Comparison of high power short time flywheel storage systems

Uninterruptible power supply (UPS) systems are supported mainly by batteries to cover short network breakdowns. The advantages of batteries in this application are their high degree of modularisation, low charging regime losses and not least their wide spread availability. Disadvantages are their weight, high maintenance costs and their high price if storage times of less than one minute are desired and are sufficient like in the area of power quality improvement. As an alternative to lead acid batteries different storage methods have been investigated. Storage systems like new type batteries, superconductive coils (SMES), pressure reservoir storage and supercapacitors have been taken into consideration. But most of these new techniques are still in the early test phase, run with high losses, require high investment costs or space or are not proven enough. The flywheel technology is the most suitable solution for a high reliable storage in the megawatt/second range. The paper describes the state of the art technology, explains the action principles and compares in particular the two different systems "high speed flywheel" and "low speed flywheel".