Study On Lightning Protection For PV System.

STUDY ON LIGHTNING PROTECTION FOR PV SYSTEM

MOHD HISANUDDIN BIN ZAMHARIR

A report submitted in partial fulfillment of the requirements for the Degree of Electrical Engineering (Industrial Power)

Faculty of Electrical Engineering

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

I declare that this report entitle “Study on Lightning Protection for PV System” is the result of my own research except as cited in references. The report has not been accepted for any

degree and is not concurrently submitted in candidature of any other degree.

Signature : …………..……….

Name : MOHD HISANUDDIN BIN ZAMHARIR

“I hereby declare that I have read through this report entitle “Study on Lightning Protection for PV System” and found that it has comply the partial fulfillment for awarding the degree of

Bachelor of Electrical Engineering (Industrial Power)

Signature :…………..……….

Supervisor’s Name : MR. ZIKRI ABADI BIN BAHARUDIN

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ACKNOWLEDGEMENT

I would like to thanks to all individual that has been involved in this project. Great deals appreciated go to the behalf of university which are Universiti Teknikal Malaysia Melaka (UTeM) and Faculty of Electrical Engineering specifically for giving me opportunity to me takes the final year project subject. My grateful thanks also go to Mr. Zikri Abadi Bin Baharudin, my supervisor for guiding the steps and ideas, for patience and time in guiding me and all his kindness throughout this semester. Not forget, great appreciation go to Mrs. Junainah Binti Sardi who help me from time to time during doing this project is in first stage. Special thanks go to my beloved parents and family members for supporting and encouraging me to success complete this project. I am also would like to thankful my friends for helping me in all situation during completion of this project. Last but not least, special acknowledgment to others, as for journals, conference papers and reports that has been used as the references throughout this project.

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ABSTRACT

This thesis presents the Study on Lightning Protection for PV System. Lightning protection on photovoltaic system is very important to avoid the effect of the strike damaging the photovoltaic system. An experiment was set up to study the propagation effect of the induce voltage to the solar panel by the horizontal discharge which produced by 1.2/50µs lightning wave shape. The propagation effect of the induce voltage lead to the existence of unwanted signal which may cause damage to the sensitive device. The experiment was conduct using impulse voltage generator in high voltage lab to generate impulse voltage. The impulse voltage was generated to represent 1.2/50µs lightning indirect strike. Source for the photovoltaic system tested. The experiment strategies are testing the photovoltaic system without shielded cable and with shielded cable. The main consideration for the parameters of unwanted signal such as the peak voltage and duration were analyzed. It is found that maximum voltage of unwanted signal is 1.64kV for unshielded cable. The maximum duration of unwanted signal is 0.82μs. On the other hand, the maximum voltage and maximum duration for shield cable are found to be 0.702kV and 0.14μs, respectively. Mean that, for photovoltaic system with proper shielded to the cable can reduce the unwanted signal effectively by reducing the peak voltage about 0.938kV while reducing the unwanted signal duration about 0.68μs. This thesis can be guidance to improve the protection system for photovoltaic system in future.

