Highly-charged vision

For example, Scandlines wasn’t pushed into change by the efficiency arguments, says Fini Hansen, the company’s technical officer. He admits the real ‘break point’ came in 2011 with the dawning realisation that upcoming 2015 regulations meant fitting a scrubber to each of the five stacks on each vessel – and at a few million Euros each, there had to be a better answer.

But a good look showed “there was a real win-win” case on the Rødby-Puttgarden route: five, 3.5MW gensets running at between 40% and 50% during transit and at 8 to 10% at berth were reduced to just one engine with an attendant, single scrubber and a 2.7MWh battery bank on the Prinsesse Benedikte. The genset charges the batteries at the quayside which then provide a needed boost during transit.

Admittedly the project has been expensive: Mr Hansen puts the total cost around €25m for all four vessels on the route. However, the savings have been impressive – in the region of 15% “so even with the drop in oil price, the payback time is around five years,” he says.

Given heart by this win, Scandlines now has its eye on a zero emissions operation although this will require another step change and a hard look at all the parameters. Mr Hansen explains a shoreside plug-in will be needed to replace the charge gained from the onboard genset – again initially using the Prinsesse Benedikte as a test-bed.

However, there are a number of considerable ‘roadblocks’ to overcome.

“These vessels do something between 7,500 and 8,000 trips per year and on each trip we use about 4MW of energy – it’s a large amount. But, we still only have around 12 or 15 minutes so charge up at berth”.

“We have calculated that to give us a lifetime of about 10 years means about 120,000 cycles,” he explains. “So to take this charge and give us the cycle life we have to oversize the batteries substantially – in fact it means a battery bank of between 10MWh to 12MWh.”

Further, the shoreside installation will need more capable connections – so, there needs to be some careful negotiation with the grid providers “and we might also have to use a large battery bank on land in order to be able to give the vessels the necessary amount of charge very quickly”.

Getting clever

As Mr Hansen says “the capacity of these batteries is growing all the time – and the price is dropping”. But there may be interesting ways to tailor the onboard energy storage.

Firstly, it’s worth noting the difference between ‘energy density’ and ‘power density’ is, as Alexander Breijs of RH Marine (previously Imtech) says, “the difference between having the energy onboard to drive from here to Switzerland, while the power is about how fast you can accelerate over the mountains”.

These are two related but separate dimensions: if you try to cover both angles you could be faced with an unfeasibly expensive bank.

But, as Sean Puchalski of battery maker Corvus Energy explains, a battery tailored for peak load shaving won’t necessarily be able to handle the deep cycling you need for all electric propulsion – and it could shorten the lifetime. On the other hand, demanding a surge from a lower-power battery will heat it up and could degrade it.

Further, he adds: “Most cell manufacturers are shooting for one or the other characteristic now; take the new titanate chemistry – it’s got fantastic power output but half the energy density of the current, more usual NMC cells.”

Despite this he says “it’s very difficult to boil it all down,” and owners would do well to talk to the battery suppliers as it could save them money. For example, “energy cells are becoming a lot cheaper” so despite the drive toward differentiation, “in the near future installing an energy-dense battery bank big enough to handle a high power requirement may work out to be more economical”.

However, there are other elements that could absorb some of the demands.

For example, take hydrogen. Fuel cells didn’t burst onto the maritime scene as expected a decade or so ago, but development has been ticking along and the possibilities afforded by pairing up these two forms of energy storage is beginning to draw attention.

Mr Breijs’s colleague, Walter van der Pennen explains that in the main fuel cells “tend to be a little slow in changing demand”. Therefore, while they provide a very useful, clean power reserve the best way to keep a fuel cell stack happy is to keep it producing energy in a more or less steady stream and use this to charge up a battery bank – which would give you that fast response.

Certainly a handful of north European governments have picked up on the potential: “Norway, Scandinavia and Scotland have been drivers for this technology, and in fact CMAL is looking at viable, concrete plans for a new build.”

However, Scandlines’ is beginning to investigate another, interesting element: capacitors. Capacitors and their relative, supercapacitors (a half-and-half battery-capacitor combo), could prove a congenial playmate for batteries.

