Flywheel vs. battery for data center uninterruptable power supply (ups) – wood harbinger 3 gases that contribute to the greenhouse effect


Nobody likes an interruption, whether it’s when you’re speaking, working, or perhaps enjoying a good movie, or if it involves the functionality of some piece of equipment on which you rely, like your computer, lighting at night, or your TV during that good movie. For most applications, being interrupted is just a mild annoyance; you pick back up where you left off and everything’s fine. But some interruptions can have deeper consequences, particularly if we’re talking power and electronics. A power interruption can have real repercussions in the way of downtime, damage, data loss, lost revenue, safety risks to equipment and people, and the associated costs. These problems are magnified if we’re dealing with mission critical electronic elements, such as data center servers. If you’re a data center owner or operator, your mantra is “failure is not an option”.

This is where an uninterruptable power supply, or UPS, system comes into play and can save the day. In the event of a disruption or failure in your main power source, a UPS system provides immediate, but temporary, backup power to support the load until your emergency backup generators kick in. It’s your barrier against system interruption due to power loss. Clearly, an important requirement in a UPS system for an essential facility is dependability – will it work when you most need it to work? – but there are other options and features to consider when choosing a system for your data center. What are My Options and Which Do I Choose?

There are two primary approaches to UPS systems for data centers: Battery UPS, and Flywheel (Rotary) UPS, and the main conceptual difference is energy storage. A battery stores energy and converts it to electrical power through a chemical reaction, while a flywheel mechanically stores and converts kinetic energy through the spinning of a large, heavy disk. The basics of flywheel technology are old and tested, but currently less common in data center UPS usage; batteries have been the traditional and proven option, primarily due to misconceptions that flywheels are a new and un-vetted technology, first costs, and the anticipation that a longer runtime is needed in your UPS.

Batteries with enough capacity to carry data center power loads take up a lot of space. Inclusive of room for service access, a 500kW VRLA battery would need 60 to more than 100 square feet, and a 500kW flooded battery would require 200 square feet or more.

A flywheel contains no hazardous materials to manage or maintain, while a battery contains toxic chemicals that require special HazMat disposal, spill containment, and personal safety procedures subject to EPA regulation. They must also be replaced about every 5 years, creating a greater waste.

Flywheels are also more energy efficient, requiring less energy to stay “charged” and to be cooled, and they generate less heat in operation, meaning it puts less of a load on the HVAC system to cool the room in which it resides. Conversely, batteries require air conditioning and ventilation to maintain reasonable space temperature and humidity. Runtime

The difference in run time is significant. A battery UPS system can typically sustain a load for about 10 to 15 minutes, while a flywheel’s runtime is a matter of seconds, generally around 20 to 30 seconds. The cutover time to standby generators is approximately less than 10 seconds, from detection of main source power failure to your servers being supported by generator power. Cost

Based on requiring four sets of VRLA (10-year life) batteries over a 20 year period, the flywheel system has an approximately 35% higher initial cost, but up to a 60% less life cycle cost than a battery UPS. Batteries, while less expensive up front, require routine maintenance and testing, which involves downtime, and will require multiple replacements over a 20 year span.

Currently, battery UPS systems are still the standard, but the flywheel alternative is gaining momentum and warranting a closer look by many data center professionals. Both UPS systems can effectively mitigate the problems associated with a main source power interruption in a data center. The choice between them will depend on both objective and subjective parameters. Do you have the space for a battery UPS room? Do you have the upfront costs for a flywheel system? Are you looking to “go green” and make all efforts to reduce energy use and promote environmentally friendly solutions? Will a 10-15 second runtime keep you up at night?