Stored energy - Short-term and long-term energy storage methods

This paper deals with the short-term and long-term energy storage methods for standby electric power systems. Stored energy is required in uninterruptible standby systems during the transition from utility power to engine-generator power. Various storage methods provide energy when the utility source fails. For batteries in cycling duty, Li-ion and Ni-MH cells are coming into wide use to displace VRLA batteries. For float duty, VRLA and NiCd batteries predominate. Flywheel-generator units are being offered to replace batteries in UPS. Fuel cells require a warm-up time and, hence, are suitable for long-term operation. Ultracapacitors are proposed to replace batteries for short-term discharge. CAED and hydrogen energy storage are suitable for large projects.