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COMPARISON OF CONCENTRATING PHOTOVOLTAIC (CPV) CONFIGURATION FOR PHOTOVOLTAIC (PV) APPLICATION MURNIZA BT MOHD ISA UNIVERSITI TUN HUSSEIN ONN MALAYSIA

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Page 1: COMPARISON OF CONCENTRATING PHOTOVOLTAIC (CPV ...eprints.uthm.edu.my/9095/1/Murniza_Mohd_Isa.pdf · COMPARISON OF CONCENTRATING PHOTOVOLTAIC (CPV) CONFIGURATION FOR PHOTOVOLTAIC (PV)

COMPARISON OF CONCENTRATING PHOTOVOLTAIC (CPV)

CONFIGURATION FOR PHOTOVOLTAIC (PV) APPLICATION

MURNIZA BT MOHD ISA

UNIVERSITI TUN HUSSEIN ONN MALAYSIA

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This thesis has been examined on the date 25th May 2016 and is sufficient in

fulfilling the scope and quality for the purpose of awarding the Degree of Masters in

Electrical Engineering.

Chaiperson: PROF. MADYA DR. KOK BOON CHING

Faculty of Electrical and Electronic Engineering

Universiti Tun Hussein Onn Malaysia (UTHM)

Examiners: PROF. MADYA DR. GAN CHIN KIM

Faculty of Electrical Emgineering

Universiti Teknikal Malaysia Melaka (UTEM)

DR. WAHYU MULYO UTOMO

Faculty of Electrical and Electronic Engineering

Universiti Tun Hussein Onn Malaysia (UTHM)

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COMPARISON OF CONCENTRATING PHOTOVOLTAIC (CPV)

CONFIGURATION FOR PHOTOVOLTAIC (PV) APPLICATION

MURNIZA BT MOHD ISA

A thesis submitted in

fulfillment of the requirement for the award of the

Degree of Master of Electrical Engineering

Faculty of Electrical and Electronic Engineering

Universiti Tun Hussein Onn Malaysia

MAY 2016

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For my beloved beloved parents, Mohd Isa Hamid and Zabidah Yunus and beloved

siblings,Norafiza, Norizwana, Muhammaed Zakree, Muhammaed Fikree and

Muhammaed Azree for their motivation and inspiration.

To all those who believe in the richness of learning

iii

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ACKNOWLEDGMENT

Alhamdulillah. I am so grateful to Allah s.w.t for giving me strength and guidance

throughout my studies. Again, thank you Allah for easing my path towards Your

knowledge.

I would like to express my deepest and sincere gratitude to my supervisor Dr.

Rahisham bin Abd.Rahman for his excellent guidance, supervision and abundant

support which help me a lot to complete this thesis successfully.

My special thanks to PM. Ir. Dr. Goh Hui Hwang for his excellent guidance

and knowledge of solar energy. Thanks to all Lab technicians who had contributed to

the completion of this project.

Lots of gratitude to financial support of “Research Acculturation Grant

Scheme (RAGS)” and Kementerian Pengajian Tinggi Malaysia (KPM) for granted

me the scholarship.

Last but not least, I would like to give my big thanks to my parents, brothers,

sister and friends for their support, love and patience. Without their encouragement,

motivation and understanding it is hard for me to complete this work

iv

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ABSTRACT

Concentrated Photovoltaic (CPV) is a well-known technology that relies essentially

on the design and fabrication of a concentrator optic part and with the use of

Compound Parabolic Concentrator (CPC) as a basic shape. However, common

drawbacks of the 3-dimension (3-D) CPC are the decreasing geometrical

concentration ratio which leads to the reduction of the optical and cell output

performance. The aim of this research is to perform comparative studies of the

Rectangular Compound Parabolic Concentrator (RCPC) by combining reflective

surface and refractive dielectric materials. The proposed concentrator model was

designed by intersecting two 2-dimension (2-D) compound parabolic concentrators

(CPC). A basic formulation characteristic of CPC shape was used to create RCPC

design configuration with a geometrical concentration ratio of 4 and a maximum half

acceptance angle = 14.5° as the final parameters. A typical silicone PV cell was

used as a receiver for the RCPC design. An optical ray-tracing simulation technique

was employed to measure and evaluate the optical performance for three different

RCPC cases in terms of surface and dielectric material selections. The comparison of

optical performance of RCPC mirror, RCPC dielectric and RCPC coated solar

concentrator was studied and the effects of light distribution on the receiver was also

analyzed. Simulation results showed that the RCPC coated maintained the half

acceptance angle when the incidence angle was larger, that is with a maximum half

acceptance angle, = 14.5° and the flux distribution on the PV cell was uniformed

compared to the RCPC mirror and RCPC dielectric. It is illustrated that the RCPC

coated which was orientated facing toward the sun based on site location resulted in

12% higher in total collected energy at the PV cell detector and a 95% increase in

electrical efficiency compared to conventional PV.