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ABSTRAK

Tesis ini membentangkan mengenai Kajian Perlindungan Kilat untuk Sistem PV. Perlindungan kilat pada sistem fotovoltaik adalah sangat penting untuk mengelakkan kesan buruk yang merosakkan sistem photovoltaik. Satu eksperimen telah disusun untuk mengkaji kesan penyebaran voltan teraruh kepada panel solar oleh menunaikan mendatar yang dihasilkan oleh bentuk gelombang kilat 1.2/50μs. Kesan penyebaran voltan teraruh mendorong kepada kewujudan isyarat yang tidak diingini yang boleh menyebabkan kerosakan kepada peranti yang sensitif. Eksperimen ini dijalankan menggunakan penjana voltan dedenyut dalam makmal voltan tinggi untuk menjana voltan dedenyut. Voltan dedenyut telah dijana untuk mewakili 1.2/50μs kilat tidak langsung. Sumber untuk sistem photovoltaik diuji. Strategi eksperimen adalah menguji sistem photovoltaik tanpa kabel berperisai dan dengan kabel berperisai. Pertimbangan utama bagi parameter isyarat yang tidak diingini seperti voltan puncak dan tempoh telah dianalisis. Ia didapati bahawa voltan maksimum isyarat yang tidak diingini ialahi 1.64kV untuk kabel tidak berperisai. Tempoh maksimum isyarat yang tidak diingini pula adalah 0.82μs. Sebaliknya, voltan maksimum dan tempoh maksimum kabel berperisai masing-masing adalah 0.702kV dan 0.14μs. Ini bermakna bahawa bagi sistem photovoltaik dengan melindungi kabel boleh mengurangkan isyarat yang tidak diingini secara berkesan dengan mengurangkan voltan puncak kira-kira 0.938kV pada masa yang sama mengurangkan tempoh isyarat yang tidak dikehendaki sehingga 0.68μs. Tesis ini dapat menjadi panduan untuk memperbaiki sistem perlindungan bagi sistem fotovoltaik dalam masa akan datang.

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TABLE OF CONTENTS

CHAPTER 1 2 TITLE ACKNOWLEDEMENT ABSTARCT ABSTRAK

TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS

INTRODUCTION

1.1 Introduction

1.2 Problem Statement

1.3 Objective

1.4 Scope

1.5 Thesis Outline

LITERATURE REVIEW

2.1 Introduction

2.2 Photovoltaic (PV)

2.2.1 Photovoltaic Cell 2.2.2 Photovoltaic Module 2.2.3 Photovoltaic Array

2.2.4 Stand Alone Solar System 2.2.4.1 Charger Controller 2.2.4.2 Battery PAGE iii iv v vi ix x xii 1 1 2 2 3 3 4 4 4 5 7 8 8 9 10

vii

3

4

2.2.4.3 Inverter

2.2.5 Grid-connected Photovoltaic System

2.2.5.1 MPPT

2.3 Standard Lightning Impulse

2.4 Impulse Generator Circuit

2.5 Lightning

2.5.1 Type of Lightning Discharge

2.6 Lightning Protection for PV System

2.6.1 Lightning Protection System (LPS)

2.6.2 Surge Protective Device METHODOLOGY

3.1 Introduction

3.2 Literature Review

3.3 Set up an Experiment

3.3.1 Circuit Elements of Impulse Voltage Generator

3.3.1.1 Diode

3.3.1.2 Smoothing and Energy Storage Capacitor

3.3.1.3 Parallel Resistor 3.3.1.4 Series Resistor 3.3.1.5 Measuring Resistor 3.3.2 Impulse Voltage Configuration

Circuit

3.4 Conduct an Experiment

RESULT

4.1 Project Background

10 11 12 13 13 15 16 17 18 19 21 21 23 23 23 24 24 25 25 26 26 27 29 29

viii

5

6

4.2 Solar Panel without SPD

4.3 Solar Panel with SPD

4.4 Solar Panel with Shield Cable but

without SPD

4.5 Solar Panel with Shield Cable and SPD ANALYSIS & DISCUSSION

5.1 Capacitance Divider

5.2 Peak Induced Voltage

5.3 Duration of Induced Voltage

5.4 Discussion

CONCLUSION & RECOMMENDATION

REFERENCES

APPENDIX A APPENDIX B APPENDIX C APPENDIX D

30 33 36 39 42 42 43 46 48 49

50

52 89 122 141

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LIST OF TABLES

TABLE 2.1 5.1 5.2

TITLE

Possible installation of surge protective device depending on LPS

Results of peak induced voltage from the experiment The duration of induced voltage in the photovoltaic system

PAGE 20 46 47

x

LIST OF FIGURES

FIGURE 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 3.1 3.2 3.3 3.4 3.5 3.6 TITLE

