How to charge electric semi trucks at a depot without a grid upgrade

Electric semi trucks arrive on a truck schedule. Power arrives on a utility schedule. This guide is for the fleet or depot leader who has trucks on order, a utility upgrade in the queue, and a gap between the two measured in years. It walks through sizing, energy sourcing, layout, operations and exit, with sources dated so you can check them.

The gap, in months

Three timelines matter. First-time depot electrification, from plan to energized chargers, typically runs 8 to 18 months according to Oxmaint's 2026 fleet charging infrastructure planning guide. Utility service upgrades alone run 3 to 18+ months, and major grid work 18 to 36 months, per Fleet Rabbit's 2026 infrastructure planning guide. And in 2025–26, grid constraints have become the critical path for fleet electrification rather than vehicle availability, as Charged Fleet reported in 2026.

Put those together and a yard that ordered trucks in 2026 with no service upgrade started should expect its permanent chargers in 2027 or 2028. The trucks will be on the lot long before that.

Step 1: size from energy, not from chargers

Most RFPs start with "how many chargers do we need." Start instead with energy per day, because that determines everything else.

Take a 100-truck regional-haul yard. A loaded Class 8 electric truck uses roughly 2 kWh per mile, so a 175-mile day needs about 350 kWh returned overnight. One hundred trucks need 35,000 kWh a night. If the trucks are back for 10 hours and chargers run at 92% efficiency, required power is 35,000 ÷ 10 ÷ 0.92, or about 3.8 MW.

That single number tells you three things. It is far beyond any low-voltage service. It is a medium-voltage project, which is why it takes years. And it is the number your bridge has to deliver, whatever form the bridge takes.

The site power calculator on this site does this arithmetic with your fleet's numbers.

Step 2: pick dispenser power for the window

Depot DC fast charging today is dominated by dispensers of 150 to 400 kW, with the Megawatt Charging System (MCS) entering corridor deployment, according to Joint Charging's 2026 truck charging trends. Overnight, a 350 kW dispenser returns 350 kWh in a little over an hour. With a 10-hour window that dispenser can serve six to eight trucks in sequence if someone moves cables, or two to three if trucks stay put.

Design for the actual behavior of your yard. Drayage yards where drivers drop and leave suit sequential charging with a yard hostler. Sleeper-cab regional fleets suit one truck per dispenser with lower power. Either way, the number of dispensers follows from sessions per window, not from truck count.

MCS at 1 MW+ per truck matters for daytime turns and corridor stops. The San Bernardino hub reported by Electrek in February 2026 can charge 200 trucks a day with MCS, which shows what megawatt charging does for throughput. For an overnight depot, MCS is a later upgrade, not a day-one requirement.

Step 3: source the energy three ways

A mobile megawatt block is a trailer with battery storage, power electronics and dispensers. The battery is the point: it converts hours into kilowatts. Three sources fill it.

A small existing service. Most yards have some power. A 200 kW service delivers 4,800 kWh over 24 hours, enough for about 13 trucks at 350 kWh. That is not the whole fleet, but it is a meaningful first tranche with zero generation, and it recharges blocks continuously while trucks are out.

On-site generation. Where the service is too small, tiered generation in an enclosure at the edge of the pad tops up storage. Battery-first design keeps generator hours low, which keeps air permits simpler and noise away from drivers. Emissions tier and fuel are stated per site in a Site Power Plan.

Scheduled energy delivery. For sites with no service and no permit path, charged blocks are swapped or topped up on a schedule. It is the least elegant option and sometimes the only one.

Which mix fits your site is the first output of a Site Power Plan.

Step 4: lay out for trucks, not cars

Class 8 tractors need drive-through lanes, no reversing, and cable management that reaches either side of the cab. Blocks sit at lane heads on a level pad with trailer access. Dispenser lanes are 12 to 14 feet wide with overhead or boom cable management. Plan for yard tractors and the occasional bobtail day cab in the same lanes.

Two things procurement teams forget. First, fire access lanes must remain clear around battery equipment. Second, blocks need a place to go when the permanent chargers arrive, so keep the pad away from where the switchgear will be built.

Step 5: operate it like infrastructure

A bridge that fails is worse than no bridge, because the trucks are now on the road. Require the same operating terms you would demand from a permanent installation. Procurement guidance in 2026 calls for monthly per-charger uptime of 97 to 99% with penalties, treats mean time to repair as the metric that matters, and requires OCPP and ISO 15118 support, per Charged Fleet's reliability feature and Evaisun's EV charger RFP checklist, both 2026.

Ask for a 24/7 network operations center, a named escalation contact, session telemetry into your fleet system, and a credit schedule you do not have to claim. Our SLA is published so you can compare.

Step 6: plan the exit on day one

The mobile deployment exists to bridge the utility project, not to replace it. Keep the service application moving. When the permanent chargers energize, blocks relocate. Some fleets keep one as backup for outages and overflow; most send them to the next yard. A contract that has no penalty when your utility service lands after month 12 is the right structure. See pricing terms.

What it costs to wait

The cost of the gap is the cost of trucks doing nothing. For a 30-van fleet, Evaisun's 2026 RFP checklist puts downtime at roughly $800 to $1,500 an hour. Class 8 tractors with drivers and freight commitments run higher per hour. Whatever your number, multiply by idle hours and by the months in the utility timeline above. The downtime calculator turns that into a weekly figure.

Checklist for the RFP

• Daily energy per truck and charge window, stated in kWh and hours
• Required kW at the site, with efficiency assumption
• Dispenser count from sessions per window, not truck count
• Connector mix today (CCS1, NACS) and MCS timing
• Energy source options and emissions tier per site
• Uptime, response and MTTR commitments with credits
• OCPP 2.0.1 and ISO 15118 support
• Exit terms when utility service is energized

A yard that answers those eight items can be charging trucks in days rather than in 2028. The Site Power Plan answers them for your site in 48 hours.

Common mistakes in the first 90 days

Sizing to the charger catalog. Fleets buy the dispenser count a vendor suggests and discover the yard's window cannot use it. Sessions per window is the number; dispensers follow.

Ignoring the return profile. A yard where all trucks return between 6 and 8 p.m. has a very different peak than one with staggered returns. Log return times for two weeks before sizing; the difference can be a whole block.

Treating the bridge as a pilot. A short pilot is the right way to start, but the operating terms should be production terms from day one. Trucks will depend on the bridge the week it goes live.

Parking the utility project. The bridge is not a substitute. The cheapest kWh a yard will ever buy is from the utility; keep the application moving and use the bridge to stop paying for idle trucks.

Forgetting the hostler. Sequential charging with cable moves needs a person on the yard at night. If that person does not exist, design for one truck per dispenser at lower power and more dispensers.

A worked example

Take a 60-truck drayage fleet with 500 kWh packs doing two port turns a day, returning around 300 kWh per truck each night over an 8-hour window. Daily energy is 18,000 kWh. Required power is 18,000 ÷ 8 ÷ 0.92, or about 2.4 MW. With 350 kW dispensers and a hostler moving cables, each dispenser can serve roughly six trucks a night, so 10 to 12 dispensers cover the fleet with headroom. That resolves to three 1 MW+ blocks on a shared DC bus, recharged during the day from a 500 kW service plus enclosed generation to cover the shortfall, with an MCS dispenser reserved for the first MCS-inlet trucks. Days to first charge from a signed plan is stated in the plan; the utility project continues in parallel. When the medium-voltage service lands, two blocks leave and one stays for outages.