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A battery powered future for shipping?

A battery powered future for shipping?
Two years ago, Seatrade Maritime News reported on the cutting-edge battery-powered ferry Norled Zerocat. Delivered by shipyard Fjellstrand in May this year, the new vessel uses 150kwh per voyage, carrying 120 cars between the mainland and various Norwegian islands.

Since that time a number of other full-electric ferries have been unveiled and entered into production, and the concept of batteries has rather caught on.

DNV GL has been championing the notion for a while, and at Nor-Shipping, it was revealed by its incoming group executive vp Tor Svensen that, “Currently, there are already 33 hybrid vessels in operation or on order, and looking ahead it is possible this number will top 100 by 2020."

The difficulty with Svensen’s statement is that the class society has a number of definitions for “hybrid” ships. For instance, there are “simple” hybrids, which use features of everyday ship operation to generate power and store it in a battery, in the same way a hybrid car might convert heat from its brake pads and store it as energy. Technology including waste heat recovery systems, such as the steam boiler system fitted by Green Power aboard Cruise ship P&O Britannia, which left Fincantieri in March. The system uses waste heat from the main and auxiliary engines to create steam and heat the ship’s otherwise oil-fired boilers, saving fuel.

Meanwhile DNV GL expects “plug-in hybrids”, with onboard batteries charged by shore power, to hit the market eventually. Like Zerocat, these would use shoreside charging facilities, but unlike the ferry, would also feature a main, hydrocarbon-fired engine to get the vessel where simple battery power could not.

Seatrade Maritime News caught up with Arne Færevaag, principal engineer of DNV GL’s Electrical Systems section, to ask him why batteries are more feasible now than ever before.

“Mostly the development of lithium-ion batteries,” said Færevaag. “The energy density of the batteries has increased, and now it is feasible whereas five or ten years ago it would be expensive and inefficient.”

Technology companies are looking into a way to increase the efficiency of electricity generation on board by changing the way fuel is converted into power. “One very important thing is you may have generators – diesel or LNG-fueled – running at a variable speed. Traditionally, power plants have to move at a fixed speed to generate 60hz. But now with a modern electronics you can have inverters creating your 60hz, which means that the generators can run from 40-60, or 40-100, whatever. As long as you can run the generator set at a low power, you could increase efficiency a lot.”

Hooking gensets up to a battery would enable each to run at maximum efficiency, rather than fixed speeds, to charge the battery, running the propulsion on discharged power. “If you have an operating pattern which is more variable – so some generators operating at full steam ahead and parts that are running at low load on your diesel or LNG fired engines – then it gets interesting for hybrids.

“Traditionally, you’d use the batteries when you have need of little power, while your peak power is created by diesel engines. But the ferries going from Denmark to Germany are doing the opposite – they’re using batteries to provide full propulsion power, utilising their batteries to exceed maximum speed, and then while in harbour they use the diesel generators to charge the batteries.”

There are a variety of technologies still being considered, said Færevaag. “You have waste heat recovery, you have batteries, you have mechanical flywheels which some people are looking at, and you have supercapacitors. We haven’t seen those proposed yet but there is interest in the market.

“A supercapacitor is an analogue of a battery but with a much shorter charging time, but it has a shorter discharging time as well, so you can have more cycles than on a battery. So for dynamic positioning it could be interesting, for peak saving, and it could make the diesels go much smoother at lower load. [For batteries] we know there’s major interest for dynamic positioning. When a ship is operating with dynamic positioning it has a lot of diesel engines running at very low load, and that is where the batteries could typically be used. That is a situation where batteries could mean a lot.”

So, would incorporating batteries into ship designs be prohibitively expensive? Impractical due to size constraints? “I think the main barrier is uncertainty – we don’t have enough experience. I don’t think there are technical obstacles. It’s more a question of getting more experience.”