Putting the safety into battery-driven propulsion

by | 29th August 2017 | News

Home News Putting the safety into battery-driven propulsion

The Naval Architect: September 2017Module - CellSwap (small)

Whether for hybrid or fully-powered, advances made in lithium-ion batteries have allowed the technology to quickly establish itself as a viable solution for marine propulsion. Since the launch of the first diesel-electric hybrid ferry, the 43m ro-ro MV Hallaig, in December 2012, the scale and ambition of such projects has moved on leaps and bounds with new projects, both retrofits and newbuildings, announced almost monthly.


Ferries, offshore and smaller vessels remain the focus for battery-powered innovation, spurred on in no small measure by the impetus of tightening emission-control regulations. However, Norwegian travel company Hurtigruten’s announcement in September 2016 that its forthcoming polar expeditionary ships, Roald Amundsen and Fridtjof Nansen (due for delivery in 2018 and 2019 respectively), would deploy sustainable hybrid technology is seen by many as a watershed moment. And while its seems unlikely that we will see battery-powered vessels engaged in long-haul transportation any time soon, it no longer seems beyond the realms of possibility.


One company with a vested interest in the technology’s continued progress is Canadian manufacturers, Plan B Energy Storage (PBES). Founded in early 2015 by Brent Perry, the former CEO

and founder of rival battery supplier Corvus Energy, PBES has quickly established itself with an outspoken commitment to marine energy storage ‘done right’, placing a strong emphasis on quality.


Grant Brown, PBES’s VP for Brand and Marketing (and, like Perry, also one of the co-founders of Corvus) explains: “Due to our experience with other products and projects in the past, when we designed this battery we really looked at how we could make it as safe as possible. The last thing anybody wants is a fire on board a ship. Lithium fires are very unpredictable and difficult to extinguish when they start propagating.”


In order to achieve this, PBES incorporated a number of unique safety features into its batteries. The most important of these, according to Brown, is a patented liquid cooling system they call CellCool. “CellCool liquid cooling does two things: it provides a safety feature in that it prevents our battery going into thermal runaway [when the heat generated within the cell causes a reaction between the cathode material and electrolyte], because the cooling system can extract more heat than the cells can produce.  We’re the only battery in the world that can actually prevent thermal runaway from occurring, not just spreading from cell to cell.”


While other battery systems rely on air cooling, the PBES method is similar to that found in the engine block of a car. Water is circulated through and around the components before exiting. Because the water is low pressure (around 4psi) it doesn’t put strain on the internal seals and components of the cell.


The cooling system is further enhanced by the use of cooling elements within the holders of the battery cells. Unlike many of their competitors, PBES has elected to use aluminium housing for their cells, rather than the more typical (and cheaper) glued-in plastic casing which can’t be serviced and requires the replacement of the entire battery. It also facilitates a unique CellSwap system which makes it possible to replace the cell core — each cell is roughly the size of a magazine and slots into the 10mm thick aluminium housing — without any interruption to the vessel’s service, not to mention cutting down on electronic recycling.


Safety features are integral to every aspect of the PBES battery design, says Brown. The battery’s contactor is built-in and opens up in such a way that there is no voltage or danger of electrocution while it is inactive. Another is the patented E-Vent system, which channels fumes away through a chimney that leads outside in the event of thermal runaway. Brown says: “The reason for this is that when lithium cells start to combust they create a combination of hydrogen gases that is very flammable. The smoke in a lithium fire is actually hydrogen gas. You can’t have that in the engine room of a vessel where the firefighters wouldn’t even be able to re-enter the room because of the potential for an explosion.”


PBES – which has already opened regional plants in Norway, Denmark and China – produces two battery solutions: the PBES Power 65, a 6.5kWh (75Ah cells) module optimised for high performance across a five-year lifespan, and the PBES Energy 97, a 9.7 KW/h (112Ah cells) battery comprised of the same parts but a higher energy density cell. Brown explains: “It’s a 30% decrease in size, weight and ultimately cost. With cell swap it means the owner can start with one type of cell and potentially change them if the ferry changes its route and has different energy needs.”


