Power BATTERY TECHNOLOGY FUTURE

Transcription

1 Power Despite the emergence of rival solutions based on solar and wind energy, battery-powered propulsion technology continues to be the preferred eco-friendly choice for most marine operators around the world, thanks mainly to the further advancement of cells, chemistry, pack and management systems rangerswords: STEVIE KNIGHT Together with the Norwegian shipyard Fjellstrand, Siemens has developed the world s first electrically powered car ferry. The 80m vessel, which will be operated by Norled from 2015, can carry 120 cars and 360 passengers. It features an 800kW battery pack that weighs 11 tons and replaces the 2,000hp IC diesel engine traditionally used in marine applications such as this 14 // October 2013 // Electric & Hybrid Marine Technology International

2 The advent of lithium-ion chemistry has become a key building block for battery supporters and developers looking to further establish battery-powered marine propulsion solutions around the world, in the process fending off new-generation designs that are based on solar and wind energy. The key for many in the industry, including Steven Tartaglia, engineering manager for Lithionics, is that new lithium designs allow for little voltage sag to occur until right at the end of the power band, meaning that engine stop/start functionality can be easily employed and without having to resort to using heavy AGM batteries. Such capability, adds Tartaglia, is a blessing for hybrid setups, which need to bind together a number of subsystems that play very specific parts on the power curve. Although the energy density of a battery is very low in comparison to most liquid fuels a pack of 2.5kW will weigh in at 25kg Prins Doornekamp, CEO of Super B, says there are many engineering and end-user benefits to be had: Battery technology has a huge advantage in that it only consumes space, not fuel or energy sources like other solutions. Also, you can use the battery power efficiently for the peak loads or for the troughs, which means you don t drain the batteries right down and the main power source or genset just keeps ticking over. Energy waste from existing propulsion systems has become a critical issue facing all marine operators, and Doornekamp says this point can t be ignored when discussing advanced battery developments: You can have backup marine generators running on standby, but they don t use the energy as they are there for failure mode only, so they are wasting 3 to 4 liters per hour of diesel! Batteries in these types of applications earn their money back and break even within a year. Electric & Hybrid Marine Technology International // October 2013 // 15

3 A matter of control The trusty charging algorithm of the new lithium-ion batteries has taken a lot of time and cost to develop, explains Didier Bouix, researcher for CEA, who points out that the charging stages are not exactly based on the same three phases as lead batteries. There has been a lot of work in the lab as the charge management depends on so much: you ve got to get the characterization of the cells and the life of the battery right. For example, you have to keep an eye on the temperature, plus after some time you have a loss of energy density so that the power these cells can take decreases over time, and this means taking on another strategy, he explains. Bouix says that the sensitivity of the state-ofcharge control device is particularly important as a voltage readout tends to be an inaccurate method of inferring the level of the charge inside new, next-generation lithium-ion cells. As a result, it s worthwhile having a BMS inside each battery so that they can be supervised individually, says Doornekamp at Super B. A decentralized system is not only simpler to wire together, it also gives you more redundancy as there s not one master running the system; even if one battery fails, the rest can keep working and you don t get the cascade effect that happens if a battery stops and dumps its charge onto the next in line. Doornekamp continues: If you are clever you can use smaller generators and also take advantage of the extra power that the gensets are producing to recharge the batteries. In addition to this, on board a bigger ship fewer engineers are needed. So the overall cost savings, if you look at a big commercial system, can run into the millions per year. According to the Super B founder, larger marine fleets such as ferry operators are looking today at new battery technology as a way of reducing the need for backup power, but in addition to this, some forwardlooking companies are even assessing options related to replacing some of the redundancy required by dynamic positioning systems, which are used typically by offshore support craft or marine construction vessels, although such a move will need class certification. While this will ultimately mean huge banks of packs delivering around 2MW of power, batteries do have one Above: Wärtsilä says that the primary potential benefit of a battery hybrid energy system for a ship like the Viking Lady is a reduction in total fuel consumption and CO2 emissions of up to 30% through smoother and more efficient operation of the engines and fuel cell subsystems. What s more, the reductions of other exhaust components are even higher very important design advantage, says Doornekamp: You can place batteries almost anywhere you want, even building up quite high stacks. It s not like generators that come with dimension and weight distribution issues that have to be worked around in terms of the application design. Safety first With so many system advantages, including the big two of lower cost and emissions reduction, it would seem that the future for battery technology in the marine world is plain sailing. Except that s not quite the case; a massive agenda has complicated things, namely issues surrounding safety. Discarding the very public lithium-ion pack problems Boeing is having with the new 16 // October 2013 // Electric & Hybrid Marine Technology International

