Electric propulsion through diesel-electric hybrid vessels is increasingly the technology of choice in the shortsea sector
These systems feature a common power management system fed by multiple sources which are chosen and operated as per load requirements and emissions limits.
In an effort to expand electricity use, batteries are being incorporated whose capacity is increasing with almost every new project. As battery capacity expands, plug-in hybrid ferries are becoming more common. “10-MWh battery capacity is the record now but it will soon be broken, perhaps even this year,” said Corvus chief executive officer Geir Bjørkeli at the Maritime Hybrid & Electric Conference held at Bergen, Norway, in September this year.
However, not all new ferries feature bigger batteries. In April, Danfoss Editron supplied a hybrid electric drivetrain system for a new ferry on the Thyborøn-Agger route in north-west Denmark. The Editron system included two 374-kW electric propulsion motors, two 323-kW diesel engines driving generators, and two 75-kVA hotel load outlets. Two propulsion motors are supplied for redundancy.
The two 78-kWh battery packs on board can be charged through a 45-kVA shore charging connection and a couple of DC panels form the power management system. With capacity to carry 22 vehicles, the new Thyborøn-Agger ferry can also transport 5,000 trucks and 50,000 passenger vehicles annually.
In August this year, Color Hybrid started operations with the capability to ferry 2,000 passengers and 500 cars from Sandefjord to Strømstad. The ship’s batteries have a capacity of 5 MWh and weigh 65 tonnes. A rapid charging facility at the quay in Sandefjord enables charging in an hour.
These ferries represent two among the many technology combinations available to electrify marine systems, but both involve using batteries. Today there are 182 ships operating with batteries of which 100 are car/passenger ferries, according to DNV GL. Of these 51% are hybrids while 23% are plug-in hybrids and 8% are pure electric.
All-electric operation in ports and during manoeuvring depends on battery capacity, footprint, cost, weight and charging facilities available in ports. “Plug-in hybrids are highly appropriate solutions, especially if the electricity is made from renewable energy. Losses in the electric solution are roughly 10% compared to 60% on a diesel engine,” says Corvus Energy’s chief commercial officer, Halvard Hauso.
The battery pack in the Thyborøn-Agger ferry can be charged from shore and serves hotel loads. The ferry features a serial hybrid system in which the engines feed the power system that takes on electrical loads including drive motors for propulsion.
In the past, battery capacity was the show-stopper in electric propulsion, according to Danfoss Editron’s marine sales director, Philipp Fedorov. Now, battery capacity is expanding quickly. Leveraging the quick loading ability of electric propulsion, ice breakers have long used serial hybrids, he said. Today, more and more ship types are adopting electric propulsion, he adds.
While series hybrids feature a centralised set of prime movers, in parallel hybrids, a shaft generator is provided along with the main propulsion to feed the auxiliaries. The shaft generator can function in motor mode, too. In ports or areas where quiet operation is necessary, the propeller shaft is decoupled from the engine and driven by power generated from auxiliary engines. “If 15 knots is full power, the shaft generator-motor can operate at 6 knots,” says Mr Fedorov.
Mr Fedorov talks about a patrol boat in Estonia with Danfoss Editron systems that started operations in September 2018. While the ship will also be used for patrolling, firefighting and search and rescue missions in Estonian waters, its main role will be monitoring and responding to pollution threats, using state-of-the-art radar that can detect surface contamination, such as oil spills, from up to 8 km away.
The 45-m boat built by Baltic Workboats may need speeds of 20 to 30 knots for swift response, but such high speeds are not always required. Electrical systems can provide considerable fuel savings in such applications, he says.
The parallel hybrid electric benefit of engine redundancy is important for the Estonian Coast Guard — in case of engine failure, diesel-electric or batteries can kick in. “In a vessel 30 m to 40 m long, the main engine is the biggest noise maker. Cruising up to 10 knots with the shaft motor can ensure quiet operation. Using battery power, the cruising patrol boat is almost silent,” he adds. The low vibrations and silence allows the patrol boat to run in stealth mode while carrying out anti-smuggling operations.
Meanwhile, all-electric propulsion continues to be the lodestar for ferries. The Ellen E-ferry covers a 22 nautical mile distance between the Danish islands of Ærø and Fynshav. Capable of speeds 13 to 15.5 knots, it can carry 198 passengers in summer months, with capacity dropping to 147 during the winter. The ferry can also carry 31 cars or five trucks on its open deck.
Danfoss Editron supplied the full-electric drivetrain powering the ferry to operator Ærø Kommune. The system comprises two 750-kW propulsion motors and two 250-kW thruster motors, both of which run off synchronous reluctance assisted permanent magnet technology and are controlled by DC/AC inverters. The E-ferry project is supported by the European Commission’s Horizon 2020 initiative in research and innovation.
The battery pack of 4.3 MWh was among the largest when the ferry was launched in June. In a few months, however, the biggest battery pack on a ferry doubled.
In September, Corvus Energy signed a contract with AIDA Cruises to supply a 10-MWh energy storage system to be installed on board AIDAperla in 2020. AIDAperla, built in 2017, has capacity for 3,300 passengers and a crew of 900.
Corvus’ flagship product is the Orca introduced in 2016. A 10-MWh Orca Energy will have 80 packs, with each pack having a footprint of 865 mm x 738 mm and a height of 2,241 mm, says Mr Hauso, adding the total weight will be around 130 tonnes. “The Blue Whale (Corvus’ new product) with a 10-MWh capacity will require half the footprint and 30% less weight,” he added.
Orca was introduced in 2016, meaning in just three years the battery footprint has reduced by half and weight by 30%.
In September, Corvus Energy opened its automated battery factory in Bergen. The factory comprises a robotised and digitalised production line with nine robotic stations and a capacity of up to 400 MWh per year. From unpacking incoming parts to testing the finished battery module, the entire factory is completely automated.
Corvus’ Vancouver facility will continue to supply North American and Asian markets, where demand for hybrid and zero-emissions solutions is emerging and expected to grow rapidly. Vancouver will also manufacture prototypes and production runs of new products.
Mr Bjørkeli told the Maritime Hybrid & Electric Conference the company now has seven battery types. From the Corvus Orca, an early and widely deployed product, through the Blue Whale with a slow recharge and discharge rate suited to big vessels, to the Blue Marlin for oil rigs, the batteries need to be tailormade for their applications, he said.
The Blue Whale does not require maintenance aisles unlike Orca and the Blue Marlin can handle significant load variations occupying half the space, he said. So far, batteries have been applied in ferries, cruise liners, offshore vessels and port cranes. But now ocean-going merchant ships are also showing interest, Mr Bjørkeli said.
Future-proofing the ship
ABB Marine & Ports’ product manager for energy storage and fuel cells Jostein Bogen says having an electric solution can help to future-proof the ship. “We need to have a platform that can combine these energy sources and support technologies that will be available in the future so their retrofitting can be seamless as far as the power management system is concerned,” he adds.
Mr Bogen stresses the importance of a DC system. A DC-based power system enables simple, flexible and functional integration of energy sources such as variable-speed gensets and shaft generators, batteries and fuel cells, he adds. For ferries, a DC platform provides a cost-efficient and functional method of integrating energy storage, making hybrid and fully electric operation a reality.
While electric propulsion is already mature technology in the shortsea sector, deepsea shipping remains a challenge. In deepsea vessels including cruise ships, LNG is seen as an alternative that can help ships meet emissions mandates, says Mr Bogen. “In the LNG vessels, we will see a shift towards batteries or fuel cells for more efficient load management. Approaching emission control areas, these ships can switch off the main engine and operate on motors,” he says.