New solutions are emerging as increasingly complex ship arrangements bring complications for onboard power distribution systems
Whether shipowners are installing new emissions-abatement technology or making the move to hybrid propulsion, each new consumer that is added to a vessel brings more potential complexity to power arrangements. But there is help at hand as some enterprising system integrators and component suppliers are finding innovative ways to simplify the process of adding new equipment.
Hamburg-based engineering company E-MS has developed a standardised solution for supplying power to scrubbers. Using its scrubber power-pack technology, the relatively high power consumption of the scrubber can be integrated simply into the existing onboard electric network. Container shipping company Peter Döhle is the first to use it.
“Scrubber manufacturers, shipyards and shipping companies all face the challenge of how to accommodate exhaust scrubbers on ships and how to connect them to the onboard system,” explains E-MS managing director Peter Andersen. “The energy required just to operate the scrubber on large container ships is around 2MW. The technical complexity and expenditure associated with this is immense and often underestimated.”
The standardised system is based on a tried-and-tested solution developed by E-MS for supplying power to electric networks and propulsion systems on board megayachts, cruise ships and research vessels. This space-saving propulsion technology allows precise control of the required electrical energy. This both reduces fuel consumption and lowers exhaust emissions. It is especially effective where there are large fluctuations in power requirements.
The power supply to the scrubber is controlled directly from the medium voltage circuit of the main switchboard and requires the addition of a single cabinet. The resulting AC voltage can be adapted to requirements and so is available independently of the rest of the low-voltage network on board. This eliminates the need to build a complex and expensive decentralised power supply with additional electrical components.
“We are implementing this new technology as part of exhaust scrubber retrofitting on our four biggest container ships,” said Peter Döhle naval architect Philipp Hesse.
One of four container ships to feature scrubber power packs from E-MS that simplify electrical installation
The four ships involved – Fabiola, Filomena, Fillippa and Faustina – each has a cargo capacity of 13,400 TEU and propulsion power of 41,000kW.
Mr Andersen reports that negotiations are in progress with large charter and liner shipping companies, as well as scrubber manufacturers.
“The energy required just to operate the scrubber on large container ships is around 2MW... the technical complexity and expenditure associated with this is immense”
Stena’s first E-Flexer ropax vessel, of which eight are to be built, was floated out from AVIC Weihai’s shipyard in China in January. The efficient ferry features technologies developed by WE Tech, including a permanent magnet shaft generator that the company says is 5% more efficient than traditional shaft generators. In part load the efficiency gain from permanent magnet motors is even higher.
The system significantly decreases ships’ fuel consumption, operational costs and maintenance by allowing them to turn off auxiliary generators during sailing. In power take-out mode, the permanent magnet shaft generator is driven by the main engine to generate the ship’s electrical power without using the auxiliary generators. The shaft generator operation is made possible by a variable frequency drive – the WE Drive – which ensures that propulsion machinery can operate in variable speed mode while feeding into the shaft generator.
Large electrical consumers can have their inverter units connected directly to the WE Drive’s DC-link switchboards for more efficient power distribution, rather than through an AC switchboard. The drive also conditions electricity received via shore power for the ship’s electrical system, managing the variation in voltages and frequencies of national power grids worldwide.
Although not deployed on Stena’s current vessels, an energy storage system (ESS) can be added to the WE Drive and shaft generator configuration, to further improve the efficiency of vessel electric power generation. ESS can be used as a spinning reserve and to avoid blackouts, as well as decreasing the use of generators on low load during maneuvering. It can also be used as peak shaving to avoid the unnecessary starting of additional generator sets for a short increase in load. This will result in a more optimal running condition for the auxiliary generator that remains online.
After its work with AVIC on the Stena project, WE Tech has earned more support for its technology. “We strongly believe that WE Tech’s technology will help to further develop the shipping industry”, says AVIC International Ship Development CEO Hongbing Liao.
Even in the mighty arena of subsea construction vessels, the 153.6 m long, 18,151 gt North Sea Giant is an impressive specimen. Last year it became even more so; its six 3,600kW GE engines (driving five Voith-Schneider thrusters and a Rolls-Royce tunnel thruster) were supplemented by an ESS designed and installed by Wärtsilä. The result is arguably the most capable DP3 vessel on the market.
“By rapidly connecting and disconnecting energy sources from one another they can be optimised for efficiency”
That capability is not just thanks to the vessel’s battery system, which provides over 2,000kWh across three modules. As owner North Sea Shipping intends to use the vessel, those batteries would be irrelevant if it was not for an even newer technology: the electric bus link (EBL), developed by Yaskawa Environmental Technology, enables the operator to link battery systems in series and (more importantly) to disconnect them at previously unachievable speed.
“The EBL splits the onboard grids in a matter of microseconds, isolating faults and protecting the complete operational system,” says Yaskawa general manager Asbjørn Halsebakke. “This offers significant savings on maintenance costs. Also, by rapidly connecting and disconnecting energy sources from one another, including batteries and engines, they can be optimised for efficiency.”
In theory, that rapid shutdown capability means that the North Sea Giant can operate in DP3 mode with a single engine, the first vessel capable of this feat. Safety requirements previously required ships to perform several operations, including DP3, with engines providing power to each grid, rather than using one engine to power the grids in series, or using batteries to power each grid. But with approval from DNV GL – which will now revisit its DP3 class rules – the ultra-fast line breaking technology deployed on North Sea Giant means that just one engine can be used, with the three battery packs providing redundancy.
Wärtsilä Norway general manager Tore Marcus explains that the ship is currently performing these operations with three engines, each supported by one battery string, while the companies await a slot in the ship’s busy charter schedule for final testing. When North Sea Giant finally meets its potential, Mr Marcus predicts that the vessel’s unique DP3 power arrangement will save up to 2M litres of fuel a year.