# EV Fleet Charging and the Demand Charge > The energy to charge a fleet is predictable. The demand charge it creates depends almost entirely on when the vans plug in and whether anything limits how fast they all draw at once. Section: Demand Charges Author: Nil Masferrer Jiménez Published: 2026-09-24 Reading time: 4 min Charging a fleet has two costs, and they behave nothing alike. The energy cost follows the miles driven: so many kilowatt-hours per van per day, bought at whatever the energy rate is. The demand cost follows something else entirely — how many vehicles draw power in the same fifteen minutes. That second cost is the one that surprises people, because the vehicles do not change and the miles do not change. Only the timing does. The Alternative Fuels Data Center says it directly: DC fast charging equipment is more likely to trigger demand charges than Level 1 and Level 2 charging. The worked example below shows why, and why even slow charging can do it if every van plugs in at once. ## The site A depot with a daytime building load. The fleet returns in the evening. **Starting point** Before any chargers are installed. - Building peak, mid-afternoon: 420 kW - Building load, 6 pm to 5 am: 150 kW falling to 80 kW - Demand charge, facility maximum: $15.00 / kW-month - **Monthly demand charge today: $6,300** *The afternoon sets billed demand. The evening and night sit well below it — which is capacity already paid for. Rates illustrative.* The fleet: 20 vans, each needing about 60 kWh a night, parked from 6 pm to 5 am. Twenty Level 2 chargers at 19.2 kW each. ## Case 1: everyone plugs in at six With no control, every charger draws its full rating from the moment the vans arrive. **Unmanaged evening charging** All twenty chargers start together. - Chargers × rating: 20 × 19.2 kW: 384 kW - Building load at 6 pm: 150 kW - (New facility maximum): 534 kW - Increase over the afternoon peak: 114 kW - **Added demand charge per month: $1,710** *The chargers finish in a little over three hours and then sit idle for eight. The demand charge is priced on those first fifteen minutes. Figures illustrative.* The energy is the same as it would be under any schedule. The $1,710 is purely the price of doing it all at once. ## Case 2: the same energy, spread across the night The fleet needs 20 × 60 = 1,200 kWh, and it is parked for eleven hours. That is an average of about 109 kW. **Managed charging with a power ceiling** Combined draw capped at 150 kW. - Energy required per night: 1,200 kWh - Hours available: 11 - (Average power needed): 109 kW - Ceiling set on the chargers as a group: 150 kW - Building load at 6 pm plus the ceiling: 300 kW - Afternoon peak, unchanged: 420 kW - **Added demand charge per month: $0** *The ceiling leaves headroom for late arrivals and a colder night. The fleet charges entirely inside capacity the site already pays for. Figures illustrative.* This is what the Federal Energy Management Program describes as smart charge management: adjusting charging power or shifting sessions, and enforcing a power ceiling across multiple chargers. The mechanism is the same one described in [demand limiting controls](https://thedemandcharge.com/articles/demand-limiting-controls), applied to a load that is unusually easy to move, because a parked van does not care when its battery fills. ![The area under both curves is similar; the height is not. A demand charge prices the height.](https://thedemandcharge.com/assets/img/diagrams/peak-shave.svg) *The area under both curves is similar; the height is not. A demand charge prices the height.* ## Case 3: two fast chargers at lunchtime Now add two 150 kW DC fast chargers for midday top-ups, used by a few vans around 1 pm — the hour the building peaks. **Midday fast charging** Two DC fast chargers used during the building peak. - Building peak: 420 kW - Two fast chargers at full output: 300 kW - (New facility maximum): 720 kW - Increase in billed demand: 300 kW - (Added demand charge per month): $4,500 - Energy delivered: 2 sessions × 40 kWh × 22 days: 1,760 kWh - **Demand cost per kWh delivered: $2.56** *On top of the energy rate. A few sessions in the wrong fifteen minutes turn fast charging into the most expensive energy on the site. Figures illustrative.* The point is not that fast chargers are a mistake. It is that their demand cost has to be priced before they are bought. One session inside the peak interval is enough to set the month, as [the fifteen-minute demand interval](https://thedemandcharge.com/articles/demand-interval-15-minutes) explains, and under a ratchet it can set a floor on the months after it too — see [ratchet clauses](https://thedemandcharge.com/articles/ratchet-clause-explained). ## The separate-meter question The Alternative Fuels Data Center notes that some utilities offer time-of-use rates or other incentives for charging infrastructure, and a separate meter is often the way onto them. It is worth modeling, and it is worth modeling both ways. On a separate meter, the chargers get their own peak. Unmanaged, the twenty Level 2 chargers in Case 1 would bill 384 kW on their own account: 384 × $15.00 = $5,760 a month, against the $1,710 they added when their load sat partly inside the building's headroom. A dedicated account only wins if its rate structure is genuinely better for charging — lower or no demand charges, or time-of-use energy pricing that rewards overnight charging — and if charging is managed either way. [Time-of-use rates](https://thedemandcharge.com/articles/time-of-use-rates-commercial) covers how those windows are set. ## What to do before the chargers arrive **Pricing a fleet's demand cost** 1. **Pull interval data for the site** and find the headroom: the gap between the monthly peak and the load in each hour the fleet will be parked. 2. **Size the energy, then the power.** Kilowatt-hours per night divided by hours parked gives the average power the fleet actually needs. 3. **Specify managed charging in the purchase,** with a site-level power ceiling, not as a later upgrade. 4. **Price fast charging separately,** at the hours it will really be used, including its effect on any ratchet. 5. **Ask the utility about charging rates and metering** before choosing where the chargers connect, as the Alternative Fuels Data Center advises for fleet planning. The fleet's energy is set by its routes. Its demand charge is a choice made when the charging system is specified, and it is far cheaper to make that choice before the first van comes home. ## Sources - [AFDC — Operation and maintenance for EV charging infrastructure](https://afdc.energy.gov/fuels/electricity-infrastructure-maintenance-and-operation) - [AFDC — Electric vehicles for fleets](https://afdc.energy.gov/vehicles/electric-fleets) - [DOE FEMP — Managed EV charging for federal fleets](https://www.energy.gov/cmei/femp/managed-ev-charging-federal-fleets) - [National Laboratory of the Rockies (formerly NREL) — Transportation](https://www.nlr.gov/transportation/) ## Frequently asked questions ### Will adding EV chargers always raise my demand charge? No. They raise it only if charging adds load during the interval that sets billed demand, or creates a new, higher interval. A depot that charges overnight under a power limit can add a great deal of energy and no billed demand at all. ### Is a separate meter for the chargers a good idea? Only if the rate on that meter is better for charging. A dedicated meter gives the chargers their own peak, and unmanaged charging on its own meter can produce a larger demand charge than the same load hidden under the building's daytime peak. ### Why is DC fast charging singled out? Because a single DC fast charger can draw as much as a small building in one interval. The Alternative Fuels Data Center notes it is more likely to trigger demand charges than Level 1 and Level 2 charging. ### What does managed charging actually do? It schedules sessions and sets a ceiling on the combined draw of the chargers, spreading the energy the fleet needs across the hours it is parked instead of delivering it all at once. ### Does a ratchet make this worse? Yes. Under a ratchet, a single unmanaged evening can set a floor on billed demand for months afterward, so one bad night costs far more than one month's charge. --- Canonical URL: https://thedemandcharge.com/articles/ev-fleet-charging-demand-charges Site index for agents: https://thedemandcharge.com/llms.txt