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CHAPTER 6
FEASIBILITY INVESTIGATION OF ENERGY STORAGE
SYSTEMS FOR HYBRID POWER SYSTEMS
6.1 INTRODUCTION
Due to the rapid depletion of conventional energy resources, an alternative
search to meet the present load demand came in existence. Renewable energy
resoueces like PV, Wind, Fuel Cell are clean and environment friendly technologies.
A system in which renewable energy resources feed the local load demand is called
a microgrid [125]. Due to variation of sun light during day and night, and change in
wind speed, PV power and wind power are considered as instable sources. Hence to
stabilize the operation of such hybrid systems, batteries are incorporated in the
hybrid system. The fluctuation in these resources results in batteries being discarded
in short time of their life span. So the cost of batteries has covered a large part of
total cost of PV-Wind hybrid system. Hence, the battery life time and reduction in
life cycle cost of hybrid energy systems are critical points to be considered. By using
PV-Wind hybrid power generation system, effective charging time of batteries can
be increased as well as electricity production cost can be reduced.
The optimum design of micropower system is challenging due to large
number of design options and uncertainty in important parameters such as load size
and availability of solar and wind resources. The optimization of the hybrid system
using hydrogen storage and hybrid iterative genetic algorithms for rural
electrification are also proposed by some researchers. Penetration of DG in the
power system determines the Green House Gas emissions and the impacts of
distributed generation with battery energy storage [6]. These emerging technologies
have lower emission and potential to have lower operating cost. An assessment of
hybrid systems with battery energy storge systems was discussed in [122]. A better
way to realize the potential of distributed generation is to take a system approach
where load and generation acts as a subsystem called “microgrid” . This is a
decentralized and bidirectional pattern permits electricity import from the grid and
electricity export to the grid. A plant that produces electricity less than 500 kW
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comes under micro generation technologies. Microgrid sources can produce
electrical energy and thermal energy both. Hence, the penetration of distributed
energy resources both at low voltages and medium voltages (LV and MV) in utility
and downstream networks have been increased in developed countries. Computer
simulation is an increasingly popular tool for determining the most suitable hybrid
energy system type, design and control for an isolated community or a cluster of
villages. This chapter presents the the life cycle cost benefit analysis of battery
energy storage system using different types of battery in a hybrid system. The main
purpose of the hybrid system with battery system proposed here is to reduce, as
much as possible, the economic parameters. Three different hybrid systems are
considered to decide the type of battery to be used for hybrid system. The
incorportation of a battery bank makes the control operation more practical.
6.2 TYPES OF BATTERY ENERGY STORAGE SYSTEM (BESS)
For very large energy storage applications, only pumped hydro and
compressed gas are cost effective at this time. These technologies, however, are
limited by geography, while electrochemical energy storage devices such as batteries,
fuel cells/flow batteries, and electrochemical capacitors are among the leading EES
technologies for the future because of their scale-ability and versatility.
Figure 6.1 Power and Energy Densities of Various Energy Storage Systems
155
In remote locations, isolated hybrid systems are found favourable for
electricity generation. Wind generation and Photovoltaic Systems are the most
promising technologies for supplying load in remote locations. As both PV and Wind
are intermittent sources, battery energy storage system (BESS) is used to enhance the
performance of intermittent renewable energy resources. In this paper, a new Life
Cycle Cost Benefit Analysis is presented to select the type of battery by comparing
the performance of hybrid system considering Net Present Cost (NPC), Initial Cost
(IC), Operation Cost (OC) and Cost Of Energy (COE). The performance of Lead-
Acid, Zinc-Bromine and Vanadium Redox batteries are placed in hybrid PV-Wind
system and life cycle cost benefit is analyzed. Advance flow Zinc-Bromine Battery is
cost effective for all considered hybrid systems.
6.2.1 Lead Acid Battery
A lead-acid cell is a basic component of a lead-acid storage battery (e.g., a car
battery). A 12.0 Volt car battery consists of six sets of cells, each producing 2.0 Volts.
A lead-acid cell is an electrochemical cell, typically, comprising of a lead grid as an
anode and a second lead grid coated with lead oxide, as a cathode, immersed in
sulfuric acid. The cell potential (open circuit potential or battery voltage, OCV) is a
result of the electrochemical reactions occurring at the cell electrode interfaces. The
electrochemical reactions that convert chemical energy into electrical energy in a
lead- acid cell.
