Renewable energy storage comparison and applications in vietnam

Hanoi University of Science and Technology
School of Electrical Engineering

Renewable energy storage
Comparison and applications in Vietnam
A report in Introduction to Electrical
Engineering (EE1024E)
Instructor: Nguyễn Đức Tuyên,PhD, professor of
SEE,HUST
Reported by: Bùi Hải Đăng, student of
SEE,HUST
Student ID:20173723

Hanoi, June 2019


Abstract
As the drastic exhaustion of the Eatrh’s fossil resources and the concerned about
environmental issues of using them, the world now incresingly switch the power supply to
renewable energy resources such as solar, wind, biomass, tidal, wave, etc. Solar power plants
and Wind power plants are the most popular. Howerver, these types of energy is intermittent
in nature and hence the energy storage systems is required to provide stable energy supply. In
this report, electricty storage technologies for renewable energy power plants will be
disscussed. This report will focus on the existing technologies such as pumped hydro, flywheel, compressed air, capacitors, batteries and superconducting magnetic storage.
Comparison between these technologies is made regarding technical characteristics, operating
requirements, applications and installation availabilities in Vietnam’s situations.


1

Content

List of abbreviations …………………………………………….
1.

Introduction………………………………………………………
1.1 Iperativeness of Renewable energy storage system
1.2 Application
1.3 Classification

2.

Theoretical Information………………………………………….
2.1 Pumped Hydro storage system
2.2 Flywheel energy storage system
2.3 Compressed air anergy storage system
2.4 Superconducting Magnetic storage system
2.5 Capacitors/Supercapacitors storage system
2.6 Batteries

3.

Comparison and Disscusion……………………………………...
3.1 Specification differences
3.2 Installation availability in Vietnam
3.2.1 Discussion
3.2.2 Remarks

4.

Conclusion
……………………………………………………….

References

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LIST OF ABBREVIATIONS
RE: Renewable energy
ESS: Energy storage system
PHES: Pumped Hydro energy storage

CAES: Compressed Air energy storage
SMES: Superconducting magnetic energy storage
VSC: Voltage source converter
AC: Alternating current
DC: Direct current


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1.INTRODUCTION
1.1 Imperativeness of a energy storage system
During the industrial revolution, fossil fuels (coal, oil, gas,..) become the main energy
resources of human society. However,in recent decades, people have concerned about the
rapid exhaustion of fossil fuels and the adverse effects of using them on global climate, thus
the clean and renewable energy is being develop and utilize more and more widely.
Renewable energy is energy obtained from natural repetitive and persistent flows of energy
occurring in the local environment[1]. Renewable energy includes sources like wind, solar,
geothermal, biomass, tidal, waves, etc. These types of energy is discontinuous in nature
especially will and solar power, their meteorological parameters changes on daily, weekly,
anually even hourly and depend on weather and location of the installed location[2]. Hence,
the lacking of producing continuous and stable anergy capacities is recognizable. In addition,
not only the power of RE is intermittent but the electricity demand also varies with time, the
maximum demand only last for a few hours each day. This
leads to inefficient and expensive power plant. The solution to
meet renewable energy with the main grid’s demand and assure
quality power supply is Electricity Storage System.

1.2 Application
Generally, ESS has two main purpose: peak-shaving and loadleveling. In peak shaving mode, electricity from off-peak time
is stored in ESS and then discharge to the grid during on-peak

time, it means that the power plants can save fuels or prevent
overloading. In load-leveling mode, ESS acts like a alternating
load. When the load is low such as in off-peak period, ESS play
the part of a “positive-load” (i.e it is charged by the remainder
of power). On the other hand, when the consumed power is
higher than average, ESS acts like a “negative-load” (i.e it

Fig.1 Load profile of a large scale ESS[3]
a)Peak shaving mode;b)Load leveling mode

discharges and supports the generator).These mean that the load
profile of the whole system is kept at a nearly constant rate which is good for the grid.
For Renewable energy, detailed applications of ESS to enhance the integration of wind
energy are reported in Ref.[4]: (i) Transmission curtailment: compensation of power delivery


