What is the difference between low- and high-voltage systems?
Low-voltage systems use multiple cables, making it more labour-intensive to hook vessels up to the grid. The position of the voltage transformer may also differ, depending on the system, being located on the quay or on the vessel itself. At some ports a crane is used to take the cables to the ship. At the Port of Los Angeles, with the best known low-voltage system, the transformer was set up on a work barge. This system is not used anymore, however. Most of the systems currently in use are high-voltage; see the section on ports using OPS. The main reason for this is that most ships can be connected using 1 or 2 high-voltage cables on a reel rather than 15 to 30 low-voltage lines.

What is the cost for the port?
The cost of supplying high-voltage electricity to the port and then to the berth can differ significantly from one port to another. This is mainly because of variations in the distance to the nearest high-voltage supply and, more importantly, the number of substations/connections that require upgrading. Other costs that vary include the need for additional overhead electricity lines, poles and underground cables. In addition, the cost of retrofitting cables into an existing terminal is usually significantly higher than installing cables in a new-build terminal.

How much power is needed for an average stopover in a terminal?
Power requirements depend very much on the type of vessel and the time at berth. According to available information, cruise vessels require up to 16 MVA, container vessels up to 6.5 MVA and ferries and RoRo vessels up to 3 MVA load. Energy consumption is calculated by multiplying the vessels power consumption (MW) with the total time (hours) of consumption.

Who benefits most from the implementation of OPS?
Apart from achieving a much better working environment onboard and in the port, the environmental benefits are the great driving force. Studies show that society is the big winner. This means OPS can help ports demonstrate they are local environmental leaders and responsible citizens whose activities take place for the benefit of local communities. This helps counter any perceptions of the port as a “dirty neighbour” and can provide a platform for the port to intensify both its environmental activities and its cooperation with the local communities. Putting environmental interests at the heart of port activities affirms a port’s place at the heart of its community – a “win-win” scenario for all concerned.

Pros and Cons
There are several advantages and disadvantages of using OPS.

  • Major reductions in local emissions (air pollutants and greenhouse gases).
  • Reductions in noise levels (improves working and living conditions).
  • Reductions in vibration levels (improves working and living conditions).
  • Improvement in license to operate and company image.


  • The emission reductions are only achieved when a ship is at berth.
  • Electrical frequencies differ between regions.
  • Different systems have and are being installed.
  • Implementation of OPS requires large investments on the quay and on the ship.

More detailed information on the pros and cons can be found in Environment & Health section and in the C40 WPCI guidance document.