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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

158

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.

167

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

168

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.