DESIGN AND TECHNO-ECONOMIC ANALYSIS

OF A GRID-CONNECTED

PHOTOVOLTAIC POWER SYSTEM

AT

FIJI NATIONAL UNIVERSITY SAMABULA CAMPUS

by

Ravinesh Tendra Nand

A supervised research project submitted in partial fulfillment of the requirements for

the degree of Master of Science in Physics

Copyright©2010 by Ravinesh Tendra Nand

Division of Physics

School of Engineering and Physics

Faculty of Science, Technology and Environment

The University of the South Pacific

Suva, Fiji Islands

November, 2010

i

ii

DEDICATION

THIS WORK IS DEDICATED TO MY FATHER LATE MR SHANTI NAND WHO

ALWAYS PROVIDED THE RESOURCES FOR MY EDUCATION AND ALWAYS

ENCOURAGED AND INSPIRED ME AS A CHILD.

iii

ACKNOWLEDGEMENTS

I express my gratitude first and foremost to God Almighty for helping me throughout

this project.

My profound thanks go to my mother Mrs. Deo Mati Nand and my siblings for their

unwavering support and encouragement during the duration of my studies.

I thank my supervisor Dr. Atul Raturi, Head of School of Engineering and Physics

for his professional guidance and support throughout the duration of this study. I am

also indebted to Rajneel Prasad and the numerous staff at the University of the South

Pacific Physics department for assisting in collecting the solar data and giving timely

advice and suggestions. I also acknowledge with thanks the financial help given to

me in the preparation of this thesis by the University of the South Pacific.

My thanks also go to Mr Amit Singh of CBS Power Solutions for providing

quotations and other valuable information about the available solar technology. I also

acknowledge Mr Ravendra Chand for his advice on electrical wiring aspects of the

power system.

I appreciate the words of encouragement from my brother Rohitendra Nand, uncle

Satya Nand and my colleagues at the Fiji National University.

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ABSTRACT

Grid-connected photovoltaic systems are becoming attractive due to the continuing

decrease in the cost of PV modules and through the possibilities of integration of

renewable resources generated power into the traditional power systems. The heavy

dependence on expensive imported diesel for power generation in the Pacific Island

Countries (PICs) makes renewable energy based systems more viable.

For large buildings where electricity demand is high and the lighting and other energy

needs are provided mainly by fossil fuel based grid delivered electricity, grid-tied

building-integrated photovoltaics should be examined carefully to assess their

technical and economic potential.

This research was undertaken to design and carry out a techno-economic analysis of a

5 kWp grid-tied PV system for the C block of the Fiji National University Samabula

campus. The system design was done using the software PVSYST and then techno-

economic analysis was carried out using HOMER. The net present cost of energy was

estimated to be $0.69/kWh. The PV array production would meet 31 % of the

electricity demand at C block at FNU. On a yearly basis, this system could feed in

1347 kWh of electricity, thus saving $469 on electricity bill at current rates.

This project also outlines the many aspects of grid connected solar power system and

the benefits of using PV generated electricity over conventional forms of electricity

generation. However, economically it is not a viable option at current electricity

tariffs.

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SYMBOLS

iA Beam radiation transmittance

� Absorptance

p� Temperature coefficient of power

β Slope of surface

f Horizon brightening factor

pvf PV derating factor

� Solar declination angle

oG Extraterrestrial solar radiation incident on a horizontal surface

oG Average extraterrestrial solar radiation incident on a horizontal

surface

TG Global radiation incident on the PV array surface

NOCTTG , Solar radiation at defined NOCT

γ Azimuth of surface

c� Cell efficiency

mp� Maximum power point efficiency

STCmp,� Maximum power point efficiency under standard test

conditions

θ Angle of Incidence

Z� Zenith angle

RP Rated power

g� Ground reflectance

� Solar transmittance of PV cover surface

aT Ambient temperature

NOCTaT , Ambient temperature at defined NOCT

cT Cell temperature

ct Civil time in hours

NOCTcT , Cell temperature at defined NOCT

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STCcT , Cell temperature at standard test conditions