4 You can place batteries almost anywhere you want, even building up quite high stacks. It s not like generators that come with dimension and weight distribution issues that have to be worked around in terms of the application design Prins Doornekamp, CEO, Super B Above: The Super B battery technology provides high levels of performance through high energy density along with a reduced weight Above right: Prins Doornekamp founded Super B only four years ago Left: Corvus Energy battery packs have become well established in the industry, powering many applications around the world, including the Viking Lady, Scandlines Ferry and the RT Adriaan E-KOTUG Dreamliner, and the numerous battery-exploding laptops that computer hardware makers continue to face (both are, after all, totally different industries), in the marine world, there have recently been some high-profile thermal runaway incidents that have got close to denting the reputation of new lithium-ion technology. In fact, opponents to battery electric propulsion in this industry are quick to cite thermal runaway concerns that occur when the reaction rate of the system swells due to an increase in temperature, which then adds to the overall reaction rate, allowing the entire phenomenon to spiral upward and making it possible for the charge and heat of a failing cell to move across to its neighbor, thus creating a chain reaction that could result in a lengthy system downtime. However, the development of lithium iron phosphate (LIP) cells has helped no end to alleviate such safety fears. Although lower in power, these new cells are by nature far more agreeable to work with. Doornekamp, a fan of LIP, says that the chemistry is emerging as an industry favorite, and that s especially the case for marine engines, whereas other solutions such as cobalt-based lithium-ion batteries are much more touchy about tolerances, despite having far more power per kilo. They also tend to allow for fewer recharging cycles and given the realities of the marine environment, they could easily collapse within just a year. Yet according to Tartaglia, lithium iron phosphate exists in nature in both discharged and charged forms, which is in stark contrast to many other chemistries. For the engineering manager at Lithionics, it s a point worth noting: The oxygen in the phosphate is fixed to the phosphorus by naturally strong covalent bonds, while other cathode materials tend to release their oxygen at over 230 C, he says. All this has a bearing because the battery can go on burning despite CO 2 extinguishers and this includes underwater. There is an interesting story from the early days of development about a prototype Electric & Hybrid Marine Technology International // October 2013 // 17

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6 We don t believe that CANbus is stable enough for lithium-ion batteries. There is no worldwide standard and while it s okay for most automotive systems to take the risk with entirely digital system processing, marine builds are filthy, noisy, they have ripple currents and all sorts of other things Steven Tartaglia, engineering manager, Lithionics marine battery unit catching fire, resulting in the crew panicking and throwing it overboard, only to watch it continue burning some 2m beneath the surface for around 36 hours. So, lithium-ion batteries have had to become very clever at protecting themselves, and in some cases have got too smart for their own breeches, adds Tartaglia. His point is that the real issue now is not that lithium-ion batteries can slide into thermal runaway, but rather the chastity belt of charge management these batteries usually wear under their clothes for safety s sake stops them from being properly married to the other subsystems on board, in turn causing another problem. Dumb lead battery People are getting in trouble because they are used to a dumb lead acid battery. They don t understand that the lithium-ion battery s BMS can make independent decisions. It s actually a whole other dynamic in the system, Tartaglia says. Today s lithium-ion batteries have to take input from power take-offs, gensets, solar, wind and shoreside power, but the usual switching systems and charger management on a vessel could easily make the sensitive lithium battery management circuit stop interacting and shut off all input circuits leaving the generator to still try pushing some charge into it and thus wasting fuel. More importantly, if the onboard system is denied access to the battery because of an engineering blip, the crew is denied power Center top: Lithium-ion has become the mainstream choice for many battery electric marine developers Image courtesy of AquaWatt Center: A materials engineer looks into a burned out Boeing battery casing. Safety has also become a critical issue in the marine world. Image courtesy of the National Transportation Safety Board Right: Standard and bespoke battery systems can be built to suit all vessel fleets and applications, with packs available from Goodwolfe Energy, ranging from 2kWh to 4MWh and a vessel without power can be a vessel in danger, warns Tartaglia. Depending on who one speaks with, there are several different responses to this pressing issue, but Lithionics, after extensive talks with engineers at genset manufacturer Fischer Panda, decided that it was best to put some of the power management outside the box. This resulted in a system design that has kept the cell balancing on the inside of the battery, but on the outside now is the intelligent overmanagement system that can be routed round and disabled if there s an emergency. It s a clever design that s even more impressive when Tartaglia explains that the banks can be added as well, meaning that end-users need not overprescribe at first unlike when using lead acid counterparts. He says that as the batteries are naturally very efficient you can cost up for the bottom end of the loads, adding to the package if you don t think there s enough power there. However, Tartaglia points out that safety is managed by an independent island principle essentially pairs of batteries are wired back to a busbar before looping out to the next set so that the thermal and power cascade from a failure won t propagate through the system. Retrofit requirements Another interesting battery development issue and one that s particularly so for the retrofit market is that of consistency. It has been accepted by many that new and novel technology requires massive system upgrades but why try to make people reinvent their system just to put in the lithium-ion batteries? asks Tartaglia. He says that Electric & Hybrid Marine Technology International // October 2013 // 19

