Emissions alongside are unusual in two ways: they are concentrated in populated areas, and they come from auxiliary engines running at part load, which is where marine diesels are least efficient and dirtiest per kilowatt-hour. That combination is why at-berth emissions attract local air-quality regulation as well as carbon regulation, and why several different technologies are competing to address them.
Shore power
Connecting to the quay removes the on-board combustion entirely for the duration of the stay: no NOx, no SOx, no particulates and no noise at the berth. That local elimination is total, which no other option matches. The carbon result, however, is a transfer rather than a deletion — the emissions move to whatever generates the electricity ashore. The capital cost sits mostly on the ship, and the operating economics depend on the spread between shore tariff and marine fuel plus allowances.
Battery hybrid and peak shaving
An energy storage system lets the auxiliaries run at a steady, efficient load instead of chasing peaks, and can cover short stays without running an engine at all. It reduces fuel burn and running hours across the whole operating profile, not just alongside, which is its main advantage over shore power. It does not eliminate emissions at berth for a long stay, and it brings its own class, fire safety and space constraints.
Alternative fuels on the auxiliaries
Running the gensets on LNG, methanol or a biofuel blend reduces emissions without depending on port infrastructure — a real advantage for vessels whose berths will never be equipped. The reduction is partial rather than total, particulates and NOx improve but do not disappear, and the fuel has to be available where the vessel actually trades. For biofuel blends in particular, compatibility with the existing fuel system needs checking rather than assuming.
Shore power is only as clean as the grid behind it
It is worth being honest about this. In a port drawing on a largely renewable or nuclear grid, shore power is close to a genuine elimination of the vessel's berth emissions. On a coal-heavy grid, the carbon benefit narrows considerably, even though the local air-quality benefit remains complete. Owners comparing options across a trading pattern that spans both should expect the answer to differ port by port.
How owners are actually choosing
In practice the decision is driven less by carbon accounting than by three practical questions: how long the vessel sits alongside, whether her berths will be equipped, and when the next dock window is. Long stays at equipped terminals point clearly to shore power. Short stays across many small ports point to storage or fuel measures. Most owners we work with end up with a combination, phased across two dockings rather than attempted in one.
- Long stays at equipped terminals — shore power gives the largest and most defensible reduction
- Many short calls at unequipped berths — storage or alternative fuel on the auxiliaries does more
- Mixed trade — size the shore connection for the berths that will have it, and cover the rest another way
- Whatever the choice, get the at-berth load measured first; every option is sized from it