Facebook Testing Lithium-Ion Batteries For Backup Power

itwbennett writes Facebook has just started testing lithium-ion batteries as the backup power source for its server racks and plans to roll them out widely next year. Lithium-ion has been too expensive until now, says Matt Corddry, Facebook's director of hardware engineering, but its use in electric cars has changed the economics. It's now more cost effective than the bulky, lead-acid batteries widely used in data centers today.

Comments

Li-Ion batteries aren't good for this role

[ZorinLynx]

Lead acid batteries last longest when they are fully charged and kept that way, and discharged infrequently. This makes them excellent for use in standby power situations, where they are almost always topped up ready for the power to go out.

Li-Ion batteries last longest when they are actively used. Keeping a Li-Ion battery fully charged all the time is bad for its longevity; the battery structure breaks down faster at a high state of charge. This is why it is recommended to store Li-Ion batteries half-charged in a cold environment, and why cars like the Tesla Model S normally only charge up to 80% unless you require a "full-range charge" for a road trip. Not topping off to 100% extends battery life.

Maybe Facebook intends to keep the batteries at 80%, but it's hard to believe the economics are going to work in their favor.

Not to mention that lead-acid batteries are mostly water and non-combustible sulfuric acid. A Li-Ion battery fire is 50 times nastier than a lead-acid battery fire, and produces a hell of a lot more noxious gases.

Re:Li-Ion batteries aren't good for this role

[jandrese]

I got a Lenovo laptop awhile back and it noticed that I keep it plugged in most of the time. It sets itself to keep the battery between 70-80% charged in this state. I thought it was a really cool feature, although it does take a little getting used to. "Why is my battery low? Oh right, battery saving mode."

Re:Li-Ion batteries aren't good for this role

[i kan reed]

What about energy density?

Wasn't that the driving force for li-ion adoption in computing? It's a 10x difference, according to Wikipedia.

How much space, comparatively would it take for an UPS of each size to keep a given collection of servers running for an hour? If one doubles the physical size of your server farm, and the other increases it by 10% that might be sufficient motivation.

Re:Li-Ion batteries aren't good for this role

[fuzzyfuzzyfungus]

It presumably depends on how your UPS capacity is distributed, as well.

Lead acid is damned heavy, and offers mediocre density; but if you are just going to shove them in the basement, or are building on the cheapest flat land in the middle of nowhere that you can find, that may not be a problem. However, if cabling costs or resistive losses make 'distributed' UPSes, with fewer big battery banks and more, smaller, battery packs powering individual systems (presumably also cutting DC/AC inverter losses out of the equation and providing DC directly to the motherboard) the superior density and lighter weight of Li-ion is much more attractive.

Re:Li-Ion batteries aren't good for this role

[fustakrakich]

If you want longevity, you can't go wrong with Nickel–iron... I heard about those things lasting 80 years. But, you'll need another building big enough to put them in.

Really?

[Anonymous Coward]

Is the data kept by Facebook worth anything?

This makes no sense to me.

[gewalker]

Given then Facebook should have acres of servers, why are their data centers not using a flywheel / diesel combo for power backup.

If you only have a couple of racks of servers, batteries make sense, but they should have thousands and you need something like a generator if your power can be longer than your battery will last. Its not like this is a new and unproven technology.

Is there really any good reason to consider batteries for a large data center?