PBES received a notable endorsement in October 2016 when it was awarded the contract to supply the energy storage solution for what will be the world’s largest battery-powered ferries: the Tycho Brahe and Aurora, operated on the Helsingborg–Helsingør route by Scandlines, as part of a modernisation package under the auspices of ABB. Each ferry will be supplied with 640 lithium-ion batteries (a total capacity of 4,160kW/h placed in four 32-foot containers at the top of the vessel, between its two chimneys.


It followed approval of the PBES energy storage system by the Norwegian Maritime Association, which CEO Perry described at the time as “the most important validation PBES could receive.” Brown says that flag approval from the Danish Maritime Authority is also imminent, adding: “Right now the ferry market in Scandinavia is very big. Most ferries have been in existence for decades and have a very well logged dataset of how many hours a year they operate, what the wind, weather and tide patterns are and the energy consumption on each route. And by having a battery on shore on each side you can peak shave using the local electrical grid, and the batteries on board the vessel can be smaller.”


The big question with battery power is if and when it can be applied to larger deep-sea ships. According to Brown it really depends on the type of vessel under consideration: “Cruiseships I can see it happening right away because it makes a lot of sense. Not only for peak shaving, because of the way the turbines are set up and the different loads, but also when they’re berthed and require a UPS [uninterruptible power supply] or for spinning reserve. I personally couldn’t imagine being on a vessel with thousands of people and no bathrooms or water.


“But in terms of larger bulk carriers etc. it’s going to be a much more gradual process. It just doesn’t make sense in terms of efficiencies to buy a big battery when a vessel already runs very efficiently when it’s going across the ocean. Even though there are engine pollution issues there’s not a lot a battery can do; the efficiencies come from slow steaming, hull design and those kinds of things. But it might be that larger vessels use energy storage for cold ironing when tied up.”


Nevertheless, for vessels with the right operational profile, Brown is confident PBES’s solution represents a sound investment. After the inevitable start-up costs of the business, it is now in the process of lowering capital costs, savings it hopes to pass onto the customer without compromising on safety or quality. He adds that the “hard lessons” PBES’s founders learned during their time at Corvus has made them wary of the cheaper homogenised cells many of their competitors are choosing. 


“The marine industry has a tendency to drive prices right down and it may take some sort of horror accident to see the value of the safety features that we’ve integrated into our system from the beginning. The larger companies almost don’t want to acknowledge how important the longevity and reliability of the battery actually is. It’s being treated like a little widget.”


It goes without saying that not all lithium-ion batteries are built the same. Whereas a Tesla car is powered by 18650 cells (18mm diameter by 65mm length – slightly larger than a ‘c’ type battery) these would never be suitable for the 24/7 industrial use required by commercial maritime. Brown says PBES batteries are now capable of 15,000 cycles, a 50% increase on what was achievable just two years earlier. However, working in close partnership with its cell supplier, the company is confident of further advances in increasing the energy density and C-rate (the amount that can be discharged in a single hour). This includes investigating the potential of lithium-titanate cells and research with silicon nanoparticles on the anodes and cathodes of the battery that would allow for higher discharge rates.


Brown adds that claims being made by some of PBES’s rivals need to be treated with scepticism: “Some companies are talking about discharge rates of 10C, 20C or 30C but they’re living in a dream because we know what we have to do in order to get a reliable 3C without damaging or overheating the battery. There are very few pieces of equipment in the world robust enough to handle those discharge rates. You would need to have a circuit breaker the size of a house to disconnect it from the DC bus.”


With the growing presence of battery power on board vessels there have been suggestions that separate battery rooms might in time be dispensed with to economise on space, but Brown points out that the advantages in terms of weight reduction compared to an equivalent generator already compensate and there are always alternatives. “The reality is you want these things to be in a central location so that the power transmission from the battery to the DC bus is located in a single area. If you have cables snaking all over the vessel there are going to be line losses and for reasons of serviceability you don’t want them hidden.”


“Obviously you want the weight as low as possible. There’s a vessel I know of in Denmark right now that has four shipping containers with 4MW/h of batteries situated on the roof of the top deck, but it was more practical that way and it passed all the stability tests.”

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