Only two or three years ago, the idea of fitting batteries on an offshore support vessel (OSV) – or any other vessel – as a source of electricity for power and propulsion would have seemed unlikely, but a seeming revolution in marine propulsion seems to be gathering pace, with offshore vessels among the vessel types leading the way.
As highlighted previously in OSJ, batteries have been successfully tested on OSVs and have been proved to provide owners with a number of advantages. Newbuild vessels are being ordered with battery power, and existing vessels are being retrofitted with batteries. Were it not for the steep fall in the oil price, undoubtedly more would have been ordered with battery power, and when the market recovers from the trough in which it currently finds itself, it seems highly likely that hybrid propulsion systems with battery power included will be part of a new wave of more fuel-efficient, environmentally friendly offshore vessels.
Why, then, has the potential of battery power suddenly become recognised? As is usually the case in the offshore vessel sector, far-sighted Norwegian owners and vessel designers and builders are working with propulsion system providers to find new ways to build more efficient vessels. Other forms of hybrid machinery have already made their mark in the offshore vessel industry, and now, thanks to work carried out primarily in Norway, hybrid solutions with batteries are on offer – and they work.
As classification society DNV GL points out, the focus on hybrid propulsion systems is one reason why battery power is suddenly enjoying this level of attention. Another is a focus on ship electrification, where batteries can play a leading role and promise more efficient use of energy.
Speaking to OSJ earlier this year, Narve Mjøs, director, battery services and projects at DNV GL, highlighted the fact that all electric ships and hybrid ships with energy storage in batteries with optimised power control can significantly reduce fuel costs, maintenance and emissions. In addition, he explained, hybrid systems with batteries can significantly enhance responsiveness and enhance safety when vessels are operating in safety-critical situations.
Mr Mjøs noted that the initial focus of DNV GL’s attention on marine applications of batteries was primarily environmental. The environmental advantages of vessels burning liquefied natural gas (LNG) rather than conventional fuel have long been recognised, but questions have been raised about a phenomenon known as ‘methane slip’ or the loss of unburned methane into the environment. One drawback of gas engines is their proneness to methane slip due to incomplete combustion of the methane in the engine – a problem exacerbated by the fact that the global warming potential of methane is 25 times higher than that of CO2. Engine manufacturers are working on ways to prevent methane slip, but in the meantime, incorporating batteries into LNG-fuelled vessels can help reduce methane slip and deliver even better fuel efficiency, reduced emissions, reduced maintenance costs and optimised engine performance.
However, since this initial focus on compensating for methane slip, the class society has come to see batteries not just as a way to reduce emission of methane into the environment but as a way of improving performance and safety onboard.
Mr Mjøs highlighted the fact that Eidesvik in Norway – one of the first companies to appreciate the potential advantages of battery power – had found that its platform supply vessel (PSV) Viking Lady “was even more responsive” with batteries onboard. This proved to be particularly advantageous in heavy weather. “It gives the vessel instantaneous access to power, when it’s needed,” he said. “Diesel engines can’t give you that instantaneous response.” They also have other advantages, he added. They can store energy harvested from waste heat recovery, regenerative braking of cranes and/or forms of renewable energy such as solar energy.
Evidently, owners and the supply chain are waking up to the potential advantages of hybrid battery power, and more propulsion solution providers are offering battery-based solutions. “Last year, DNV GL trained more than 100 participants in our introduction course to maritime battery systems,” Mr Mjøs told OSJ, noting that DNV had facilitated the establishment of the Maritime Battery Forum, which already has more than 50 members, including shipowners, yards and vendors as well as government agencies.
“Although we are at an early stage with battery-powered ships, there is significant interest among stakeholders, and the number of ships with battery technology is rapidly increasing worldwide,” Mr Mjøs told OSJ, noting that, in Norway, financial support for realisation of electric and hybrid ships can be made available from sources such as Innovation Norway, Enova and the NOx-Fund.
As Remi Eriksen, ceo and president of DNV GL, noted, the price of batteries has fallen by some 60–70 per cent in the past four years. “My guess is that this trend will continue,” he said, “with as much as a further 50 per cent reduction in price compared to the current level.”
Mr Eriksen also highlighted the advantages of batteries combined with LNG engines in a hybrid arrangement. “Battery hybrids enable a vessel to run its engines at more favourable loads. This reduces fuel consumption and therefore emissions to air,” he noted, also highlighting the benefits Mr Mjøs drew attention to – improved response time in safety-critical operations, extending engine lifetime and reduced engine maintenance – along with reduced noise and vibration on board.
Louise Dunsby, lead electrotechnical specialist in Lloyd’s Register’s marine technical policy group, agreed with Mr Mjøs and Mr Eriksen about the advantages and potential benefits of using batteries in a hybrid arrangement. She agreed that the development of battery and hybrid technology is helping the maritime industry overcome the challenges of emission regulations and shipowners’ desire to maximise efficiency. However, she said, it is also helping shipowners address more stringent emissions regulations, with recent technological developments leading to an increasingly efficient alternative to traditional power sources.
In an ideal world, she suggests, it would be possible – and economically feasible – to change or ‘switch out’ the batteries on a ship with new ones, just as one does with a remote control for a television. In reality, the batteries used in shipping are big enough to fill a large compartment – because ultimately the physical size of a battery directly relates to the power it can produce – and are far too big to change in and out, so research and development is focused on secondary or rechargeable technology.
Batteries of this size use a variety of chemical processes, she explained, the two most common being lead-acid and lithium-ion batteries. Both have been tried and tested over many years, and are robust,
Article published in the Guide to OSV Propulsion, a supplement to Offshore Support Journal
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