The project has selected a Houlder designed harbour ferry as the most suitable vessel to be studied for further evaluation due to its short crossings and subsequent low energy usage, coupled with regular charging opportunities during its daily operation.

Naval Architects and project partner, Houlder undertook an initial feasibility design study to look at a range of vessels to understand their technical suitability to use a flow battery in power generation for either propulsion or auxiliary loads. 15 vessels from small river passenger vessels up to coastal tankers were evaluated to give a cross-section of the type of vessels currently operating around the UK coast, whose service characteristics could viably integrate the advantages of a flow battery.

The requirement for regular replenishment of the flow battery was an important consideration which led the team to identify three, out of the fifteen vessels, for further investigation. Two of the vessels selected were ferries; one a 74m Ro/Ro freight ferry, the other a 32m harbour passenger ferry and the third vessel a product tanker.

Existing battery powered vessels all currently use lithium chemistry batteries which require substantial shore-side infrastructure. Recent developments have made flow battery technology suitable for marine applications and they have the added advantage of offering much faster charging in port, coupled with cost-effective, high-capacity storage. Project partner Swanbarton, specialists in energy storage and control technologies, reviewed a number of existing electric vessels in Europe and China as well as existing technology in flow batteries, and have held discussions with specific technology companies. Based on the research, Swanbarton specified the most suitable battery option for each of the vessels selected by Houlder, based on the power utilisation requirements. Their findings suggest a hybrid power system of bespoke flow battery and capacitors would be most suitable for the Houlder designed harbour ferry selected, whilst a bespoke flow battery would be required for the freight Ro/Ro ship and product tanker.

The classification society Lloyd’s Register will now use their Approval in Principal methodology to conduct risk assessment and certification requirements and to identify any potential hazards in the design and operations of this emerging technology.

David Wing, Director Ship Design & Engineering, Houlder, commented “We see the market for flow batteries as a source of power being similar to the current areas in which Li-ion batteries are currently being deployed for all-electric propulsion. The flow battery offers advantages where the driving requirement for sizing the battery is energy storage and high numbers of charge/discharge cycles rather than peak power delivery. This, combined with the capability to trickle-charge a shore-based electrolyte storage and quickly replenish the ship’s battery by exchange of electrolyte fluids, means it is well suited to a typical passenger/commuter ferry having peak demands at the morning and evening rush-hour. A typical UK harbour ferry has been selected as a case study for further design assessment.”

Anthony Price, Director of Swanbarton, said “Flow batteries in stationary applications are supporting the drive towards net zero carbon electricity generation and use. This study shows the potential for flow batteries in other applications, including the transition to zero emission shipping.“

Marine South East, is project managing the project which will present its final assessment in early 2021.