With 2020 almost in sight, classification society DNV GL recently revisited its Shipping 2020 report, published in 2012. Three years later, it says hybrid propulsion systems have emerged much more quickly than it anticipated. Speaking at Nor-Shipping 2015 in Oslo in June, DNV GL CEO Tor Svensen noted that, when the report was published, the rise of hybrid vessels had not been anticipated. However, a significant reduction in battery prices and improved energy storage capacity means hybrid systems are now becoming a real option for the shipping industry. They are, he explained, best suited for vessels with large variations in power demand, coastal trades and operations within emission control areas, although not all ‘hybrid’ machinery solutions necessarily make use of batteries.
“Pilot projects indicate that hybrid technology is robust and leads to fuel savings of 15 per cent for an offshore vessel,” he explained. “A hybrid engine system allows the ship to operate at its most efficient point, regardless of power requirement or load. There are already 33 hybrid vessels in operation or on order, and looking ahead, it is possible this number will top 100 by 2020,” said Mr Svensen.
As class society Lloyd’s Register noted recently, a number of hybrid vessels are already in service in other sectors. These include the LR-classed ferry Hallaig, the first diesel-electric hybrid ferry in the world. Developed under the Low Emission Hybrid Ferries Project, the ferry has a pioneering hybrid diesel-electric propulsion system with two 16R5 EC/90-1 Voith Schneider propellers (VSPs) providing a total power of 750kW and two lithium-ion batteries. The lithium-ion batteries are connected to a 400V switchboard to power the propellers and are connected directly to a DC link without requiring either additional electronics or voltage conversions.
Another interesting hybrid unit is the Svitzer ECOtug, of which four examples have been built for Svitzer by ASL Marine. The 33m long, 13m beam vessels are powered by diesel-electric hybrid engines that can achieve a maximum bollard pull of 75 tonnes. They were preceded into service in 2012 by the revolutionary E-KOTUG, a 32m long vessel with hybrid technology that allows its main engines to be shut down while the vessel is in transit. It can rapidly switch from hybrid mode using its electrically powered motors to conventional mode using its diesel engines. For low power operations, E-KOTUG can run on battery power alone.
Norwegian Electric Systems was heavily involved in the design of Fafnir Offshore’s Havyard 833 WE platform supply vessel (PSV), which is due to be delivered later this year. The vessel has a diesel-electric and battery-based hybrid propulsion system. Norwegian Electric Systems’ vice president (sales) Paul Winson said a hybrid system of this type can avoid some of the problems otherwise encountered when owners need to meet class rules requiring ever greater redundancy (which typically means increasing the number of gensets or more redundant switchboards and more busbars, which leads to more components and more inefficiency). A hybrid approach such as that on Fafnir Offshore’s newbuild also addresses issues relating to the low loads associated with operating in dynamic positioning (DP) mode. A hybrid system can address both issues, he explained, with the gensets running at 80 per cent loading or higher while charging up the battery bank and providing power for other systems. “You are only looking at the batteries stepping in while the engines get going and synchronise so they only have to take the strain for minutes, not hours,” he explained.
ABB’s Onboard DC Grid was introduced in 2011 and made its debut on the PSV Dina Star in 2013. This kind of optimised propulsion concept enables power to be distributed through a single DC circuit. Significant power savings result, with safety and redundancy enhanced over traditional AC systems. Distributing electricity in DC form allows engines to be operated at different speeds, substantially reducing fuel consumption and emissions compared with established propulsion systems. The dynamic response of the engines is also said to be improved, and batteries and other energy-storage devices can be integrated into the system.
More recently, Wärtsilä launched its Low Loss Hybrid (LLH) energy system, which it believes will offer significant fuel savings and reduce emissions. Unveiled at ONS 2014 in Stavanger, the Wärtsilä LLH utilises different power sources in combination with energy storage devices to operate the prime movers closest to their optimum performance. In addition to annual fuel savings of up to 15 per cent, depending on the type and configuration of the engine and mission profile, the LLH ensures a substantial reduction in exhaust gas emissions. The company notes that the control system for hybrid arrangements such as this is one of the keys to its success. A key feature of the LLH is its ability to reduce transient engine loads that cause increased fuel consumption and added emissions. Furthermore, by increasing the power redundancy, the system allows the engine to operate closer to its optimum design point where it has highest efficiency and least emissions. Reduced maintenance and increased system performance through rapid response from the energy storage system are also among the benefits offered. A LLH system was tested aboard the PSV Viking Lady and confirmed fuel savings of 15 per cent.
