Category: Articles

DNV-GL recently found that more fully-electric or hybrid-electric vessels were under in operation or under construction than there are LNG vessels, while projects like the installation of a 600kWh battery on the Maersk Cape Town and the construction of the zero emission hybrid container ship the Yara Birkeland provide proof that energy storage is viable on larger vessels.

One of the main misconceptions around electrified shipping is the understanding of the roles that Energy Storage Systems (ESS) can play on board a vessel. Using an ESS means different things in different vessels today.

Short range or smaller vessels are able to take advantage of huge fuel cost savings from fully-electric propulsion, while passenger vessels are also able to take full advantage of the operational benefits of the systems – with fewer vibrations, less noise and no emissions on deck improving passenger experiences. Hybrid propulsion is proving its value for more versatile or mid-range vessels, while battery solutions are gaining traction in the containership and tanker markets for auxiliary power supplies.

This is set to become an even more important factor for shipowners over the coming years.

Regulators are setting their sights on decarbonisation, both internationally and regionally, and new several new ‘zero-carbon’ fuels are in the latter stages of development. All of these fuels can benefit from energy storage for efficiency and viability; we believe that in the near future, all commercial ships will have a battery room to supplement other energy solutions.

Expansion of energy storage supply is therefore expected to accelerate in the next few years. As this happens, the industry must be cautious to ensure that safety is not side-lined in a rush to provide systems quickly – or that look to be cheaper on paper. To facilitate this, suppliers must take an honest and safety-focussed approach.

Modern ESS utilise lithium-ion cells as the energy source inside the battery. The most prominent risk with these cells is thermal runaway.

Thermal runaway starts when a single lithium-ion cell is damaged. This damaged cell then heats up, releasing toxic, flammable gasses. Unmitigated, the heat from one failed cell will damage surrounding cells. To deliver a valuable amount of energy, a maritime battery requires many banks of cells – meaning that a damaged cell can quickly turn into a potentially catastrophic chain reaction.

Excess loads placed on the battery such as those from over or under charging, as well as physical damage and general wear and tear, increase the risk of cell failure. However, even when a battery operates at optimum levels non-stop throughout its lifecycle, there is always a small risk that a cell is delivered with an undetectable fault.

Many manufacturers have not yet been clear about the significance of these risks, or how they can by managed. Holistic ESS design, starting with the cooling system and the space around the battery, can bring these risks to near zero, while delivering a less expensive system.

Ensuring safe systems

The space surrounding a marine battery must form part of the system’s design to ensure safety and efficiency. Safety systems must be integrated from the start of this design process to make sure that they work as efficiently as possible and ensure that these systems work together in harmony. They are not optional add-ons, but vital parts of any system that should not be sold separately.

The first stage of this design must look at cell cooling. Cell cooling can cut the risk of thermal runaway, or slow or stop a chain reaction when a damaged cell starts to heat. Integrated liquid cooling can stop thermal runaway – and deliver better battery performance.

A truly effective cooling system must cool the whole of the cells uniformly. When designed as part of the system from inception, water cooling can deliver uniform temperature control and remove “hot spots” on the cells. These hot spots will degrade the cells, and over time will cause premature failure.

Liquid cooling systems designed in this way are also able to stop thermal runaway before it starts. By ensuring that a cell is operating in optimal conditions at all times, it also improves performance and lifespan, but even in the case of a damaged cell failing, the cooling system will be able to remove more energy than is produced, keeping adjacent cells cool. The battery avoids the chain reaction of thermal runaway and stays within operational parameters.

Some systems today are designed as add-ons that only cool the exterior of the cell or use air cooling technology – which requires 3,500 times more air flow volume to achieve the same heat removal, and require expensive add-on HVAC systems.

Despite the confidence that manufacturers can provide with holistically designed cooling systems, the risk of thermal runaway from incidents of catastrophic failure will always persist to some degree. Shipowners must also be confident that such a failure would not put their crew or vessel in danger.

