Pros and cons of deploying Li-ion batteries
Li-ion batteries burn hotter than lead-acid batteries, and if the battery-containment unit is damaged, it doesn’t react well with oxygen or water, Chris said.
“We’re finding that we do not completely, truly understand all the failure modes of lithium-ion batteries at the moment, and the charging circuits are not able to cope with them all,” he said.
As with any battery, once a Li-ion battery starts to burn, it’s hard to put out. “It’s going to burn until it expends all of its energy, and just dumping water on it doesn’t really help. It keeps it from spreading, perhaps, but it doesn’t help,” Chris said. “And the fact that it burns much hotter than lead-acid batteries [means] it’s going to do a lot more damage. It’s going to burn a lot longer because it stores a lot more energy. And so that’s the problem we’re seeing with lithium-ion everywhere.”
In response, local authorities and regulatory agencies are enacting requirements related to the storage of Li-ion batteries. Chris recommends data-centre operators pay close attention to facility design if Li-ion batteries are part of the plan.
“If you are looking at using lithium-ion batteries, then definitely look at segregating them into their own battery room,” he said. A battery room should have at least a couple of fire-rated walls and ceilings, and operators should consider using a foam fire-suppression system “because at least foam will smother the fire and help to extinguish it, whereas water is just going to keep it from spreading.”
When asked about the use of distributed batteries, as opposed to a centralized UPS system with banks of batteries, Chris advises caution.
In the past, a conventional approach was to remove every type of combustible unit from the data hall itself. Now, with distributed batteries being installed in racks and rack-mounted UPSs, data-centre operators have to weigh the energy-efficiency gains of distributed Li-ion batteries against the fire risks, Chris says.
“The good thing is that if it does catch fire, these are much smaller batteries, so you might be able to contain it to a few racks. However, there’s going to be smoke, and in the end, any racks in that vicinity are going to suck some of that debris into them. And while it may not cause failures today, that’s going to lead to premature failures in the future.”
People need to go into it with eyes wide open, perform a cost-benefit analysis, and do what’s best for them, Chris says. “But my recommendation is that you get batteries out of the data hall. That’s the most reliable, most resilient thing you can do.”