This is because while batteries build the charge into a chemical matrix, capacitors hold the charge electrostatically, ‘bouncing’ the energy in and out again. While the energy can only be held for minutes (or hours in the case of supercaps), these components can absorb a whopping great belt of electricity – certainly more than enough to fry a battery.

Further as there’s no moving parts there’s very little to wear out; this means the cycle life of capacitors is in the millions while supercaps’ are measured in the hundreds of thousands – making them better-than or comparable to a ship’s lifetime.

Mr Hansen says these developments may eventually help Scandlines tie together a number of green sources: lighter, hydrogen fuel tanks could find a home in a superstructure on top of the vessel, the fuel cells themselves and large battery banks will be deep in the hold, while solar cells will cover the available upper areas (possibly with Flettner rotors being placed forward). On shore, the plug-in charge will come from wind farms, a battery bank could be used to stabilise the draw from the grid – and at least some of this electricity could be used to generate hydrogen.

More than the tech

The innovations are not simply technical.

“If I had to point to one big lesson that the hybrid industry has learned, I’d say it was to bury any complexity under the hood,” says Walter van der Pennen.

The RHM team has first-hand experience of hybrid projects where promised operational savings have fallen short of expectation – not because there was a fault with the technology but because the crew hadn’t made the best use of the alternative running modes.

So when it came to assisting CMAL with its replacement programme, they had a fair idea of the pitfalls. Further, as the ferries had been in service for around three decades “the crew had to get familiar with a vessel light-years ahead of anything they were used to”, says Mr van der Pennen. RHM therefore decided on “a highly guided operation”, largely taking the decision for the most appropriate combination of batteries and diesel away from the driver.

However, these vessels are still under the overall control of the captain. “We aim to present the operator with something they can relate to – like the cost of the fuel running through the engines… actually you can see the result of your actions, right in the moment, in Scottish pounds,” says Mr van der Pennen. The approach seems to have worked,

overall CMAL has seen an overall drop in fuel costs of around 38%, alongside a 28% reduction in running hours with 22% higher average diesel engine loading.

Interestingly, ‘big data’ could further shave running costs on CMAL’s third hybrid. Based on monitoring information coming back from its two sister vessels (MV Catriona and MV Hallaig), the battery bank has been tweaked, boosting it from 750 kWh to 800 kWh: “It’s shown you can use back data to achieve a finer balance between the investment and operational costs,” says Mr van der Pennen. However, alongside this there’s been a change of battery manufacturer due to bankruptcy. “It’s a problem with the market right now,” he says, “There’s a lot of start-ups, and a lot of turmoil…” he adds as the banks will need to be refreshed within the vessel’s lifetime it’s been thought prudent to change strategy and link up with an established manufacturer, “for instance, Saft”.

What’s more of a surprise is the growing interest in hybrids shown by the less-obvious sectors.

For example the subsea construction industry: “The reason that semisubmersible crane ships are looking into batteries is because they need something that will stabilise the on-board grid,” explains Mr van der Pennen.

These are really big beasts with lifting capacities of up to 5,000 tonnes and at present the power installation is sized for the failure case, “so these vessels usually sit there with a lot of engines idling away in the background” using fuel, creating emissions and, he adds fouling the engines – increasing maintenance and potentially decreasing up-time. Therefore some owners have started looking into replacing some of these units with a battery bank which could handle peak loads – including a power outage. Further, the battery bank could be used to absorb energy from the cranes’ lowering action.

But when it gets to vessels this size “designing in battery capacity precisely is quite a challenge” he explains; it’s nowhere near as easy to size the banks on these vessels as it is on the more predictable ferry routes and with a vessel this large there’s no room for going back later and messing around with the parameters.

Information, he reiterates, is key. “It’s important to have real data to see, for example, what’s happening during, say, that 25% of the time the vessel is on DP or in transit and exactly how much lifting they are doing,” he says. “It wouldn’t be worth it to scale the battery bank just for the cranes if they are only actually hoisting10 days a year.”

However, Mr Breijs points out if you can use the batteries to help, for example, to transit to and from site, it’s a different story as the investment and the potential gain is spread out over a larger percentage of the operational profile. “Although the oil and gas industries are concerned about their image, at the end of the day it is still about cold, hard cash.”

