News / Ferry electrification takes a major step forward with Aurora Botnia retrofit

Aurora Botnia, a hybrid ferry in the Wasaline fleet (pictured), is to be retrofitted with a dual-chemistry battery system, bringing its capacity up from 2.2MWh to 12.6MWh.

In keeping with a ferry segment stepping up its adoption of battery-electrification, the new system on Aurora Botnia will cover some 23% of the ferry’s energy demand. But the battery system will also provide outsize fuel efficiency savings, using peak-shaving, allowing the vessel’s LNG-burning engines to spend entire voyages operating at their most efficient load range.

Ship engine efficiency peaks at around 80%-load, but considerably more fuel is burned when vessels are in low-power manoeuvring mode or when a second generator is needed. With a battery system to act as a buffer between the vessel’s propulsion, which varies constantly in wind and waves, and its gensets, drastic efficiency improvements are possible.

Aurora Botnia will switch between using LNG gensets in this high-efficiency mode, and using 100% stored battery power, assisted by the setup’s unique dual-chemistry battery system. This includes lithium nickel manganese cobalt oxide (NMC) batteries, designed to provide large amounts of energy in short bursts – ‘power’ batteries – and long-life lithium iron phosphate (LFP) ‘energy’ batteries, designed to maximise energy density for onboard storage.

“To our knowledge, it is the first time this dual-battery approach has been realised in a maritime retrofit… [and] one of the most technically ambitious hybrid conversions yet attempted on a ro-pax ferry,” said Joonatan Haukilehto, head of new technologies at Foreship.

Since entering service in 2021, Aurora Botnia has been a testbed for new decarbonisation technologies, including experimentation with biogas, an environmentally friendly alternative to LNG, requiring less refinement than its close relative, bio-LNG.

But even for a vessel originally equipped with 2.2MWh of batteries, a sixfold increase in capacity is ambitious. The AYK battery system will be built in Zhuhai, China, which opened in 2023, and hopes to expand from 300MWH to 1GWH of annual production capacity. The system will then be retrofitted to Aurora Botnia at Finland’s Turku shipyard, with it set to return to service in 2026.

Despite muted interest from the feeder and shortsea container sector, the ferry segment has been forging ahead with ship electrification and hybrid-isation projects, The Loadstar reported last week.

Typically, the continuous running of a fuelled genset throughout the voyage, with a complement of batteries for propulsion peak-shaving and load-levelling, can by itself reduce fuel consumption by around 15%. But by adding additional power into their onboard energy systems using shore charging, hybrid ferries like Aurora Botnia will be able to support a growing proportion of the total voyage energy consumption using clean energy. An operating profile of short routes and predictable dockings provides ample opportunity for shore-charged batteries to replace gensets for stretches of voyage.

Since Aurora Botnia’s original 2.2MWh batteries were installed, there has been a 20% to 30% improvement in battery energy density and, in the future, The Loadstar expects to see such battery installations replaced with increased-capacity versions – allowing for a yet greater proportion of ferry crossings to be powered using clean energy from shore.

The potential benefits for hybridised and electrified ferries are threefold. It will reduce operating costs for ferries, which will be less sensitive to oil price fluctuations and the expected cost delta between fossil and renewable-derived fuels. Secondly, it will likely extend the useful life of the vessels in a segment that already gets 30 years out of them.

Thirdly, it will increase the amount of renewable energy that can be put to good use, rather than wasted in the conversion to e-fuels; ten battery-electric ferries could be powered with the energy required to fuel one ammonia- or methanol-powered engine.

“From the beginning, Aurora Botnia was built to evolve, and Foreship has been with us at every step of that journey,” said Peter Ståhlberg, MD Wasaline. “This latest upgrade represents a significant leap toward our 2030 climate goals. By integrating advanced battery solutions and maximising our use of clean shore power, we are proving that sustainable ferry transport is wholly viable.”