HYBRID PROPULSION
HYBRID SYSTEMS OFFER PROPULSION OPTIMISATION Hybridisation does not in itself change propulsor choices, but it does offer opportunities for design optimisation, Wendy Laursen hears Hybridisation is accelerating in all vessel segments, including very large ships including PCTCs, tankers and container vessels. “Given the uncertainty around operational profiles and power sources in the future, propulsion trains in all vessel segments will be further electrified, whether with a PTO/PTI solution or by moving from diesel-mechanical to diesel-electric,” says Dr Torsten Büssow, Director Electrical & Power Systems, Wärtsilä Marine Power. “Any optimisation opportunity will be taken onboard, and hybrid will be a choice for many, not only reducing installed power but also optimising the operation of the propulsion train and allowing for zero emission operation, for example close to ports and populated areas.” Optimisation is important given the uncertainty around future operational profiles, power sources and fuel costs, and reducing fuel consumption by lowering installed power and optimising operations will become even more important as the industry moves into alternative fuels which are likely to be more costly than today’s fuels. However, hybridisation does not change propulsor choices, he says. “If you take a diesel-electric propulsion system as an example: because an electric motor provides constant high torque across all speeds, you can optimise the fixed pitch propeller (FPP) design for a wide operational range rather than focusing on a narrow speed/draft point. “But if a large diesel-mechanical propulsion system has a FPP, the same system with a PTO/PTI hybrid arrangement will also use an FPP. If a smaller version would have a controllable pitch propeller (CPP), it would also do so with a hybrid system, and if you need station-keeping, you will opt for thrusters regardless.” Büssow says the most important piece of technology in a hybrid system is the energy management system, the control software that optimises the propulsion system on a microsecond level. It is this that ensures that the fuel savings promised by hybridisation are delivered. “Shipowners should be sure to choose energy management systems that truly optimise efficiency during operation. Many off-the-shelf systems do little more than turn the battery on and off.” Helge Asle Lundeberg, Managing Director of Brunvoll MarEl AS, says that for hybrid configurations it is important to have flexible propulsion configurations so you are able to achieve dynamic optimisation depending on vessel operation/mode and other external impacts like weather, current, etc. “With a CPP system and advanced gearbox configurations you are able to optimise propulsion efficiency for any speed and mode of the vessel.” He says the operating profile is the most important parameter to consider. This will determine the optimal system for everything from propeller design to battery sizing and charging solutions. “The propulsion system is normally the largest energy consumer on a ship. For pure electric propulsion the energy is limited due to the energy density of the battery systems. Therefore, propulsion efficiency in electric systems is crucial. We have placed a strong focus on
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8 Torsten Buessow
developing efficient propulsion system configurations, including the Brunvoll Counter Rotating Propulsion System.” Asbjørn Halsebakke, Manager, Technical Solutions, Marine at Yaskawa Environmental Energy / The Switch, says that with full electric or battery y hybrid vessels it is important to have very efficient propulsion sion for all different load profiles. “Energy storage does cost a bit of money and it has therefore fore a much bigger impact if you have an efficient propulsion system that can increase the total efficiency.” However, the choice between tween FPP and CPP depends on the vessel type and operation profile. With The Switch DC-Hub, C-Hub, the installation can easily be rebuilt to make a more environmentally friendly vessel or convert a fully electric vessel to a fuel cell powered vessel. “For fully electric vessels, essels, a DC-Hub is definitely the best solution. ion. Good energy distribution, higher efficiency ency and easy to control. For battery hybrid d vessels, it is a bit more complicated. With big AC loads, like a reefer vessel, it might be better to use AC switchboard and shaft generator, with batteries and thrusters connected nnected to a DCHub and auxiliary generators ors connected to the AC switchboard together gether with the reefer loads. But all off this needs to evaluated according to the operation profile and load profile. “We always work closely ly together with system integrators, ship designers, ship operators and shipownerss to design the best possible solution for today and for the ldren will have a future – so that our children better place to live.”
8 Asbjørn Halsebakke
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