This type of catastrophic failure is extremely rare in a liquid cooled system, but a last layer of safety can be delivered through direct venting mechanisms which, despite the clear need for this to work seamlessly with other safety mechanisms, are not often integrated with the ESS design. Such venting mechanisms remove flammable and toxic gasses from the battery, never allowing them to even enter the machinery room. Not only does a directly vented battery reduce explosion risk, it also allows emergency and service personnel to renter and secure the area far sooner than an unvented system. This venting system must be explosion-proof, and it must be entirely fool-proof – it must be designed to work regardless of how other parameters have been set by crew. This means it must be provided alongside specialised control units, and architecturally it must vent the gas to an appropriately safe environment.

Safer systems can cut costs

Safe design, as well as proper maintenance, means better performance – and a longer service life before replacement.

Using a fully optimised cooling system can aid efficiency to such a degree that an ESS can operate at an average continuous rate of 300%. This means that a 1MWh system can be met with a 333kWh battery; meaning a smaller, lighter, lower cost and easier to install system. It also means that systems degrade slower, and less redundancy must be built in.

Lower discharge rates mean a much bigger battery must be created to do the same duty, increasing costs and adding to the space and weight used.

Reducing the need for full system replacements is also important as many companies adopt rigorous sustainability standards.

One of the most important innovations in this space comes in the form of Sterling PBES’s CellSwap technology. As part of the battery architecture, CellSwap allows for individual battery cells to be easily removed and replaced without the replacement of an entire battery system. This simple maintenance can be performed at sea, reducing downtime. Because only the cells are replaced, the vessel owner only pays for the cells and the service to install them.

CellSwap also allows shipowners to benefit from consistent advances in battery cell technologies over time, as battery science constantly finds new ways of storing more power in smaller cells and improving cell safety and lifespan.

Demand for marine energy storage is already soaring. Countless vessels are already proving the cost benefits of electric of hybrid electric solutions, while future technologies and regulation – coupled with improvements in system technology – are expected to make it an even more attractive prospect for shipowners.

At this crucial time for the industry, suppliers must ensure that they build trust with shipowners and integrators by designing the safest, and most efficient, complete systems. In this way, the shipping industry will realise the full potential of energy storage and maximise their return on investment.

Owners may have a dilemma when picking an energy technology capable of lasting a vessel’s 20 or 30-year lifetime, writes Stevie Knight

Published In The MotorShip Magazine on June 12, 2020 by Stevie Knight. Link to the article can be found here.

Eco-legislation ensures shipping has to move on, but “being locked to a single option could make it tough to adapt” says Kjetil Martinsen of DNV GL: he points out that the fuels of today may not be those of tomorrow and choosing a low-emission alternative that turns out to be extortionately priced or unavailable “could result in stranded assets”.

But there is already a dizzying array of potential solutions “and everybody is considering everything… so all the cards are in play” he adds. Therefore, some believe the answer may lie in judicious spread betting.

MODULAR DESIGN

Modular design may provide an answer: it certainly stands to relieve owners of a lot of drudge work as maintenance could be performed by the OEMs themselves, the result assured by the class societies. But it also holds the potential for shaking the industry to its foundations.

As Martinsen’s colleague, Knut Erik Knutsen of DNV GL remarks, “there’s been a gradual move by the big manufacturers toward ‘power-by-the-hour’… a service agreement rather simply selling an engine”.

Modularity could be seen as a logical extension of this approach, especially as it paves the way for greater standardization. That in turn broadens the appeal of remote, condition-based monitoring, “something that’s been held back by the number of unique, custom-built ships” he adds.

The potential is already being explored. The MIDAS project, that experiments with modules installed on Subsea7’s PSV Seaway Moxie and the Norwegian Coastal Administration ship OV Ryvingen, have navigation, communication and propulsion modules operating onboard to yield “continuous monitoring and specific health indicators”, says Knutsen.

But what’s so different about it, really? “At the moment the mechanical drives, the electrical lines and the control systems are not just in different packages but also different disciplines,” he remarks. “Instead, we suggest tying it all together into one module with one, single concern, how to maintain the function.”

This approach has a number of advantages. Firstly, “embedding a propulsion system inside a standardised unit gives you a much better idea of its performance and reliability”, he explains. “If something goes wrong, it’s far easier find out who’s responsible for putting it right.”

Follow the implications through and logically, this puts as much emphasis on defining the boundaries as system integration, inherently tightening up the scope for each OEM. In itself that will yield efficiency benefits for manufacturers.