4

restraint caused by insufficient transmission line. (ii) Time-Shifting: firming and shaping of
wind-generated energy by storing power from the grid when wind generation is inadequate
and discharging during the high demand period. (iii) Grid Frequency Support: Energy storage
supports grid frequency during sudden, large decreases in wind generation over a short
interval. (iv) Fluctuation suppression: Wind farm generation frequency can be stabilised by
suppressing fluctuations (saving and releasing energy during short duration variations in
output). Eventhough the work reported in Ref. [4] only focuses on wind energy, these key
applications for storing the renewable electricity should be equally relevant to solar or wave
power generation as well as other intermittent renewables sources.
1.3 Classification
Electricity is not easy to be stored directly but it can be converted to another form for storage
then converted back to electricity when needed. This is the more convenient and costeffective method rather than store electricity directly. According to the form of energy to

which eletricity is converted, ESS can be catergorized in to classes:
(i)

Mechanical energy: Potential energy (Pumped hydro, Compressed air) or Kinetic
energy (Flywheel)

(ii)

Electromagnetic energy: Superconducting magnetic

(iii)

Electrostatic energy: Capacitors and supercapacitors

(iv)

Chemical energy: Batteries

2. THEORETICAL INFORMATION


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2.1 Pumped Hydro Electricity Storage
A PHES plant consists of three main
component: (i) Lower reservoir; (ii) reversible
turbine generator/turbine pump; (iii) Higher
reservoir as shown in Fig.2[5]. PHES stores
electricity in the form of potential energy of
water that is pumped from the lower to the

higher reservoir. In this kind of ESS,
electricity in off-peak time is used to operate
the turbine pump to raise water from the
bottom reservoir to the top reservoir. When
high demand occurs, water form the upper
reservoir fall through the generator and
generate electricity just the same as a

Fig.2 Conceptual Pumped Hydro storage system[5]

hydropower plant. The water on the high
altitude has potential
U =mgh , it is clear that the maximum amount of energy stored in a PHES plant
proportion to the height difference between two reservoir and the volume (mass) of water.
Although the energy density of PHES is relative small in comparison with other conventional
fuel (calculating show that the energy density per unit volume of a
W V =1.0 MJ / m

3

100 m height water is

) but total energy stored in a PHES still can be very large due to the large

volume of water.
PHES is a developed technology with large volume, long storage period, high efficiency
(varies between 70% to 80% even up to 87%[6])and relatively low capital cost per unit of
energy[3]. This technique is currently the most cost-effective way to increase the penetration
level of Renewable energy into power system, particular in small autonomous island grids[5].
According to Hino and Lejeune[7], pumped hydroelectric storage plants have several

advantages, such as (i) flexible start/stop and fast response speed, (ii) ability to track load
changes and adapt to drastic load changes, and (iii) can modulate the frequency and maintain
voltage stability. However, the installation availability of PHES is highly depend on the area
geographical characteristic. PHES should be built in the area with sufficient water supply and
favorable topography (i.e the height difference between two reservoir must be significant). In


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flat are are such as delta or highland, underground cavities or even open sea can be used as
the lower reservoir[8].
2.2 Flywheel energy storage sytem
Ancient world had used flywheel as a mechanical energy storage device for a long time, its
earliest form is the spinning table for clay pottery making. Flywheel stores energy in the form
of anggular kinetic energy. The amount of energy
inertia I

spinning with angular velocity

E stored in a flywheel with moment of

ω is

1
2
E= I ω .
2
Let consider the simplest case that the flywheel is a uniform disk with radius

r

which has

moment of inertia:
1
I = mr 2
2
Therfore, the energy density per unit mass of the flywheel is obtained by:
E 1 2 2
W m= = r ω
m 4
Hence, the faster the flywheel rotates, the larger amount of energy can be stored. However
Shape
K
the angular velocity of a real flywheel is limitted by
its material strength resisting the centrifugal force

Constant stress disk

0.931

which tends to tears the wheel apart. For a a uniform

Constant thickness disk

0.606

Thin rim

0.500

Constant stress bar

0.500

Flat pierces disk

0.305

wheel of density

ρ , the maximum tensile stress

is:
σ max =ρ ω 2 r 2 (Ref.[1])
In general, the moment of inertia of a solid shape is
I =Km r

2

where K is called shape factor of the

wheel (given in Table.1). So:
Table.1 Flywheel shapes factor

max

E 1
1 Kσ
W m = = K r 2 ω2=

m 2
2 ρ

Much larger energy density can be obtained by using lighter composite
material such as fiberglass in epoxy resin[1], which have higher tensile
strength

σ max and smaller density

ρ .

