Posted by UNS News on June 4, 2012
Energy storage technologies in data centers play an important role in maintaining system uptime. Should utility power fail, the first line of defense is usually batteries that are incorporated as part of an uninterruptible power supply (UPS) system. Although alternative energy storage technologies such as fuel cells, flywheels, lithium ion, and nickel cadmium batteries are being explored (see White Paper 65, Comparing Data Center Batteries, Flywheels, and Ultracapacitors for more details) data center and network room UPS systems almost exclusively utilize lead-acid batteries. This paper reviews and compares the three major lead-acid battery technologies available today.
The lead-acid battery is the predominant choice for uninterruptible power supply (UPS) energy storage. Over 10 million UPSs are presently installed utilizing flooded, valve regulated lead acid (VRLA), and modular battery cartridge (MBC) systems. This paper discusses the advantages and disadvantages of these three lead-acid battery technologies.
- Lead-acid battery technologies
Vented (flooded or wet cell) batteries have a very long life but present significant complexity of installation and maintenance, the most significant being the need to build a separate battery room. These limitations have historically restricted the application of vented cells to very high power installations.
The VRLA battery was developed in response to the limitations of the wet-cell battery, and provides significant benefits in the area of installation costs, maintenance costs, energy density and safety. However, VRLA reliability can be compromised through improper installation and / or misapplication. Although the battery life of the MBC is shorter than that of vented cells, the benefits of this technology, even with a shorter battery life, present a compelling value proposition for today’s data centers and network rooms, especially in systems smaller than 500 kW.
All of the hazardous failure modes can be controlled by appropriate system design. Parallel string designs, ventilation, overcharge protection, temperature compensated charging, and battery monitoring are the principal techniques utilized to eliminate battery failure hazards.
White Paper Written By:
Stephen McCluer is a Senior Manager for external codes and standards at Schneider Electric. He has 30 years of experience in the power protection industry, and is a member of NFPA, ICC, IAEI, ASHRAE, The Green Grid, BICSI, and the IEEE Standards Council. He serves on a number of committees within those organizations, is a frequent speaker at industry conferences, and authors technical papers and articles on power quality topics. He served on a task group to rewrite the requirements for information technology equipment in the 2011 National Electrical Code.
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