Taking Your Data Center to Next Level With Lithium-Ion Power

Taking Your Data Center to Next Level With Lithium-Ion Power

It's been quite some time since Uninterrupted Power Systems (UPS) have undergone a substantial upgrade, but lithium-ion batteries are changing that. Once expensive to use, prices continue to fall for the batteries as the life cycle lengthens to around seven years for UPSes.

Emilie Stone is General Manager for Methode – Active Energy Solutions.

In 1859, Western Union installed one of the first lead-acid battery rooms to provide back-up power for its telegraph services. Since then, advances in power electronics efficiency, battery packaging (sealed versus valve-regulated), and capacity have been made, but the technology is fundamentally the same. The back-up battery and uninterruptible power supply (UPS) market is ripe for innovation. Lithium-ion batteries, with their high energy density, minimal maintenance, and low capacity fade, are poised to upend our existing assumptions about what a UPS is capable of doing.

The term “lithium-ion” is used to describe a class of batteries, typically with rechargeable/secondary cells and a lithium-based cathode. While the precise capabilities of each lithium-ion chemistry vary, they all perform better than lead acid. For example, a common lithium nickel-manganese-cobalt (Li-NMC) cell compared to a common VRLA (valve-regulated lead-acid) cell will have 150 percent of the energy density (W∙h/L) and 275 percent of the specific energy (Wh/kg), meaning it is smaller and lighter for a given capacity. For the data center, the benefit equates to a battery offering more power in a smaller footprint, freeing up valuable data center real estate.

In addition, Li-NMC exhibits 190 percent of the cycle life at a higher depth-of-discharge (80 percent versus 50 percent for VRLA), which translates into more useable capacity for the UPS. NMC cells are typically rated to a full-power operating environment of 40-45°C versus 25°C for VRLA. NMC batteries also maintain 92 percent efficiency at a 1C° discharge versus 60 percent for VRLA. This results in less waste heat in a rack.

There are, however, two major obstacles to widespread lithium-ion use: cost and safety. Just a few years ago, lithium-ion batteries were roughly four times the cost of lead-acid batteries. However, as cell production has increased to support the Electric Vehicle industry and consumer products, the cost will continue to fall. Lithium-ion production is projected to grow by 67 percent over the next five years.

Another cost driver for lithium-ion technologies is the use of a battery management system (BMS). While the primary function of the BMS is to maintain a safe operating environment for the cells, voltage, current and temperature, the BMS also provides invaluable insight into the state-of-charge and health of the battery – all key for making more informed decisions about if and when to replace the battery.

In addition to the BMS, safety technology within a lithium-ion cell, such as current-interrupt devices, positive temperature coefficient fuses, and vents are commonly implemented. Pack-level safeties such as fusing and thermal dissipation measures also guarantee a safe operating environment for the cells, making them a stable solution for data centers.

In a data center environment, these benefits translate into savings in space, weight and replacement that directly contribute to the bottom line. It is now possible to get 6kW of power in a rack in a 2U package, weighing less than 100lbs. Rather than employing a heavily cooled and reinforced battery room, the UPS can be deployed in the rack or end-of-row to offer flexibility and simple power runs. Higher cycle life means a lithium-ion UPS can last up to seven years without service. Combined with fast recharge time, this also means lithium-ion batteries can be used for non-traditional UPS functions like supplementing the grid to load balance to maintain power budget at the rack level. All of these compelling benefits are bringing lithium-ion batteries to the forefront of stationary storage applications and forging the path for their future in the data center.

Industry Perspectives is a content channel at Data Center Knowledge highlighting thought leadership in the data center arena. See our guidelines and submission process for information on participating. View previously published Industry Perspectives in our Knowledge Library.

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