When selecting a UPS system to protect your server room or other critical IT applications, how do you choose between a traditional lead acid battery for your UPS and the latest lithium-ion battery backup solutions? Whilst lithium-ion battery packs offer longer working lives, lead acid are the more cost effective and to a wider degree more environmentally friendly. The choice often comes down to cost, availability, and the application needs.
Most people are aware that a UPS system provides battery backup, but few are aware of the three major types of UPS available. The three types of uninterruptible power supply include:
In a typical UPS system, a battery is used to provide backup power when there is a power outage or unstable mains power supply. Lead acid batteries are ideal for this type of standby power application and this type of battery is the same as can be found in several other standby applications including generator starter sets, fire, and alarm panels. The primary type of lead acid battery used in a UPS is AGM (absorbent glass mat) but in larger online three phase UPS installations, flooded or wet cells can also be found.
So where does lithium-ion fit it and what are the key advantages compared to lead acid AGM or wet cells?
Lithium batteries have been in development as a rechargeable backup power solution since around 1917. It is only in recent decades that the technology has evolved into the type of battery we commonly find in mobile phone, tablets and other products requiring a rechargeable battery.
The key benefits of lithium-ion batteries over lead acid types are their energy density, lack of memory and recharge times.
Lead acid batteries are exothermic on recharge and give out heat when charging as the cells generate heat from the chemical reaction going on inside them. Thermal runway is unlikely in a lead acid battery and the primary flammable material (the plastic case) can be made from flame retardant materials complying to BS6290 Part 4.
In a lithium-ion battery, the lithium itself is highly flammable when exposed to air (oxygen). Whilst vehicle manufacturers have been quick to embrace lithium batteries to move away from fossil fuel engines, they are very conscious of the potential thermal runaway problem of lithium-ion batteries. A fire can start if the battery is cracked (during a car crash) or has a manufacturing defect leading to an area where heat can build-up leading to thermal runway and potential fire. A fire that due to nature of the combustible material can take days to put out and cool.
More information on battery types:
The first point to note is that not all UPS manufacturers offer lithium-ion powered UPS systems. Those that do provide limited offers in their UPS ranges. For example, a UPS manufacturer may offer smaller single-phase UPS up to 2-3kVA with lead acid or lithium-ion battery options. These are specific UPS systems designed to work with the respective battery technology and they are not interchangeable. The reason being the unique charging and management characteristics of each type of battery. Prices will also be different with a 20-30% premium being charged for lithium, whether the UPS is an online, line interactive or standby system.
For larger online uninterruptible power supplies, a UPS manufacturer will offer discrete systems or solutions that can be charge either lead acid or lithium batteries. The option is often a firmware setup choice on installation. Again, there will be a price premium for lithium over lead acid. A point to note is that as the size of the UPS in kVA/kW increases so does the size of the UPS battery.
With larger sets this can mean the installation of a sizeable battery within a server room or data centre and if the battery is lead acid, fire suppression should be a key consideration in a risk assessment. If thermal runway were experienced this could lead to fire in the room and the need to evacuate safely and suppress the fire. In addition to a fire suppression system, placing the UPS system and lithium battery set in a separate UPS room that can provide containment of any such and rare issue could help to further reduce the impact of such an event.
At their end of useful life, recycling lithium-ion batteries is a major issue. For lead acid batteries there are multiple established recycling centres and companies. Ups to 90% of a lead acid battery can be reclaimed and recycled including the plastic case, lead terminals & plates, and hydrochloric acid. This is not the case for lithium-ion batteries.
Almost everyone with a mobile phone has become accustomed to the features and benefits offered by lithium-ion battery sets. Older handsets are often sold-on to the second-user market and if a battery requires recycling it is important to place this in the correct waste stream and to consider the battery as general waste.
Lithium battery recycling for electric vehicles (EV) is a problem. So far there is only one dedicated recycling centre in Belgium, Europe. Most of the time EV batteries are repurposed into applications where they can be used for energy storage. Over time the number deployed whether in mobile goods, EVs and UPS systems could lead to a major recycling problem. It is extremely difficult and costly to break down a lithium-ion battery into its components for recycling. Until this problem is solved, and lead acid batteries are on a par for first purchase and recycling, lead acid remains the most sustainable technology.
Today, lead acid batteries remain the first choice for uninterruptible and backup power systems. Not only are they more cost effective when it comes to their purchase, but they are also easier to recycle. Lithium battery installations require less floorspace and offer faster charge/discharge cycles & design lives have a 20—30% greater capital outlay. The are also other installation expenses to consider including environmental monitoring and fire suppression. Lithium therefore has still some way to go before it can dislodge lead acid as the ‘go to’ battery type for UPS installations. Above all the choice depends on how often you expect your UPS battery to discharge. In a typical server room or data centre the UPS battery will either provide short term power as a standby power generator starts up or a longer runtime (using battery extension packs) to either ride through long duration power outages or provide enough time for a controlled shutdown. The fast recharge/charge advantages of lithium only come into play if the site experiences frequent power outages and/or is looking to export excess stored energy to a national grid to benefit from feed-in tariffs. Whilst these may be financially attractive, exporting to an electricity grid could reduce the overall resilience and purpose of the UPS system – to protect critical loads from power outages.
An uninterruptible power supply is a product designed to provide protection from mains borne power problems and a source of backup power when the mains power supply fails. For most people, the two main questions when deciding on the right UPS solution for their application is what size UPS do I need and how long a runtime is required.