v

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ABSTRAK

Penumpu Fotovolta (CPV) merupakan teknologi terkenal yang bergantung pada

dasar reka bentuk dan fabrikasi bahagian penumpu optik dan Penumpu Kompaun

Parabola (CPC) digunakan sebagai bentuk asas. Walau bagaimanapun, salah satu

kelemahan 3-dimensi CPC adalah pengurangan nisbah kepekatan geometri yang

member kesan kepada prestasi optik dan sel. Tujuan utama kajian ini bagi

melaksanakan kajian perbandingan Segi Empat Tepat Penumpu (RCPC) dengan

menggabungkan permukaan reflektif dan bahan dielektrik. Cadangan model

penumpu solar ini telah direka dengan persilang dua 2-D penumpu kompaun

parabola (CPC). Formula asas ciri bentuk CPC telah digunakan untuk mencipta reka

bentuk konfigurasi RCPC dengan nisbah kepekatan geometri 4 dan maksimum

setengah sudut penerimaan = 14.5 ° sebagai parameter akhir. Sel silikon PV yang

biasa digunakan telah di pilih sebagai penerima. Teknik simulasi sinar-kerja optik

telah digunakan untuk mengukur dan menilai prestasi optik tiga kes RCPC yang

berbeza dari segi permukaan dan pilihan bahan dielektrik. Perbandingan prestasi

optik RCPC cermin, RCPC dielektrik dan RCPC bersalut penumpu solar telah dikaji

dan kesan taburan cahaya pada penerima juga sedang dianalisis. Hasil simulasi

menunjukkan bahawa RCPC bersalut mengekalkan sudut penerimaan separuh

apabila sudut tuju adalah lebih besar, di mana maksimum sudut penerimaan separuh,

= 14.5 ° dan taburan fluks pada sel PV adalah seragam berbanding dengan cermin

RCPC dan RCPC dielektrik. Ini menggambarkan bahawa RCPC bersalut yang

berorientasikan menghadap ke arah matahari berdasarkan tapak lokasi menghasilkan

jumlah tenaga yang dikumpul 12% lebih tinggi pada pengesan sel PV dan 95%

peningkatan kecekapan elektrik berbanding konvensional PV.

vi

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CONTENTS

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

CONTENTS vii

LIST OF FIGURES xii

LIST OF TABLES xvi

LIST OF SYMBOLS AND ABBREVIATION xvii

LIST OF APPENDICES xx

CHAPTER 1 INTRODUCTION 1

1.1 Project background 1

1.2 Problem statements 2

1.3 Objectives 4

1.4 Project scope 5

1.5 Contribution of the thesis 5

1.6 Thesis organization 6

CHAPTER 2 REVIEW ON CONCENTRATING

PHOTOVOLTAIC (CPV) TECHNOLOGY 7

2.1 Introduction 7

2.2 Solar energy technologies 7

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2.2.1 Concentrated solar power 7

2.2.2 Photovoltaic (PV) 8

2.2.3 PV technology in Malaysia 10

2.3 Concentrating Photovoltaic (CPV) 11

2.3.1 History of CPV 12

2.3.2 Terms and Concepts 14

2.4 CPV configuration 15

2.4.1 Concentration factor 15

2.4.2 Optic 16

2.4.2.1 Reflective optic 17

2.4.2.2 Refractive optic 18

2.4.3 Solar cell 18

2.4.4 Cooling 18

2.4.5 Sun tracking system 19

2.5 Fundamental optics applied to solar

concentration 19

2.5.1 Concentration Ratio ( 20

2.5.2 Aperture ( 21

2.5.3 Acceptance angle 21

2.6 Review of solar concentrator design 21

2.7 Concentrator design work in Malaysia 24

2.7.1 Summary of previous R&D solar

concentrator 27

2.8 Previous research on NIO solar

concentrator using CPC 31

2.9 Summary 32

CHAPTER 3 METHODOLOGY 33

3.1 Introduction 33

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3.2 Non-imaging solar concentrator design 33

