Analysis of Energy Storage Systems: A Detailed Research Paper

This research paper provides a comprehensive overview of energy storage systems, focusing on field grid-based approaches. It begins by defining and illustrating the principles of operation for such systems, highlighting their advantages, including emergency preparedness and price stability. The paper then delves into specific energy storage technologies, particularly flywheel and compressed air energy storage systems, detailing their mechanical design features, materials, and construction. Real-world examples of energy storage schemes in operation, such as the Compressed Air Energy Storage plant in Huntorf, Germany, and the Li-ion battery system in Chile, are discussed. Finally, the paper outlines the design considerations for a flywheel energy storage system, emphasizing the importance of the rotor's material and shape in determining energy storage capacity. Desklib offers this report, along with a wealth of other study resources, to aid students in their academic pursuits.

Energy Storage 1
ENERGY STORAGE
A Research Paper on Energy By
Student’s Name
Name of the Professor
Institutional Affiliation
City/State
Year/Month/Day

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INTRODUCTION
This is an electrical power research paper that seeks to evaluate the impacts within
final and primary power distribution system, modelling and critically analysing the control
and flow of electrical energy within the final and primary distribution system, as well as
evaluation of generation and energy storage methods. The subtopic discussed in this report
paper include principles of operation of a field grid-based energy storage system, mechanical
design feature materials, energy storage schemes, design of energy storage system based on
existing the technology, and outline of the Electricity Market Reform.
Principles of Operation
A field grid-based energy storage system which is also known as a large-scale energy
storage can be defined as a collection of approaches utilized in storing electrical energy on a
huge scale within a grid of electrical power. An electrical energy is stored when production is
more than consumption and then the electrical energy can then be returned to the grid when
production is beneath the demand (Barnes, 2015). The figure below shows an illustration of
this grid-based energy storage system:
Figure 1: Field based energy storage system (Carnegie, 2014)
During peak periods when the consumption of the electricity is greater than average,
the suppliers of power should complement the power plant with is more flexible and less
cost-effective such as a flywheel. During the period of off-peak when the consumption of

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electricity is low, then the types of generation can be halted. In case a required electricity
quantity cannot be given at the moment when the consumers require it, the quality of power
will diminish and it may result in interruption of services (Denholm, 2013).
In order to meet the variations in the consumption of power, there is need of
generating continuously appropriate electricity amount to meet demand variations. Some of
the examples of the field based energy storage system include compressed air, batteries,
electric vehicles, flywheel, hydrogen, hydroelectricity, supper conducting magnetic energy,
thermal, and gravitational potential energy storage using solid masses (Dincer, 2016).
Advantages of Energy Storage Systems
The energy storage systems are used to feed power to the grids at a period when the
power consumption is more than its production and cannot be delayed or deferred. Hence
there is need of scaling up or down the electricity production so as to attain the consumption
momentarily. Every grid of electric power should correspond production of electricity to the
consumption, each of these drastically varies at a given period. These energy field based
energy storage system has the following advantages:
Emergency preparedness: Critical demands may be reliably met with no generation or
transmission takin place while needs that are non-essential are deferred. There are times when
there is need of an emergency demand in the industrial sector, this can be achieved through
the acquisition of the energy from the storage system that is connected to the grid.
Stability in pricing: The cost of demand or storage management is incorporated in pricing
hence the customers will be changed less variation in rates of power. In case the rates are
expected to be stable by the law of that state, low loss to the utility from on-peak power rates
of the wholesalers which is expensive when optimum demand should be attained by the
wholesale power that is imported (Gazarian, 2016).

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The peak capacity of transmission or generation may be minimized by the total potential of
all deferrable plus storage loads hence leading to the expense of this capacity to be saved.
The electricity produced by the intermittent sources may be used later or even stored.
Majority of the energy storage systems are advantageous since they are more efficient and
can be operated easily at levels of production at are constant. The types of energy storage
systems that are discussed in this paper include flywheel and compressed storage systems
(Gogus, 2011).
The reason why the flywheel storage system have been selected for the design of an
energy storage system is because it has the ability to deliver a high energy at a relatively high
efficiency than other energy storage systems such as batteries. The compressed air and
flywheel energy storage systems are also more advantageous than majority of other energy
storage systems like batteries, electric vehicles, hydrogen, hydroelectricity, supper
conducting magnetic energy, thermal, and gravitational potential energy storage using solid
masses since it is very easy to access information concerning the compressed air and flywheel
from numerous sources making their design to be easier than the rest.
The plants that have implemented the compressed air and flywheel can easily be
accessed during the process of design (Carnegie, 2014). These are the major reasons why the
flywheel and compressed air energy storage systems are the best and frequently used across
the world and not hydro energy storage system which possess similar advantages but is not
used since it requires a dam. Majority of industrial companies such as petroleum and power
generation are using nickel-cadmium batteries for retrieving data and systems through UPS
and not other energy storage system since the nickel-cadmium batteries have a very high
discharge rate than other energy storage systems. The high discharge rate is critical when a
huge amount of energy is needed for drive huge machines in the industries.