But further, standardised interfaces “allow freedom to design alternatives” to meet the specified demand, says Martinsen.

This, in turn, ushers in a still more radical concept – what about swapping out the onboard kit if another solution appears more appropriate? After all, a defined output within a particular footprint appears supremely well-matched to a ‘plug-and-play’ approach.

DNV GL’s laboratory ship concept does just that. Envisioned as a vessel to test, qualify and benchmark new maritime technologies,  Experior is designed to be flexible in terms of interchanging onboard components and systems. Therefore, it holds the potential for interrogating a vast array of alternatives, from superstructure and cabins to power and manoeuvring kit, to comms and control, mostly by sitting them in dedicated containers with monitored interfaces.

Although not a commercial vessel, the ideas behind Experior may hold a clue to the future: its set up allows clients to calibrate and optimise their own innovations against the lab ship’s digital twin before installation.

ANALYSIS

In fact, according to Knutsen, a digital twin may be part of a modular delivery, allowing systems to be pretested in the factory.

There’s a further advantage. “So far full vessel reliability modelling has been challenging,” he says. However, since each module will have a health check element, it’s possible to network these together, creating a “system of systems”. It would, he remarks, gradually build up over time, being far less costly and troublesome to implement than dropping an entirely new, ship-wide layer into place.

It may also help resolve another niggling issue: cybersecurity. There’s often persistent doubt that the vessel’s onboard systems are as watertight as the hull, so modularity should provide more reassurance – firstly, it could potentially reduce shared weak points, secondly it “ensures that software systems are always up to date and robust in the face of challenges”, says Sverre Torben of Kongsberg Maritime Digital.

COMPLEXITY

However, the MIDAS project has shown there are a few knotty issues to overcome – not all purely technical in nature.

Knutsen explains: “You can create a health indicator for a bearing with no problem, but doing the same for the power management involves thousands of signals. If the manufacturers are tasked with keeping their modules running, they will need to be able to pull the data out in the same way from any ship.” And, he adds, without it being “the labour-intensive process” it is at present.

It’s not just the OEMs: the information will have to be shared with owner, systems integrators and last but not least, the classification societies. As Knutsen underlines, “there are more than 10,000 ships on DNV GL’s books so we’ll need a good, sanitized way of sorting it all out”.

Although there is “some movement” toward developing an industry-wide ISO standard, he admits rather than trying to make existing arrangements line up, it’s far easier to accomplish coherency on a newbuild where a useable format can be implemented from the very start.

SAFETY

Any module worth its salt would need to cover all the bases: “Besides the monitoring, maintenance plans, approvals and so on, it would need to include designed-in safety systems,” points out Knutsen. The latter presents its own challenges as its characteristics change with the fuel. Take LPG, he says: “It’s heavier than air, so standard gas detection equipment in the ceiling won’t work.”

Further, while modularity relies on a set of discrete systems, safety kit appears to pull in the other direction. Ammonia, for example is toxic and corrosive, so if there’s a failure in any part of the fuel supply, the entire ship could be endangered. Therefore, these safety systems have to extend throughout the whole vessel.

“There is no perfect fuel, no perfect way forward”, underlines Niclas Dahl of Alfa Laval. “They all have pros and cons: some may simply be limited in supply. Some, like ammonia, require more in handling the risks.” But he stresses, this should not stop development.

FUELS AND ENGINES

Wärtsilä has been playing with modularity for a while: Nico Höglund explains that development really picked up with the release of the Wärtsilä 31 medium-speed four-stroke: “Before that, if you wanted to change from diesel to dual fuel, you’d have to re-machine the engine block…. but the 31 makes it all much more straightforward, you basically only need to add the gas components.”

It sets the scene for what lies ahead. Höglund adds: “Both methanol and ammonia are currently being evaluated as potential next-generation fuels, partly because they have the potential of being created in a completely green supply chain.” Interestingly, both can also be kept in liquid form with a modest amount of pressure and cooling.

Therefore, Wärtsilä’s modular approach should enable easier conversions: “If you have a dual-fuel engine running on LNG, the installation already contains the majority of what’s required, such as the fuel storage tank,” says Höglund, although both methanol and ammonia will need modified fuel injection along with process equipment and corresponding safety systems.