Single diode model of PV cell

V-I Characteristic by assuming �� is negligible and ��ℎ

is infinite

V-I characteristic of PV module (Varying cell temperature) V-I characteristic of PV module (Varying sun intensity) Block diagram for stand alone solar system

Charger controller DC-AC converts process

Grid-connected Photovoltaic System

Impulse wave (double exponential waveform) Circuit for produce impulse wave

Lightning phenomena

Type of lightning discharge a) negative downward lightning, b) positive downward lightning, c) negative upward lightning, d) positive upward lightning

Effect of lightning strike on PV module Destroyed inverter

Cone protection zone provide by air terminal Flow chart of project methodology

Diode

Smoothing and Energy Storage Capacitor Measuring capacitor

Circuit to generate impulse voltage using impulse voltage generator

Impulse voltage generator configuration in lab

PAGE 5 6 7 8 9 9 10 12 13 14 16 17 18 18 19 22 24 25 26 27 27

xi 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 5.1 5.2 5.3 5.4 5.5 5.6 5.7

Impulse voltage as input when the solar panel without SPD

The unwanted signal from solar panel without SPD Impulse voltage and unwanted signal from solar panel without SPD

Impulse voltage as input when the solar panel with SPD The unwanted signal from solar panel with SPD

Impulse voltage and unwanted signal from solar panel with SPD

Impulse voltage as input when the solar panel with shield but without SPD

The unwanted signal from solar panel shield cable but without SPD

Impulse voltage and unwanted signal from solar panel with shield cable but without SPD

Impulse voltage as input when the solar panel with shield cable and SPD

The unwanted signal from solar panel with shield cable and SPD

Impulse voltage and unwanted signal from solar panel with shield cable and SPD

Capacitance divider on measuring capacitor Peak induced voltage on solar panel without SPD

Peak induced voltage on solar panel with SPD Peak induced voltage on solar panel without SPD but

with shield cable

Peak induced voltage on solar panel with SPD and shield cable

Induced voltage gradually decrease

The duration of induced voltage in the photovoltaic system 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 45 46 47

xii

LIST OF SYMBOLS

��ℎ - Shunt Resistor

�� - Series Resistor

���. - Current generated by the incident light

�� - Diode current

�� - Current through shunt resistor

�� - Leakage current of diode

� - Electron charge

� - Boltzmann constant

� - Ideality factor

�� - Band energy gap of the semiconductor

�� - Nominal temperature (298 Kelvin)

� - Voltage

� - Current

� - Temperature

��� - Short circuit current of the PV module

��� - Open circuit voltage of the PV module

�� - Thermal voltage

������ - Wave front time

�ℎ��� - Half amplitude time

CHAPTER 1

INTRODUCTION

1.1 Introduction

In less than 10 decades, the energy crisis will happen cause from exhausted of fossil fuel reserve such as oil, coal and gas. This issue was discussed in World Energy Forum. Over 79% of energy consumed in the world is from fossil fuel. About 57.7% of energy is used in transportation sector and it increase rapidly day by day [1]. These facts show the energy is very important in our daily life. So, another way must be found to overcome this problem. Renewable energy is a way to overcome fossil fuel crisis because renewable energy is kind of energy that resources that are regenerative and the source of renewable energy will not be over. One of source of renewable energy is radiation of sun. Unlike fossil fuel, the energy from sun is good for environment because it does not have any kind of matter that can give negative impact to atmosphere and environment. The renewable energy that generates form sun is call solar energy. Solar have many advantages compare to other type of energy. It has no emission of greenhouse, not deplete natural source, clean and consistent. Solar energy that comes from radiation of sun is also available at any location on earth. Recently, photovoltaic source is widely use in the world such as in home for water heating system. A lot of researches about photovoltaic have been conduct to improve the photovoltaic system. This project focuses on lightning protection for photovoltaic system. The main objective of this project is to investigate the effectiveness of lightning protection on photovoltaic system.

