Stored energy - Short-term and long-term energy storage methods for standby electric power systems

The need for uninterruptible power for electronic loads and telecom equipment will only increase the need for new stored energy methods. Standby systems are categorized as being short-, medium-, and long-term systems. There are various energy storage methods depending on plant specifications and needs. Batteries are the most common type and is readily available for a wide range of applications and ratings. They also have different types including lead-acid batteries, valve-regulated lead-acid batteries, lithium-ion which have high energy to weight ratio, nickel-metal hydride which are optimum for optical fiber cable installations and flywheels for no-break engine-generators. Another type of storage system is fuel cells which are used for systems that require frequent and rapid start-ups and where hydrogen and air are the available reactants. Fuel cells utilizing hydrogen as fuel can operate for long periods of time (hours) or for short ones in standby service. There are also other types of energy storage methods that are less popular or relatively new, including ultracapacitors which utilize electrodes of highly porous carbon to achieve large values of capacitance per unit weight; superconductivity magnetic energy storage which has the capability to absorb and release active and reactive power; compressed air energy storage which release air and mixed with gas on a combustion chamber that drive a gas turbine and hydrogen which are seen in wind turbine, photovoltaic arrays and other renewable energy sources.