MANAGEMENT

Despite sounding deceptively simple, these fuel changes “require very good engine management”, adds Höglund: ammonia ignites and burns differently compared to other methane fuels and likewise, methanol has a lower calorific value requiring a change to the automation software.

This is central, he says: “Outside its operational parameters, the engine can start to knock or miss-ignite. The engine’s automation system has to take action to ensure proper combustion in order to avoid a potential escalation of the situation, which could lead to shutdown. So it’s not just about optimising performance, it’s also about safety.”

Moreover Alex Grasman of MARIN points out: “One important factor is that burning alternative fuels in a combustion engine makes for a narrow ‘operational envelope’ compared to diesel.” Further, heavy seas compound the issue by adding dynamic loads to the system.

In short, new fuels require “tests on timing and management, and a lot of time spent searching for the sweet spot”, says Höglund.

TWO STROKES

While it might be expected that four-stroke, diesel-electric vessels like Moxie are the first candidates for a modular approach, Knutsen points out the big container vessels also tend toward fairly typical drive lines “with one or two two-stroke engines, propeller shafts and so on… so you could create a complete propulsion package delivered in a range of vessel sizes”.

Martinsen adds that when it comes to cargo ship engines “we are not suggesting swapping big lumps of metal, instead we’re talking about transitional technologies that can adapt to new requirements”.

In fact, large, robust two-strokes don’t need so much in the way of modification. For example high-pressure engines like those from MAN ES currently allow for mixing different energy sources such as methanol and ammonia with more standard LNG: “This strategy allows you to step down in stages over time, all the way to zero emission fuels.”

FUEL PATHWAYS

Ammonia and methanol aren’t the only candidates: there are potential crossovers from a number of directions. Wärtsilä has already equipped ethane carriers with 50DF engines, and within the company’s landside power generation arm are plants running on LPG.

But there are varying levels of challenge inherent in repurposing the different engine systems and so fuel ‘pathways’ will likely open up.

For example, Höglund points out that as liquid petroleum gas, LPG, consists largely of propane and butane, “it needs rather different treatment to LNG – which is mostly methane”.

However, when it comes to big two-strokes, Dahl adds: “While ammonia is still in the development phase, LPG is a good first step.” The two have enough characteristics in common that MAN’s ME-LGIP engine can burn ammonia, using the same cylinder cover, injection valve and gas block – albeit with the addition of larger tanks.

FUTURE KIT

It’s worth mentioning alternative power technologies: “If you’re considering modularity, there’s a lot to be said for batteries,” says Höglund. And since the cells are now half the size and double the capacity of a decade ago, producers such as Stirling PBES are recoring their systems, retaining the cooling and control architecture but swapping the old cells for more efficient versions.

There are certain limitations: “If the amount of power taken out in one go stays at a similar level, your electrical equipment can remain roughly the same,” explains Höglund. However, increasing peak power output may impact other components, such as converters, transformers and switchboards – so those too could require future-proof capacity.

Likewise, ABB is now collaborating with Hydrogène de France on megawatt-scale fuel cell systems able to power ocean-going vessels. Further, since they’re going to be based on proton exchange membrane (PEM) solutions developed by Ballard, they only need pure hydrogen and oxygen feeds, allowing flexible positioning around the ship. In fact, PEM cell stacks are almost ideally suited to modular, distributed energy configurations.

RELIABILITY

For owners, yards and equipment manufacturers, modularisation promises greater reliability, lower lead and build times and generally far less fuss. Moreover, for class societies like DNV GL it could mean “a move toward system-level analysis, the focus shifting from individual ships to repeatable modules” says Knutsen.

What it doesn’t promise is lower CAPEX. In fact, some research suggests that it will initially be more expensive – how much isn’t currently known – though as Martinsen has already pointed out, placing the wrong bet on the future will likely cost more in the long run.

Energy storage safety for commercial vessels; lessons learned in practical application

By Brent Perry, CEO, SPBES

Published in G Captain on February 3, 2020. https://gcaptain.com/advances-in-battery-safety-and-technology/

Forward

A Li-ion battery has several potential hazards that must be considered in order to keep people and equipment safe. It is important to consider these hazards for each stage of the battery life, not just the day it is installed. From manufacturing through to delivery, installation, commissioning, maintenance and eventually the recycling of the battery, safety must be first and foremost.