3.3 Design consideration Compound

Parabolic Concentrator 33

3.3.1 Design principle of geometrical

CPC 34

3.3.2 Dimensions of CPC 35

3.4 Edge ray principle 37

3.5 Ray-tracing technique 37

3.6 Designing Rectangular Compound

Parabolic Concentrator (RCPC) 38

3.6.1 Design principle of geometry

RCPC 38

3.6.2 3-D RCPC Simulation

Construction Model 40

3.6.3 Surface and material selection 42

3.6.4 Optical modeling simulation

using ray-tracing TracePro 43

3.7 TracePro Solar Emulator 45

3.8 Cases Optical Analysis of 2D-CPC using

TracePro 46

3.8.1 Case 1:2-D Common CPC

mirror 46

3.8.2 Case 2: 2-D CPC dielectric

material 47

3.9 Cases Optical Analysis of RCPC using

TracePro 48

3.9.1 Case 1: RCPC mirror 48

3.9.2 Case 2: RCPC dielectric material 48

3.9.3 Case 3: RCPC coated 49

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3.10 Summary 50

CHAPTER 4 RESULTS & ANALYSIS 51

4.1 Introduction 51

4.2 Truncation of 2-D compound parabolic

concentrator 51

4.2.1 Truncation analysis 53

4.2.2 Initial 2-D CPC design 54

(a) Flux distribution on

concentrator 54

(b) Flux distribution on PV

cell 55

4.2.3 Truncated CPC design 57

(a) Flux distribution on

concentrator 57

(b) Flux distribution on PV

cell 58

4.2.4 Summary 60

4.3 Case: Optical Performance for 2-D

Compound Parabolic Concentrator 62

4.3.1 Case 1: 2-D common CPC

mirror 62

(a) Optical efficiency of

concentrator 62

(b) Flux distribution on PV

cell 63

4.3.2 Case 2: 2-D dielectric 64

(a) Optical efficiency of

concentrator 64

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(b) Flux distribution on PV

cell 64

4.4 Cases Optical performance for RCPC

using TracePro 66

4.4.1 Case 1: RCPC mirror 66

(a) Optical efficiency of

concentrator 66

(b) Flux distribution on PV

cell 67

4.4.2 Case 2: RCPC dielectric 68

(a) Optical efficiency of

concentrator 68

(b) Flux distribution on PV

cell 69

4.4.3 Case 3: RCPC coated 70

(a) Optical efficiency of

RCPC dielectric at

different positions 70

(b) Optical efficiency of

concentrator 71

(c) Flux distribution on PV

cell 72

4.5 Summary of RCPC cases 73

4.6 Ray-tracing analysis based at UTHM

location 75

4.6.1 Flux distribution on PV cell 75

4.7 Summary 76

CHAPTER 5 CONCLUSION & FUTURE WORKS 81

5.1 Conclusion of research 81

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5.2 Limitations of research 83

5.3 Recommendations for future work 83

REFERENCES 84

APPENDIX A 90

APPENDIX B 92

APPENDIX C 94

APPENDIX D 95

VITA 96

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CHAPTER 1

INTRODUCTION

1.1 Project background

The demand electricity and its consumption have been constantly growing year by

year to meet the daily needs of developing countries. The growing demands

exacerbate the challenge connected to the limitation in energy supply, and the

resulting competition for resources. Most of energy sources are produced by fossil

fuel and coal. According to International Energy Agent [1], 41.1% of the world

electricity is generated using coal in supply generation system and there has been as

much as 32310 million metric tons of carbon dioxide emissions from the

consumption of energy [2]. Due to that reasons, scientist are very interested in

exploring the potential of alternative and clean energy sources such as wind, hydro,

biomass and solar energy.

Renewable energy is a source of energy that is not destroyed when being

harnessed. According to the predictions made from Renewable Energy Policy

Network for 21st Century [3], in the near future, as much as 19% of global energy

consumption will be mainly from renewable energy. Solar energy is one of the

renewable energy that can reduce the carbon dioxide emissions and the green house

effect. Earth receives an estimate of 1000W/m² solar irradiation a day and 1.5x10

kWh/year [4] total amount of a solar energy. This amount of solar irradiance could

generate 85000 TW and it is estimated that the current global energy is at 15000 TW

as reported by International Energy Statistic. Therefore, the direct and simplest

method to generate electricity from solar radiation is by using photovoltaic (PV)

module.

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PV is a technology that converts the light from the sun into electricity using

PV modules [5] without using any moving mechanical parts, it operates quietly

without emissions, and is durable for long term use. Malaysia is located in equatorial

regions and receives sun penetration throughout the year. It is estimated to receive

huge solar radiation as much as 400 – 600 MJ/m² per month [6], 1643 kWh/m²

average irradiance per year [7] with ten sun hours daily [8]. Therefore, the country is

suitable for implementing photovoltaic system. However, the very-high initial cost of

PV cells is the main barrier for PV commercialization where silicon is the most

expensive material in the production of PV cells. As much as 72% of the overall

fabrication cost of PV module goes to PV cells [5]. Therefore, an alternative method

in making this renewable energy to be more effective is by using solar concentrator

where the expensive solar cells are replaced with inexpensive concentrator optic

materials to make Concentrated Photovoltaic (CPV) system.

In CPV system, the main reason of using the concentrator optic is to reduce

the cost of PV module and at the same time cutting down the cost of solar energy

produced. The concentration is achieved via an optical device with the objective of

reducing the area of expensive solar cell with the addition of increasing its

efficiency. One of the disadvantages in CPV system is the tracking mechanism used

in medium and high concentration of the PV system. However, the advantage of low

concentration PV system is the exclusion of the tracking mechanism. In addition to

that, the type of solar cell used in low concentration level is usually silicon cell. The

existence of CPV technology relies on the design and fabrication of the concentrator

parts. There are many types of optical concentrator which can increase flux of

radiation on the receiver. They can be classified into two major optical categories

which are imaging optic and non-imaging optic. Compound parabolic concentrator

(CPC) is a well-known non-imaging type optical concentrator in which it does not

use image forming and focusing the light source on a receiver within its acceptance

angle; producing a different prescribed illumination pattern.

1.2 Problem statements

Several paths are being explored for desired PV cost reduction and efficiency

improvement. The PV system efficiency and capital cost from the year 1995 to 2020

for three different types of materials are shown in Figure 1.1 and Figure 1.2 below.

2

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As can be

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There have been rapid developments involving solar concentrator designs. One of the

most studied talking points is the characteristic parameters of the CPC shape. The

most efficient solar concentrator for non-imaging optic type is due to it characteristic

of collecting and concentrating all rays within its acceptance angle. However, from

previous circular 3-D CPC, the geometry of the entry and exit aperture are circular.