It is not just batteries that are contributing to the fast growth in hybrid vessels, however. Gearing designers, electric drive and energy storage device specialists are also contributing to advances in the hybrid propulsion systems. Their challenge is to maximise efficiency in each mode of operation so that fuel consumption and emissions can be minimised. Moreover, say manufacturers such as Rolls-Royce, electric or hybrid propulsion promises operators an inbuilt flexibility that reduces emissions and optimises fuel economy but also releases more space and lowers weight, noise and vibration as well as maintenance costs. Interestingly, says the company, hybrid systems are best suited to tonnage featuring frequent transient operations, such as offshore support vessels. It has developed a range of electric propulsion systems that can also accommodate batteries or be plugged in to a shore connection of variable frequency.
Earlier this year, Norwegian marine drive specialist Kumera delivered its Norgear advanced multistep hybrid gear solution for an anchor-handling tug/supply (AHTS) vessel newbuilding contracted by Buksér og Berging for delivery from Vard Brevik. The innovative hybrid gear plays a key role helping minimise the vessel’s environmental impact. By enabling different operating modes for different duties, it can reportedly achieve fuel savings of 40–50 per cent, depending on the duty.
A number of other gearbox designers are also targeting the market for hybrid drives, including Reintjes, which is offering its RHS series of hybrid gearboxes for fixed pitch propeller applications. The hybrid package typically includes the gearbox itself, with the combined electric motor and generator already flanged to the gearbox and a separate frequency converter. Main input and output shafts are vertically offset, and the gearbox incorporates integrated hydraulic clutches to control drive options.
Another German contender, ZF Marine, has strengthened its programme to support hybrid drive installations. Its 5000 series, introduced in 2012, offers higher power transmission capability and a wide range of gear ratios (up to 5.5:1 in the case of the ZF 5300 model). More complex transmission systems are available to serve integrated power and propulsion configurations where more than one power take-off (PTO) or power take-in (PTI) is required. The 5000 series has a supplementary PTI arrangement to accommodate flexible input and output variants in a compact space, making it suitable for hybrid operations exploiting power from auxiliary sources. More recently, ZF Marine extended the range of its hybrid-ready transmissions with the ZF 3300 PTI. Designed to be powered via a standard diesel engine input or other power sources through a PTI, the new transmission provides a hybrid-ready solution suitable for high speed pleasure and commercial applications. The ZF 3300 PTI is designed with the flexibility to be integrated into a wide variety of hybrid vessel propulsion solutions and is rated up to 1,940kW at 2,450 rpm, offering a wide range of basic ratios from 3.00 to 5.00. As with most ZF Marine transmissions, the ZF 3300 PTI can be configured to suit any application in the appropriate power range.
De Hoop shipyard in The Netherlands recently completed Karina, the first example of a new type of fast supply intervention vessel with another form of hybrid machinery. The design goal for the vessel was to be able to maintain speed irrespective of how much cargo it is carrying or what draught it is operating at and to transport cargo and offshore personnel in the most fuel-efficient way. At low speed (up to 13 knots) and in DP mode, the vessel operates in diesel-electric mode, with electrical power generated by a shaft generator. In the higher speed range, propulsion is provided by two diesel engines (both Cat 3516s), which are directly coupled through a gearbox to the shaft. The gearbox has a PTI for a 350kW motor to propel the vessel at low speed. No reversing gear is fitted, and astern propulsion is only possible in diesel-electric mode. With this particular type of hybrid propulsion system, full rpm control of all propellers, including the bow thruster, is available, while at low speed, only one engine is running, which saves fuel and reduces maintenance. Switching between diesel-electric and diesel-direct is automatic, and De Hoop claims that the arrangement results in fuel savings of up to 40 per cent.
Recognising the way that the market is developing, Volvo Penta recently announced an agreement to work on diesel-electric projects with Callenberg Technology Group. Under the agreement, the companies, who have worked together for years, will explore approaches to future hybrid electric projects. The company cited growing marine genset sales and becoming more competitive in the market for diesel-electric projects as key factors in their decision to work together.
Article published in the Guide to OSV Propulsion, a supplement to Offshore Support Journal