outage. Sized in hours of critical load, which is a different and usually larger number.
Most depots get the first two from the same battery. The third should be specified explicitly, because it is the one that changes the size.
The distribution board is part of the design
Chargers are large, continuous, and usually added in phases. The distribution board should be specified with spare ways, the capacity for the later phases, and per-way metering if energy cost is allocated per vehicle or per department. Adding a board later, in a live depot, is the expensive version.
Where the depot is adding both storage and charging, a single board with metering for both is usually simpler than two, and it makes the energy flows visible — which is what turns a charging schedule from a guess into something you can tune.
Specifications at a glance
Configuration reference
Swipe horizontally to view all columns →
| Item | Typical specification | What decides it |
|---|---|---|
| Fleet size | From a handful of vans to several hundred vehicles | Number of vehicles, daily mileage and dwell time |
| Charging power | 7 to 22 kW AC per bay, or 60 to 350 kW DC | How long each vehicle is parked and how far it must go |
| Depot load | Commonly 100 kW to several MW of charging capacity | Simultaneous charging and the duty cycle |
| Storage | Typically 100 kWh to several MWh | Peak shaving, demand charge management and backup |
| Grid connection | Existing capacity assessed before charger count is fixed | Available capacity and the upgrade cost and lead time |
| Array size | Set by roof and canopy area, not by the charging load | Usable roof and parking area |
| Charge management | Load balancing across bays, scheduled by departure time | Whether all vehicles must be ready at the same hour |
| Distribution | LV board with per-way metering, or dedicated charger board | How the energy cost is allocated and whether it is sub-metered |
| Compliance documentation | Applicable inverter interconnection documents, storage listings and safety test reports confirmed for the proposed equipment | Utility requirements, destination market and local authority review |
| Documentation | Load study, single-line diagram, charging schedule and commissioning requirements as applicable | Document scope and responsible parties confirmed in the proposal |
| Warranty | Battery 10 years; inverters 10 years; modules up to 30 years performance | Model and order terms |
Figures are selection references. Confirm the final ratings, dimensions, available certifications and warranty against the current datasheet and written proposal for the selected model or system.
Questions buyers ask about depot charging
Do we need DC fast charging?
Long dwell times can make AC charging suitable for some fleets. Compare required energy per vehicle, accepted charging power, departure times and connection capacity. DC charging may be appropriate where the vehicle duty or available dwell time requires it.
How much of the fleet’s energy can solar cover?
It depends on roof and canopy area relative to the duty, and on whether charging happens during the day or overnight. Day-return fleets do much better than night-only fleets, because overnight charging is supplied by storage rather than directly by the array.
What if our connection cannot take it?
Then storage plus charge management is usually the answer, because it lets the connection carry the average rather than the peak. The alternative is a connection upgrade, and the lead time on that is worth checking early.
Can we phase it?
Yes, and it is the sensible approach: duct and spare capacity for the full build now, chargers in phases as the fleet converts. The board and the ducting are the parts that are expensive to add later.
Who handles the utility interconnection?
Confirm the application process and required documents with the serving utility. The proposed interconnection equipment, available listings or test reports and single-line diagram are checked against that utility’s requirements; document scope and responsibilities are confirmed in the proposal.
What to send us
Send the fleet size and daily mileage, when vehicles are parked and when they must be ready, the available roof or parking area, and your existing supply capacity if you know it. We come back with a charging schedule, the storage and array configuration, and a written delivery date.
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Send the available capacity and the dwell time
With your present grid capacity, how long vehicles dwell, and the number of bays, we confirm what can be installed now and what the demand charge exposure looks like.
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