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1.2 Problem Statement

Solar energy is a kind of renewable energy that is widely used nowadays. Solar energy is an alternative solution to overcome fossil fuel crisis. It is come from radiation of sun coming to earth in a day[1]. Photovoltaic (PV) is a term that refers to convert solar energy that come from sun to electrical energy by solar cell. The research of photovoltaic system is very useful and relevance nowadays. To generate electricity in large amount, solar cell that expose to radiation of sun must be in large size. However, large size of solar cell may have a tendency to increase the probability to be effected by lightning strike activity. Lightning strike is a natural phenomenon that caused by electric discharge in the atmosphere. Lightning produce very high voltage that can damage photovoltaic system by creating the streamer from sharp edges or the around the corner. Furthermore, the lightning strike can induce the unwanted signal that may propagating the radiation electric field through the solar panel and pass the unwanted current to the electrical system. For that reason, lightning protection on photovoltaic system is very important to avoid the effect of the strike damaging the photovoltaic system. This thesis is purposely to study the propagation effect of the induce voltage to the solar panel by the horizontal discharge which produced by 1.2/50µs lightning wave shape. This lightning wave shape is generated by the impulse generator in FKE’s HV lab. The results from experiments were used to observe and to investigate the characteristics of unwanted signal that couple to the solar panel system.

1.3 Objective

The objectives of this project are

1. To investigate the characteristics of unwanted signal that propagate and couple to the solar panel system by generating the lightning artificial discharge (1.2/50µs) in horizontal orientation layout.

2. To analyze the major parameters of unwanted signal such as, the highest peak voltage and the duration that couple to the solar panel system

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3. To investigate and provide the effective of shielding technique in reducing the effect of unwanted signal for photovoltaic system.

1.4 Scope

The scope of this project includes

1. Generating the lightning impulse voltage (1.2/50µs) with of 20 to 30kV which connected with measuring unit (DMI551)

2. The photovoltaic system comprising 12V solar panel, tube gas discharge as surge protective device (SPD) and coaxial cable 75Ω impedance connected to oscilloscope.

3. The spark gap was set in horizontal in such a way that it can produce the induce voltage discharge in horizontal orientation while the panel was located approximately 3 meter from the spark gap and set as vertical position.

1.5 Thesis Outline

This report consist 5 chapters. In Chapter 1, problem statement, objective and scope of this project was discussed. Chapter 2 was discussed about literature review based on journal, books and other source. The literature review consists of theory, idea, practical and info that related this project based on previous research. Chapter 3 was discussed about methodology of this project. The methodology of this project is summarized in a flow chart. Chapter 4 presents result of this project consists of result. In Chapter 5, analysis and discussion were discussed. In Chapter 6, conclusion and recommendation was summarized.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Literature review is implemented to understand the concept of lightning protection on photovoltaic system. Literature review is executed by using several references such as IEEE journals, book and some internet resource. It is important to understand the concept of this project before proceed with conduct an experiment on lightning protection on photovoltaic system. Several concepts of cases which are related to the project will be explained in this chapter.

2.2 Photovoltaic (PV)

Renewable energy is not a new phenomenon nowadays. The supply of fossil fuels would one day run out and an alternate source of energy is need. Solar energy is a kind of renewable energy that widely use nowadays. So, using solar energy is one of good solution to overcome this problem. Photovoltaic (PV) is a term that refers to convert solar energy that come from sun to electrical energy by solar cell. As long as there is sunlight, solar cells can convert it to electrical energy. The most interesting of solar energy is there is no forms of pollution that effect the environment while produce electrical energy [2].

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2.2.1 Photovoltaic Cell

Photovoltaic cell is also known as solar cell. It is not work during darkness and usually is made from semiconductor material such as silicon. When the photovoltaic cell exposed to sun, the photons in form of light are converted into electrons. The photons that flow through the PN junction in solar cell randomly strike the atom and give energy to the outer electron that make the electron can break freely from the atom. The photons in the process are converted to electron movement are called electric energy [2]. Photovoltaic cell is a simplest component of a photovoltaic module that can generate very small current. A photovoltaic cell usually represented as an equivalent single diode model. Figure 2.1 show single diode model of photovoltaic cell.