There are challenges to development, says Mr van der Pennen. “The shipyard only builds what the owner specifies… and of course the batteries only earn their keep in the operational phase and that’s not particularly interesting to the yard.” Plus of course, the owner often doesn’t have the breadth of engineering experience to know the potential that hybrids offer.

A new pattern for shipbuilding?

It’s a point picked up by Mr Heikki Bergman of Visedo who says the e-ferry project for the island community on Aero, Denmark, has broken new ground in more ways than one.

Firstly, it’s big. At 4.3MWhs the batteries total a hefty 47 tonnes – which could present a hazard. However the chemistry is pretty stable, and separating the installation into 20 small strings of 210kWh each means there’s little chance of thermal runaway propagating through the system. Further he says “you can lose a few of these strings and still have the majority working”.

Secondly, the conversion from AC to DC takes place on the quay instead of onboard which drops the weight of the onboard installation by thousands of kilos. It also assists the efficiency of the hookup; although the bank receives a complete charge overnight the ferry still needs a top up between trips but there’s only seven or 15 minutes to deliver it. A DC link doesn’t require synchronising the grid and vessel network, saving valuable seconds.

Further, “many smaller operators have been put off by the significant costs on the shore” he says. The deceptively simple design by MobiMar puts the connection at the front, integrated with the ramp and aligned with the king pin connection, to minimise movement. The overall cost of this element has been reduced by about half.

But more this project “could be the beginning of a new pattern for shipbuilding” says Mr Bergman.

He explains that the usual approach is that owner and supplier speak about performance, maintenance and so on while owner and yard are talking about cabins and vehicle capacity etc. At the same time the yard and supplier are communicating on installation, price and so forth… “and as a result, what comes out is something different to anything anybody had envisaged”. However this project is being run as an open consortium, with no hierarchy and an emphasis on working as a group.

“Trust and integrity is necessary to generate the right kind of team,” he says, but points out cohesion relies on everyone needing the vessel to be a success.

Despite this Mr Bergman adds there is a sticking point – it requires choosing the supplier beforehand. Further, he adds: “You shouldn’t take partners which don’t have the same call.”

On the quay

Although the technology is spreading into other areas, ferries remain the beating heart of hybrid development if only because they have a regular, point-to-point operation. This doesn’t necessarily translate into ‘straightforward’: despite being charged overnight most plug-in concepts have to rely on intermittent replenishment at the quay.

The problem is that double ended ferries usually have a very limited time at berth and getting enough charge during turnaround has been an ongoing issue.

However, “you can’t always compensate for limited docking time by simply adding more power”, says Ingve Sorfonn of Wärtsilä; he points out the total transfer of energy depends on the dimension of the batteries, the power available on shore and last but not least, the duration of the hook-up.

While all these dimensions are under pressure, this last is the least expensive as increasing shoreside infrastructure and batteries has a big price impact but “adding time has no investment cost” directly associated with it.

Therefore, Wärtsilä has been looking at crossover concepts which ‘cuts off the plug’, raising the connection time. The breakthrough has been the kind of solution made popular by mobile gadgets: inductive charging.

It relies on resonant coupling technology which allows a less than perfect alignment between transmitting and receiving coils: energise the first and the power will still flow through the second even with a short distance between the two explains Mr Sorfonn. “You don’t need 100% overlap between the charging plates to get a 1MW charge across a 0.5m gap – and you can even have 5° of tilt… ferries do tend to tilt a little at berth,” he adds.

In fact, the company’s first installation on Norled’s Folgefonn, a double ended battery ferry that’s been working the Norwegian fjords for the last year will be able to put through a 1mW charge during a docking time of between 5m and 10m using the new inductive link.

In order to automate and speed up the connection Wärtsilä’s idea is being paired up with Cavotec’s automatic mooring system: this uses remote controlled vacuum pads on the quayside to moor and release in seconds.

The price, however, is still being evaluated: it’s just coming off the testbench and Mr Sorfonn says costs will depend on the specific installation. However, it will provide an interesting solution for an industry which can’t afford the luxury of a few extra minutes on the quay.