ELECTRODES: Lead (Pb) and lead oxide electrodes from Leoch Battery Technology
Company, LTD. Tin (Sn) and Pb-Sn (50% by mass) wires from
Amerway Inc. Pb (99.998%) foil, 1.0 mm thick from Alfa Aesar
ELECTROLYTE: Sulphuric Acid (96%) from Mallinckrodt
6.2.2 Zinc Bromine Battery (ZBB)
Batteries and flow batteries/fuel cells differ in two main aspects. First, in a
battery, the electro-active materials are stored internally, and the electrodes at which
the energy conversion reactions occur are themselves part of the electrochemical fuel.
The characteristics of the negative and positive electrodes determine both the power
density (e.g., electrical, transport, and catalytic properties of the active material and
non-reactive materials) and the energy density (e.g., mass of active materials) of the
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battery. As a battery converts its chemical energy to electrical energy, electrodes are
consumed and undergo significant physical and chemical changes which affect its
electrical performance. Second, because of the dual functions of the electrodes
described above, a conventional battery has minimal or no scale-up advantages.
Instead, it can only be scaled-out. That is, if more energy is needed, then more battery
modules with identical components are required. As the amount of electro-active
materials increases in a battery, more current collecting materials, electrolyte,
separators, and enclosure materials are also needed. Consequently, a battery can never
approach its theoretical energy density. Furthermore, increasing the capacity of a
battery almost always increases internal resistances and consequently decreases power
density and efficiency. Systems in which one or more electro-active components are
stored internally are called hybrid flow batteries. Examples include the zinc– bromine
and zinc–chlorine batteries.
Similarly to conventional batteries, the energy densities of these hybrid flow batteries
are limited by the amount of electro-active materials that can be stored within the
batteries and they have limited scale-up advantages.
6.2.3 Vanadium Redox Battery (VRB)
A flow battery is an electrochemical device that converts the chemical energy
in the electro-active materials directly to electrical energy, similar to a conventional
battery and fuel cells. The electro-active materials in a flow battery, however, are
stored mostly externally in an electrolyte and are introduced into the device only
during operation.3 True flow batteries have all the reactants and products of the
electro-active chemicals stored external to the power conversion device. Systems in
which all the electro-active materials are dissolved in a liquid electrolyte are called
redox (for reduction/oxidation) flow batteries (RFBs). VRB Power Systems marketed
an all vanadium battery for remote area power systems, emergency power supply and
kW scale to MW scale load leveling and renewable support. VRB Power
manufactured and installed the VRB-ESS (vanadium redox battery–energy storage
system) range of batteries, which had a typical discharge–charge range of 20–80%.
An overall efficiency of 65–70%.
Redox flow batteries store energy in two tanks that are separated from the cell
stack (which converts chemical energy to electrical energy, or vice versa). This design
enables the two tanks to be sized according to different applications’ needs, allowing
157
VRBs’ power and energy capacities to be more easily scaled up than traditional sealed
batteries. There are many kinds of VRB chemistries, including iron/chromium,
zinc/bromine and vanadium.
Unlike other redox flow batteries, VRBs use only one element (vanadium) in
both tanks, exploiting vanadium’s ability to exist in several states. By using one
element in both tanks, VRBs can overcome cross-contamination degradation, a
significant issue with other redox batteries chemistries that use more than one
element. The energy density of VRBs depends on the concentration of vanadium: the
higher the concentration, the higher the energy density. Sulfuric acid solutions, the
electrolyte used in current VRBs, can only hold a certain number of vanadium ions
before they become oversaturated, and they only allow the battery to work effectively
in a small temperature window. In addition, VRBs usually require expensive polymer
membranes due to the highly acidic and oxidative environment, which lead to high
system costs. The low energy densities and small operating temperature window,
along with high capital cost, make it difficult for the current VRBs to meet the
performance and economic requirements for broad market penetration.
6.3 FLYWHEEL ENERGY STORAGE SYSTEM (FESS)
Many years ago, pure mechanical flywheels were used solely to keep
machines running smoothly from cycle to cycle. Apart from the traditional use, now a
days, flywheels are becoming more popular for energy back up in power system. In
recent years, flywheel energy storage systems (FESS) have been rediscovered by
industry due to their advantages in comparison with other short-term energy storage
system. Flywheels are simple and characterized by high power and energy density,
longer-life, low-maintenance, highly cyclic (charge-discharge) capability, and zero
fuel consumption or CO2 or other emissions that makes them environment friendly.