The schematic of a Flywheel storage system is shown in Fig.3[9]


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Power
source

Fig.3 Basic diagram of a Flywheel storage system

This system has three operation mode:
(i)

Charge mode

(ii)

Stand-by mode

(iii)

Discharge mode

During charge mode, the Voltage Source Converter (VSC) interfacing the power source runs
as a rectifier and the other as an inverter, with the transferred energy accelerating the flywheel
to its rated speed. In this mode, energy is stored in the flywheel in the form of kinetic energy.
Once the flywheel reaches its charge speed, the storage system is in standby mode and is
ready to discharge. In this mode a little energy from the power system is used for redeem the
converter and machine losses. During discharge mode, the VSC interfacing the power system
runs as an inverter injecting the required power to the grid. The flywheel VSC runs as a
rectifier. The flywheel slows as it discharges. The reason that the electriccity is convert ACDC-AC from source to flywheel is to simplify the control of flywheel. It easier to manipulate
the speed of the wheel by manipulate the DC voltage (by pulse width modulation or other
methods) rather than work with AC voltage.
The advantage of Flywheel over PHES is that they take a little land area, not require any
special condition thus can be installed almost everywhere. Flywheel also have long life
capable, it can make thousands of fully charge-discharge cycle without requiring
mantainance[10]. Although flywheel is not widely used in commercial (there is only a pilot
project by Amber Kinetics in Hawaii), but it offer a promising theoretical method for
electricity storage, especially for eectric vehicles since its energy can be refill more quickly
than batteries.


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2.3 Compressed air electricity storage system
Beside the PHES, Compressed Air Energy Storage system is the only other commercially
available technology capable of providing very large energy storage deliverability (above
100 MW with a single unit).A CAES system consists of five major components as shown in
Fig.4[11]: (i) A motor/generator with clutches to control engagement with the compressor or

turbines. (ii) An two-stage air compressor, to achieve cost-effection and reduce the moisture
in compressed air. (iii) A turbine train, containing both high- and low pressure turbines. (iv) A
cavity/container for storing compressed air. (v) Equipment controls and auxiliaries such as
fuel storage and heat exchanger units.

Fig.4 Compressed air storage system[11]

CAES works on the basis of conventional gas turbine generation. It separate the compression
and expansion process of a conventional gas turbine into two independent processes and
stores the energy in the form of elastic potential energy of compressed air. Energy is stored by
compressing air into an air tight space (tank or carven) with high pressure between 4.0–8.0
MPa. Energy is extracted from CAES by two steps: (i) Compressed air is released from the


9

storage tank, heated and expanded throug the high pressure turbine (ii) then the air iss mixed
with gas or fuel and burned and exhauted through a low pressure turbine. Both the turbines
are connected to a generator to produce electricity. The heat of the exhaust is potentially
captured by a recuperator and used to heat the high pressure air in the next cycle
CAES is not an independent system, it has to be combined with a conventional gas turbine
plant. It cannot be used with other types of power plants such as hydropower, coal-fired,
nuclear, wind turbine or solar photovoltaic plants. Moreover, the requirement of combusting
fossil fuels and the contaminating emission also makes the CAES less attractive [12].

