Shore Power for Container Ships: The Reefer-Load Problem

A container ship at berth is not a fixed electrical load. Her hotel and service demand sits under a much larger, shifting draw from the refrigerated boxes stacked on deck and below, and that draw changes with the weather, the cargo mix and the hour of the day. Sizing a shore connection for a boxship is therefore a load-engineering problem before it is a connector problem, and it is one the regulator has put on a clock.

We size and install these systems for a living, and the container fleet is where the two hardest constraints meet: a berth load that resists a single number, and a compliance date that is closer than most owners are treating it. This article works through both, and through the high-voltage scope that turns the answer into installed equipment.

Why are container ships first in line for shore power?

Because the EU has aimed its earliest and firmest at-berth obligation directly at them. Under FuelEU Maritime, from 1 January 2030 containerships above 5,000 gross tonnage must cover their electrical demand at berth from onshore power supply while moored for more than two hours at a TEN-T core maritime port. Container trades also make the best target for the rule: liner services run fixed rotations, call the same terminals week after week, and stack up more berth-hours at Europe's largest ports than any other sector, so the emissions saved per socket installed are high and the scheduling is predictable.

• Fixed liner rotations mean the same vessels call the same equipped berths repeatedly, so an on-board conversion earns its keep quickly
• High call frequency concentrates at-berth auxiliary emissions in port cities, which is precisely what shore power is meant to remove
• TEN-T core ports — the container gateways — are where AFIR obliges the matching shore-side supply to exist by 2030
• Non-compliance is priced: FuelEU sets a penalty for the energy a ship should have taken from shore but did not

Why is a container ship's berth load uniquely hard to size?

Because most of it comes from reefers, and reefer load is peaky, ambient-driven and invisible on the ship's rating plate. A refrigerated container adds on the order of 4 to 5 kW to the ship's demand on average, but a single plug can draw up to roughly 15 kW while it pulls a warm box down to temperature, and dozens of boxes can be in that state at once on a hot afternoon after loading. The number of reefer plugs energised is not a fixed ship characteristic either — it is a property of that particular voyage's cargo. Size the connection to the average and it trips on the peak; size it to the theoretical maximum and you pay for a transformer and cable the vessel will rarely use.

• Per-plug reefer draw swings widely between steady running and pull-down, so the aggregate is a moving peak, not a plateau
• Ambient temperature drives the load — the same box list demands more power in a Gulf summer than a North European winter
• Reefer plug count changes call to call with the booking mix, so historical berth data beats any single design assumption
• Hotel and service load, cargo-gear standby and pump load sit underneath the reefer curve and must be added, not ignored

How much power does a container ship actually need at berth?

Anywhere from a few hundred kilowatts to well over 10 MW, depending on size and reefer count. A small feeder ship may peak around 1 MW alongside; a mid-size vessel sits in the low single-digit megawatts; and a fully laden large boxship with a heavy reefer manifest can require something in the region of 10 to 15 MW. That spread is the whole point: the design figure must come from the vessel's real berth-load profile — measured over representative calls or reconstructed from reefer logs and generator records — rather than from her installed generating capacity, which reflects sea-going margins she never uses at the quay. We treat that survey as the first deliverable, because it sets the transformer, the cable and the breaker, and those three items dominate both the cost and the lead time.

What does the high-voltage connection scope involve?

For a multi-megawatt boxship the connection lands as high-voltage shore connection to IEC/IEEE/ISO 80005-1, typically at 6.6 kV or 11 kV and stepped down on board. The standard sets a practical cable ceiling that shapes the design: one cable serves an HVSC system up to about 3.5 MVA at 6.6 kV, or up to about 6.5 MVA at 11 kV, so a large reefer load pushes you toward 11 kV or toward multiple cables. The on-board scope is a full electrical package, not a socket.

• A shore-connection switchboard and a step-down transformer sized to the measured peak, with cooling and space found on a ship not designed for them
• HV plugs, sockets and couplers to IEC 62613, and a cable management system able to handle tidal range, surge and emergency release under load
• Protection and interlocking that make it impossible to parallel shore supply with running generators outside a controlled synchronisation window
• Earthing and bonding, emergency disconnection, and an alarm and monitoring philosophy documented for class acceptance
• A revised single-line diagram — which makes the whole job a class-approved modification, with approval sitting on the critical path

Why does connection speed matter on a container turnaround?

Because a boxship's berth window is short — often around a day, sometimes less — and every minute spent rigging up is a minute not covered by shore power or a minute lost to cargo operations. Rig-up time is therefore a design input, not an afterthought. Whether the cable is handled from the quay or the ship, how many cables the load demands, and where the connection point sits relative to the terminal's socket all decide whether the crew can make and break the connection inside the operational window. A system that is technically compliant but slow to connect on a tight schedule tends to stay disconnected, which defeats both the regulation and the investment.

Retrofit or newbuild? Staging shore power around the liner schedule

For ships already in service the realistic path is a staged retrofit planned around the rotation, not a single yard visit. Much of the work — cable routing, transformer foundations, switchboard preparation — can be done by a riding crew while the vessel keeps trading, leaving only the heavy lifts, hull penetrations and the final tie-in to the main switchboard for a short dock window. That only holds if the long-lead items, the transformer and any converter above all, are ordered against the dock date rather than the survey date, because that market is where every owner working to 2030 competes at once. We delivered an AMP retrofit on the 4,402 TEU container ship OOCL Montreal at Sefine Shipyard, and that job is the pattern we work to: survey the real load, get the class-approved design moving early, and split the scope so the vessel loses as little service time as the deadline allows.