Flywheel Energg Storage: An Alternative to Batteries For UPS Systems

摘要

Direct current (DC) system flywheel energy storage technology can be used as a substitute for batteries to provide backup power to an uninterruptible power supply (UPS) system. Although the initial cost will usually be higher, flywheels offer a much longer life, reduced maintenance, a smaller footprint, and better reliability compared to a battery. The combination of these characteristics will generally result in a lower life-cycle cost for a flywheel compared to a battery. Flywheels intended for UPS application are typically designed to provide power at their maximum rate for a period of about 15 seconds. In contrast, most batteries for UPS applications are designed to provide their maximum rated power for about 15 minutes. Therefore, using a flywheel instead of a battery will generally require a generator that can come up to full power within about 10 seconds, which is well within the capabilities of standby generators. With or without a standby generator, flywheels could be used to significantly extend battery life and reliability. The vast majority of power quality events last five seconds or less. A flywheel could be added to an existing battery-backed UPS system and controlled so that the flywheel provides backup power for short-duration events while the battery is saved for longer outages. Such an approach plays to the inherent strengths of each technology; i.e., flywheels are highly tolerant to frequent cycling (while batteries are not) and batteries can provide power for a longer period. The first section of this article describes the technology, its variations, and installation requirements. This is followed by a section providing application advice. One federal application is highlighted as a "case study," followed by an illustrative life-cycle cost comparison of batteries and flywheels. A list of manufacturers, with contact information, is provided at the end. This article is based on work conducted for the U.S. Department of Energy's Federal Energy Management Program (FEMP) by the Pacific Northwest National Laboratory.