At the core of the system is the lithium-ion cell; a chemical power plant that cannot be simply switched off in order to make it safe. A battery cell is by its nature always live; therefore, it is important to ensure the safety of personnel from this potential hazard. The voltage on a single cell is low and therefore not hazardous, however the potential current is very high since the internal resistance of the cell is low. Shorting the positive and negative with a metal object will either result in the battery terminals evaporating or the metal object getting very hot.

During manufacturing, special tooling and processes are used to decrease the risk of short circuit of a cell. When the cells are assembled in series to form higher voltages collectively in a module, the voltage becomes more dangerous. Again, special assembly tooling is used to protect personnel against accidental shorting. Once assembled it is important to protect personnel from this voltage during transportation, installation, commissioning and de-commissioning.

For this, SPBES uses a contactor inside the module to isolate the battery voltage from the battery terminals. This contactor can only be closed by the Battery Management System (BMS) during operation, therefore eliminating all voltage related hazards when it is not in use. The total battery voltage once installed is very dangerous considering we commonly install batteries at bus voltages higher than 700VDC and up to 1500VDC. The protection for this is done through proper isolation design, the use of breakers and independent safety circuits like high voltage interlocks, independent breaker trips and ground fault detection.

The system is also designed to reduce the voltage anywhere on the installation to less than 100V when the system is off. This ensures that any unintentional shorts will not result in a dangerously high current and potential damage to the system.

Thermal runaway is a potentially catastrophic hazard that must also be in the front of an engineer’s mind when designing a lithium-ion battery. It is rare that thermal runaway occurs, but the impact can be devastating when it does . Our design philosophy is to eliminate the risk completely through our patented cooling system, CellCoolTM.

Rather than trying to manage the potential consequences of a thermal runaway event, SPBES has always focused on removing this hazard completely.  Even if the cell heats up, regardless of the reason, SPBES’ system can remove the heat quick enough to prevent thermal runaway from occurring. Additionally, SPBES’s cooling system protects the cells from external heat sources such as a fire outside the battery.

Our philosophy has always been and always will be to protect the vessel and crew to the best of our ability, incorporating new safety innovations from our R&D team as they become available.

Advances in Battery Safety and Technology

Battery technology has evolved very quickly, but hybrid and electric marine propulsion is still a relatively young industry.  As of today, there are still no commercial systems that can claim to have been in operation for 10 years.  Despite this, the economic and environmental advantages of battery storage have meant that there are now dozens of ships operating in hybrid and full electric modes. By recent estimates, Energy Storage Systems (ESS) are now being incorporated in roughly 75% of refits and new build vessels around the world.

In 2009 I designed my first lithium batteries for marine applications.  These were designed to demonstrate the principal that MW scale ESS could work like traditional propulsion while delivering real commercial value; and there were a lot of doubters.  Today, we have evolved not only performance, but safety, integration, cost and risk management to much more predictable levels.  The data obtained from constant commercial use of the battery system provided invaluable information that allowed us to evolve and continuously improve our systems.

The Classification Societies and Flag Authorities have also constantly pushed for better and better systems.  These agencies have been incorporating powerful risk evaluation tools to ensure operator and passenger safety as system capacities got bigger and bigger.

Operational data and experience have led to significant improvements in battery design resulting in improved safety, system life, risk reduction and overall performance. The improved performance of modern marine batteries have also changed the market. Lower system cost means more and more marine verticals are now finding ROI from energy storage. For example, during the formation of the marine ESS industry, tugboats and ferries represented the best commercial applications for energy storage systems. Today we can add cruise ships, oil and gas, offshore and wind farms vessels to a never-growing list of commercial vessels that are making an ever-greater use of energy storage.

The key considerations of effective battery design start with two principal issues 1) an ESS must be an improvement to the existing methods of operating ships, and 2) the solution has to deliver financial benefits without external support (government grants or tax credit schemes) in order to permanently earn its place as a part of system design.

