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.
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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).
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).
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).
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
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.
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)
The cost is between $425/kW and $450/kW, whereas maintenance cost is between $3/kW and $10/kW.
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).
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 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.
Flywheels are mostly used for power quality improvements, particularly in environments affected by frequency discrepancies or served by unbalanced electrical output (Perfomak, 2012)
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)
Flywheels have a tremendously quick dynamic response, long life, need little maintenance and are more environmentally responsive, but it is difficult to transfer the needs of one application to another due to design issues (Connolly, 2009).
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The technology has a bright future due to low maintenance costs and capacity to operate optimally even under challenging environmental conditions.
Thermal Energy Storage
This technology stores energy in a thermal reservoir, with the view to recovering it at a later date for use. There exist two types, namely air-conditioning thermal energy storage (ACTES) and thermal energy storage system (TESS)
ACTES creates ice that is utilized to provide the cooling load for the air conditioner, whereas TESS is often used to improve the flexibility within an energy system (Connolly, 2009).
The cost for ACTES is between $250 and $500 per peak kW, whereas that of TESS is much lower as it only combines the electricity and heat sectors with one another (Connolly, 2009).
A major advantage is low maintenance costs, whereas a major disadvantage for this energy storage technology is that it cannot be implemented as a standalone project.
The future is bright for both ACTES and TESS due to the number of flourishing installations that have already been implemented in the market.
Connolly, D. (2009). A Review of energy storage technology for the integration of fluctuating renewable energy. Retrieved from http://dconnolly.net/
Perfomak, P.W. (2012). Energy storage for power grids and electric transportations: A technology assessment. Congressional Research Service. Retrieved from https://fas.org/sgp/crs/misc/R42455.pdf