Short-term energy storage like FESS can be a good choice in this situation to reduce
the number of switching and to make the system more stable. The latest advances in
power electronics, strength of materials and high performance bearings have seen the
flywheel exploited for various applications including attitude control in space crafts,
pulsed power in military vehicles, frequency regulation and energy storage among
others. Research continues in these applications to increase the efficiency and
performance of the flywheel. The advantages associated with flywheels include: long
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life, environmentally friendly, high depth of discharge, large number of
charge/discharge cycles, high energy density and fast response time among others.
Flywheels are mainly considered for uninterrupted power supplies (UPS), vehicles,
space and energy storage applications.
Table 6.1 Comparison of Various ESS
159
6.4 PROPOSED METHODOLOGY FOR BESS
Figure 6.2 Flowchart of Proposed Methodology – Life Cycle Cost Benefit Analysis of
Battery
Apply System Controls and System Constraints
Carry out Modeling of PV- Wind Battery DC Hybrid
System
START
Read hourly data for Wind generator, Load Demand &
Radiation
Select Suitable Sizes of PV, Wind and Battery Components
Change the type of batteries (1) Lead- Acid Battery (2) Zinc Bromine Battery
(ZBB) (3) Vanadium Redox Battery (VRB)
(3) Advance Flow (VRB – Vanadium Redox) Battery
Simulate the system performance of PV-Wind Dc Hybrid System in terms
of Net Present Cost (NPC), Initial Cost (IC), Operating Cost (OC) and Cost
Of Energy (COE)
Select the Battery with minimum NPC, IC, MC
and COE for Life Cycle Cost Benefit
STOP
160
System Schematic and Components
Figure 6.3 Schematic Diagram of PV-Wind Battery System
System Controls and Constraints
Wind Turbine
A 3 kW DC, wind turbine is chosen for the system. Availability of energy from the
wind turbine depends greatly on wind variations. Wind data for a site Kutch, Gujarat
is considered. The parameters considered for wind turbine are : anemometer height :
10 m, Weibull K: 2, auto correlation factor: 0.85, scaled annual averages 4.5 and 5.5
m/sec, turbine life time : 15 years and hub height : 25 years. The capital cost,
replacement cost and O&M cost considered for the wind turbine are 1200$/KW, 1100
$/KW and 20 $/yr respectively.
Photo Voltaic System
A 1 kW DC PV system is chosen for the hybrid system. Availability of energy from
the PV depends greatly on solar radiation variations. Solar data for a site Charanka
near Kutch, Gujarat is considered. The parameters considered for PV are: lifetime: 20
years, ground reflectance: 20%, scaled annual average 5.2 kwh/m2/day. The capital
cost, replacement cost and O&M cost considered for the wind turbine are 8000 $,
7000 $ and 10 $/yr respectively
Battery Bank
In case of excess energy from renewables, storage battery bank is used in the hybrid
system design. Commercially available battery models, like Surrett 4KS25P Lead
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acid, advance flow VRB and ZBB batteries are considered one by one for hybrid
system simulation. Each battery costs capital cost 130$/KW, 117$/KW to replace the
battery and 4$/yr for O&M. For different types of batteries, for optimal operation, the
cycle charging dispatch strategy is set.
System Controls:
Multiple generators can operate simultaneously, with minimum renewable energy
fractions (MRF) considered = 0% and 20%, annual interest rate = 6%, plant working
life span = 20 years, wind speed = 0, 4.5 and 5.5 m/s, scaled annual average = 5.2
kwh/m2/day, scaled annual average of temperature : 25
0 C, Dispatch strategy : Cycle
Charging
In this modeling, 3 kW DC rated power is used for the wind turbine. The life time is
taken as 15 years and Hub Height is 25 meters for the wind turbine considered. 1 hr
auto correlation factor is 0.85. 1kW DC PV is used for the simulation. In addition to
PV, wind turbine and storage battery, a primary load is used in the modeling of hybrid
systems.