2.4 Superconducting magnetic storage
Super conducting magnetic storage (SMES) is the only established technology which store
electrical energy directly by electric current[13]. It store energy in the form of magnetic field
energy created by a DC current passing through an inductor made from supercnducting
material which have been cooled down to

4° K

in oder to maintain the coil’s

superconducting threshold. Theoretically, any coil can be considered as a ideal inductor in
series with a pure resistance, let emulate the coil with a DC current flow in it as the R-L
circuit in Fig.5[14]

Suppose both switch

S 1 and

S2

closed at the beginning. First,

are
S 1 is

closed, after a long time, the current through
the circuit is steady and equal:
I 0=

ε
R

Then the magnetic enargy stored in the coil
is:
1

U = L I 02
2
Fig.5 R-L circuit[14]

Now closed

S2

and open

S1

at the

same time, take the EMF source out of the circuit,


10

denote that moment as t=0,the current through R and
but decay smoothly as shown in Fig.6[14]. The curren

( RL )t

−

i=I 0 e

Then the time rate of energy losses due to heat is equal:

Fig.6 Graph of current from t=0[14]

Ploss=i2 R
Hence, if the coil is forced to reach superconducting state (i.e its resistance apprximate 0), the
heat loss is approach zero and the current

i

is conserve at

i=I 0

and can circulate

indefinitely.
Fig.7 shows the main components of a SMES system: (i) a superconducting unit (ii) a
cryogenic refigerator and a vaccum insulated vessel (iii) a power conversion system

Fig.7 Schematic of a SMES[15]

SMES systems have been in service for some years to improve industrial power quality and
to provide a fnest quality electricity for users who are the most vulnerable to voltage sag. An
SMES recharges within minutes and can repeat the charge/discharge cycle thousands of times
without any degradation of the coil. Although SMES also is a promissing technology to store
large amount of electricity,but the high cost prohibit the widespread use of them.
2.5 Capacitor/Supercapacitor
The simplest capacitor consists of two conducting plates (metal) separated by a layer of
insulating material (dielectric). When a capacitor is charged, the two plates carries charges
with the same magnitude

|Q| and opposite in sign. The potential V of the positive plate


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with respect to the negative one is proportional to
as

Q and the capacitance

C

is defined

Q
.
V

Capacitors can be charged significantly faster than batteries and have long life span with a
high efficiency. However, the main drawback of conventional capacitors is the low energy
density. The energy stored in the capacitor is:
1
U= C V 2
2
For a conventional parallel-plate capacitor: Capacitance

C

is proportion to the area of

plates, thus if a large capacity is required, the area of the dielectric must be very large. This
makes the use of large capacitors uneconomical especially in stationary EES applications
[16].
Recent progress in the electrochemical capacitors/supercapacitors could lead to much greater
capacitance and energy density than conventional capacitors[3]. Electrochemical capacitors
(supercapacitors) consist of two electrodes separated by an ion-permeable membrane
(separator), and an ionical electrolyte touching both electrodes,[17] the construction of a
double layer capacitor is shown in Fig.8[17]. The electrodes are often made from porous
carbon or another large surface area material.
When a voltage is applied between two
electrodes, the electrodes are polarized, ions
in the electrolyte form electric double layers
of opposite sign of charges to the electrode's
charges. For example, positively polarized
electrodes will have a layer of negative ions
at the electrode/electrolyte interface along
with a charge-balancing layer of positive ions
adsorbing onto the negative layer and vice
versa. Since the surface area of activated
carbons is very high (about

2000 m

2

per

gram), moreover the distance between the
plates is very small (less than

Fig.8 Typical construction of a double-layers capacitor
(1)power source; (2)colector; (3)electrodes; (4)double
layer ; (5)electrolyte with ions; (6)separator

1 nm ) thus much larger capacitances and stored energy are

obtained by using supercapacitors rather than using conventional capacitor.


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Table.2[18] present the most prospective technologies for short-term power exchange in
terms of cost, time scale, and rate of efficiency. The two most promising short-term storage
devices: flywheels and supercapacitors, both offer similar characteristics and are both suitable
for renewable energy applications[19].
Technology

Energy cost

Power cost

Time scale

Roundtrip

Flywheel
Supercapacitor
SMES

($/kWh/year)

96
711
370000

($/kWh/year)
1.2
6
59

(minutes)
0.006-6
0.006-6
0.006-0.06

efficiency
89%
86%
21%

Table.2 Properties of short-term energy storage technologies[18]

The major problems with capacitors, similar to flywheels, are the short durations and high
energy dissipations due to self-discharge loss. On the other hand, although the small
electrochemical capacitors are well developed, large units with energy densities over
20 kWh / m3

are still in the development stage.