These are the key questions that we asked when at the design table for our current systems, understanding that they are the key to success. However, we also knew from years of real-world experience that the following criteria are also critically important to long term commercial success:

Safety: we had to be able to effectively eliminate the possibility of thermal runaway in a battery system, otherwise we will never see true acceptability in the markets and growth in system size.  This challenge was at the top of our minds in every design decision, and we addressed it by creating our patented CellCool^TM cooling system that effectively removes the risk of thermal runaway.

The principal is very simple; reduce the temperature of the cells at a faster rate than the cell increases in temperature. No matter how hard you work them, with CellCool^TM they will not achieve the temperature required to go into thermal runaway.  We worked in cooperation with Classification Societies and Flag Authorities to developed what we all felt were difficult to pass safety tests designed to demonstrate that batteries are inherently safe.  We took this to another level and set our own gold standard as safety in the face of spontaneous combustion- the most difficult test that a battery can face.

Even in this very demanding test, we have proven success. Our systems are able to prevent significant damage to the battery (including propagation at the cell level) and ultimately make every system safe to operate.  This is done with an inherently simple liquid cooling system.  It cannot be achieved with air cooling systems due to the issue of managing transfer of heat with something as energy dense as most lithium chemistries.

Safety has other considerations as well; there is disaster safety at the cell level, and then there is safe use of batteries. We designed a BMS that is inherently focussed on protecting the ship, the battery system and the cells.  This is done at its core by monitoring the voltage and temperature of every individual cell in the system, and then balancing the performance of the vessel within the safe operating principals of the ship.

There are two different ways to design a BMS; one that is ideal for a fully electric ship and one that suits hybrid applications.  While both in principal will give the operators choices in the event of a battery failure, in a fully electric ship, the safe operation of the vessel becomes the guiding principal of the decision making of the BMS and Power Management System (PMS). In a hybrid application, the batteries can become the focus of the performance of the PMS as the vessel has alternative propulsion systems and is not totally reliant on the battery for operation.  Once we define the type of application as either hybrid or electric, we can optimize the operational logic of the BMS as it pertains to the PMS/operator decision making criteria.

Another critical element of safety in design has been the inclusion of contactors in our building block modules.  Basically, as we are building DC voltage systems that range from 300-1500VDC, the risk of personal injury in transportation and service are very high. For example, a 1500 VDC arc flash can permanently disable a technician.  By adding contactors in the individual battery modules, we eliminate voltage at the terminals until the system is fully engaged and the BMS can approve that all cables are correctly sequenced and protected.  There is no voltage or power on the terminals as long as they are open.  We also reduce the risk by isolating the building blocks as single units no matter how large the overall size.  The element of crew safety of our technicians and the operators of the vessels cannot be overstated in terms of benefit to our customers. We can now train ships engineers and crew to do maintenance on the batteries, we don’t need to bring in specially qualified electricians to do basic maintenance.  This design decision was not free, but it is the right way to go to improve overall safety for our customers ships.

Cost: Another critical part of the design of a battery is not the actual battery itself, but the space the battery operates in. The impact of incremental costs of necessary added systems required for safe operations is significant. In most cases, and in our earlier designs, things like fire safety, fire detection, gas detection, gas extraction, cooling and emergency ventilation were left to other contractors and not included in the cost of the battery system.  These so-called add-on systems are actually critical to the performance of a battery and are not optional, but in most cases battery suppliers will leave these added costs to the ships builders.

Our approach became more holistic and covered all parts of the battery system as our design evolved, which means less added cost per kWh and more integrated engineering.  Our next evolution in development is to validate the design of our core modules to withstand an A60 battery test. Validation of this test will eliminate the need to build an A60 enclosure for the batteries.

To put this in context, one of our integrator partners determined that the typical added cost of a battery system could be as high as $275/kWh for a total battery installation, this cost comes on top of the cost of the batteries themselves.

It is essential that integrators and end customers always understand the overall system costs to allow decisions to be made on return on investment based on the actual installed system costs not just the battery cost.  In fact, SPBES is not completely immune to this cost; our liquid cooling requires chillers sized to meet the power demand of the system and our gas extraction system must be correctly vented, but instead of $275/kWh, we face a cost typically of $20/kWh for the added components and to meet all performance requirements.

