Batteries could soon make operations in port more sustainable on big ships – but don’t expect emission-free sailing on large vessels anytime soon.
The launch of a new shuttle tanker series by Teekay this year poses several challenges to conventional propulsion principles. The e-shuttles – the first of which was launched in March – feature LNG engines (rare in an oil tanker); the selection of medium-speed engines and diesel-electric propulsion where low-speed direct drive is the norm; and the very first use of volatile organic compounds (vapour discharged from oil cargo) as a marine fuel. The Samsung-built series are also among the first big, ocean-going merchant vessels to deploy batteries to assist propulsion.
The battery packs on-board Teekay’s new shuttle tankers are small, but they have made a big impact. In April Samsung Heavy Industries (SHI) and Wärtsilä, having cooperated on the Teekay project, signed an agreement to further develop efficient solutions for shuttle tankers and LNG carriers. Samsung was granted access to Wärtsilä’s Hybrid Centre testing facility in Trieste to develop its own lithium-ion batteries.
At the end of July, the shipbuilder confirmed that it had received type approval from DNV GL for its lithium-ion marine battery, developed in conjunction with its sister company, battery and energy storage specialist Samsung SDI. SHI Ship & Offshore Research Institute vice president Yong-Lae Shim notes potential for batteries on ships far bigger than the ferries and offshore support vessels on which early marine systems were installed.
“The modular battery system will provide high versatility to meet capacity according to vessel size and power usage,” he says. “Not only that, we will be able to achieve cost competitiveness by using a domestic system.”
But putting batteries on bigger ships is not straightforward. Purely battery powered sailings are unlikely for deep-sea cargo ships due to the huge propulsion power needed for long journeys. So, if deep-sea ships are to deploy batteries, operators need to consider carefully which aspects of the ship’s operations can benefit from batteries.
Local vs global
A study by TU Delft and Harbing University, presented at CIMAC World Congress in June, highlights that this is not an easy assessment. The research explores the impact of battery hybrid operations on emissions during the close-to-port operations of a 13,000 dwt chemical tanker. It considers the emissions and fuel consumption of three different hybrid arrangements across a 131.43 nm approach to port comprising open sea, coastal and harbour journey segments.
The difference in emissions across hybrid modes is telling. Genset-only propulsion and power close to the coast improves local emissions (of NOx and hydrocarbons) compared to main engine propulsion and power, due to the better emissions profile of smaller engines. But these engines are less efficient and so a genset-driven strategy also increases fuel consumption and therefore greenhouse gas emissions. It is a similar story when considering battery-only port approaches. The absence of local or greenhouse gas emissions in coastal and harbour waters is counterbalanced by the fact that extra power (accompanied by extra emissions) is needed to charge the batteries during open sea transit.
So although it is possible to use hybrid propulsion arrangements to reduce local emissions near the coast and harbours, this comes at the expense of higher greenhouse gas emissions. The authors note: “Sailing in electric propulsion modes can reduce the local emissions and can even result in zero local emissions when the ship is powered by batteries. However, total fuel consumption will be higher compared to conventional mechanical propulsion.”
The authors note that while batteries could help to eliminate local emissions while sailing into and out of port, the financial case has yet to emerge. The batteries required for electric propulsion are too big, heavy and expensive. The Delft study is not the only one to reach this conclusion.
A consortium comprising DNV GL, MAN Energy Solutions and battery maker Corvus Energy recently investigated the impact that batteries could have on a 1,700 teu container feeder vessel. Their 2030 scenario, seeing whether an 11 MWh battery pack could provide zero-emission sailing into and out of port, proved unfeasible. The large battery system increased the costs of the vessel significantly, meaning that only with a combination of lower prices for the batteries and higher fuel costs than today would the system be economically attractive.
“Perhaps we will not have to wait until 2030,” says Corvus Energy executive vice president strategy Sean Puchalski. “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 than later.”
Until then, zero-emission sailing may make little sense for cargo ships. But according to the study’s present-day scenario, an economic rationale already exists for supporting auxiliary loads with batteries. This time the focus is not on sailing into and out of ports, but operations within port.
DNV GL maritime programme director Hans Anton Tvete explains: “We were looking at where hybrid systems could offer significant efficiency gains, which pointed to operational states with fluctuating power demand. This typically occurs with large consumers such as cranes, pumps, ventilation fans, or manoeuvring equipment, especially in port. Container feeders, with their frequent port stays and increased time in port, are ripe for efficiency gains using hybrid solutions.”
It helps the financial case that the aged global container feeder fleet will need rapid replenishment, adds Tvete. A vessel built in 2020 could conceivably replace one of its gensets with a 500kWh battery system used for peak shaving and as a spinning reserve, to handle the surges in power demand during quayside cargo operations. Under this scenario, the hybrid power train would represent around 13% of the total cost for the vessel. The study forecast that this cost could be paid back in two to three years.
Unless battery development accelerates rapidly – and becomes far cheaper – there is little prospect of huge battery packs being used for purely electric propulsion on big ships, even relatively close to ports. But for ships with regular stops, battery-assisted port operations on deep-sea going ships could already cut both cost for ship operators, and emissions in coastal areas.