2.6 Batteries
Rechargeable battery is the oldest form of electricity storage which stores electricity in the

form of chemical energy. A battery have of one or more electrochemical cells and each cell
consists of a electrolyte together with a positive electrode (anode) and a negative electrode
(cathode). During discharge, electrochemical reactions occur at the two electrodes generating
a flow of electrons through an external circuit these reactions are reversible, allowing the
battery to be recharged by applying an external voltage across the electrodes. Batteries can
respond very rapidly to load changes and accept co-generated and/or third-party power, thus
increase the system stability. Modern batteries usually have very low standby losses and high
energy efficiency (60–95%)[3]. Batteries are an essential component of most autonomous
power systems However, large-scale utility battery storage has been rare up because of high
maintenance costs, low energy densities, small capacity, a short life span and a limited
discharge capability. In addition, most batteries contain toxic materials. Hence the ecological
impact from uncontrolled disposal of batteries must always be considered . Batteries that are
either in use and/or potentially suitable for utility scale battery energy storage applications
include lead acid, nickel cadmium, sodium sulphur, sodium nickel chloride and lithium ion.
These type of batteries only different in the element of electrodes and electrolyte.


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3. COMPARISON AND DISSCUSSION
3.1 Specifications differences
Fig.9[1] summarizes the performance of various storage mechanisms. ‘Performance’ can be
measured in units such as

MJ / $ ,

3

MJ /m

or

MJ /kg . Of these, the cost-

effectiveness ( MJ / $ ) is usually the main concern for commerce, but is the hardest to
estimate note that ‘cost’ here is wholesale cost before taxes and that taxation, especially of
transport fuels, varies greatly between countries. The second unit is important when space is
at a premium (e.g. in buildings of fixed size vehicles). The third unit is considered when
weight is vital (e.g.in aircraft). In this chapter we indicate how these performance figures are

Fig.9 Energy per unit cost and energy per unit volume of some storage methods (US$ in 2012)[1]

estimated


14

The more detailed characteristics of all energy storage technologies examined in this report is
shown in Table.3[1]. The conventional fossil fuels are included in Table.3 as points of
reference (data and information from Ref.[1] and Ref.[3]).


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Storage

Conventional
fuels
Diesel oil
Coal

Wood
Electrical
storage
Capacitor/Super
cap
SMES
Mechanical
storage
PHES
Flywheel(compo
site)
CAES
Battery
Lead-acid
Lithium based

Energy density

Operating
Temperatu
re
( °C )

Commercial
development
time
(years)

Operating
cost

(MJ/USD)

Discharge
time

Power
rating
(MW)

Efficiency
(%)

MJ/kg

MJ/L

45
29
154

39
45
7

Ambient
Ambient
Ambient

In use
In use

In use

100
500
200

-

-

30
30
60

-

10^(-2)
10^(-3)

-

Unlikely
Unlikely

0.005
-

Miliseconds
-8s
Milisecs60min

~0.05
0.1-10

-

0.001
0.05
0.2-2

0.001
0.15
5

Ambient
Ambient
20-10000

In use
In use
In use

0.2-20
0.2
1

1-24h+
Milisec15min
1-24h+

1005000
0-0.25
5-300

80
80
50

0.15
0.5

0.29
0.8

Ambient
Ambient

In use
In use

0.02
0.04

Secondshours
Minuteshours

0-20
0-0.1

75

80

Table.3 Detail comparison between methods of energy storage[1][3]


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Hence, Energy storage technologies can be compared by these perspective:
(i)

Technical maturity: Developed technique (PHES,Lead-acid battery) and

(ii)

Power rating and discharge time: Large-scale plant (PHES, CAES) can store more

developing technique (other types).
than 100 MW and provide power for hours, days; Lead-acid battery is suitable for
medium-scale storage system; other technology with smaller power rate can be
used for correcting voltage fluctuation in short time interval.
(iii)

Cost: Large-scale, developed system (PHES,CAES,battery) tend to be cheaper
than other modern technologies

3.2 Installation availability in Vietnam
3.2.1 Disscussion
The historical and forecasted need for electricity energy in Vietnam since 1990, when the
Vietnamese Government launched a comprehensive reform. This reform has helped to
improve people’s living conditions and has driven the development of the national economy..

