By Grant Brown, Vice President, Marketing, PBES
The growing numbers in hybrid or fully electric ships navigating waters worldwide has increased concerns about their onboard power supply requirements, reports Marine log.
Although some estimate that all modern commercial vessels will soon have some form of energy storage on board, however, safety concerns still linger and should be kept at the utmost of considerations for this new technology.
Not all battery systems are equipped with the same safety systems. Testing and certification for battery systems aboard ships has increased, but room remains to raise the bar higher.
Here are some pointers that might be worth looking at to bridge the gap in the improving battery safety.
Current Marine Battery Testing & Certification Failings
One of the biggest risks for batteries is thermal runaway. Thermal runaway occurs if the lithium-ion cells used in marine batteries are subjected to mechanical abuse, suffer from internal manufacturing defects, or operate over or under the correct voltage or temperature, heat is generated within the lithium-ion cells and causes a reaction between the cathode material and electrolyte. This can result in the cells’ temperature increasing until the cell vents toxic and flammable gasses. If ignition occurs, these gases can create an unpredictable fire, which can be very difficult to extinguish.
The minimum requirement by the Norwegian Maritime Authority for batteries used in commercial vessels in Norway is the Propagation Test Type 1. NME Propagation Test Type 1 is intended to prevent propagation of the thermal event from one module to the next. This test simply means that if a cell in a single module enters thermal runaway and ignites, fire will consume the module but will not ignite the other modules in the pack, and thus the larger system remains safe.
However, in the event of an overcharge situation where it is most likely a fault of charging software, or in event of catastrophic mechanical damage, it is much more probable that,
a) the entire system was damaged or
b) any number of individual modules were damaged.
In a multi module event, it is my assertion that NMA Propagation Test Type 1 may not prevent propagation from module to module.
Using an air cooling system in an attempt to try to maintain safe internal temperatures questions the effectiveness and the reliance on a thin-layer fire-resistant separator between cells which only reduces the fire risk from thermal runaway – it does not prevent it.
Almost all of these manufacturers claim this “inherent” and “passive” system prevents propagation from one module to the next. This is the minimum requirement by the Norwegian Maritime Authority Propagation Test Type 1 for batteries used in commercial vessels in Norway.
The Solution – Prevent Thermal Runaway
Liquid cooling is the only safety system currently tested and proven to prevent thermal runaway. Liquid cooling prevents batteries from entering thermal runaway by simply extracting more heat than the cells can produce.
Its similar to an engine block of an automobile, a low pressure, high volume closed loop of chilled water is circulated through the battery. PBES has developed a proprietary cooling system, CellCool that takes the idea one step further and circulates coolant through the alloy core of the battery, around each individual cell in every battery.
The PBES CellCool is able to remove more thermal energy than the cells can produce when in an overcharge or damage scenario. Testing shows that the PBES system is so effective enough even if the coolant pump is disabled, i.e. in the event of catastrophic damage to the vessel, the system will still protect the batteries.
Due to its patented design, CellCool also eliminates hot spots on the cells and maintains optimal cell temperature thus increasing lifespan.
In comparison, forced air cooling only cools the external surfaces of the module and is ineffective at eliminating hot spots in the cells. An air-cooled battery requires around 3500 times more air flow volume than water flow volume to achieve the same heat removal.
Additional Safety Considerations – Thermal Barriers and Venting
An internal thermal barrier is an essential part of lithium battery safety systems. PBES Thermal-Stop has a metal barrier integral to the structure of the battery that works similar to a firewall. It prevents an overheated, overcharged or damaged cell from propagating to the adjacent cell.
This isolates one cell with another and does not affect others. Ignition will not jump to adjacent cells because of the metallic barrier between them.
In the event of a damaged cell within a module, dangerous gases can be released. It’s important for every supplier to create safe venting for battery systems. E-Vent is a PBES patented system to vent flammable gasses from a damaged module safely away from the battery area. It reduces risk of a secondary explosion and allows the crew to re-enter the vicinity of the battery system sooner to make repairs and restore power.
Using the PBES CellCool system, the cells simply do not combust. In fact, when the test modules were disassembled and inspected, the cells that had been overcharged looked virtually identical to untested units, save a small rupture on the top of the cell near the terminals.
Conclusions – Will it happen on your watch?
Given the rapid rise in the use of large format lithium-ion batteries in commercial marine vessels, I believe that energy storage system safety is lacking.
It is the responsibility of industry and regulators to do everything possible to ensure a major incident does not occur. Unfortunately, the majority of the industry has responded to price pressure from owners and operators by reducing costs and subsequently, safety systems do not meet the bare minimum of requirements.
In the interest of hastening the adoption of energy storage in industry, PBES has always been willing to license its safety systems. This will help those who wish to go beyond the minimum requirements and help make the clean marine industry move forward. Otherwise, the industry may have to suffer the consequences of inaction.
Disclaimer: This video is intended for informational purpose only. This may not be construed as a news item or advice of any sort. Please consult the experts in that field for the authenticity of the presentations.
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Source: Marinelog
