For UPS system builders and users today, two battery chemistries predominate; lead acid, typically VRLA, and lithium ion (Li-ion). VRLA is long-established with a majority market share, while champions of the relatively new Li-ion products claim them as superior UPS standby power solutions.
Kohler Uninterruptible Power (KUP) is neutral in this debate, without commitment to either battery type. From this position, Alex Emms, Operations Director at Kohler Uninterruptible Power, compares the two chemistries. Then he considers why, given Li-ion’s claimed benefits, VRLA types remain dominant for UPS standby applications. Finally, he speculates on the future balance between Li-ion and VRLA.
Primarily, Li-ion batteries have a better power-to-weight ratio than similarly-rated VRLA types, as shown in Table 1:
hey also discharge more efficiently than VRLA at high C (discharge) rates, although this advantage erodes at lower C rates. Charging rates from fully-discharged are also higher with suitable chargers. Another claimed advantage is a very wide usable temperature range, although discharge rates and longevity can be optimised by operating at 23°C ± 5°C. Li-ion batteries have improved resilience to temperatures outside this range, with much better low-temperature discharge capabilities, than VRLA. However, like VRLA, operating at excessively high temperatures significantly reduces Li-ion batteries’ useful life.
Cost is another critical factor. Prices have fallen significantly – up to 85% - over the last decade, and these reductions naturally increase Li-ion’s appeal. However, as Table 2 shows, Li-ion pricing is still a barrier.
NB: VRLA systems include PowerNSURE battery management system.
Adoption & Pricing
However, we are definitely in early stages of adoption. While prices aren’t decreasing as fast as previously, they are still tracking down, creating a significant uptick in adoption. EMEA lags in Li-ion adoption but deployments are picking up in NAM and Asia much faster. Fig.1 shows historical and projected future trends for battery pack manufacturing costs.
Fig.1: Electric vehicle battery manufacturing cost trends
Design life is another factor, for which manufacturers are quoting up to 15 years. Operational life is probably nearer 10-12 years, but not yet proven. This compares with a real-life norm of 7-8 years for VRLA.
So why don’t Li-ion batteries dominate the UPS market?
Li-ion protagonists point to the batteries’ longevity as an advantage offsetting its higher capital cost. However, KUP’s experience shows that UPSs correctly installed in a suitable environment and properly maintained and supported are typically reliable for 15 years. This neatly matches two consecutive 7-8 year VRLA lifetimes but raises replacement co-ordination issues with 12-year Li-ion batteries.
Li-ion is also disadvantaged by the true costs of achieving suitable autonomy, which is traditionally 10-15 minutes for UPSs. However, in reality most blackouts last either for three minutes or less or for closer to three hours. While VRLA costs can be decreased by designing for this lower autonomy, the same isn’t true for Li-ion. Such short autonomies can only be achieved from more expensive higher discharge-rate cells. Accurately and cost-effectively sizing for different loads is also difficult, with Li-ion’s currently very limited choice of capacities.
There is also an element of mistrust. In reality, manufacturers have considerably progressed in addressing safety fears through highly-segregated cell designs and mandatory advanced monitoring and management systems. Yet Li-ion is still sometimes seen as unproven - and thus a safety risk.
End-of-life creates further problems; an exhausted Li-ion battery primarily comprises hazardous waste that’s difficult to recycle and subject to high costs and restrictions during transportation. By contrast, VRLA is up to 98% recyclable. However, lithium battery recycling research initiatives, including one by the US Energy Department, are now underway.
What of the future?
As prices continue falling and Li-ion becomes more accepted, the chemistry’s penetration of the data centre battery market can be expected to increase. Bloomberg New Energy Finance forecasts a market share increase from 1 per cent in 2016 to 35 per cent in 2005.
However, VRLA will also continue developing and fighting for its market share. While not mandatory for VRLA, increasing use is being made of battery monitoring and management systems. Kohler Uninterruptible Power’s PowerNSURE, for example, can increase battery life by up to 30 per cent, while also increasing reliability and reducing maintenance costs.