The next generation of cargo feeder vessels are ideal candidates for the profitable application of hybrid-battery technology
A joint study looking into new applications for hybrid power generation on larger ocean-going cargo ships has determined that the characteristics of cargo feeder vessels and their operational profiles makes them good candidates for hybrid propulsion.
Titled Battery Hybrid Oceangoing Cargo Ships, the study was jointly authored by class society DNV GL’s Hans Anton Tvete, Øystein Åsheim Alnes, and Pierre Sames; engine manufacturer MAN Energy Solutions’ Carina Kern, Kim Réne Hansen and Dr Alexander Knafl; and battery hybrid specialist Corvus Energy’s Tommy Sletten and Sean Puchalski. Dr Knafl presented the study’s findings in a paper at the CIMAC Congress in Vancouver, Canada, in June this year.
Looking at a hypothetical 2020-built vessel with a 500 kwH battery system used for peak shaving and as spinning reserve, the report found payback times could be as low as two to three years.
A vessel built in 2030 using a larger 11 MWh system for zero-emission port entry and exit was also considered, but it was determined that lower costs for battery systems and higher fuel costs than are found today were needed for this to be economically attractive.
Why feeder ships?
So far, battery-hybrid technology has seen the most uptake as a solution on coastal and short sea shipping such as passenger ferries and offshore support vessels, in part due to the infrastructure required and the nature of operations carried out by these vessels. But if IMO’s climate objective of reducing greenhouse gases by at least 50% by 2050 is to be met, owners of other vessel types need to consider their options, the report’s authors note.
Mr Tvete noted: “Container feeders, with their frequent port stays and increased time in port, are ripe for efficiency gains through the use of hybrid solutions.
“Also, as this fleet is aging, new tonnage is likely to be on order in the near future,” he added.
Most efficiency gains, and consequently greenhouse-gas (GHG) emission reductions, for hybrid power systems take place when a ship’s power demand is fluctuating, for example due to onboard power consumers being brought on- and offline the onboard grid. Onboard cargo ships, such larger consumers are typically equipment relating to cargo operation, eg cranes, pumps, ventilation fans etc, or equipment relating to an increased need for manoeuvring, like thrusters. The common denominator for both types of equipment is that they are often utilised in connection with port stays.
that the potential for greatest gains in efficiency and emissions reductions stemming from port stays, the study’s authors used a combination of AIS data, vessel technical data and engine characteristics to review dry bulkers, chemical tankers, container ships, general cargo ships, LNG carriers, oil tankers, reefers and roro vessels.
The authors also assumed that smaller vessels that generally undertake short-sea voyages would experience more frequent port calls than larger vessels engaged in deepsea shipping, and set a maximum size of 25,000 DWT for the vessels they considered.
Under these criteria, container feeders were identified as the best candidates for the project, with Neptun Ship Design’s TOPAZ 1,700 TEU vessel a good match in both size and topology. TOPAZ was therefore used as a representative container ship design.
Reference vessel particular – TOPAZ:
Length: 169.99 m
Breadth: 28.1 m
Design draft: 8.5 m
Design speed: 19 knots
Main engine: 11,280 kW MAN 6S60ME-C10.5
Diesel gensets: 4 x 1,254kWe MAN 6l21/31
Cranes: 2 x 530 kW
Bow thruster: 950 kW
Reefer capacity: 250
The challenge of battery systems
Sizing and dimensioning of battery systems can be more challenging for a container vessel, according to the study. This is because routes are likely to be variable, and propulsion and ship system load profiles tend not to be documented and so are more uncertain than for other types of hybrid vessels.
“Focusing on a container feeder vessel we were able to generate a typical propulsion power profile from vessel speed data, as well as an artificial time-resolved electrical load profile from the according electrical load table,” said Ms Kern, noting that MAN’s ECO-ESS simulation tool was used to simulate two scenarios, one for a 2020-built vessel using a battery for peak shaving and as spinning reserve, and another for a 2030 built vessel using batteries for zero-emission manoeuvring on port entry and exit.
The authors considered four operational modes in each scenario:
Under this scenario, simulations showed a battery with a size of 500 kWh could replace one genset. The hybrid power train represented approximately 13% of the vessel’s total cost.
The total number of reefers and subsequent increased power demand on board a container ship have a significant impact on the electrical load, the study found, and therefore also affect the potential benefits to be gleaned from hybridisation. By installing batteries to provide a spinning-reserve capability and avoid or delay start-up of additional gensets, substantial savings were to be found, with payback times of two to three years.
Savings potential and positive net present value (NPV) – a measure of investment profitability – with short payback time was found in all cases presented. A discount rate of 10% and an inflation rate of 2% was used, and a battery price of $500/kWh and MGO fuel cost of $750 tonnes was used to identify the NPV.
Battery size in this scenario was determined solely by power demand and duration of manoeuvring, so a total installed capacity of 11 MWh was needed.
Under this scenario, zero-emission mode only looks economically viable if battery costs are to drop lower than today, fuel prices rise and incentive schemes or more strict emissions regulations are implemented. However, the report’s authors note, this may very well be the case. If fuel costs in 2030 are $1,000/tonne and battery costs drop to $400/kWh, the NPV becomes positive.
Why should operators adopt hybrid technology?
While the study was carried out with an eye to helping achieve IMO’s target of reducing emissions by 50% by 2050 compared with 2008, the challenge now is to convince owners and operators of cargo vessels that investing in battery hybrid technology is worth their while.
The authors set out to address this challenge by seeking to answer the question of whether GHG emissions can be reduced while staying profitable.
Corvus’ Mr Puchalski said: “It is our hope that these study results will increase cargo shipowner confidence in seeking out new energy solutions, as a good economic rationale already exists for supporting auxiliary loads with a hybrid configuration.
“As for the future propulsion scenario, perhaps we will not have to wait until 2030,” he added.
“We are already seeing strong demand for high capacity energy storage systems in passenger vessels.
“With the right leadership from cargo owners, we may see this translate to the merchant sector sooner [rather] than later.”
This is especially true in the case outlined in the 2030 scenario, where at current prices, fuel economically wins out over battery technology and outside assistance may be required to bring owners and operators on board.
“Container vessels are often ’low cost’ vessels and there is a reluctance to invest in green technology without other initiatives in place,” said Mr Sletten.
"To reach the global goal of 50% carbon emission reduction by 2050, strict regulations and various governmental initiatives are required.
“Initiatives such as funding for newbuildings, slot priority in harbours and reduced port fees for vessels with improved environmental systems will help greatly."
However, the report’s conclusion does note that lower battery prices and fuel costs than today “might well be possible” by 2030.