Figure 2.1: Single diode model of PV cell [3]

A practical photovoltaic cell is deemed to be current source with a parallel forward diode [4]. This model contain a current source �_�ℎ with a parallel forward diode, a parallel resistance �_�ℎ and a series resistance ��. Series resistance, �� represent the resistance inside PV cell.

Forward current �� that flow through the diode is view as dark current or diode current.

Parallel resistance �_�ℎ is mainly cause by the surface leakage current along the edge of a PV cell. The net current of a photovoltaic cell can be represent as �=�_�� − �_� − �_�. The relation between current and voltage of photovoltaic cell can be express in equations (2.1) and (2.2).

6

�= �_�� − �_� − �_� (2.1) �=�_�� − �_��exp��(�+���

��� � −1� −

�+��_�

��ℎ (2.2)

Where,

��� : current generated by the incident light

�� : diode current

�� : current through shunt resistor

�� : leakage current of diode

� : electron charge (1.6 × 10−19_�)

� : Boltzmann constant (1.38 × 10−23_�/�)

� : ideality factor that varies between 1.0 to 1.5

Equation (2.1) and (2.2) can be representing by applied Kirchoff’s current law to the circuit. The V-I characteristic of PV module when assuming that �_� is negligible and �_�ℎ is infinite is shown in Figure 2.2.

Figure 2.2: V-I Characteristic by assuming �� is negligible and ��� is infinite[4]

Leakage current of diode or diode saturation current,�_� can be expressed by Equation (2.3). �� = ��,��

��

� �

3

��� ���_{�� �}� _�1

� −

1

��� (2.3) Where,

�� : band energy gap of the semiconductor

�� : nominal temperature (298 Kelvin)

7

��,� =

���

��� ����

���� −1

(2.4) Where,

��� : short circuit current of the PV module

��� : open circuit voltage of the PV module

�� : thermal voltage that can be defined as, �� =����/�

2.2.2 Photovoltaic Module

A photovoltaic module is a package of connected photovoltaic cells. The current generated by the photovoltaic module and the V-I characteristic of the module are influenced by intensity of sun and temperature. The V-I characteristic of the module when varying the cell temperature is be shown in Figure 2.3. As the cell temperature of module increase, the open circuit voltage will decrease and the short circuit current almost constant. If sun intensity increase, the open circuit voltage will maintain almost constant while the short circuit current will increase obviously [3]. The V-I characteristic of the module when varying the sun intensity is be shown in Figure 2.4. Photovoltaic module has a point that can produce the greatest output power under a certain external environment. This point is call maximum power point.

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Figure 2.4: V-I characteristic of PV module (Varying sun intensity) [4]

2.2.3 Photovoltaic Array

Photovoltaic array is photovoltaic module that connected in series or parallel. It connected in series or parallel depends on output that is needed. Solar panel arrays feature a series of interconnected positive (+) and negative (–) outputs of solar panels in a series or parallel arrangement that provides a required dc voltage to inverter[5]. Photovoltaic modules that connected in series will cause the system to produce maximum output power with the same current. Maximum output power with same voltage will be produce from photovoltaic modules that connected in parallel.

2.2.4 Stand Alone Solar System

Stand alone solar system is a photovoltaic system that not connected to the grid network. It is also known as off-grid photovoltaic system. It consists of some component to complete the system such as solar panel or photovoltaic module, battery, charger controller and inverter. Figure 2.5 show how the stand alone solar system is connected to the others components.

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Figure 2.5: Block diagram for stand alone solar system[6]

2.2.4.1 Charger Controller

Charger controller also known as regulator is design to protect the battery from overcharging. It also functions to control the energy flow to the system and by collecting information on the battery voltage and knowing the maximum and minimum values acceptable for the battery voltage. It can shut down the load when the battery reaches a prescribed state of discharge and can control the level of charging the battery before the battery is overcharging. Photovoltaic array is disconnected by charger controller when the battery reaches the maximum voltage and connected again when the voltage of battery decrease at a certain value. Figure 2.6 show the charger controller.