The drawback for this design is the decrease in its geometrical concentration ratio in

order to shift from its circular shape of entry aperture to a hexagonal shape and the

fact that the circular shape remains at the exit aperture. Due to this reason, a

rectangular compound parabolic concentrator was designed by intersecting two 2-D

CPC’s. The proposed design gives an advantage in which the entry aperture and its

exit aperture are square in shape as compared to the circular geometry of entry

aperture of typical 3-D CPC. The optical performance and characteristic of RCPC,

however, as a combination between reflective and refractive solar concentrator have

not been studied and investigated. In response to this problem, the proposed research

presents the comparative study of the RCPC solar concentrator designs in PV

application.

1.3 Objectives

Concentrating photovoltaic (CPV) technology is considered as an alternative solution

to reduce the cost of PV production. The main aim of this research work is to

perform on comparative studies of RCPC by considering reflective materials as well

dielectric materials. The research objectives in order to achieve the essential aim of

this research work are as follows:

i. To design the structural geometry of rectangular compound parabolic

concentrator (RCPC) by combining two compound parabolic concentrators

(CPC).

ii. To evaluate and analyze an optical performance of RCPC mirror, RCPC

dielectric and RCPC coated using ray-tracing technique.

iii. To enhance and proposed estimated PV cell output performance in terms of

collected energy and electrical efficiency based on RCPC coated design.

4

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1.4 Project scope

In Malaysia, solar energy is divided into two categories, namely solar thermal and

photovoltaic (PV) technology. This project primarily focuses on studying

concentrated photovoltaic (CPV) where the concentrator optic is applied by

considering at Universiti Tun Hussein Malaysia (UTHM) geographical coordinates.

The research scopes of this project are as follows:

i. The concentrator optic material is used to replace a part of the photovoltaic

cells. Standard mirror and dielectric material are chosen to focus the solar

irradiance on the receiver.

ii. The proposed RCPC design is based on a combination of non-imaging optical

concentrator with respect to its concentration ratio level and acceptance

angle.

iii. The solar concentrator optic is evaluated by ray-tracing simulation analysis

where it is used to obtain the optimum solar irradiance of which it properly

reflects and refracts sunlight to the receiver.

1.5 Contribution of the thesis

The contribution of this research project is summarized as follows:

i. The combination and intersection of two 2-D CPC’s contributes to a square

shaped entry and exit aperture of receivers. It would be more beneficial to

have a square exit aperture area for the geometry of the solar concentrator

since PV technology uses semiconductor cells (wafer), generally several

square centimeters in size.

ii. The low-cost optic material is introduced. A mirror with reflectivity of 0.94

will reflect 94% of sunlight on receiver resulting better performance of PV

cell. Schott BK7 glass is an alternative dielectric material other than

Polymetyl-methacrylate (PMMA). The material is added as lens, contributing

to more uniform flux distribution on PV cells and exceeds half acceptance

angle of a solar concentrator.

iii. The actual site and time duration in TracePro Solar Emulator are presented in

real value based on geographical map location. This gives an advantage to

5 5

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predict and analyze the optical performance of solar concentrator based on

real site location.

1.6 Thesis organization

This thesis has been organized into five chapters. Chapter 1 provides an overview of

the project that includes the project background, problem statements, objectives and

its scope. Chapter 2 reviews framework of solar energy and fundamental principles

of photovoltaic generation and technology, focusing on the third generation of

photovoltaic technology which is called CPV and finally revises previous studies on

CPV technology. Chapter 3 describes the approach of the Rectangular RCPC. In this

chapter, the basic geometry of 2-dimensional compound parabolic is referred and

using ray-tracing technique to evaluate the optical performance of RCPC and ray-

distribution on PV cells. There are three different cases that have been divided and

analyzed. Chapter 4 explains the results and ray-tracing analysis of solar concentrator

and PV cell. The truncation of RCPC is shown and analyzed together with analysis

on optical efficiencies at different incidence angles and flux distribution on PV cell.

The data were acquired at UTHM campus. Finally, Chapter 5 draws the conclusion

of this project and recommendations for future works

6

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CHAPTER 2

REVIEW ON CONCENTRATING PHOTOVOLTAIC (CPV) TECHNOLOGY

2.1 Introduction

This chapter reviews some fundamental knowledge and relevant research works

related to this project. Section 2.2 describes the photovoltaic technologies, while in

Section 2.3, the CPV technology and its terminologies and concept related to CPV

are explained. Section 2.4 and 2.5 depicts the CPV configuration and reviews of

solar concentrator design. The concentrator design work in Malaysia is reviewed in

Section 2.6 and the fundamental optic that is applied to the solar concentration is

discussed in Section 2.7. Lastly, Section 2.8 summarizes the entire Chapter 2.

2.2 Solar energy technologies

Solar power is a relatively simple and direct method to convert the sunlight into

electricity. It is a big potential alternative energy source as the earth receives 1000

W/m² light intensity per day and 1.5x10 kWh/m² per year. There are two different

approaches to harvest the sun’s energy, namely the concentrated solar power

technology or called solar thermal and photovoltaic technology.

2.2.1 Concentrated solar power

Concentrated solar power (CSP) technology is the one of ways to generate electricity

by producing heat when sunlight focuses on a receiver [12, 13] . This system uses

optical component either mirrors or lenses and tracking mechanism to concentrate a

large area of sunlight into a small beam to heat up the receiver and thus produces

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steam to generate electricity. There are three common methods to concentrate the

sunlight, i.e. solar trough, solar dish and a solar tower as illustrated in Figure 2.1.

