White Paper compares lithium-ion and VRLA batteries for data centre applications

Now, driven by interest in the development of electric cars, Li-ion batteries are becoming available in formats that make their deployment in uninterruptible power supply (UPS) systems used in data centres increasingly attractive.

A White Paper from Schneider Electric, a global specialist in energy management and automation, WP #229 Battery Technology for Data Centers: VRLA vs. Li-ion compares the two technologies from the viewpoint of total cost of ownership (TCO) and highlights the benefits and drawbacks of each option.

The benefits of Li-ion battery technology over VRLA include a much less frequent need to replace batteries over the life of a UPS, thereby reducing the risk of downtime; much lighter batteries for an equivalent amount of energy; up to ten times more discharge cycles depending on chemistry, technology, temperature and depth of discharge; about four times less self-discharge, or slow discharge of a battery while not in use; and four times or more faster charging, a key benefit in multiple outage scenarios.

The main drawback of Li-ion is much greater (perhaps two to three times greater) capital cost for an equivalent amount of energy due to higher manufacturing costs and the need for a battery-management system. There are also stricter transportation regulations, which also add to the cost of deployment.

The White Paper examines the functional differences between power cells, designed to provide a relatively large amount of power in a short amount of time; and energy cells, which are designed to provide a relatively small amount of power over a long period of time. Li-ion batteries can be used as either power cells or energy cells whereas VRLA batteries are used solely as energy cells.

Although some TCO studies for Li-ion batteries have been carried out before, they tend to focus on the requirements of electric vehicles, as that sector is the driver for much Li-ion battery development. The financial analysis in this White Paper is focussed specifically on the requirements of a UPS system for a data centre.

The analysis shows that because of the performance characteristics of Li-ion batteries, systems based on this technology can produce savings of 39% over a ten year period compared with VRLA batteries despite the initial cost premium. Although there are some situations in which the greater capital expenditure will discourage switching over from VRLA batteries in the short term, the likelihood is that Li-ion batteries will fall in price in forthcoming years as new chemistries and technologies come to market.  As prices fall, they are likely to become increasingly attractive for data centre operators.