Another benefit of SPBES CellCool liquid cooling is the ability to actually predict the life of our systems. Air cooled systems are very dependent on the ambient battery room temperature to be able to manage the overall life of a lithium battery, and they are very fickle. Even a small increase in ambient battery room temperature will affect the temperature of the lithium cells andcan have a significant reduction in calendar life.  In contrast, liquid cooling maintains the temperature of the cells at a fixed range and we can eliminate the impact of ambient temperature on the performance life of the cells.

As system life continues to be in the 10-year range and with many operators seeking longer-life solutions, eliminating temperature as a variable goes a long way to meeting lifespan requirements.  There are still a large number of factors that will influence battery life, but temperature is by far the most impactful.

System Size: Another area where we have seen a significant evolution both in the use of cells and the design of a battery is size. Cell manufacturers have significantly improved energy density over the last ten years. By increasing the energy density of the lithium-ion cells, a significantly smaller system can be created. For example, a system with 88kWh per module versus a battery that has 65kWh per module has already achieved 35%improvement of weight and space required for an installation.  As long as the cycle life meets the lifetime need, this is a huge improvement. In my experience, increases in energy density tend to a reduced cycle life.

The other significant feature of any system is the percentage of energy available on a continuous basis. On our first-generation air-cooled design, the continuous rating was about 70%. This meant that if we needed 1MW of energy, we needed to have about 1.4MWh of capacity to operate at 1MW load. This meant a larger, heavier system that was also significantly more costly to install and maintain.  If we assumed that the battery system cost $100/kWh, then a 1.4MWh battery would add $140,000 to the capital cost of the system – and does not even consider the ongoing performance and financial impacts of the increased size, weight and maintenance!

A liquid cooling system allows SPBES to use significantly more of the battery capacity. This really means we can greatly reduce the size and the associated costs of the battery. In our case, the battery can now operate at an average continuous rate (charge and discharge) of 300%.  In the example above, a 1MWh system can now be met with a 350kWh battery; much smaller, much lighter, and much less costly to install, with only a $35,000 budget needed (if the necessary costs were $100/kWh).

While the above model is not always accurate, it is more reflective in what we call power systems.  In energy systems where a slower, more steady output of energy is required, size is totally dependent on capacity.  Clients and operators will understand the concept that their vessels are operating underpower or energy requirements and where energy is the driver, we have engineered a battery system where we can simply use the same battery with all of the same components, but with cells that have higher energy density- so we can significantly reduce the footprint of the battery system.

Sustainability: A battery that can last for ten years is a pretty amazing thing, but it will never match the lifespan of the vessel itself. This equates to significant costs to replace a battery system every five or ten years on a vessel that will be in service for up to 50 years.  We took this challenge, and in analyzing a system, realized that while all components will require some maintenance, the most significant reason for ESS replacement was the fact the cells will age.

The answer to continuous replacement (and the capital costs associated with it) is a design that allows us to remove and renew the cells regularly, i.e. every 5 to 10 years.  If we can keep the bulk of the infrastructure and safety systems in place, then we can reduce the cost of replacing the system to the cost of cell replacement and cell recycling. This radically reduces the total cost of operating an electric or hybrid vessel over its lifetime.

Cell Swap^TM has been at the core of our design since 2015, with every module core (regardless of chemistry of the cells) able to be replaced within 30 minutes.  SPBES technicians can perform CellSwap refurbishment while the ship is running or in for maintenance.  Cell swap means that the battery system life span is now the same as that of the vessel; it is similar to engine maintenance and rebuilds.  With this inclusion, the design of the battery system is now in line with marine market requirements.

Recycling will have an increasingly prominent role in decision making over the next generation. This is part of the benefit of a cell swap; we can safely support the recycling of the lithium cells and do this at a very low cost and impact of operational budgets.  Part of our contracting now is to include end of life recycling with every system. While often overlooked, it is necessary for any company that uses ESS in commercial operations to include this operational expenditure in their impact analysis of utilizing energy storage systems in day to day application.

Where to next?  I think that commercial needs are going to continue to drive improvements. Natural evolution of clean maritime propulsion with products such as fuel cells will significantly improve environmental impact and cost-effective operations.  Organizations like the IMO and Class and Flag Authorities will continue to motivate us to move the technology forward in order to meet the needs not only of our industry, but those of society as well. We look forward to the challenges of the future and the next generation of developments to come.