The simulation is carried out for three different types of batteries (i) lead-acid
battery (LAB) (ii) Zinc-Bromine Battery (ZBB) and (iii) Vanadium-Redox Battery
(VRB) and considering three different configurations (i) Wind-Battery (ii) PV-Battery
and (iii) PV-Wind-Battery.
(a) PV-Wind-Battery HPS in HOMER (b) PV-Wind-FESS HPS in HOMER
Figure 6.4 PV- Wind Hybrid System in HOMER
162
PARAMETERS NPC
$
COE
$/kWh
IC
$
O&M
$/yr
Lifetime
Throughput
kWh
WIND-BATTERY 2,316 0.496 1,460 66.9 21,137
PV-BATTERY 3,661 0.785 2,920 57.9 42,274
PV-WIND-BATTERY 2,968 0.636 2,130 65.6 10,569
Table 6.2 Lead Acid Battery Results
PARAMETER NPC
$
COE
$/kWh
IC
$
O&M
$/yr
Annual
Throughput
kWh/yr
WIND-BATTERY 2,028 0.435 1,330 54.6 71
PV-BATTERY 2,485 0.533 1,840 50.5 325
PV-WIND-BATTERY 2,924 0.627 2,130 62.1 59
Table 6.3 Zinc Bromine Battery Results
PARAMETER NPC
$
COE
$/kWh
IC
O&M
$/yr
Annual
Throughput
kWh/yr
WIND-BATTERY 7,582 1.625 4,980 204 41
PV-BATTERY 18,196 3.900 16,180 158 231
PV-WIND-BATTERY 2,991 0.641 2,180 63.5 56
Table 6.4 Vanadium Redox Battery Results
Figure 6.5 Comparison of economics of LAB for Different Configurations
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
NPC COE IC OC
WTBTY
PVBTY
WTPVBTY
LEAD - ACID BATTERY (LAB)
163
Figure 6.6 Comparison of economics of ZBB for Different Configurations
Figure 6.7 Comparison of economics of VRB for Different Configurations
PARAMETERS
LEAD ACID
BATTERY
(LAB)
ZINC BROMINE
BATTERY
(ZBB)
VANADIUM
REDOX BATTERY
(VRB)
INITIAL COST $ 1,460 1,330 4,980
O & M COST $/yr 66.9 54.6 204
NPC $ 2,316 2,028 7,582
COE $/kWh 0.496 0.435 1.625
BEGED (km) 0.16 0.155 0.708
Table 6.5 Wind-Battery Hybrid System with Different Types of Batteries
0
500
1,000
1,500
2,000
2,500
3,000
NPC COE IC OC
WTBTY
PVBTY
WTPVBTY
ZBB BATTERY
0
5,000
10,000
15,000
20,000
NPC COE IC OC
WTBTY
PVBTY
WTPVBTY
VRB BATTERY
164
PARAMETERS
LEAD ACID
BATTERY
(LAB)
ZINC BROMINE
BATTERY
(ZBB)
VANADIUM
REDOX BATTERY
(VRB)
INITIAL COST 2,920 1,840 16,180
O & M COST 57.9 50.5 158
NPC 3,661 2,485 18,196
COE 0.785 0.533 3.900
BEGED 0.318 0.201 1.76
Table 6.6 PV-Battery Hybrid System with Different Types of Batteries
PARAMETERS
LEAD ACID
BATTERY
(LAB)
ZINC BROMINE
BATTERY
(ZBB)
VANADIUM
REDOX BATTERY
(VRB)
INITIAL COST 2,130 2,130 2,180
O & M COST 65.6 62.1 63.5
NPC 2,968 2,924 2,991
COE 0.636 0.627 0.641
BEGED 0.249 0.245 0.248
Table 6.7 PV- Wind-Battery Hybrid System with Different Types of Batteries
6.4.1 CASE : 1 – Wind-Battery System
Figure 6.8 Comparison of economics of Wind-Battery Hybrid System
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
NPC COE IC OC
LAB
ZBB
VRB
WIND-BATTERY
165
6.4.2 CASE : 2 – PV-Battery System
Figure 6.9 Comparison of economics of PV-Battery Hybrid System
6.4.3 CASE : 3 – Wind-PV Battery System
Figure 6.10 Comparison of economics of Wind-PV-Battery Hybrid System
Figure 6.11 Comparison of Cost of Energy for different Hybrid Systems
0
5,000
10,000
15,000
20,000
NPC COE IC OC
LAB
ZBB
VRB
PV-BATTERY
0
500
1,000
1,500
2,000
2,500
3,000
NPC COE IC OC
LAB
ZBB
VRB
WIND-PV-BATTERY
0
0.5
1
1.5
2
2.5
3
3.5
4
WIND-BTY PV-BTY WIND-PV-BTY
LAB
ZBB
VRB
COST OF ENERGY (COE)
166
6.4.4 Results and Discussions
The hybrid systems with different configurations (i) Wind-Battery (ii) PV-
Battery and (iii) Wind-PV-Battery are simulated with every time battery replaced. The
system is simulated with different types of batteries like Lead-acid, Zinc-Bromine and
Vanadium-Redox in different hybrid systems. In each figure it shows that Zinc-
Bromine Battery (ZBB) gives less Initial Cost (IC), Operation Cost (OC), Net Present
Cost (NPC) and Cost Of Energy (COE). This shows that the life cycle cost of a hybrid
system is less for ZBB than other types of batteries taken for simulation.