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2.2.4.2 Battery

Radiation from sun only can be used by solar panel to supply power during day. So, storage must be added to the system. Battery is a storage device that can be used to store energy from solar panel during daylight. During night, load that connected to the photovoltaic system will get supply voltage from the battery that has been charged. Size of battery that is use for photovoltaic system is depends on the demand voltage by the load that connected to the photovoltaic system. Battery usually size in ampere hour (Ah) unit. For photovoltaic system, the battery that is use is rechargeable battery. There are many type of rechargeable battery such as nickel-cadmium, nickel-metal hydride, lead-acid and nickel-zinc that can be used for photovoltaic system. However, the lead-acid battery is still most common use as storage in photovoltaic system.

2.2.4.3 Inverter

Solar panel only generates direct current (DC) that only can be used by limited number of load. When a photovoltaic system has an alternating current (AC) load, an inverter must be included in the system to convert DC output to AC output. Most of residential devices and appliances need AC as the supply. An inverter is a converter where the power flow is from the DC to the AC side, namely having a DC voltage, as input, it produces a desired AC voltage, as output. The process of convert DC to AC output is shown in Figure 2.7.

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The function of the inverter is to keep on the AC side the voltage constant at the rated voltage 240V (single phase). Inverter also functions to convert the input power Pininto the output power P

out with the best possible efficiency. The inverter’s efficiency is shown in Equation (2.5)

� =����

��� =

����������

������ (2.5)

Where,

���: current required by the inverter from the DC side

���: input voltage for the inverter delivered by the DC side

2.2.5 Grid-connected Photovoltaic System

A grid-connected photovoltaic system is a photovoltaic system that connected to the national grid network. It consist components likes solar panel, MPPT controller, inverter, power conditioning and grid connected equipment. Grid connected photovoltaic system have slightly different system compare to stand alone solar system. The inverter that converts from DC to AC output is connected to the kWh meter. The kWh meter will measure the power produce by the photovoltaic system. When the power produce is exceed the demand supply of the user, the over power produce will be export to the grid but when power demand is high than power produce by the photovoltaic system, national grid will supply the power to that user. Figure 2.8 show grid-connected photovoltaic system and how it works.

�= �_�� − �_� − �_� (2.1) �=�_�� − �_��exp��(�+���

��� � −1� −

�+��_�

��ℎ (2.2)

Where,

��� : current generated by the incident light �� : diode current

�� : current through shunt resistor �� : leakage current of diode � : electron charge (1.6 × 10−19�)

� : Boltzmann constant (1.38 × 10−23_�/�) � : ideality factor that varies between 1.0 to 1.5

Equation (2.1) and (2.2) can be representing by applied Kirchoff’s current law to the circuit. The V-I characteristic of PV module when assuming that �� is negligible and ��ℎ is infinite is

shown in Figure 2.2.

Figure 2.2: V-I Characteristic by assuming �� is negligible and ��� is infinite[4] Leakage current of diode or diode saturation current,�� can be expressed by Equation (2.3).

�� = ��,�� ��

� � 3

��� ���_{�� �}� _�1 � −

1

��� (2.3)

Where,

�� : band energy gap of the semiconductor �� : nominal temperature (298 Kelvin)

��,� =

��� ��� ����

���� −1

(2.4)

Where,

��� : short circuit current of the PV module ��� : open circuit voltage of the PV module

�� : thermal voltage that can be defined as, �� =����/�

2.2.2 Photovoltaic Module

A photovoltaic module is a package of connected photovoltaic cells. The current generated by the photovoltaic module and the V-I characteristic of the module are influenced by intensity of sun and temperature. The V-I characteristic of the module when varying the cell temperature is be shown in Figure 2.3. As the cell temperature of module increase, the open circuit voltage will decrease and the short circuit current almost constant. If sun intensity increase, the open circuit voltage will maintain almost constant while the short circuit current will increase obviously [3]. The V-I characteristic of the module when varying the sun intensity is be shown in Figure 2.4. Photovoltaic module has a point that can produce the greatest output power under a certain external environment. This point is call maximum power point.