The strong economic growth is the main reason that electricity demand has rapidly grown as
presented in Fig.10[20]

Fig.10 History and forecasts of electricity energy and peak load demand in Vietnam, 1995–2030


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According to this forecast, the electricity peak demand is expected to rise by 7.5% and 9.1%
per year in the low and high scenario, respectively, over the period of 2010–2030. Although
the penetration of enewable energy is quite small, but it will be the fastest growing segment
of power structure in Vietnam in future:

Vietnam Power supply mix [20]
10

18

38

34
Hydropower

Coal

Gas

Renewables

Renewable energy potentials are commonly classified in different categories of theoretical,

technical, and economic potential. Theoretical potential is defined at the maximum energy
that could be exploited in a region considering only thermodynamic constraints[20].
Technical potential is the amount of energy that could be utilized using existing technology,
as technology changing every years, technical potential also depends on the date of
assessment. Economic potential is defined by the energy that could be used using
economically feasible installations. The limits of the economic potential is highrly depends
on infrasstructure and economic aspect (Voivontas et al., 1998). Vietnam has a huge potential
of renewable energy that are not yet fully exploited. The government has been issuing
investment to realised its potential in renewable energies. Fig.11[21] and Table.4 illustrated
the installed and potential cappacity of renewable sources of Vietnam:


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Renewable energy-Realizing Vietnam potentials
Biomass

Small hydro power

Solar

Wind
0

50000

100000

150000

Installed

200000

250000

300000

350000

Column1

Renewable sources

Installed Capacity

Potential capacity

Biomass

(MW)
270

318630 (theoretical)

Small hydro power
Solar

1648
8

7000 (technical)
7140 (commercial)

Wind

189

26763 (technical)

3.2.2 Remarks
3/4 land areas
moutains

Table.4 Vietnam’s Renewable Energy potential[21]

or

of

Vietnam

highlands

is
with

average altitude 381m above sea level[22]. Vietnam has 2400 rivers 10km or longer cover all
around the country. These mean Vietnam has the favorable topology and water supply to
install PHES, it has economic potential is over 10,000Mw of hydro pump capacity[20]. In

addition, the capacity of small hydro power in Vietnam also large, thus PHES is a promising
technology to provide quality power for civilations, especially for people living in remote
area such as high moutans.
Vietnam’s economy still depends on agriculture. The agriculture produces a huge volume of
bio-waste material and have nothing to do with them rather than burn or bury into ground
(only a little is used for further purposes). For example, the amount of rice husk waste is 50
million tons each year, approximately[23]. Almost all the amount of rice husk is burned after
harvesting, this is not only a waste in energy but also a source of air polution. The initial


19

biowaste material may be transformed by chemical and biological processes to produce
biofuels (i.e. biomass processed into a more convenient form) as methal gas (main product),
liquid methanol and solid charcoal. The capacity of Biomass power in Vietnam is
significantly unnegligible as shown in Fig.10. Therefore the hypothetical of making bio-fuel
power plants associating with CAES system is very bright in Vietnam’s situation since CAES
must be installed with a gas turbine power plant as disscussed above.
4.CONCLUSION
Fossil fuels are on their way out one way out, and nuclear energy is a dead end. That leaves
renewable energy sources, such as solar, wind, hydro, geothermal, and biomass, to shoulder
the burden of powering future society. Vietnam society is not an exception, forecast reported
that in the near future 2020-2030, conventional fossil fuels power will grow slowly while
renewable resouces will see a fast rate growth. As the rapid development of RE electricity
power plants, it is clearly to see that RE energy storage system is vital for helping intermittent
RE source to provide nameplate capacity and quality power. The technologies have been
disscussed in this report are : Pumped Hydro energy storage, Compressed Air energy storage,
Flywheel

energy

storage,

Superconducting

magnetic

energy

storage,

Capacitor/Supercapacitor and batteries. By comparison between these technologies in term
of

technical characteristics, operating requirements, applications and

installation

availabilities and examnining the condition in Vietnam, it is clear that PHES and CAES are
the most favorable technology for increasing RE penetration to Vietnamese power structure.

