Feature 3 | GREEN CRAFT TECHNOLOGY


The batteries, an integral part of the new hybrid solutions, have been developed in collaboration with olls-oyce’s partners and


investigated on the MTU test-bench


 holistic view Still, this offering isn’t simply down to demand. “An important factor is both the technology and component readiness – it’s the right time,” Riegger tells Ship & Boat International. Despite this, he believes that successful utilisation depends on far more than a thorough shopping list. “We are convinced that it isn’t sufficient


to have good or even perfect components, architecture and so on,” he says. “We need to integrate the system on all levels. Besides mechanical unity, electrical and thermal interactions and auxiliary loads need to be considered. Te system needs a holistic view.” Take thermodynamics, for example.


Te engines are cooled to roughly 85°C and the power electronics usually need to be kept below 60°C, but the batteries are happiest at around 30°C – “and, when it’s very cold, you might even have to warm them up to gain the best lifetime performance,” Riegger adds. While, normally, this entails several


separate cooling circuits, a completely integrated package allows for a more efficient solution. However, workboats have a broad


set of operations which reach beyond the typical requirements for low-power electric propulsion, peak shaving, boost and regeneration modes. “You need the ability to look at a whole range of targets: these could be related to


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environmental compliance, component lifetime or speed, or could be as specific as giving a tug a certain period of maximum bollard pull,” says Riegger.“Not all of the aims will point in the same direction”. Moreover, he says, one change will influence another: “Batteries today are still the most cost-intensive element but if you install a smaller bank you have to consider the ageing effect from deeper cycles.”


apable architecture Given so many variables, Rolls-Royce has evolved a complete ‘building kit’ that allows virtual testing of a range of architectures and parts. At its simplest, it sketches out the overall energy exchanges, but this can be developed into a sophisticated model which includes components, logical interfaces and even diagnostics. Te simulation, he says, finds a balance between the various objectives – and also helps create some interesting alternatives. For example, on fast-paced vessels


like pilot or patrol boats, “top speed isn’t much influenced by the batteries as the energy density isn’t sufficient – although batteries do take the load steps from the acceleration which helps protect the engine”, he explains. However, a capable electrical architecture means that other sources, like auxiliary gensets normally reserved for picking up thrusters and hotel loads, can be utilised to yield a sustained, additional boost.


It’s also useful for liſt and lay vessels: the


fast (one seven-hundredth of a second) battery reaction time means that it can be used as spinning reserve during dynamic positioning, instead of keeping an engine running. It also yields another kind of ‘peak shaving’ capability: “You can use batteries for intermittent onboard loads,” says Riegger. “During cable-laying operations, for example, you have to compensate for the wave motion: if the vessel has electrical rather than hydraulic equipment, batteries can cover the fluctuations.” The simulation also embraces new


developments: the previous generation of batteries used by the Rolls-Royce team were lithium phosphate but now Rolls-Royce is working with partners on lithium nickel manganese cobalt oxide (NMC) chemistries, “which are lower-cost, safer and have more power density,” Riegger


explains. Further,


lithium-


titanate cells look promising for specialist applications and other alternatives may well cross over from the automotive sector. Tis has an impact on today’s choices.


Riegger says: “Flexibility has been an important design requirement at an early stage for this range. We see a variety of different technologies developing at a fast pace, so it might be reasonable to buy quite a small energy storage module, knowing it will age more quickly but anticipating swapping it over in five years for another battery with a different make-up and/or lower costs.” SBI


Ship & Boat International January/February 2019


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