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The cost of set up and the cost of maintainace required in the installation of the
flywheel energy storage system is relatively lower compared to the initial cost of installing
the hydro energy storage system as well as its maintenance cost.
Flywheel Energy Storage System
A flywheel is an example of field-based energy storage system that is currently being
used in numerous industries factories for industrial and domestic purposed. This storage
system uses mechanical inertial where rotational energy is kept in an accelerated rotor which
is a huge revolving cylinder. The major constituents making up the flywheel energy storage
system include transmission device which is made of generator or motor attached to the
stator, the bearings, and rotating cylinder which is composed of a rim joined to a shaft (Ham,
2012). The mechanical design features materials and construction of a flywheel is as shown
in the figure below:
Figure 2: Mechanical parts of a flywheel energy storage system (Ham, 2012)
The energy is maintained in this energy storage system through maintaining the
rotating body at a velocity that is constant. When the velocity increases, there will be an
increase in the quantity of stored energy. If the speed of rotation of the flywheel is
minimized, the electricity that has reduced can be removed from the system through a similar
device of transmission. The rotors are made of carbon filaments of high-strength, spinning at

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a velocity of 40000rpm, and suspended by magnetic bearings in an enclosure of vacuum. The
following are some of the features of the flywheel energy storage system:
 Made using materials that are environmentally inert
 High density of power
 Little maintainability
 Long life
 Excellent cycle stability (Huggins, 2012)
The initial construction cost and the cost of maintainace required in the installation of
the flywheel energy storage system is relatively lower compared to the initial cost of
installing the hydro energy storage system as well as its maintenance cost. However, the
installation cost and maintenance cost of batteries, hydrogen, supper conducting magnetic
energy, thermal, and gravitational potential energy storage using solid masses are lower
compared to the flywheel energy storage system.
Compressed air energy storage
The compressed air energy storage system is a technology that has been used by
numerous industrial applications since the 19th century. In this system, air used as the storage
medium because of its accessibility. The design of the compressed air storage system
includes generator, low-pressure turbine, high-pressure turbine, recuperator, compressor, and
motor (Kilkis, 2013). The mechanical design features materials and construction of the
compressed air energy storage system is as shown in the figure below:
Figure 3: Mechanical parts of a flywheel energy storage system (Komarnicki, 2013)

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Electricity is used for compressing air and storing it in an above-ground system of
pipes or vessels or underground structure. When required, the air compressed is mixed with
natural gas, expanded and burned in the gas turbine that has been modified. Normally, the
options of underground storage include abandoned mines, aquifers, or cavers. In case the heat
produced in the process of compression is dissipated through cooling and not kept, the air
should be reheated before expansion process. The following are some of the features of the
compressed are energy storage system:
 Large capacity
 High reliability
 Low round-trip efficiencies lower than 50% (Osaka, 2010)
Energy storage schemes in operation
One of the field grid-based energy storage schemes that are currently operating is the
Compressed Air Energy Storage power plant which was built in Huntorf, Germany in the
year 1978. This system functions as a diabatic energy storage plant with an efficiency of
round-trip of approximately 41%. This system is composed of compressors of low-pressure
and high pressure intercooler, low pressure turbine (945oC, 13 bar), a high pressure inlet
condition turbine (490oC, 41 bar), a motor generator (321 MW discharging, 60 MW
charging), tow salt caverns (72 to 46 bar pressure range, usable volume of 2*1500 00m3)
(Roboam, 2010). The figure below shows the energy storage plant in Huntorf:
Figure 4: Compressed Air Energy Storage Plant in Huntorf (Rufer, 2014)

