A Battery of Options
Connectivity can disappear in the blink of an eye, and in the data center world, time is critical to maintaining reliability. In the fractions of a second between an unexpected power outage and back-up power generation firing up, servers could be forced into reboot if they lose power. That can disconnect vital data streams for minutes or even hours – unacceptable in today’s hyper-connected world.
Data centers use Uninterruptable Power Supply (UPS), a battery back-up system that fills in that crucial few milliseconds of gap between power outage and back-up power generation to ensure no loss of service. Typically, this includes valve-regulated lead acid batteries (VRLA) or lithium-ion batteries, but each has its positives and negatives.
VRLA offers a certain set back-up time, and CyrusOne has chosen to use VRLA at an 8-to-10-minute interval. When used, its voltage drops off drastically for a brief period and then rebounds. That means users must customize the battery size to accommodate the voltage dip. At the beginning of its life, it has an 8-to 10-minute back-up time. By the end of its life, it has a four-minute back-up time. In total, VRLAs have a five-year lifespan.
About 96% of utility outages last 10 seconds or less – a short period of time when a data center would have to run on batteries. The idea is to provide a power source allowing two chances for the back-up power generator to start. Normally, they start on the first try. Occasionally they don’t, and they’ll go through a timing sequence and then try a second time.
When the VRLA is hit with a load, it has some degradation. Over a five-year period, it can sustain about 500 hits before needing replacement.
VRLA are also heavy. If a data center wanted to set up a VRLA battery for a 2-megawatt UPS, the VRLAs would weigh about 55,000 pounds. That requires more storage space within a data center.
The time from when the manufacturer ships VRLA batteries until they get installed cannot exceed about 30 days. Once shipped, they must be installed and charged, or they’ll start losing their capacity.
In terms of cost, a VRLA battery needs more frequent charging. While cheaper than lithium-ion, the more frequent need to replace makes them more expensive in the long term. Plus, there are other costs and environmental considerations when having to dispose of them safely every five years.
Lithium-ion batteries also provide a certain set back-up time and can be hit with a load anywhere from 5,000 to 17,000 times over the course of their 15-year lifespans. CyrusOne uses lithium-ion with a 3-miunte back-up time. And often, lithium-ion is used in peak shaving and other applications besides just transitioning to generator because it can be hit it so many times without affecting its overall life.
If a data center wanted to set up a lithium-ion battery for a 2-megawatt UPS, it would weigh about 14,000 pounds, compared with 55,000 for a VRLA. Additionally, lithium-ion can go six to eight months without needing to be charged. It’s a more versatile option than VRLA.
No two lithium-ions are alike – each manufacturer has a different recipe or chemistry in their batteries. Some are safer, some have better run times. A data center must pick the right chemistry to suit its needs, which requires investigation.
In terms of cost, a lithium-ion battery lasts longer, and environmentally safe disposal is therefore also less frequent. But lithium supplies are increasingly limited, making cost fluctuate based on supply and demand.
Lithium-ion batteries have also developed a reputation for being a fire hazard. This might have been true with earlier lithium-ion technologies. But today, lithium-ion systems all have computerized monitoring systems that prevent those fires. Every cell in a lithium-ion application is monitored by a computer. If it starts to overheat, that cell’s is taken out of the circuit. So, the chances of actually having a lithium-ion fire are small.
But because past incidents, using lithium-ion in a data center depends on the market. Each market will have different regulations and inspectors who must approve a lithium-ion system to ensure safety.
CyrusOne is currently testing lithium-ion systems on-site to ensure efficiency and safety.
Nickel-zinc could lead the charge
The future of UPS could be Nickel-zinc (NiZn), an option that doesn’t have the same supply issues as lithium-ion and offers more power density and a smaller footprint than VRLA.
These types of batteries can operate at a temperature of 85 degrees, while VRLA require a top temperature of 77 degrees. The lifespan for NiZn batteries is 10 to 15 years, with a warranty of 10 years – significantly higher than VRLA. They also weigh 33% less than VRLA.
It’s also a cheaper option, with a total cost of ownership over its lifespan some 60% less than VRLA. Even better, NiZn is more sustainable – 98% can be recovered to battery-grade specs without the use of high heat during recycling.