Energy can be stored in Lead-Acid (LA), Nickel-Cadmium (NiCd), and Sodium-Sulphur (NaS) large-scale batteries, which function when two electrodes are immersed in an electrolyte to allow a chemical reaction and subsequent production of power. Applications Batteries are used in situations that require short bursts of strong power, portable and rechargeable power, and low steady power over a long time. Additionally, they can be used as backup energy (Connolly, 2009). Cost LA batteries cost between $200/kW and $300/kW although the outlay may elevate to $580/kW, NaS batteries cost $810/kW, and NiCd batteries cost $600/kW (Connolly, 2009). Advantage/Disadvantage Although most batteries are flexible, portable and respond at full power within milliseconds, they are extremely sensitive to environmental contexts as sharp shifts in temperature cut their life substantially (Connolly, 2009). Future The future is bright as batteries have low production and maintenance costs, can be used in multiple situations, (Connolly, 2009), and are environmentally friendly (Perfomak, 2012). Compressed Air Energy Storage Overview This facility “comprises a power train motor that drives a compressor (to compress the air into the cavern), high pressure turbine (HBT), a low pressure turbine (LPT), and a generator” (Connolly, 2009 p. 11). The facility functions by releasing pre-compressed air produced using cheaper off-peak base load electricity to drive a motor which generates electricity. Applications The facility is a large-scale energy storage technique, therefore very ideal in areas requiring bulk energy supply and demand, settings necessitating recurrent start-ups and shutdowns, and also in ancillary services such as frequency regulation, load following, and voltage management (Connolly, 2009) Cost The cost is between $425/kW and $450/kW, whereas maintenance cost is between $3/kW and $10/kW. Advantage/Disadvantage The facility does not suffer from efficiency reduction reminiscent of other traditional gas turbines, or from excessive heat when operating on partial load; however, a major disadvantage is that it is dependent on geographical location (Connolly, 2009). Future Facility developments are expected to take place in the future, with the U.S. and Europe expected to take the lead as they have tolerable geologic characteristics for the development of underground reservoirs (Connolly, 2009). Flywheel Storage Overview Flywheel technology is able to store “energy by accelerating the rotor/flywheel to a very high speed and maintaining the energy in the system as kinetic energy” (Connolly, 2009 p. 22). Energy is then released for useful purposes by reversing the charging procedure to provide capacity for the motor to be used as a generator. Applications Flywheels are mostly used for power quality improvements, particularly in environments affected by frequency discrepancies or served by unbalanced electrical output (Perfomak, 2012) Cost Currently, flywheel applications “cost between $200/kWh to $300/kWh for low speed flywheels, and $25,000/kWh for high-speed flywheels” (Connolly, 2009 p. 23) Advantage/Disadvantage Flywheels have a tremendously quick dynamic response, long life, need little maintenance and are more environmentally responsive, but it