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Another compressed air energy storage plant is situated in McIntosh which if found in
Alabama in the United States of America. This energy storage plant was commissioned in the
year 1991 and has a net output of electricity of 100MW. The system also utilizes the process
of diabatic compressed air energy storage. This has led to an achievement of a higher
efficiency of the round-trip of 54%. The two systems utilize electricity off-peak for
compression of air and are operated for optimum levelling daily (Rufer, 2014).
Li-ion battery situated at AES Gener’s Los Andes is another example of energy
storage scheme in operation that was installed in 2009 by the A123 Systems and the US
companies. This energy system is a 12 MW system with 3 MWh Li-Ion battery located in the
desert of Atacama. The battery assists the operator of the system to manage variations in the
demand, providing regulations in frequency is a more responsive and less expensive manner
compared to upgrades in the transmission line (Sumper, 2014).
Energy Storage System Design
The field grid-based energy storage system that is to be designed in this section is the
flywheel energy storage system. A flywheel energy storage system is based on the principle
of rotating mass. The energy at the input of this system is normally gotten from electrical
source from the grid. The velocity of the flywheel is high during storage of energy and then
lowers during discharge of the energy so as to give out the energy accumulated. The rotation
of the flywheel is controlled by electrical motor-generator carry out the interchange of
mechanical energy from electrical energy (Wei, 2013).
The motor-generator and the flywheel are connected coaxially, this indicates that
when the motor-generator is controlled, then the flywheel will also be controlled. The
flywheel energy storage system consisting of housing, power electronics interface, bearings,

Energy Storage 9
motor-generator, and the spinning rotor. The figure below shows the components and
structure of the flywheel system:
Figure 5: Design features of a flywheel system (Barnes, 2015)
Flywheel rotor: The energy stored in a flywheel is determined by the material and shape of
the rotor. It is the square of its angular velocity and proportional linearly to the moment of
inertia.
(i)
Where E is the kinetic energy stored which is 0.5 MVA, ɯ is the angular velocity, and I is the
moment of inertia. This design is expected to deliver 0.5 MVA to a 50 Hz grid system on a
short-term basis depending on the evaluation of the restrictions that would be in place
(Carnegie, 2014).
The value of E can be converted to Watts by:
Power factor = 0.8
KVA = kW/Power factor
Power in kW = KVA * Power factor
= 500KVA * 0.8
= 400kW
The flywheel will be rotating at an angular velocity of 5, 000 rpm, the value of the moment of
inertia I can be gotten by:

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400kW = ½ * I * 5000 rpm; I = 160 kgm2
The flywheel’s useful energy within the range of maximum velocity and minimum velocity
can be gotten by:
(ii)
Where E is gotten from real power = 400kW, Energy produced in every hour by the flywheel
will be: Power = Energy*Time, Time = 1hour, therefore Energy = 400,000Joules
For a cylinder flywheel that is hollow of inner radius ‘a’ and outer radius b, the moment of
inertia can be gotten by:
For this design a = 15cm, b = 16.68cm and m = 6 kg (iii)
For a flywheel with mass density ɋ and length h, the energy E and moment of inertia I can be
obtained by:
(iv)
Mass density, ɋ = 1.9*10-3kg/m3 = 1.9g/cm3 and Length, h = 2m
To attain the required energy of 400, 000J, a high-speed flywheel of up to 5, 000 rpm with
being used (Gazarian, 2016).
Motor-Generator: The electrical machine that would be used as motor-generator for induction
to the flywheel will be permanent magnet synchronous. This is because it has low rotor
losses, high power density, and higher efficiency. The following are some of the
specifications of the permanent magnet synchronous induction machine:
 High efficiency of about 95.5%
 High specific power of about 1.2 KW per kg
 Sinusoidal vector control
 Low maximum/base speed of 2
 Medium torque ripple of 10%
 Size of 2.3 L/kW (Gogus, 2011)

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Power Electronics: The conversion of energy by the flywheel is done by power converter
which is the bi-directional and electrical machine. The switching devices of the converter of
power will be the silicon controlled rectifier. A cascaded DC-AC and DC-DC converter
configuration can be used for applications of flywheel joined to a DC micro-grid. If the speed
of discharge of the flywheel system is low, a DC-DC boost converter is joined at the link of
DC amid the converters of BTB so as to vary the voltage at the output (Roboam, 2010).
Bearings: The bearings are needed to maintain the rotor in the position with low friction
while given support mechanism to the system. The bearings that can be used in this case are
the permanent magnetic bearings which are characterized by low losses, low cost, and high
stiffness.
Housing: The housing should be made of the high tensile material such as steel to give an
environment for low gas drag as well as for rotor containment in case there is a failure (Ham,
2012).
Impact of Life time of Flywheel Energy Storage System
The life time of the flywheel energy storage system is characterized by the numerous
operational cost as well as its productivity. The operational lifespan of a flywheel system is
20 years and the power delivered during this period is 400kW. The installation cost has been
approximately to be $3 million since this is a medium sized system with a medium mass
density of 1.9*10-3kg/m3. The cost of a system is directly proportional to the mass density and
the expected energy output. The protection required in the flywheel system are on the parts
of the system that can be dangerous to the users which may cause accidents during the
operation of the system. Some of the parts of the system that requires protection include
motor-generator, bearings, and power electronics. Some of the protections that are performed

