Tired batteries? Go lithium-ion
Lithium-ion has revolutionised battery energy technology storage across multiple industries, offering unrivalled performance, capacity, weight and longevity advantages. But what are the cost implications of upgrading to lithium-ion?
Lithium-ion battery technology offers unrivalled performance, capacity, weight and longevity advantages. But what are the cost implications of upgrading?
Jeremy Peacock, co-owner of marine energy specialists Enertec, likes to illustrate the cost vs performance profile of the technology through examples, and stresses that not all lithium-ion batteries are created equal.
A typical lead-acid (flooded/agm/gel) battery bank for this size vessel is a 12-volt system of around 400 AH capacity. Two of the biggest issues with lead-acid battery technology are the small amount of usable capacity and the slow recharge ability.
Li-ion batteries have created a far superior alternative in both areas, along with a vast reduction in battery weight and size, better voltage stability and far greater cycle life. To accurately compare the two types of batteries, let’s first look at the differences between the two technologies.
USABLE CAPACITY
All types of lead-acid batteries use the same chemistry, which limits the technology’s performance. One limiting factor is ‘usable capacity’. This refers to the percentage of the battery that can be discharged and recharged (depth of discharge – DOD) without seriously degrading the cycle life. Users are advised not to discharge the battery below 50% State of Charge (SOC).
Recharging lead-acid batteries is very slow – around four hours to fully recharge from 50% SOC. The slowest portion of the battery to recover is the last 15% which takes around three hours to recharge – no matter how powerful the charging system.
Away from the marina most vessels of this size rely on engine and/or solar charging. So, because of the time it takes to recover lead-acid batteries it is not practical (often impossible), to recover a lead-acid battery bank past 75% SOC when at sea.
Realistically this only allows for a usable capacity of approximately 35% of the total battery capacity (see Fig 1).
In our typical 40-43 ft vessel with 400 AH of house battery capacity, this equals around 140 AH of usable energy.
Li-ion batteries use a different chemistry which allows them to be discharged to a far greater depth than lead-acid batteries while still offering a vastly superior cycle life. They can also be charged much faster making it possible to recover them to 100% SOC from an engine alternator or solar. (See Fig 2.)
Using Juice PRO Series Li-ion batteries as an example, these can be discharged to 20% SOC and then fully recharged to 100% SOC in an hour – with the correct charge ratio. In most cases the vessel’s charging system will not be powerful enough to achieve charging this quickly, but even with a smaller system, charging will be considerably faster than for lead-acid technology.
These two advantages allow Juice PRO Series Liion batteries to deliver 80% of their rated capacity as usable energy (see Fig 1).
In our typical 40-43ft vessel this would allow the installation of a single 12V 200 AH Juice PRO Series battery in the place of the 400 AH lead acid bank. This single 12V 200 AH Li-ion battery would provide 160 AH of usable energy, require less space and reduce battery weight from around 140kg to only 27kg.
The end result is a battery of half of the nominal capacity providing the same, and often greater, usable energy.
CYCLE LIFE
Cycle life refers to the number of times a battery can be discharged and recharged before it is degraded beyond viability.
Li-ion batteries offer far greater cycle life than lead-acid, allowing them to deliver considerably more energy during their service life (see Fig 3).
A typical lead acid AGM battery will have a cycle life rated at approx. 500 cycles to 50% DOD. Li-ion tecšology, like that used for the Juice PRO Series batteries, offers 3000+ cycles down to 80% DOD.
Combining their greater usable capacity and far greater cycle life, Li-ion batteries deliver around 9-10 times the energy throughout their life than conventional lead-acid tecšologies.
LI-ION BATTERIES OFFER FAR GREATER CYCLE LIFE THAN LEAD-ACID...
From a cost perspective, while a high-quality Li-ion battery will cost around two or three times as much as lead-acid variants, the cost analysis stacks firmly in favour of Li-ion batteries. No surprise then, that today nearly every industry sector reliant on stored energy uses Li-ion tecšologies.
INSTALLATION
Full disclosure: changing from lead-acid to Li-ion batteries is not as simple as removing the old and dropping in the new. Installations in New Zealand or Australia must comply with the marine electrical regulations (AS/NZS 3004.2:2014). These specify the requirements for installing Li-ion batteries.
Among other things, these regulations require the battery to be able to disconnect the load (after a prealarm) to prevent it from over-discharge. It must also be able to disconnect all charge sources (after a pre-alarm) – preventing charging issues from damaging the vessel’s Li-ion batteries and wider electrical system.
When installing compliant li-ion batteries, the biggest variable is how the charge control side of the battery system will work. This feature allows the battery to disconnect charge sources in the event of any problems.
Some manufacturers require all the charging equipment (alternator regulators, AC battery chargers, solar regulators etc.) to be the same brand as the batteries. Others, like the Juice PRO Series, are designed to work with a variety of makes and models and don’t require specific Li-ion settings on the equipment.
This reduces installation time when swapping to Li-ion batteries and significantly lowers the overall cost of the changeover. The flexibility in controlling charge sources is achieved by using an integrated solid-state charge control relay on the battery, sending a signal to each charge source to switch off if there is a charging issue.
Although it takes longer to install compliant Li-ion batteries compared to traditional lead-acid batteries, a correctly designed Li-ion installation is relatively straight forward. Suppliers will advise on the best system design for your vessel and ensure compliance with the marine electrical regulations.