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Characteristics of electrical energy storage & Energy Storage Technologies
Introduction
reduction for the EU countries by up to 95% by 2050 is needed [1]. Towards this
goal, the integration of renewable energy sources in the energy mix of the future is expected to rise
(Figure 1). However, the output of many renewable energy sources, such as wind and solar, is highly
variable, producing fluctuating and partly unpredictable amounts of electricity over time [2I5]. Therefore,
the constant mismatch between supply and demand can have a serious impact on grid reliability and
security of supply. This constitutes a new challenge, which requires the
introduction of advanced energy storage solutions.
There are a number of benefits associated with the introduction of energy storage systems in the built environment.
Electrical energy storage (EES) systems can contribute to increasing power systems’ efficiency, as they can effectively
manage the surplus electricity generation from renewable energy technologies, which would otherwise be wasted.
In this way, electricity storage helps to maximize the value and the contribution of intermittent renewables [2, 6].
Furthermore, EES systems can assist in the improvement of the electrical grid stability and reliability, as they can
address the fluctuations in consumption and generation by providing the necessary flexibility [2]. In addition, EES
solutions can contribute to the increase of energy security and quality of supply, by sustaining frequency and voltage
at the required levels [2, 7]. For example, electricity storage options could deal with the occurring
voltage sags in case of a power failure, ensuring reliability of supply.
With growing concerns about the environmental impacts of the electricity sector, the EES market is developing quite
rapidly and the performance characteristics of the technologies are constantly improving. Furthermore, there are a
limited number of inter institutional collaborations in
The EES technologies considered in this review are the following:
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Superconducting magnetic energy storage (SMES),
Supercapacitors/electrochemical double layer capacitors (EDLCs),
Pumped hydroelectric storage (PHS),
Flywheels,
Compressed air energy storage (CAES),
LeadHacid (PbHacid) batteries,
LithiumHion (LiHion) batteries,
Nickel/Cadmium (NiCd) batteries,
NickelHmetalHhydride (NiMH) batteries,
High temperature Sodium/Sulphur (NaS) batteries,
High temperature Sodium nickel chloride (NaNiCl) batteries,
Zinc/Bromine (ZnBr) batteries,
RedoxHflow batteries,
MetalHair (ZnHAir) batteries, and
Hydrogen storage used with either a fuel cell or a gas turbine.
Classification of EES technologies
EES technologies, according to [2, 11, 25], can be separated into two categories: “high power” and “high
energy” storage systems. High power storage systems deliver energy at very high rates but typically for short
times (less than 10s), while high energy storage systems can provide energy for hours. There are also
technologies that can be used either in high power or high energy systems and these are the electrochemical
storage systems. The classification of the technologies into the above categories is shown in Table 1. In addition, with
regard to the mechanisms for storing electrical energy, EES can use electrical fields, mechanical energy or
chemical energy
2.2 High power EES technologies
2.2.1 Superconducting Magnetic Storage Systems (SMES)
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This technology has installed capacities of up to about 10MW and is most commonly used for power quality
improvement. According to [3, 22], soHcalled microHSMES devices in the range of 1H10 MW are commercially available
and as [11] observes, they are used in a number of technical applications where very high magnetic fields are required,
such as in medical devices. It should be noted that SMES cannot be currently used as high power storage systems for
gridHscale storage. Issues related to the complexity, the efficiency, the high cost and environmental impact of the
system have hindered the widespread deployment of this technology
2.2.2 Supercapacitors /Electrochemical
double@layer
capacitors (EDLCs)
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These systems would be more suitable for applications with many charge and discharge cycles and discharge times around
10 seconds [11]. EDLCs can be used in various applications, but are particularly common in energy smoothing and
momentaryHload devices. For example, they serve as efficient battery packs in vehicles, in wireless communications or in
mobile computing [30]. According to [31], they are also used in industrial applications (e.g. electronic door locks) or smaller
installations like home solar energy systems where very fast charging is sometimes required. Furthermore, they can be used
in combination with battery storage in uninterruptible power supplies (UPS) and similar applications. Such hybrid storage
facilities provide the flexibility to use the most appropriate system between the two according to the duration of the
interruption. On this occasion, EDLCs can deal with short interruptions, while the batteries are required to handle only long
interruptions. For example, EDLCs would operate in the cases that interruptions are in the order of milliseconds or seconds,
while batteries would only be used when disruptions in the range of minutes to hours occur. This results in the reduction of
the batteries’ cycling duty and the extension of their lifetime
2.2.3 Flywheels
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These are typical high power storage systems and are used in applications that intersect the areas of
capacitors and batteries for provision of power over 80 kW over a period of 1 to 100 seconds [30]. They are
suitable for use in uninterrupted
power supply systems (such as those in large data centres) for ride through power necessary during transfer,
as well as in electric vehicle applications (buses, trams, rail, subways) and in lifting devices (e.g. container
terminals in harbours). They can also be used for grid energy storage for frequency regulation
2.3 High energy EES technologies
2.3.1 Compressed air energy storage (CAES)
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They are used to store energy during periods of low demand and release the stored energy during
periods of high demand (i.e. load shifting). These systems are a mature storage technology for high
power, long term load leveling applications, which is suited to build storage systems in the range of
several 100MWh or more [11]. There are currently two large CAES systems installed worldwide
2.3.2
Pumped@hydro
energy storage (PHS)
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This is the oldest kind of large scale energy storage being used since the 1890’s and currently accounts for 95% of the global
storage capacity [32]. These systems have installed capacities in the GW range and are typically used for load leveling on a
daily basis [11]. Exhibiting a rapid response speed (½H3mins), they also serve as an emergency reserve in case of sudden
changes in demand or sudden shutdowns of power plants [41]. The construction time for such systems is usually over 10
years
2.4 Electrochemical storage systems
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These are classified into two groups; systems with integrated energy storage (e.g. leadHacid batteries, NiCd
batteries, NiMH batteries, LiHion batteries, NaS batteries, NaNiCl/ZEBRA batteries) and systems with external
energy storage (e.g. VHredox, ZnBr, ZnHair batteries, hydrogen storage systems).
3.3 Metal resource availability
Types of Energy Storage Technologies
• Hydraulic
• Pumped Hydro Storage (PHS)
• Pneumatic
• Compressed Air Energy Storage (CAES)
• Kinetic
• Flywheel Energy Storage (FES)
• Electromagnetic
• Superconducting magnetic energy storage (SMES)
• Electrical
• Double Layer Capacitors (DLC)
Types of Electro-Chemical Energy Storage Technologies
• Electro-chemical
• Nickel Cadmium (Ni-Cd)
• Iron Chromium (Fe-Cr)
• Lithium Ion (Li-ion)
• Sodium Sulfur (NaS)
• Lead Acid (LA)
• Zinc Air (Zn-air)
• Sodium Nickel Chloride (NaNiCl)
• Vanadium Redox Flow Battery (VRFB)
• Zinc-Bromide Hybrid Flow Battery (ZnBr HFB)
Factors Affecting Electro-Chemical Storage Technologies
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• Falling price of batteries
• Battery improvements allow new devices to be built
• Increased capacity for size – miniaturization
• More units combined – modularization
• Availability – quantity of batteries in market place affects price