Benefits And Challenges Of Lithium Ion Batteries For UPS Systems

- Nov 24, 2016 -

A confluence of events is setting the stage for what may well be dramatic change in a key component of uninterruptible power supply (UPS) technology that really hasn’t changed much for 40 years or more.

I’m referring to the lead acid battery, the energy storage technology used in UPS systems, which remains much the same now as it did decades ago. But as the industry develops new types of batteries for devices ranging from smart phones to electric automobiles, we can clearly see the day when UPSs take advantage of these developments.

It’s coming at a good time, because customers are facing some difficult challenges with respect to UPSs, whether they’re for data centers, critical buildings, industrial processes or critical infrastructure. These challenges are driving the need for specific UPS requirements, including:

·         Reduced UPS footprint and weight to allow for a more effective, flexible use of space

·         Reduced cooling capacity

·         Increased energy storage availability and ability to predict UPS failures

·         Extended UPS life and reduced maintenance overhead

I believe lithium ion hold great promise to address all of these challenges and requirements. In this post I’ll explain the four main reasons why.

First, Li-ion batteries provide multiple times the energy and power density as compared to valve-regulated lead-acid batteries (VRLA), which are the most common type currently used in UPS systems. As a result, UPSs built with Li-ion batteries take up only about one-third the space or less of a VRLA-based solution that delivers the same power.

That smaller footprint translates to reduced cooling requirements as well as about a two-thirds reduction in weight, at least. That means customers have more flexibility in terms of where they install the systems and can often avoid costly building modifications.

Li-ion batteries can also withstand a wider temperature range than VRLA batteries. The rule of thumb is that VRLA battery life is reduced by half for every 10°C (18°F) increase above 25°C (77° F) ambient temperature. Li-ion batteries are far less sensitive to temperature fluctuations and can accept spikes in temperature with almost no effect on battery life. This again allows customers to reduce cooling capacity as well as the size of the room that houses the UPS.

A third benefit is that Li-ion batteries always come with sophisticated battery monitoring systems (BMS) that provide a clear picture of battery runtime and health. It’s essentially the same technology that enables you to easily see how much battery life is left in your smart phone.

In contrast, VRLA batteries rely on chemistry that makes it hard to accurately predict when they’re going to fail. Think about your car battery: it may crank perfectly fine one day but the next it’s a little chilly and the battery fails, without warning. That won’t happen with Li-ion batteries.

Which leads to the final benefit of Li-ion batteries for UPSs: increased life expectancy. In theory, VRLA batteries used in UPS systems have a life expectancy of 10 years. But due to the constraints around being able to determine their actual health and life expectancy, in practice most customers replace them after 5 or 6 years.

In contrast, Li-ion batteries of the sort best suited for UPSs are expected to last for more than 10 years, reducing the burden and cost of battery replacements, as well as the risks of down time or load interruption during maintenance.

Of course no new technology comes without certain implementation challenges and Li-ion batteries are no different. First is the need to find the type of Li-ion battery that’s best suited for UPS applications. UPS requirements are quite different from those for, say, an electric car battery. Car batteries are designed to store lots of energy so the car can travel as many miles as possible before recharging. With UPS batteries, the concern is not length of run time so much as the need to deliver a lot of power quickly for a short period of time, usually just a few minutes until the backup generators kick in.

For a UPS we’re also not really interested in a battery that can cycle on and off thousands of times, because a UPS kicks in only occasionally. Rather, we need it to be highly reliable and safe, with a long life expectancy.

Secondly, we need a battery that can deliver a lower total cost of ownership (TCO) as compared to VRLA batteries. Li-ion batteries are already competitive on that front. They may cost more up front, but will last about twice as long as VRLA batteries. Li-ion batteries also have a far smaller footprint, which drives down both space and cooling requirements – delivering further cost savings.

I expect the TCO story to get even better in coming months and years, since Li-ion technology is still quite new with respect to UPSs. Prices should fall at a much faster rate than that for the mature VLRA technology.

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