REFERENCES:


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[1] John Twidell and Tony Weir. Renewable Energy Resources, Third edition 2015 by
Routledge
[2] Alam MM, Rehman S, Meyer J, Al-Hadhrami LM. Extraction of the inherent
nature of wind using wavelets. Energy Sustainable Dev 2014;22:34–47

[3] Haisheng Chen, Thang Ngoc Cong, Wei Yang, Chunqing Tan, Yongliang Li, Yulong Ding.
Progress in electrical energy storage system: A critical review. In: Progress in Natural Science
19 (2009) 291–312
[4] Mears D. EPRI-DOE storage handbook-storage for wind resources. In: Annual peer
review meeting of DOE energy storage systems research. Washington DC, USA, Nov. 10–11,
2004, p. 1–18.
[5] Shafiqur Rehman, Luai M. Al-Hadhrami, Md. Mahbub Alam. Pumped hydro energy
storage system: A technological review. In: Renewable and Sustainable Energy Reviews 44
(2015) 586–598
[6] Energy Storage Hawaiian Electric Company; 2012 [accessed: 13 February, 2012].
[7] Hino T, Lejeune A. Pumped storage hydro power developments. Compre Renewable
Energy 2012;6:405–34.
[8] Ahearne J. Storage of electric energy, Report on research and development of energy
technologies. International Union of Pure and Applied Physics; 2004, p. 76–86.
[9] Modeling and Analysis of a Flywheel Energy Storage System for Voltage Sag Correction
by Satish Samineni, December 2003. Major Professor: Brian K. Johnson, Ph.D.
[10] Lazarewicz M, Arseneaux J. Flywheel-based frequency regulation demonstration
projects status. In: Proceedings of EESAT conference, San Francisco, USA, Oct. 17–19,
2005, p. 1–22.
[11] Jewitt J. Impact of CAES on Wind in Tx, OK and NM, In: Annual peer review meeting
of DOE energy storage systems research. San Francisco, USA, Oct. 20, 2005; p. 1–16.
[12] Weinstock IB. Recent advances in the US Department of Energy’s energy storage
technology research and development programs for hybrid electric and electric vehicles. J
Power Sources 2002;110:471–4.
[13] Cheung KYC, Cheung STH, Silva N, et al. Large-scale energy storage systems, Imperial
College London, ISE2 2002/2003.
[14] Hugh D.Young and Roger A.Freedman, University physics with modern physics, 13 th
edition.
[15] Beacon flywheel energy storage. .

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[16] Chen HS, Ding YL. A cryogenic energy system using liquid/slush air as the energy
carrier and waste heat and waste cold to maximise efficiency, specifically it does not use
combustion in the expansion process. UK Patent G042226PT, 2006-02-27.
[17] />[18] J. P. Barton and D. G. Infield, “Energy storage and its use with intermittent renewable
energy,” IEEE Trans. Energy Convers., vol. 19, no. 2, pp. 441–448, Jun. 2004
[19] Chad Abbey, Student Member, IEEE, and Géza Joos, Fellow, IEEE, “Supercapacitor
Energy Storage for Wind Energy Applications”,IEEE transactions on industry applications,
vol. 43, no. 3, may/june 2007
[20] Nhan T. Nguyen, Minh Ha-Duong, “Economic potential of renewable energy in
Vietnam’s power sector”, Energy Policy 37 (2009) 1601–1613,p 1601-04
[21] Vietnam Renewable energy report 2018
[22] />[23] Trần Sỹ Nam, Nguyễn Thị Huỳnh Như, Nguyễn Hữu Chiếm, Nguyễn Võ Châu Ngân,
Lê Hoàng Việt và Kjeld Ingvorsen, “Ước tính lượng và các biện pháp xử lý rơm rạ ở một số
tỉnh đồng bằng sơng Cửu Long”, Tạp chí Khoa học Trường Đại học Cần Thơ Phần A: Khoa
học Tự nhiên, Công nghệ và Môi trường: 32 (2014): 87-93