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of this energy system include oiling, replacement, fastening, dusting, fussing, and short
circuiting.
Summary
Energy Storage
System
Principles of operation Design Features
(Components)
Advantages Schemes in
operation
Flywheel Energy
Storage System
Uses mechanical inertial
where rotational energy
is kept in an accelerated
rotor which is a huge
rotating cylinder
Housing, power
electronics
interface, bearings,
motor-generator,
and the spinning
rotor.
Made using
materials that are
environmentally
inert, and long life
In Ontario,
Canada,
Temporal Power
Ltd (Osaka,
2010)
Compressed air
energy storage
Electricity is used for
compressing air and
storing it in an above-
ground system of pipes
or vessels or
underground structure
Generator, low-
pressure turbine,
high-pressure
turbine,
recuperator,
compressor, and
motor (Roboam,
2010).
Large capacity,
high reliability
, and low round-
trip efficiencies
lower than 50%
Compressed Air
Energy Storage
power plant
built in Huntorf,
Germany
The flywheel energy storage system design specifications for energy delivery of 400,000
Joules which is equivalent to 400kW for every one hour to a 50 Hz grid system include an
angular velocity of 5, 000 rpm, moment of inertia I = 160kgm2, a = 15cm, b = 16.68cm, m =
6 kg, mass density, ɋ = 1.9*10-3kg/m3, and length, h = 2m.
Electricity Market Reform
The Electricity Market Reform which is abbreviated as EMR is a program of the
United Kingdom government that aims at responding to the trilemma that is fronting the
United Kingdom. These trilemmas include reducing the cost of energy to consumers, security
of support, and decarbonising electricity supply. The Electricity Market Reform was
legislated for through the 2013 Energy Act and will lead to the institution of two new reforms
to the market of energy, these reforms include Capacity Market and Contracts for Difference
(Ham, 2012).

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The EMR ensures that there is the secure supply of electricity through the provision of
numerous sources of energy such as unabated gas, CCS-equipped plant, nuclear, and
renewables as well as making sure that there is enough reliable ability to reduce the risk of
shortages in supply. The EMR also ensures that there is sufficient investment in sustainable
technologies of low-carbon so as to place consumers on a direction consistent with the target
of EU 2020 renewables. The last advantage of Electricity Market Reform is the maximisation
of benefits and reduction in costs to the economy as wells as to the consumers and taxpayers.
This can be attained by making sure that the bills of electricity are affordable while
delivering the required investments. This program reduces costs compared to the existing
policies since it seeks to utilize the competition and markets powers. The Contracts for
Difference supports new investment in every form of generation of low-carbon such as
renewables and have been designed to give cost-effective and efficient stabilization of
process for the new generation through minimizing the exposure to the wholesale price of
electricity that is volatile (Kilkis, 2013).
The projects of low generation of carbon is applicable to a CfD and depending on if
the technology is less established or fully established, the project will have to compete in an
auction so as to acquire a contract. The CfD demands that the generators sell energy into the
market, however, to minimize exposure to variations in prices of electricity, CfD offer an
alternative top-up from the price of the market to a strike price pre-agreed (Denholm, 2013).
Conclusion
The subtopic discussed in the report paper above include principles of operation of a
field grid based energy storage system, mechanical design feature materials, energy storage
schemes, design of energy storage system based on existing the technology, and outline of the
Electricity Market Reform. The different types of energy storage system include compressed

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air, batteries, electric vehicles, flywheel, hydrogen, hydroelectricity, supper conducting
magnetic energy, and thermal. The reason why the flywheel storage system have been
selected for the design of an energy storage system is because it is less complex, economical,
and occupies less space compared to hydro system.
The compressed air and flywheel energy storage systems are also more advantageous
than majority of other energy storage systems since it is very easy to access information
concerning the compressed air and flywheel from numerous sources making their design to
be easier than the rest. The operational lifespan of a flywheel system is 20 years and the
power delivered during this period is 400kW. The installation cost has been approximately to
be $3 million, with and efficiency of about 95.5%, and high specific power of about 1.2 KW
per kg. The protection required in the flywheel system are on the parts of the system that can
be dangerous to the users which may cause accidents during the operation of the system.
Recommendation
The energy storage system that might be widely used in the future is the nickel-
cadmium batteries since they occupy a small space in the company and also can perform in
abusive and harsh environment within the company such as extreme temperatures within the
company. The nickel-cadmium battery storage system is characterized by high rate of
discharge rate making is a reliable source especially when high discharge is needed to drive
engines in the company.

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