Peak shaving and other hybrid ways to use batteries on a vessel

Many shipowners have already begun adapting and upgrading their fleets to mitigate the costs associated with inaction. This includes targeting zero-emission operation during port entry, maneuvering, and positioning, as well as improving the efficiency of existing propulsion and power generation systems.

Regulatory ambitions vary between governing bodies, but the overall direction is clear. From 2023 onwards, frameworks such as ETD and ETS began to take effect, with regulatory pressure increasing toward the first major milestone in 2030, when the EU aims to achieve a 55 percent reduction in CO₂ emissions.

How to use batteries on a vessel

Meeting these regulatory requirements will require the adoption of multiple technologies and operational strategies. The most impactful measures are typically related to reducing energy consumption and fuel use. In the ideal scenario of full electrification, battery systems can enable a 100 percent reduction in CO₂ emissions.

For many larger vessels, however, full electric propulsion is not a practical solution. Instead, batteries can be integrated into hybrid power systems, where they serve multiple roles to improve efficiency and reduce fuel consumption.

The most common applications for batteries in hybrid vessel configurations include:

• Spinning reserve

• Peak shaving

• Energy harvesting

• Backup power (UPS)

Spinning reserve

Large vessels typically operate with multiple generators running simultaneously to ensure redundancy in case of failure. From an efficiency perspective, this approach is suboptimal. A spinning reserve strategy allows vessels to operate with fewer generators online, while batteries provide additional load capacity and redundancy.

By enabling generators to operate closer to their optimal rated load, overall fuel consumption is reduced. In this configuration, batteries act as backup for onboard generators and help maintain uninterrupted vessel operation.

Peak shaving

Battery systems can also be used for peak shaving by supplying immediate power during short-duration load peaks. Combustion engines generally operate most efficiently at steady load levels, and frequent peaks and load variations reduce efficiency.

Batteries, by contrast, can respond rapidly to load changes and deliver high peak power without efficiency penalties. By smoothing load profiles, peak shaving improves overall system efficiency and reduces fuel consumption.

Energy harvesting

Energy harvesting refers to using the battery system as an energy recovery unit. Certain onboard operations consume significant power in one phase while releasing energy in another.

A common example is crane operation: energy is consumed when lifting loads and released when lowering them. By coupling such systems to a battery, released energy can be recovered, stored, and reused for subsequent operations, improving overall energy efficiency.

Backup power (UPS)

In addition to load optimization and peak power delivery, batteries can serve as backup power sources. In maritime applications, immediate access to emergency power is essential to maintain safety and operational stability.

Battery-based UPS solutions provide fast-response energy that can prevent blackouts and ensure continuity of critical systems.

What can be saved?

Spinning reserve, peak shaving, energy harvesting, and backup power represent four key applications for batteries onboard vessels. The expected benefits can be evaluated from two perspectives: fuel savings and financial return.

The impact varies by vessel type and operational profile, as battery systems fulfill different roles depending on application.

As an example, vessels using batteries primarily for peak shaving can typically achieve fuel savings in the range of 5 to 20 percent, with payback periods often between two and five years.

These figures are dynamic and are based on historically lower carbon pricing. Increases in the cost of carbon emissions have not been fully accounted for. As carbon costs rise, return on investment is likely to improve further, shortening payback periods.

How to use batteries on a vessel?

To meet these requirements a plethora of methods and technologies will have to be used, where the most impactful is intuitively on the energy and fuel consumption side. This is where in the best-case scenario of full electrification with batteries can achieve a 100 percent well-to-wake reduction in CO2-emissions.