How a Bus Depot Cut Peak-Charge Costs by 28% with a 240–720kW DC Flexible Charging Pile

Customer Background

A municipal transit operator in the Rhine-Ruhr region manages a fleet of 42 battery-electric buses and covers roughly 120,000 kilometers of scheduled service each month. The fleet is based at a single depot built in 2019, where 30 fixed 120 kW DC chargers were installed to support overnight and opportunity charging.

The operator's core mandate: keep the buses on the road for a minimum of 16 hours per day, including the morning and afternoon peak periods. That meant charging windows between service blocks were as short as 45 minutes. The existing fixed-charger layout was proving too rigid for these operational constraints.

The Challenge: Fixed Power, Fixed Rates, and Idle Chargers

Each fixed 120 kW charger was assigned to a single bus. When buses returned in waves after morning and evening service, many chargers sat idle while a queue formed at the active ones. A bus with 40% state of charge still needed 1.5 hours on a 120 kW charger—too long for the 45-minute layover.

Because the depot's grid connection was limited to 600 kW of simultaneous load, bringing more power to the yard would have required a new transformer and a lengthy permit process, with an estimated cost of $180,000. In the meantime, the operator tried two workarounds:

• Manually scheduling buses to avoid competing for power, which delayed departure times and reduced on-time performance.
• Programming the existing chargers to limit output during peak demand, but that only extended charge times and left buses undercharged for the next block.

The direct consequence was a growing pile of operational friction: queueing, missed departures, and monthly demand charges that consistently reached $24,000. The team needed a charging architecture that could adapt power allocation in real time to where it was needed, not a set of fixed outputs.

Why the 240–720kW DC Flexible Charging Pile

The operator evaluated two alternatives before settling on the Soutya 240–720 kW DC Flexible Charging Pile.

The first alternative was adding a second transformer and deploying more fixed 120 kW chargers. That approach would eliminate queueing but would still leave many chargers idle during the middle of the day, and the grid upgrade alone would eat the entire annual energy budget.

The second alternative was a central high-power charger with a mechanical switch matrix that could connect one bus at a time. It solved the power-sharing problem but created a new bottleneck: a single outage on the switch system would halt the entire depot.

The Soutya flexible charging pile stood out for three reasons:

• Dynamic power allocation: A single 600 kW unit can split its output across six to eight charging points, giving each bus only the power it needs at the moment. The allocation updates in real time without manual intervention.
• Modular scalability: The pile is built from interchangeable power modules. If the fleet grows, the operator can add modules without replacing the whole unit.
• No grid upgrade required: Because the pile can enforce a configurable maximum total load, it fits within the existing 600 kW grid connection, avoiding the $180,000 transformer project.

Implementation: Phased Deployment and Dynamic Load Management

The project was completed over six weeks, from contract signing to full operation. The implementation had four steps:

1. Site survey and layout mapping. The team mapped bus parking positions, cable routes, and the existing switchboard capacity to determine the optimal number of charging outlets per pile.
2. Installation of four 600 kW piles, each configured with eight connectors for a total of 32 charging points. The piles were placed between the parking rows to minimize cable lengths and losses.
3. Integration with the depot management system. The pile's power allocation was linked to the vehicle scheduling database so that buses with earlier departure times received priority power.
4. Staff training. Charge operators were trained on reading the power allocation graphs and on what to do in the rare case of a connection error.

A key challenge surfaced during week two. The depot's existing electrical room could not accommodate the extra surge protection and metering equipment required for the new piles without a small reconfiguration. The issue was solved by installing a compact sub-distribution board and moving the backup electrical loads to a different phase—a minor civil work that added four days to the schedule.

Quantifiable Results: Faster Turnarounds, Lower Demand Fees, Fewer Queues

The operational data from the first three months of running on the Soutya flexible charging piles showed measurable improvements across the board.

• Charging time per bus dropped by 38%. The average for a 200 kWh battery fell from 4.5 hours to 2.2 hours, because the pile could concentrate 240 kW on a single bus when the parking lot was half empty.
• Peak demand charges decreased by 28%, from $24,000 to $17,300 per month. The pile's load-limiting algorithm kept the depot's total draw below the 600 kW threshold even when 20 buses were charging simultaneously.
• Charging utilization rose from 47% to 78%. Because power is flexibly routed, a bus arriving at 2:00 pm can charge at full power while a bus scheduled to depart at 6:00 pm waits its turn.
• The $180,000 grid upgrade was avoided. The project cost, including the four piles and installation, came to roughly $96,000, meaning the payback period was over one year based on demand-charge savings alone.

The wider impact was visible in schedule adherence: the number of buses leaving the depot with less than 90% state of charge fell from 12 to 2 per week, and the fleet's on-time departure rate improved from 92% to 98%.

Client Testimonial

The depot's operations manager put it in simple terms:

"The flexible pile doesn't deliver a faster charge; it gives us back control over our schedule. I no longer have to decide which bus gets to charge first. The power goes where it's needed, and that has changed the way our entire shift plans."

Another maintenance supervisor added: "The modular design means we can upgrade capacity without ripping out the existing installation. That was not possible with our old fixed units."

Lessons for Other Fleet and Charging Operators

Three replicable lessons emerged from this project:

1. Match the pile configuration to actual bus schedules, not maximum power. The depot considered a 720 kW model, but the 600 kW units with 32 outlets fit the bus rotation better and cost less. Understanding the peak overlap of return times is more valuable than buying the largest possible unit.
2. Use the power allocation algorithm from day one. The factory default is set for a generic scenario. The depot's performance improved only after they configured the allocation priorities to match departure times and battery state of charge.
3. Plan for fleet growth by choosing a modular unit. If the operator adds another 10 buses, they can insert additional power modules into the existing piles. A fixed charger would require a whole new installation and another grid connection.

The biggest surprise for the team was how the change in charging behavior affected their overall operations. The shift from a fixed power model to a demand-driven one saved money, improved on-time performance, and eliminated a daily source of staff stress.

References

For operators evaluating DC flexible charging piles, the following industry standards provide useful context on safety and performance:

• EN 50620:2017 – Electric cables for charging of electric vehicles, defining cable flexibility, weather resistance, and voltage requirements for 0.6/1 kV DC systems.
• IEC 62196 Series – Plugs, socket-outlets, and vehicle connectors for conductive charging of electric vehicles, covering both AC and DC interface requirements (including CCS and CHAdeMO).
• UL 1699B – Photovoltaic (PV) DC Arc-Fault Circuit Protection, a reference for DC arc-fault detection methods used in high-power DC charging systems.