Wind-Battery configuration is the best suited for Lead-Acid Battery and ZBB
in terms of NPC, COE, IC and OM. Lead Acid battery placed in PV-Battery hybrid
system and ZBB placed in PV-Wind-Battery seem costliest configuration. PV-battery
configuration with VRB comes out to be the costliest system whereas Wind-PV-
battery comes out to be the cheapest configuration.
For all three types of hybrid systems configurations simulated in this
methodology, ZBB is the cheapest battery type and VRB is the costliest battery type.
6.5 PROPOSED METHODOLOGY FOR FESS
For the proposed system, a Flywheel Energy Storage System is incorporated in
place of a battery. Following are the steps for proposed methodology:
Step : 1 Read hourly data for Wind generator, Load Demand & Solar Radiation.
Step : 2 Carry out Modelling of PV- Wind DC Hybrid System.
Step : 3 Apply System Controls and System Constraints.
Step : 4 Select Suitable Sizes of PV, Wind Components
Step : 5 Incorporate a Flywheel of suitable size and number.
Step : 6 Simulate the system performance of PV-Wind DC Hybrid System in terms of
Net Present Cost (NPC), Initial Cost (IC), Operating Cost (OC) and technical
parameters.
Step : 7 Select the Flywheel with minimum NPC, IC, MC and COE for Life Cycle
Cost Benefit. Compare the renewable penetration with the increasing number of
flywheels.
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6.5.1 Effect of FESS on Renewable Penetration
There are a number of limitations to the attainable level of renewable energy
penetrations in isolated grids. These are spinning reserve requirements, conventional
generator minimum loading, conventional generator step load response, system
stability, and reactive power and voltage control requirements. High renewable energy
penetration in an isolated power system is only possible if another device on the
power system network provides the spinning reserve to cover for the changes in
output of the renewable energy plant. Earlier studies have indicated that short-term
energy storage is able to provide the spinning reserve in the power system and allow
the operation of the generation plant up to its rated power output. It can enable the
reduction of the diesel generating sets online resulting in dramatic fuel savings.
6.5.2 Results and Discussions
For the hybrid system configuration proposed in Chapter 4, Case :2, PV-Wind-Diesel
hybrid system, the simulation is carried out by including a flywheel instead of battery.
The results of configuration with FESS are shown in Table 6.8. PV penetration in this
hybrid configuration is negligible.
PARAMETERS ONE FW TWO FW THREE FW FOUR FW
NPC 2,603,243 2,882,603 3,197,941 3,469,885
COE 0.223 0.247 0.274 0.298
O&M COST 135,883 157,643 182,217 182,666
CAPITAL 866,200 867,400 868,600 1,134,800
FUEL
CONSUMED
138905 164276 192981 186864
WT 63% 59% 54% 52%
DG1 10% 9% 9% 10%
DG2 28% 32% 37% 38%
RF 0.519 0.422 0.314 0.307
CO2 365,783 432,594 508,182 492,074
CO 903 1,068 1,254 1,215
UH 100 118 139 135
PM 68.1 80.5 94.6 91.6
SO2 735 869 1,021 988
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NOX 8,056 9,528 11,193 10,838
SENSITIVITY 8m/s,
0.8$/L
8m/s, 0.8$/L 8m/s, 0.8$/L 8m/s, 0.8$/L
BEGED 413 171 202 229
Table 6.8 Effect of Flywheels on Renewable Penetration
DG share is in the range of 38% to 45%. Wind penetration is in the range of
54% to 63%. Total NPC and COE increases as the number of flywheels increases.