Figure 2.1: Concentrated solar power design [14]

Solar trough or parabolic trough consists of parabolic-shaped mirror as

concentrator and tube receiver. The mirror concentrates sunlight on receiver tube

which contains heat transfer fluid. The solar dish system uses parabolic dish shape,

where the concentrator focuses sunlight onto a receiver located at focus point of the

dish. Then, for the solar tower system, an array field heliostat (individual tracking

mirror) focuses sunlight at central receiver located on top of the tower.

2.2.2 Photovoltaic (PV)

The example of conventional photovoltaic (PV) cell is shown in Figure 2.2. PV or

known as solar cell is an electronic device that generates DC electrical power from

8

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9

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19

2.2.3 PV technology in Malaysia

PV technology was first introduced in 1980’s in Malaysia [17]. The aim was to

provide electricity and telecommunication to rural areas. In 1998, the first grid

connected was set up by Tenaga Nasional Berhad (TNB) as alternative sources for

national utility [17]. Then, six pilot grid connected PV was installed in the range of

2.8 kWp to 3.8 kWp capacity in year 1998 to 2000. The first practical PV system was

installed on the roof top College of Engineering Universiti Tenaga Nasional

(UNITEN) with system capacity of 3.15 kW by TNB. However, the installation was

still expensive even though required basic and simple connection. In the same year,

BP Malaysia had installed an 8 kWp system capacity grid connected PV at BP petrol

station along KESAS highway and 5.5 kW system capacity at the Solar Energy

Research Park at Universiti Kebangsaan Malaysia (UKM) [6].

On 25th July 2005, the Malaysia Building Integrated Photovoltaic (MBIPV)

Technology Project [17] [18] [7] was introduced and launched. A number of policies

had been introduced by the Malaysia government in terms of solar technology [19]

[20] including the MBIPV project. Since the launch of the project, PV installation

business has started to soar. The aim of this project is to reduce the cost of BIPV

project whilst reduce the greenhouse effect within the country. This project ended in

December 2010. At the time, as much as 1516.00 kWp was successfully generated

that met the demand of 109 buildings and reduced 40% of the PV cost [18]. On 24th

September 2012, Solar Home Rooftop Program (SHRP) was lunch by Sustainable

Energy Development Authority (SEDA) Malaysia to enhance the public participation

if renewable energy generation. Malaysians can participate as individuals through

this program. A total of 14.36 MW was approved based on the form of 1079 Feed-in

Approval (FiA) application for individual participant at the end of April 2013 [21].

At the end of August 2013, the number raised up to 1316 applications with the total

capacity of 16.64 MW. This is one of the steps to encourage individuals in Malaysia

to install solar panels on the rooftop of their houses. At the same time, Malaysians’

perspective towards the development of solar energy is also important to meet the

FiT mechanism success especially in the field of solar PV harvesting. Feed-in tariff

(FiT) [22] mechanism had been introduced in 2011 by Malaysia government, in

accordance with Renewable Energy Act 2011 and Sustainable Energy Development

10

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20

Authority Act 2011. The main idea is to promote the growth of renewable energy

sector in Malaysia.

However, the installation of PV systems in Malaysia has some drawbacks in

terms of high cost investment and long payback period [23, 24]. 77% among the

respondent that agreed to install the solar PV system, had changed their mind after

knowing the cost of installation is high (RM 50, 000 – RM 150, 000). Haw et.al [25]

had conducted a survey where most Malaysians only consider to install solar PV if

the cost of a solar panel is below RM 5,500 per kWp, about 30% of the market price.

The cost of PV module account for 60% [18] of total PV system cost. Therefore, the

more cost-efficient method to overcome this problem is using solar concentrator

optic [26, 27].

2.3 Concentrating Photovoltaic (CPV)

CPV system is categorized under third generation of photovoltaic technologies [5]. It

uses lenses or mirrors to concentrate sunlight on PV cells as shown in Figure 2.3.

The concept is similar to the CSP technology that uses optical component to focus

sunlight but the difference is that it concentrates sunlight to produce heat while CPV

directly focuses sunlight on PV cell to generate electricity. They entrain a large area

of solar energy onto small cell, which operates at an irradiation level many times

greater than direct and diffuse sunlight [27]. Therefore, it requires lesser solar cells,

which is the most expensive component in a PV system. The main advantage of CPV

is the decrease of PV system costs that needs less area of solar cell, silicon cells can

still be used and a higher efficiency, but the major disadvantage is the necessity to

have a sun tracking system to keep the CPV module focused in the sun throughout

the day. A CPV system is formed by three main components, namely optic, solar cell

and sun tracking system. The most expensive component in this system is solar or

PV cell [28]. Its concentration level depends on the type of solar cell being used. A

silicon cell is a suitable choice for lower and medium concentration level as the

efficiency is increases when the incident light also increases to a certain level [29]

and multi-junction cells or modified silicon cell used for the high concentration level.

As the temperature of solar cell increases, the efficiency will be decrease due to light

concentration in the CPV system. Therefore, solar cell must be kept cool in a

concentrated system, requiring practical and advanced heat transfer design [28].

