Didier Jouffroy, Saft’s marine product manager, explores the potential for lithium-ion battery systems in electric and hybrid-electric propulsion systems.

Since they were ratified in 2008, air-quality regulations brought in by the International Maritime Organization (IMO) have been taking effect in stages. Designed to reduce emissions of CO2, NOX and SO2 in shipping, the regulations have been getting tighter, with the next milestone coming at the start of 2015.

Ultimately, the aim of the regulations is to reduce greenhouse gas emissions from ships by 30% by 2025. Therefore, there is a growing interest from operators in introducing electric propulsion, with battery systems enabling diesel engines and gensets to be switched off for at least part of the day. In fact, after adopting electric propulsion, some ferry operators have reported fuel savings of 20-50%, demonstrating that battery systems can contribute not just improved environmental performance but also financial savings.

To meet this fast-growing demand, Saft has recently introduced the new Seanergy range of lithium-ion (Li-ion) batteries developed especially for the electric and hybrid-electric propulsion sector. Thanks to its modular approach, Seanergy offers flexibility to create the ideal system to meet the specific needs of a particular vessel in terms of high power performance and energy-storage capacity.

A field-proven solution

Li-ion battery systems supplied by Saft are already delivering fuel savings and low-emission operation for several operators.

These include a brand new electric ferry run by Ballerina in the city of Stockholm. Its 500kWh, 650V battery system is fully charged overnight, with two shorter charging periods during the day. In service under battery power, it completes eight circuits of a 50-minute route around the waterways of Stockholm each day.

Another example is Icade’s electric-powered passenger vessel on Paris’s Saint-Denis canal operated by Vedettes de Paris, which runs for 12 hours a day on the energy stored in its 140kWh battery system. The battery is charged overnight and powers around 30 return trips a day, equivalent to 16,000km a year, all with zero CO2 and NOX emissions.

Elsewhere, two hybrid diesel-electric ferries are being operated by Keolis on the Garonne river in Bordeaux with Saft Li-ion battery systems. The shuttles carry around 200,000 passengers a year, and the 140kWh battery systems work in conjunction with the boats’ diesel engines, providing up to six hours of autonomous electric propulsion each day as well as additional propulsion power to help the ferries navigate in the Garonne’s strong flows.

The operators of all three of these examples aimed to achieve low-emission transport as well as significant fuel savings, and the electric propulsion gives the added benefit of quiet operation when needed.

Similar Li-ion batteries have been used elsewhere in the marine sector in the rubber-tyred gantry (RTG) cranes that load ships in the port of Houston, Texas, US. Diesel-electric hybrid power systems built by MJ EcoPower Hybrid Systems have enabled significant fuel savings compared with purely diesel-powered cranes. Integrating a battery has stabilised the load on the engine, meaning it can operate at its maximum efficiency. The battery boosts power to meet peak demand and lift heavy loads. As a result, the operator has replaced the conventional diesel power plant, rated 400-750kW, with a much smaller, 100-150kW diesel generator set. Combined with energy recovery, the cranes’ Li-ion systems can deliver fuel savings of 70%.

This approach to load-levelling can also be used in applications on board work boats, such as offshore supply vessels and tugs. These typically operate on a base load before generating high-power output for short periods.

Conventionally, these are powered by diesel gensets sized to deliver the maximum peak output, but by introducing a battery system, operators can meet peak power demand from the battery, and use fewer and smaller gensets working more efficiently at a steady load. This has the potential for significant savings in fuel and the capital cost of the gensets, as well as savings in maintenance, as generators experience less wear and tear from peaks in demand.

Sized to fit

Because ships and boats come in all sizes, and have a wide variety of operational regimes and applications, Saft has designed Seanergy as a modular concept. This means it can be built up to meet the required voltage, power and energy-storage capacity, whether it is for an ocean-going cruise liner, ferry, work boat, cargo or offshore support vessel.

The smallest individual Seanergy module has a nominal 24V and 40Ah capacity. By stringing modules together in series and parallel, Saft can create a battery system that delivers up to 1,000V and stores as much energy as required, limited only by the available on-board space.

The battery modules in standard 19in racks are housed in cabinets sized between 1.2 and 2.3m high. This gives operators the flexibility to stack modules in tall cabinets for a small footprint on large vessels, or to select shorter cabinets to fit under a low deckhead on smaller boats where height is limited.

Battery management – a critical factor

Consistent and reliable operation relies on the continuous monitoring of battery voltage and temperature provided by Saft’s battery management module (BMM). This controls individual strings inside the battery system and sends operational data back to a central interface, which could be located anywhere, either on board the vessel or in a specialist facility onshore. Altogether, this electronic battery-management system ensures that battery systems work within well-defined operating parameters, supporting safety and a long service life.

Modules can be extended to include battery chargers on board the vessel, or they can be housed onshore, depending on the facilities at the port and the vessel’s planned patterns of operation. In fully electric vessels, a standby generator should be installed as a source of backup power to ensure safe operation and peace of mind.

Safety on board

Safety is a critical consideration in the maritime environment, where incidents can occur with little notice, and unlike onshore, vessels must be self-contained, meaning that any risks must be minimised and mitigated.

Each Seanergy module comprises racks of Saft’s cylindrical voltage-limiting cells. These cells draw on Saft’s long heritage of deploying Li-ion technology in the most demanding applications, including space vehicles and satellites. At their heart is Saft’s Super-Iron Phosphate (SLFP) electrochemistry, which is particularly well suited for marine applications due to its safety and because it reliably delivers power in extreme temperatures of -20 to +60˚C.

The batteries are completely sealed, meaning that, unlike some battery technologies, no gases are generated, and no topping up or other maintenance is required. The structure of the cells and modules is designed to ensure safety, and to resist electrical abuse and mishandling – and the SLFP electrochemistry itself is also resistant to electrical abuse.

All of these factors combine to make Seanergy extremely safe and reliable for the marine environment, helping to deliver low-cost and low-emission operation for a wide variety of vessels.