7 Lithionics specifically designed its technology so that the company s batteries could be accurately recharged with the use of a gel that sets common parameters to all inverters. This way, it keeps well away from that thermal runaway gradient. The result of this has been that Lithionics ditched the CANbus system during development, a controversial move that Tartaglia is keen to explain: We don t believe that CANbus is stable enough for lithium-ion batteries. There is no worldwide standard and while it s okay for most automotive systems to take the risk with entirely digital system processing, marine builds are filthy, noisy, they have ripple currents and all sorts of other things. CANbus doesn t belong on board marine craft these vessels just don t have the magnetic shielding. Instead, and interestingly on many engineering levels, the Lithionics system relies on one wire running between the battery banks and has both digital and analog communications signals running to and from the peripheral components: While some feeds are fine digital, the alternator and the generator control relays are best kept analog, further explains Tartaglia. Others developers, though, have chosen not to follow Lithionics path, instead coming up with different ideas of their own. At Super B, for example, the company s battery technology has a CANbus connection, but the battery banks also feature a wire that can route the management signals at the throw of a switch: It s not so necessary for smaller boats, but bigger craft need this type of redundancy, adds Doornekamp. In short, there s clearly more than one potential solution to consider. People are getting in trouble because they are used to a dumb lead acid battery. They don t understand that the lithium-ion battery s BMS can make independent decisions. It s actually a whole other dynamic in the system Steven Tartaglia, engineering manager, Lithionics Advanced cell designs from Sinopoly Battery are helping to ensure battery packs offer greater power and performance while drastically reducing emissions output Lithium iron phosphate exists as LiFePO4 in a discharged condition as triphylite (left) and as FeP04 (charged condition), known as heterosite (right) Image courtesy of Lithionics Below: The SeaRaider hybrid, one of the new generation of vessels that ties together solar and battery power. Image courtesy of Imran Othman As for the future, there is a whole range of chemistries already looking promising: titanium already has the support of a couple of manufacturers, while cost withstanding, magnesium might prove worthwhile too. Although most of the research to date has been toward solids, liquid-filled batteries could reduce overheads by pumping fluid from one side of the battery to the other, and there may even be open cell lithium air batteries on the horizon. But despite the possibility of a technology that could be 7-10 times as efficient, and significantly lighter than the present generation of lithium-ion batteries, there is a long, long way to go. As Doornekamp points out, not many designs have even made it out of the R&D lab yet: The problem is that you can have something that looks like it will work in the lab, but the results are not all you d expect when you get it into the field, he explains. As such, it would appear that lithium batteries of one specific chemistry or another will keep on tying the knot on most hybrid marriages for a while yet. 20 // October 2013 // Electric & Hybrid Marine Technology International