11

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12

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22

developed the first prominent demonstrator which uses an acrylic Fresnel lens with

active water cooling. In the meantime, Institute for Solar Energy of Polytechnic

University of Madrid (IES-UPM) had also developed a Ramon Aceres panel; a

silicon-on-glass point-focus Fresnel lens with a passive cooling system. During that

period, a silicon solar cell was used for both flat-plate and concentrated PV but in

1978, a group from North Carolina State University had carried out a research on

multi-junction (tandem) solar cells and came out with the first dual-junction solar

cell.

In early 1980s, the oil crisis ended and the concentrator program was put off

due to limitation of funds, most participants dropped out. Then, in 1990s, the

research on CPV restarted back when DOE created the PV Concentrator Initiative

Program (PVCI). This program involved four-cell manufacturers (ASEC, Spectrolab,

Sunpower and Solarex) and four-module manufactures (Entech, Solar Kinetics,

Alpha Solarco and SEA Corporation). Unfortunately, in 1993 the PVCI program was

terminated even though the progress achieved had been significant. A higher

efficiency solar cell was achieved in early 1990s using double-junction solar cells.

Then, in early 2000s, an improvement in this field was obtained with realization of

first triple junction solar cell on germanium substrate. This is the current state of art

technology in terms of efficiency.

Table 2.1: CPV Milestones

Year History

1973 Oil crisis

1975 Sandia National Laboratories were funded for research on CPV feasibility

1977 Department of Energy (DOE) was founded

Late 1970 Sandia National Laboratories realized the 1st prototype with active cooling

1979 1st dual junction was realized

Early 1980s -Oil crisis ended -Concentrator program was put off

Early 1990s Improved dual junction solar cells

1991 DOE created the PV Concentrator Initiative Program (PVCI)

1993 PVCI terminated

Early 2000s Realization of the first 3J III-V solar cell

2007 Spectrolab announces the 1st 3J with efficiency >40%

13

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23

2.3.2 Terms and Concepts

There have been varieties of designs in CPV technology as compare to conventional

PV system. The terms and concepts of CPV is quoted in IEC 62018 standards [32] as

summarized below in Figure 2.4

 

Figure 2.4: Term and concept of CPV [32]

Concentrator a device used to concentrate sunlight Concentrator optic

optical component (lenses or mirrors) that perform one or more of following function from its input to output that increasing light intensity, filtering spectrum, modifying light intensity distribution or changing light direction. Primary optic is a device that receives sunlight directly from sun and secondary optic is a device that receives concentrated or modified sunlight from another optical device such as primary or another secondary optic

Concentrator cell

basic photovoltaic that used under the illumination of concentrated sunlight

Concentrator receiver

group of one or more concentrator cells and secondary optic (if present) that accepts concentrated sunlight and incorporated the means of thermal and electric energy transfer. Receiver could be made of several sub-receiver which consists of smaller portion of the full size receiver

14

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Concentrator module

group of receivers, optics and other related components that accept sunlight directly from sun. All these components usually prefabricated as one unit and focus point is not field-adjustable. A module could be made of several sub-module being this physical standalone portion of a full size module

Concentrator assembly

group of module and other related component that accept sunlight directly from sun. All components usually shipped separately and need field installation and focus is field-adjustable. An assembly could be made of several sub-assemblies

2.4 CPV configuration

The CPV configuration can be classified as illustrated in Figure 2.5 below in which

the designs are mostly based on applications.

Figure 2.5: Criteria used in a CPV system [32]

2.4.1 Concentration factor

The CPV system is divided into three categories based on concentration level,

namely low concentration (less than 10 suns), medium concentration (up to around

150 suns) and lastly higher concentration (more than 200 suns) [27]. Lower level

concentrations try to assist with the benefit of conventional PV modules (high

15

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acceptance

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16

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26

Figure 2.7: Types of optic in CPV configuration [35]

2.4.2.1 Reflective optic

The reflective optical element uses mirror or a combination of mirrors to concentrate

the sunlight. It is made of different reflector materials [36], such as glass and various

types of aluminum or a special reflective coating with different shapes which have

large longevity. A higher quality mirror with better reflectivity is important for

reflecting system. Most aluminum mirrors have reflectance in the range from 80% to

86% while glass mirrors can achieve 93% to 96% of reflectance. The most common

shape is parabolic mirror. A reflective surface in the shape of a parabola will focus

all light that parallel to the axis of parabola to a point located at the parabola focus. It

comes at a point-focus configuration and line-focus configuration [4, 37, 38]. Most

material used are back silvered glass plates anodized aluminum sheets and

aluminized plastic films in solar energy applications as a reflector or concentrator.

This reflective materials are widely used and commercially available [39, 40].

17

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2.4.2.2 Refractive optic

The Fresnel lens most commonly used for refractive surface solar concentrator [4].

Material used for the lens is normally made from plastic, such as acrylic

(polymetylmethacrylate or PMMA) or glass, such as Schott glass (Appendix A). It is

molded well and durable under different weather conditions [15]. Fresnel lens is

usually incorporated into a module that contains a lens or multiple lenses in parquet

and a housing to protect the backside of the lens which is difficult to clean due to the

sharp facets and the cells. The cell also may incorporates a secondary optical

elements (SOE) whose purpose is to further concentrate the light or make the image

more uniform.