GHG emissions increases as the number of flywheels increases in the HPS. The
important observation is regarding renewable penetration. The renewable fraction
reduces after adding number of flywheels in the hybrid system.
Figure 6.12 Effect of Number of Flywheel on Renewable Fraction
Figure 6.13 Effect of Number of Flywheel on Cost of Energy
0
0.1
0.2
0.3
0.4
0.5
0.6
1 2 3 4
Renewable Fraction
Renewable Fraction
No of Flywheels
0
0.05
0.1
0.15
0.2
0.25
0.3
1 2 3 4
Cost of Energy (COE)
Cost of Energy (COE)
No of Flywheels
169
Discussions:
The inclusion of Flywheel energy storage indicate the limit on renewable
penetration. As the number of flywheels are added in the system, RF decreases every
time. The results of table 6.8 shows that the renewable penetration reduces with the
addition of FESS. Renewable fraction reduces from 0.368 to 0.277 for PV-Wind-
Diesel hybrid system and the same system with FESS added to it respectively. The
economic parameters NPC, COE increases by 5% with the addition of FESS. The
main aim of flywheel is to control the renewable penetration in the isolated systems. It
has been observed from the results that 25% reduction is noted in renewable
penetration with the addition of one flywheel. Further, if the environmental
parameters are considered for without FESS and with FESS, it has been found that
GHG emission increases by 8% due to the limit on renewable penetration.
6.6 COMPARISON OF BATTERY AND FLYWHEEL ENERGY STORAGE
SYSTEM
The proposed system is compared with BESS and FESS techniques and the
simulation results are taken. The comparison is given in the table below.
Parameters
Wind-Diesel
Hybrid System
Wind-Diesel
Hybrid System
with BESS
Wind-Diesel
Hybrid System
with FESS
NPC ($) 2,628,141 2,451,725 2,750,747
LCE ($/Kwh) 0.225 0.210 0.236
OC ($/yr) 156,582 139,574 166,079
IC ($) 626,500 667,500 627,700
WIND TURBINE 42% 43% 39%
DIESEL
GENERATOR-1
11% 22% 12%
DIESEL
GENERATOR-2
47% 35% 49%
RF 0.368 0.397 0.2777
CO2 (kg/yr) 500045 445,329 538,544
CO (kg/yr) 1234 1099 1329
170
UH (kg/yr) 137 122 147
PM (kg/yr) 93 83 100
SO2 (kg/yr) 1004 894 1081
NOX (kg/yr) 11014 9809 11862
BEGED (km) 146 128 158
Table 6.9 Comparison of BESS and FESS for the proposed system
Figure 6.14 Comparison of Economics With and Without ESS
Figure 6.15 Comparison of COE With and Without ESS
The performance of BESS and FESS can be compared in economic, technical
and environmental terms. The results show that the NPC and COE increases by 10%,
with the addition of FESS. The renewable penetration increases by 31% by adding
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
NPC IC OC
NO ESS
BESS
FESS
WITH ESS AND WITHOUT ESS
0.19
0.2
0.21
0.22
0.23
0.24
NO ESS BESS FESS
COE
COE
171
FESS compared to BESS. The environmental aspects are very key factors to study
about the GHG emissions. As per the table, it is clear that, the addition of FESS
increases the renewable penetration by 18%.
6.7 CONCLUSION
The results of Case: 1, Wind- Battery hybrid system using HOMER modeling
shows that if, initial cost, operating cost, net present cost and cost of energy is
compared for different types of batteries, zinc-bromine battery shows less life cycle
cost of the system. The analysis of Case: 2 and Case : 3, hybrid PV-battery system
and Wind-PV-battery hybrid system respectively, shows the same results as that of
case : 1. Comparing Net Present Cost (NPC), Cost of Energy (COE), Initial Cost (IC)
and Operating Cost (OC) of ZBB with lead-acid and Vanadium-Redox batteries, use
of ZBB shows less life cycle cost. Hence, use of ZBB batteries shows better
performance for hybrid systems.