Clean Silent Running
Hybrid Propulsion - Marine Professional, January 2018 edition
Lithium-ion batteries are being used in hybrid propulsion to boost power, reduce emissions and enable silent operation, explains Jayesh Vir, marine manager at battery maker Saft.
Safe and reliable battery systems will be essential for Sir David Attenborough while it works in the remote and hostile Antarctic environment
A new breed of vessels is being developed to meet the IMO’s Marpol target to reduce greenhouse gas emissions and comply with the cap on sulphur in fuel to 0.5% mass by mass, due to come into force in January 2020.
Vessels such as workboats and offshore support vessels need to boost power during dynamic positioning operations, and ferries are required to accelerate and decelerate quickly in order to maintain strict timetables and keep communities connected.
To achieve this, such vessels typically have propulsion systems that are sized to meet maximum peak demand. Traditionally, this has meant multiple large diesel engines often operating in parallel to give instant access to boost power. However, the new generation of hybrid and electric propulsion vessels now use downsized engines and lithium-ion (Li-ion) battery systems that smooth the load by compensating for peaks and troughs.
Battery systems can also support hotel loads should there be an engine outage, thereby enhancing safety levels.
By turning to hybrid propulsion, operators can complement a diesel engine with a battery system. Once the battery has been charged in port or during normal operation, it can be deployed to overcome strong currents or windage during dynamic positioning, or to help a ferry come up to speed fast.
This allows the operator to reduce the number of engines running or to downsize them. This, in turn, reduces diesel consumption, greenhouse gas emissions, and engine run-hours. In addition, because the battery can vary its output, the captain can operate the engines at their point of peak efficiency. As well as saving fuel, this also reduces the amount of wear and tear on the engine, leading to lower maintenance requirements and higher availability.
Scottish ferry company Caledonian MacBrayne is one operator that has recently turned to hybrid propulsion with the objective of saving fuel and emissions in line with the Scottish Government’s tough environmental targets for transport. The company’s roll-on, roll-off passenger ferry, MV Catriona, entered service on the Lochranza-to-Tarbert route in 2016. Fitted with an 800kWh battery system, the vessel has achieved reported savings of around 20% in fuel and CO2 emissions.
The ferry can operate in battery-only or hybrid mode in combination with a diesel generator. Its batteries are charged overnight from the shore, ensuring that there is always more than enough power to transport the maximum load of 150 passengers and 23 cars, or two HGVs, at speeds of up to nine knots.
Meanwhile, the polar research vessel RRS Sir David Attenborough, is an example that highlights the hard-working and rugged capabilities of Li-ion batteries. Rolls-Royce Marine is integrating two Li-ion battery systems that will provide a combined 1,450kWh capacity at 1,011V alongside Bergen B33:45 engines. Safety and reliability are particularly important as Sir David Attenborough will operate in the remote and hostile seas around Antarctica. Saft was contracted to develop an advanced cooling system which would maintain an even temperature in the battery systems while operating in challenging conditions.
The battery systems will deliver peak power for dynamic positioning and help Sir David Attenborough push through ice packs of up to one metre thick and while towing research equipment. The batteries have been sized to enable the vessel to be self-sufficient in fuel over voyages of up to 19,000 nautical miles.
In addition, the Li-ion batteries will help to reduce noise levels below the waterline, avoiding disruption to marine mammals, fish and survey equipment.
Rolls-Royce Marine has also installed Saft Li-ion technology on board OV Bøkford, a workboat for the Norwegian coastguard Kystverket, which entered operation in the summer of 2016. It features an 857kWh battery system which operates alongside a single diesel engine operating at peak efficiency – enabling reported fuel savings of up to 25%.
The competitive world of superyachts is now the source of many maritime ‘firsts’. One recent example is the 100m-plus superyacht Zoza, currently under construction at the Benetti yard in Livorno, northern Italy, which will be the first of its kind when launched later this year.
It will feature a hybrid propulsion system capable of long periods of silent propulsion and zero emissions. Benetti is fitting two battery systems with a total capacity of 3MWh as part of a power plant that includes six engines as well as ABB Azipod thrusters. It means that the captain will be able to turn to battery power for full electric propulsion or to use the batteries to boost engine power to enhance speed and manoeuvrability.
Fully electric propulsion systems are particularly attractive for their zero-emission operations. These rely entirely on batteries that are charged while berthed in port. A small generator provides back-up power if needed.
One interesting example is the Ballerina ferry that serves foot and cycle passengers on a 50-minute commuter route through the waterways of Stockholm, Sweden.
The vessel is constructed from lightweight composites and is fitted with a 500kWh Li-ion battery, which can accept a 95% charge within two hours, and achieves quiet zero-emissions operation throughout the year.
Two sister ferries serving the city of Bordeaux in France are also capable of fully electric or hybrid propulsion on the Garonne river – a UNESCO World Heritage Site.
Li-ion batteries have the advantages of high energy density, high efficiency, long calendar and cycling life, fast-charge capability and high power output. They can also be built into modular systems that are tailored to closely match the power and voltage requirements.
The high energy density of Li-ion technology is particularly beneficial as it helps to create a compact battery system, which leaves plenty of space for passengers and other systems.
Its wide temperature operating range is also important within the marine environment, where batteries must be able to operate reliably in hot spaces or cold conditions.
However, the most important factor in battery selection is safety, as vessels must be self-sufficient in case an incident arises.
Li-ion is an umbrella term that describes several types of electrochemistry. The electrochemistry used in mobile phones and laptops is quite distinct from the Li-ion technology on board ships and aircraft, and in offshore facilities where safety is paramount.
Saft has developed its own Li-ion formula called super lithium-iron phosphate (SLFP), which delivers stable and reliable performance over a wide temperature range, has high tolerance to electrical and mechanical abuse, and has a high level of safety. SLFP is central to the design of Saft’s Seanergy modules, which have been designed specifically for the maritime sector. SLFP has also been adopted for other battery systems for aviation, oil and gas, and data centres, which all demand the highest safety standards.
Seanergy batteries have achieved safety approval from Bureau Veritas, Lloyd’s Register and DNV GL. They have also been approved by the Norwegian Maritime Authority, which demonstrated their safety performance by using a device that tested ‘thermal runaway’ and found that the Seanergy modules contained thermal runaway inside individual cells, thereby keeping other cells safe.