In this guest post, Jack Pearce, CEO of green critical power systems manufacturer Active Power, outlines the risks involved with using battery-based power in datacentres
A datacentre uninterruptible power supply (UPS) is a piece of electrical apparatus that provides emergency power in the event of service disruption. They exist to provide reliability and reassurance. They are designed and deployed to remove risk. But not all UPSs are equal. Some also come with their own risk.
When comparing where the power for an UPS originates it is clear that not all risks are the same. Especially when it comes to fire.
There are two main UPS energy sources. The first and oldest energy source is kinetic flywheel power. The second is battery power – i.e. the first is electromechanical power and second electrochemical power.
Figures show that flywheel kinetic electromechanical power sources are inherently more reliable than batteries. The time difference of mean time between failures of the different systems is measured in decades. This is not theoretical. Through field studies and benchmarks flywheel energy storage (FES) has long been recognised for its long operational lifetime, often stretching to decades with little or no maintenance intervention.
And with continuous operation fewer failures mean less chance of escalation to catastrophic consequences.
The history of battery technologies is long and fascinating, and many problems have been overcome to give the world mobile energy sources.
Small lithium ion batteries have revolutionised the world. But even when laptop PCs first became popular, there were reports of overheating and fire risks. One does not have to be too old to recall the time when laptops on aeroplanes had to be powered down. There was even talk of banning laptops on planes.
Lithium ion has become the default energy store for devices and electric vehicles. Though in transport e-scooters overheating and causing fires are being reported.
Large scale fixed battery stores
But what about fixed energy storage in places that require a fast, large power source to maintain a load in the event of a main power outage (while the gensets fire up)?
Here a ‘battery backed UPS’ depends on rows and rows of batteries in racks connected to create modules.
These were once mainly VRLA batteries deployments. This has latterly shifted to using Lithium-ion batteries which for a variety of reasons have become more widely deployed for Energy Storage Systems (ESS).
So, what are some of the risks associated with large arrays of Li-ion batteries?
Controlfiresystems.com says: “For all their benefits, Li-ion ESSs come with significant risks. Malfunctioning cells can easily trigger a thermal runaway, where damage spreads catastrophically throughout neighboring battery racks. High heat causes flammable outgassing and explosive ruptures in the surrounding batteries, which can in turn propagate the damage outward.”
A battery fire is a chemical fire with the specific risks of any chemical ignition such as explosion. ‘Thermal runaway’ can occur from short circuit faults within the battery, excessive recharge or discharge in operation or from external factors such as excessive heat. Even where there is no ignition source toxic chemical release must be mitigated.
According to a paper written by the UK’s Fire Protection Association the basic safety evaluation requirements for battery ESS at a commercial or industrial scale are extensive. It says: “The potential for both property loss and business interruption should be considered. The fire protection and mitigation strategy should be determined on a case-by-case basis, based on battery type, BESS location, layout, compartment construction, system criticality, and other relevant factors. It should be multilayered and include a combination of; good design, thermal runaway avoidance, early detection, and automatic suppression.”
Compartmentation is a tactic which aims to hinder fire propagation and avoid a cascading failure. However, in buildings with restricted outside space this can prove difficult. And all battery systems require expensive BMS (Battery Management System).
As Li-ion use expands to more areas of life – small devices, EVs, large industrial BESS and energy grid storage it is getting more and more media attention and more attention from regulators in power, marine, aviation and manufacturing.
In comparison with electromechanical kinetic flywheel energy storage the fire risk and management overheads (fire risk insurance, aircon for cooling, monitoring, physical footprint, refresh and disposal costs) are significant.
Energy storage is too important for all risks and exposure not to be assessed before making final decisions.