2.4.3 Solar cell

A solar cell is made of semiconductor material with weakly bonded electrons

occupying a band energy called the valence band. The most abundant materials used

is silicon (Si), a semiconductor that is capable of absorbing light and deliver a

portion of that energy to carry of electric current, electrons and holes. This

phenomenon generates a direct current (DC) in a preferential specific direction,

working like a silicon diode [15]. Solar cell design involves specifying parameters of

a solar structure in order to maximize efficiency at given set of constraints. It is

usually formed by several layers, each one with specific functions. The common type

solar cells in the market are standard Si cell and multi-junction (III-V) cell.

2.4.4 Cooling

The concentration in CPV system is depends on the concentration level. As the

temperature of solar cell increases, the efficiency is decreases. [27]. For a low and

medium concentration, passive cooling will be used to cool the cell like heat sink

element. Liquid such as water is used as active cooling for high concentration level

to remove the heat out of the cell.

18

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2.4.5 Sun tracking system

The sun tracking mechanism system is important in CPV technology. As the cell

concentration is increased, lower angle of sunlight enters in the system. Since CPV

system can only operate efficiently direct to sunlight with a relative low angle of

incidence, it requires tracking system to make sure that the CPV module stay focused

on the sun throughout the day [27]. This system is divided into one or two axis

trackers depending on the configuration of the optics. For low concentration level, it

requires only one axis tracker while in medium or high concentration level, two axis

trackers are used. Trackers incur extra cost in CPV systems as compared to

conventional PV modules where the price is proportional to the tracking precision

(measured in degree). The tracking precision necessary to be imposed by the

acceptance angle which is the tolerance that the optical system has to pay attention to

a deviation in the angle of sunlight rays.

2.5 Fundamental optics applied to solar concentration

The theory of optics is related to the creation of an image from an initial object.

Imaging optical system consists of three main components which are object, optic

and image it forms. In this system, the light is emitted by a point in the object. Then

it is being captured by an optical system and concentrated onto a specific point in the

image so that it is proportional to the object [4]. Thus, in imaging the imaging optics

concentrator it is focus on the image formed by the optical concentrator on the

receiver, so that the receiver must be small enough to attain even in the distribution

of the formed image. In CPV system, the main goal is to transfer maximum energy

from a source to a receiver. It does not basically form an image of the sun in the

receiver. In non-imaging optical system, the optical system has to take the light from

the light source, instead of an object. It is then concentrated to any point of the

receiver, instead of an image. This theory is called Non-imaging Optic. Professor

Roland Winston and group from University of Chicago has found this type of non-

imaging optics [4]. Therefore, regards of the need tracking system mechanism, the

important is to make solar concentrator collect more sunlight and concentrate on

solar cell and most efficient non-imaging solar concentrator is CPC [35]. This is

19

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29

because the characteristic of CPC able to collect the solar radiation within specific

acceptance angle

2.5.1 Concentration Ratio (

In CPV system, there are three levels of concentration, namely low, medium and

high concentration which depends on concentration ratio. In general, there are two

definitions for concentration ratio. The first one is called geometric concentration

ratio is defined as the ratio between of entry aperture and exit aperture as shown in

Equation 2.1 [4]:

(2.1)

where is entry aperture and ′ is exit aperture. This equation is applied to central

concept in non-imaging optic. When the ratio of entry aperture relative to the exit

aperture is higher, the concentration of light in optical system also becomes higher

[28]. In solar energy concentration, there is a limit of concentration, so called sine

law concentration [41].

For two-dimensional concentrator, the maximum concentration ratio is given by

Equation 2.2 [4] below:

(2.2)

For three-dimensional concentrator, the maximum concentration ratio is given by

Equation 2.3 [4] below:

(2.3)

If the receiver immerse with dielectric material with refraction index, , then

the maximum concentration ratio is given by Equations 2.4 and 2.5 [4] below:

20

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30

(2.4)

(2.5)

Second alternative called intensity concentration or flux concentration and mostly

term in “suns” and represent in term “x”. It is the ratio between the average intensity

of concentrated light that reaches the solar cell (W/m²) divides by standard peak solar

irradiance 1000 W/m² [35].

2.5.2 Aperture (

The term of aperture is the opening of plane that the solar radiation passes through.

In optic, there are two common dimensions, namely two-dimensional (2-D) and three

dimensional (3-D). For the 2-D, either linear or point focus concentrator [41], refers

to the width while for 3-D concentrator, it is categorized by the diameter of opening

plane.

2.5.3 Acceptance angle

Acceptance angle is defined as the range of angle over which accepted incoming

solar radiation and finally reach the receiver without moving all or part of

concentrator.

2.6 Review of solar concentrator design

In CPV system, it is important to concentrate sunlight from mirror or lenses onto a

small area of solar cell. Some of the designs require tracking mechanism to track the

sun especially for higher concentration. As already discussed in section 2.4.1, there

are three levels of concentration factor. This section is briefly reviews CPV system

according to the amount of solar concentration measured in “suns” or term of “X” as

referred to Table 2.2.

