Why UPS needs to be Li-ion ready

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    Centiel sales and marketing director Mike Elms provides an insight into lithium-ion battery technology and predicts that it will become mainstream for UPS applications in the future

    Developments in UPS technology have focused heavily on improving efficiency, reliability and availability. Increases in operating efficiencies while in online double conversion mode have primarily been achieved by the introduction of transformerless technology
    in the 1990s. 

    The removal of the bulky transformer, with the associated significant reductions in size, footprint and weight, led to the innovation of the modular concept. This in turn reduced the important mean time to repair (MTTR) figure, thereby significantly increasing availability. 

    Development in UPS design now realises efficiency figures of 97+%, and the evolution of several generations of modular UPS systems has increased availability from 99.9995% to 99.9999999%. Downtime has been reduced from seconds to milliseconds. 

    Of course, a UPS system does not just comprise of the UPS units themselves but also includes the vital dc source needed to convert and provide outpower power in the event of a mains supply failure. 

    This dc source has predominantly remained the battery: a simple chemical device used to store energy until it is required. For the UPS world, the traditional ‘go to’ battery has been the valve regulated lead acid (VRLA) block.

    VRLA has been around for a long time for many good reasons: the technology is old but proven, it is robust, price competitive, the batteries are recyclable and, as a result, has been the backup of choice for the vast majority of UPS systems (note that batteries for UPS systems have been specifically designed for the unique characteristics of the application and therefore the correct battery type must always be used).

    Like any industry, there are always improvements in technology and a change in battery type is coming. In the not-so-distant future, UPS systems will be supported by lithium-ion (Li-ion) battery technology. 

    Li-ion batteries have their origins in the early 1970s but the commercial success was really driven by Sony with its handheld video camera of the early 1990s. Continued growth and development has been driven by laptops, then mobile phones because we all want our electronics to be smaller, cheaper, more powerful and operate for longer periods.

    While critical IT power protection solutions and handheld electronics both share the common goals of demanding more power, occupying less space, longer run times and a justifiable price point, the batteries supporting consumer electronics are not the same as those for data centres.

    Interestingly, the adoption of Li-ion within UPS systems so far has been greater in developing countries in Africa and also the Middle East, where the main power grid is less reliable than in the UK and frequent power problems are more commonplace. In these instances, the UPS and battery systems are required to be cycled several times per day. This greater adoption is primarily due to the higher cycling life of Li-ion: typically, 2,500 power-up and down cycles compared with about 300 for VRLA technology.

    In the UK and Europe, different drivers including the continued rising cost of real estate will influence the adoption of Li-ion technology far more. This is because the main disadvantages of VRLA batteries are their size and weight. Above ground-floor installation can require structural strengthening of the building simply to house the required batteries. Logistically, moving many tonnes of equipment in and out of an upstairs comms room when batteries need replacing can also present challenges.

    In terms of physical footprint, there is a significant difference in the two technologies: Li-ion occupies <50% of the size and <25% of the weight of VRLA batteries. Although they are currently a more expensive purchase option, Li-ion’s price is falling rapidly (approximately 80% since 2010) and as a result, cost models and ROI are starting to look increasingly favourable. If you consider the value of comms room space, Li-ion is now starting to be viable for data centres looking to increase their power density within the same footprint. In fact we know a small number of European facilities now incorporating small Li-ion systems in their UPS including one well-known search engine.

    A further advantage of Li-ion is that it can work at a higher temperature, therefore requiring less expensive cooling and reducing the amount of overall energy consumed in the comms room. By contrast, an industry standard estimate is that for every 10 degrees above 200C the operating life of a VRLA battery is halved. 

    As well as being much lighter and able to work at a higher temperature, Li-ion has a significantly longer design life (about 15 to 17 years) compared with VRLA, which normally needs replacing every seven to eight years for a 10-year design life battery. This level of maintenance can cause issues in itself. 

    Depending on what you read, there are numerous of sources of data that suggest a sizable proportion of problems are caused by battery systems. Of course, things are always improving and some battery monitoring systems also equalise the charge over battery systems, resulting in extended life. However, when you evaluate total cost of ownership, Li-ion is indeed becoming a more attractive solution.

    So are Li-ion batteries ready for primetime and powering the majority of critical facilities? Not all Li-ion batteries are the same; like the VRLA battery, the correct type of block must be chosen to suit the specific application. Common variants of Li-ion are cobalt, manganese, phosphate, aluminum and titanite. These all display different levels of characteristics and performance: recharge time, power density and the capability to operate at higher temperatures. Depending on the choice of material for a Li-ion battery, its voltage, energy density, working life time and safety can vary dramatically. 

    Lithium cobalt oxide (LCO) offers a higher energy density but presents safety risks, especially when damaged. This chemical composition is widely used in consumer electronics. Lithium-iron phosphate (LFP), lithium-manganese oxide (LMO) and lithium nickel manganese cobalt oxide (NMC) batteries offer a lower energy density but are inherently safer. In UPS applications, the most commonly used are LMO and NMC, which offer the best compromise between performance and safety levels currently available on the Li-ion market.

    In the past, you may have read some troubling stories in the press, predominantly about consumer electronic devices. Perhaps you remember the Samsung Note 7s catching fire and being banned from being taken on aircraft? The amount of energy density stored in these devices batteries does present specific problems. Although the incident rate is low compared with the huge quantity of devices in the field, it is still an area that needs addressing. 

    However, high-end applications such as UPS systems do not quite present the same challenges. Li-ion batteries for UPS systems offer safer chemistries, bigger operating parameters, more robust materials and less stressed user environments. Li-ion manufacturers use x-rays as part of quality control and there are safety fuses overcharge protection built in. 

    Chemistry and cell science has improved but so has the electronic management systems which monitor the battery system, obtaining details of each individual cell such as voltage, current, temperature and alarms, and control the charging regime appropriately. 

    Because nobody likes being a guinea pig and, by its very nature, the critical power protection industry tends to be particularly risk averse, the first moves to Li-ion batteries in the UPS industry will be by innovators. How soon they will be adopted by the mainstream will likely depend on the experience of these first installations.

    We believe that over time there will be a move towards Li-ion batteries as cost reductions, driven by developments in the automotive industry, flow through to the standby power sectors. 

    Incorporating Li-ion batteries will inevitably reduce the size and weight of UPS systems and the longer useful working life of Li-ion will mean fewer costly replacements. All of which will benefit customers with reductions in both capex and opex and make Li-ion batteries a winning solution for UPS applications requiring compact, innovative protection. 

    The UPS systems of the future will need to be designed with Li-ion in mind.

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