Hamburg Alsterdorf Depot — Finding the Real Peak Behind a 127-Bus Fleet

The Problem

Hamburg's Hochbahn transit authority faced the question every large transit agency eventually faces: when 127 buses all return to the depot in the evening and need to recharge before the next morning's service, what does the depot actually draw at its peak — and can the electrical service handle it?

Get the answer wrong in one direction and you've over-built a multi-million-dollar grid connection nobody needed. Get it wrong in the other direction and buses don't leave the depot on time.

The naive answer — "127 buses × 150 kW chargers = 19 MW, so build for 19 MW" — is almost never the right one. It assumes every bus plugs in and charges flat-out the instant it arrives. Real depots don't work that way: buses trickle in across the evening, some need more energy than others, and a competent charge management system spreads that load out. The question isn't "what's the nameplate sum" — it's "what does managed charging actually require, and where does it bind?"

How the Depot Digital Twin Was Used

Step 1 — Model the real fleet, not a simplification. The full 127-bus fleet was entered with its real battery capacity, dwell windows, and arrival pattern — each bus assigned its own arrival and departure time across the evening and overnight window, exactly as the depot actually operates. This single step is what separates a useful peak estimate from a back-of-envelope guess: stagger the arrivals, and the peak tells the truth.

Step 2 — Let the engine find the binding constraint. Rather than asking "will 20 MW of service be enough," the simulation was run against the depot's actual worst-plausible winter day — full cold-weather derate, every vehicle present, charging managed to stay under the service limit wherever the electrical topology allows it.

Step 3 — Read the spare-capacity breakdown. The results page doesn't just report a peak number — it walks the full chain from nameplate service capacity, through any reserved base-load, to the modeled charging peak, to what's left over:

Step 4 — Visualize the 24-hour load profile. The interactive timeline chart shows exactly how the 4,538 kW peak builds and recedes across the night, with a scrubbable playhead that reads out net load, headroom, and per-node utilization at any instant — turning a single peak number into a story a utility reviewer or capital committee can actually follow.

Step 5 — Check every electrical node, not just the headline number. The per-node view confirms that neither the service entry nor the downstream circuit is breached at any point in the simulated day — with margin. Nothing in the depot's electrical chain is close to its rating.

Step 6 — Benchmark against the industry, automatically. The results page surfaces published reference bands from real transit electrification studies alongside the depot's own numbers — in this case, a real-world managed-charging study (Clovis Transit) showing a ~40% peak reduction from smart scheduling, giving the depot operator immediate external context for what "good" looks like.

The Result

The Depot Digital Twin modeled Hamburg Alsterdorf's managed-charging peak at 4,538 kW — landing within striking distance of the peer-reviewed academic benchmark for this exact depot (Jahić, Eskander & Schulz, 2019), which reports a managed peak of 5.47 MW under equivalent winter conditions.

That means a 20 MW service connection carries this fleet with more than 3× headroom to spare — a clear, defensible answer to the only question that actually matters at the capital-planning stage: is the grid connection big enough, and by how much?