Powering cleaner, smarter vessels at sea
Batteries, Battery Energy Storage System (BESS), are transforming how ships are designed and operated. They do not always replace fuel entirely, but they enable vessels to run cleaner, quieter, and more efficiently. Depending on the vessel type and operating profile, batteries can be used in different ways:
Fully electric propulsion
For short-distance routes with frequent trips - like ferries or harbour boats - batteries can power the vessel entirely, with no emissions during operations.
Hybrid systems
Batteries work alongside diesel engines to reduce fuel use, lower emissions, and smooth out power demands (called “peak shaving”). They can also serve alongside fuel cells or as a backup power source (“spinning reserve”) and help maintain power when engines are not running. Some hybrid solutions are designed to provide full electric propulsion for short duration e.g. green transition in and out of harbour or as a zero-emission port stay.
Redundancy and emergency power
Batteries can provide an extra layer of safety by offering backup power during system failures or blackouts.
What affects battery performance?
To choose the right battery system, shipowners must understand a few key technical terms:
C-rate
How fast a battery can be charged or discharged. High C-rate batteries respond quickly to sudden power demands - useful for hybrid systems with small capacity but high charge or discharge requirements. Low C-rate batteries can provide other benefits such as lower weight or price – useful for systems where a large capacity is required compared to the charge or discharge requirements.
State of Charge (SoC) and Depth of Discharge (DoD)
SoC represents the available charge at a given moment in percent, DoD represents the charge used at a given moment or over time in percent. The sum of SoC and DoD is 100% and a battery with 30% SoC will have a DoD of 70%. Deeper discharges can shorten battery life if not managed properly. Most batteries will never reach the extremities of 100% SoC or 100% DoD.
State of health (SoH)
Indicates how much the battery has aged and how the maximum capacity has been reduced compared to when the battery was newly installed, which is an important dimensioning factor considering the expected lifetime for the batteries.
Weight and volume
Batteries are heavy and take up space. Their size and weight impact ship stability and layout, so early planning is important. Class and Flagstate selection can add further requirements to the location and safety of the battery installation.
Charging strategy
How and when a ship is charged depends on power requirements, shore power availability, turnaround times in port, and local grid capacity.
Case Study
Assumptions for case study
Allowed ΔSoC is assumed to be 70%.
SoH at the battery installations end of life is assumed to be 78%.
The continuous c-rate for charging is the same as for discharging and this example only include continuous ratings, not time depended max ratings.
BESS size depending on C-rate and charge/discharge requirements
Assumed consumption is 5000 kWh.
The charging requirements varies between 5,000 kW and 25,000 kW and the required battery pack is found for four different c-rates.
In this case study low c-rates can result in larger battery packs and will in some cases be the dimensioning factor for the battery size. Looking at the charge/discharge requirement of 15,000 kW, the batteries with c-rate 0.5 and 1 will be dimensioned based on charge/discharge requirement, but the batteries with c-rate 2 and 3 is dimensioned based on the total consumption of 5000 kWh.
Choosing the right battery
Every vessel is unique. We evaluate your specific requirements, recommend the most suitable battery solution, and support you from initial feasibility to final selection.
Get in touch for a customized battery assessment.
Contact Jeppe Elgaard Jensen, Head of Energy, at jej@oskdesign.com