21

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C.S. Sangani et al.[42] designed, constructed and experimented 2-suns V-

trough concentrator with commercial PV module and stand-alone PV module for

different types tracking mode experimentally characterized under outdoor conditions

both with and without concentrator and showed that the used of V-trough

concentrator increases the output power 44% more when compared to PV flat-plate

system. Butler et al. [43] presented a simple model of 3-suns (3X) linear trough

mirror collector to predict the illumination distribution on multi-crystalline silicon

solar cell resulting in increased module output when using reflector. Ayaji et al. [44]

described a sun tracking concentrating module that is designed to determine the one

higher power output that consist of a solar panel with diffuse reflector aligned at

23.5° with the horizontal axis and solar tracker showing that reflector system is a

better option as compared to solar tracker due to cost of fabrication and complexity

of the tracking mechanism. Nivas. V et al.[45] paper presented a simulation analysis

using TracePro and PV Syst software and experimental analysis of booster mirror

with 1X, 2X, 3X and 4X configuration on solar panel and estimated that 2X

configuration is the optimum concentration ratio for V-trough concentrator as

compared to the other three suns configurations. V. N. Palaskar et al.[46] proposed a

modified PV module consists flat reflector which is made of anodized aluminum

sheet is attached to the short side of commercial silicon based PV module at North-

South direction for Mumbai latitude producing 22% more PV power and 21% higher

efficiency as compared to simple PV module. A prototype with 11X concentration

and two axis tracking system with novelty of coupling linear Fresnel concentrator

with a channel photovoltaic/thermal collector was designed by Rosell et al [47]

showing that thermal performance of the solar system is exceed 60% and thermal

conduction between the PV cell and absorber plate is a critical parameter as

confirmed by theoretical analysis. Feurmann et al. [48] proposed a high

concentration of concentrator using miniature parabolic dish to obtain maximum flux

level on solar cell for CPV system.

These solar concentrator designs are examples that had been used for

photovoltaic and thermal application. The next following section focuses on solar

concentrator design in Malaysia.

22

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Table 2.2: Solar concentrator design based on “suns”

Year Author University/Company Concentrator design suns (X) Contribution

2007 C. S. Sangani

et.al Energy System Engineering, IIT

Bombay V-trough concentrator 2

Increasing 44% output power using V-trough concentrator as compared to PV flat-plate system for passively cooled

module

2012 Butler et.al Nelson Mandela Metropolitan

University Linear trough mirror collector 3

Increased output module when using reflector

2013 Ajayi et.al University of Lagos Solar PV panel with diffuse reflector and solar tracker

-

The reflector system is a better option to contribute higher power output as

compared to solar tracker due to cost fabrication and complexity of the

tracking mechanism

2013 Nivas. V et al Anna University Booster mirror 1X, 2X, 3X

and 4X

2X configuration is the optimum concentration ratio for V-trough

concentrator as compared to the other three suns configuration

2014 V. N.

Palaskar Veermata Jijabai Technologies Institues

Matunga Mumbai V-trough concentrator -

Producing 22% more PV power and 21% higher efficiency compared to

simple PV module

2002 Rosell et.al Universitat de Lleida, Spain Linear Fresnel concentrator 11

The thermal performance of solar system is exceed 60% and thermal

conduction between the PV cell and absorber plate is a critical parameter as

confirmed by theoretical analysis

2001 Feurmann

et.al Ben-Gurion University Miniature Parabolic dish -

Obtaining 1000 suns of maximum flux level on solar cell for CPV system

23

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2.7 Co

For the pa

for reflect

regarding

reviews re

on applica

Ch

focusing h

group of s

fixed targe

sun, and p

double sta

energy. B

as solar to

Mah

design us

obtained b

their anal

parabolic

between

increasing

oncentrator

ast four dec

tive and refr

optical co

esearch wor

ation.

hen et.al [4

heliostat use

slave mirror

et as shown

projects sola

age structur

esides, it is

ower, solar d

Figure 2

hinder Singh

sing simula

by selecting

lysis, it is

trough con

the increas

g optical los

r design wo

cades, variet

fractive opti

oncentrator

rks from un

49] and Om

ed for solar

rs that is ab

n in Figure 2

ar rays into

e into a sin

s also able t

dish and sol

2.8: Propose

h et.al [51]

ation meth

g the apertur

important

ncentrator

sing therm

ss as decreas

ork in Mala

ty designs o

ic. There ha

on PV mo

niversities r

mar et.al [

r thermal en

le to move

2.8. A fram

the fixed ta

ngle stage at

to be applie

lar laser pum

ed design no

presented a

od. Its ge

re area and

to optimiz

(CPTC) by

mal loss wh

sing the ape

aysia

of solar con

as been limi

odule desig

related to th

[50] propos

nergy appli

based on pr

me holder ro

arget. The a

t high temp

ed on high

mp.

on-imaging

a cylindrical

ometrical c

diameter of

ze long-term

y achieving

hen increa

erture area.

ncentrators h

ited researc

gn in Mala

he use of co

sed a desig

ication. The

roposed rot

otates slaves

aim is to rep

perature app

concentratio

heliostat [4

l parabolic

concentratio

f the receive

m performa

g the const

asing apertu

have been d

ch and deve

aysia. This

oncentrator

gn of non-

e design con

ation formu

s mirror to t

place a conv

plication usi

on applicati

49, 50]

trough conc

on ratio h

er paramete

ance of cy

tancy and

ure area a

designed

elopment

section

depends

-imaging

nsists of

ula and a

track the

ventional

ing solar

ion such

centrator

has been

rs. From

ylindrical

stability

and also

24

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