Figure 2.4: V-I characteristic of PV module (Varying sun intensity) [4]

2.2.3 Photovoltaic Array

Photovoltaic array is photovoltaic module that connected in series or parallel. It connected in series or parallel depends on output that is needed. Solar panel arrays feature a series of interconnected positive (+) and negative (–) outputs of solar panels in a series or parallel arrangement that provides a required dc voltage to inverter[5]. Photovoltaic modules that connected in series will cause the system to produce maximum output power with the same current. Maximum output power with same voltage will be produce from photovoltaic modules that connected in parallel.

2.2.4 Stand Alone Solar System

Stand alone solar system is a photovoltaic system that not connected to the grid network. It is also known as off-grid photovoltaic system. It consists of some component to complete the system such as solar panel or photovoltaic module, battery, charger controller and inverter. Figure 2.5 show how the stand alone solar system is connected to the others components.

Figure 2.5: Block diagram for stand alone solar system[6]

2.2.4.1 Charger Controller

Charger controller also known as regulator is design to protect the battery from overcharging. It also functions to control the energy flow to the system and by collecting information on the battery voltage and knowing the maximum and minimum values acceptable for the battery voltage. It can shut down the load when the battery reaches a prescribed state of discharge and can control the level of charging the battery before the battery is overcharging. Photovoltaic array is disconnected by charger controller when the battery reaches the maximum voltage and connected again when the voltage of battery decrease at a certain value. Figure 2.6 show the charger controller.

2.2.4.2 Battery

Radiation from sun only can be used by solar panel to supply power during day. So, storage must be added to the system. Battery is a storage device that can be used to store energy from solar panel during daylight. During night, load that connected to the photovoltaic system will get supply voltage from the battery that has been charged. Size of battery that is use for photovoltaic system is depends on the demand voltage by the load that connected to the photovoltaic system. Battery usually size in ampere hour (Ah) unit. For photovoltaic system, the battery that is use is rechargeable battery. There are many type of rechargeable battery such as nickel-cadmium, nickel-metal hydride, lead-acid and nickel-zinc that can be used for photovoltaic system. However, the lead-acid battery is still most common use as storage in photovoltaic system.

2.2.4.3 Inverter

Solar panel only generates direct current (DC) that only can be used by limited number of load. When a photovoltaic system has an alternating current (AC) load, an inverter must be included in the system to convert DC output to AC output. Most of residential devices and appliances need AC as the supply. An inverter is a converter where the power flow is from the DC to the AC side, namely having a DC voltage, as input, it produces a desired AC voltage, as output. The process of convert DC to AC output is shown in Figure 2.7.

The function of the inverter is to keep on the AC side the voltage constant at the rated voltage 240V (single phase). Inverter also functions to convert the input power P

ininto the output

power P

out with the best possible efficiency. The inverter’s efficiency is shown in Equation

(2.5)

� =���� ��� =

����������

������ (2.5)

Where,

���: current required by the inverter from the DC side ���: input voltage for the inverter delivered by the DC side

2.2.5 Grid-connected Photovoltaic System

A grid-connected photovoltaic system is a photovoltaic system that connected to the national grid network. It consist components likes solar panel, MPPT controller, inverter, power conditioning and grid connected equipment. Grid connected photovoltaic system have slightly different system compare to stand alone solar system. The inverter that converts from DC to AC output is connected to the kWh meter. The kWh meter will measure the power produce by the photovoltaic system. When the power produce is exceed the demand supply of the user, the over power produce will be export to the grid but when power demand is high than power produce by the photovoltaic system, national grid will supply the power to that user. Figure 2.8 show grid-connected photovoltaic system and how it works.