STCcT , Cell temperature at standard test conditions

LU Coefficient of heat transfer to the surroundings

� Hour angle

Longitude

vii

ABBREVIATIONS

AC Alternating Current

BOS Balance of System

CDM Clean Development Mechanism

CER Certified Emission Reductions

CO2 Carbon dioxide

COE Cost of Energy

CRF Capital Recovery Factor

DC Direct Current

E Equation of time

EIA Energy Information Administration

eV Electron Volt

EVA Ethylene Vinyl Acetate

FCC Fiji Commerce Commission

FCR Fixed Charge Rate

FEA Fiji Electricity Authority

FiTs Feed-in-Tariffs

Gb Direct or beam radiation

Gd Diffuse radiation

GDP Gross Domestic Product

GMT Greenwich Mean Time

Gn Extraterrestrial normal radiation

Gsc Solar constant

GWh Giga Watt hour

GWP Global Warming Potential

HOMER Hybrid Optimization model for Electric Renewables

IEA-PVPS International Energy Agency’s Photovoltaic power systems

IGBT Insulated Gate Bipolar Transistor

IPCC Intergovernmental Panel on Climate Change

IPP Independent Power Producers

KT Clearness index

kW kilo Watt

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kWh kilo Watt hour

MOSFET Metal Oxide Semiconductor Field Effect Transistor

MPPT Maximum Power Point Tracker

MW Mega Watt

MWh Mega Watt hour

n Day of a year

NOCT Nominal Operating Cell Temperature

NOx Nitrous Oxides

NPC Net Present Cost

NPV Net Present Value

O&M Operation and Maintenance

PICs Pacific Island Countries

Pnom Nominal power

PV Photovoltaic

PVSYST Software for photovoltaic systems

SFF Sinking Fund Factor

STC Standard Test Conditions

UV Ultraviolet

V Voltage

Vmpp Maximum power point voltage

Wp Peak Watts

Zc Time zone in hours East of Greenwich Mean Time

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TABLE OF CONTENTS PAGE

Declaration i

Dedication ii

Acknowledgements iii

Abstract iv

Symbols v

Abbreviations vii

List of tables xii

List of figures xiii

CHAPTER 1 INTRODUCTION

1.1 Research background 1

1.2 Energy Needs of Fiji 2

1.3 Electricity Consumption in Fiji 5

1.4 Objectives 6

1.5 Outline of Thesis 7

CHAPTER 2 LITERATURE REVIEW

2.1 Global Solar PV Trends 8

2.2 Grid Connected PV systems in the Pacific 9

2.3 Roof Mounted Grid Connected PV systems 10

2.4 Carbon Emissions and Climate Change 11

2.5 Sustainable Energy Development 12

2.6 Solar Energy Principles 13

2.6.1 Solar Radiation at top of the Earth’s atmosphere 16

2.6.2 Solar Radiation at the bottom of the Earth’s atmosphere 16

2.6.3 Global Radiation incident on PV 17

2.6.4 PV Operation Principle 18

2.6.5 PV array power output 19

2.6.6 PV cell Temperature 20

2.6.7 Economic Analysis 21

CHAPTER 3 METHODOLOGY

3.1 Solar Resource Data 24

3.2 Software used for the project 25

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3.2.1 Software for Photovoltaic Systems (PVSYST) 25

3.2.2 Hybrid Optimization Model for Electric Renewables (HOMER) 26

3.3 Design of PV System 27

3.3.1 Preliminary Design 27

3.2.2 Project Design Strategy 28

3.3.2.1 Selection of project site 28

3.3.2.2 Selection of Inverter 28

3.2.2.3 Selection of PV module 29

3.4 Array Sizing 30

3.5 HOMER Techno-Economic Analysis method 31

3.6 Economic Analysis methods 33

CHAPTER 4 RESULTS

4.1 PV system results 35

4.2 HOMER Techno-Economic Results 41

4.3 Inverter Output 47

CHAPTER 5 ANALYSIS

5.1 PV system analysis 49

5.2 PV Array sizing 50

5.3 Economic Analysis 52

5.4 Simple Payback Period Analysis 56

5.5 Cost of Energy Analysis 58

5.6 Life Cycle Cost (LCC) Analysis 59

CHAPTER 6 SYSTEM WIRING

6.1 Introduction 62

6.2 Wiring layout of PV system components 62

6.3 Cable Sizing 64

6.3.1 Cable sizing for PV array series connection 64

6.3.2 Cable sizing from DC Busbar to Inverter 66

6.3.3 Cable sizing from Inverter to main distribution panel 66

6.3.4 Cable selection for wiring 67

6.4 Sizing of circuit breakers 68

6.4.1 Sizing circuit protection between PV array and Inverter 68

6.4.2 Sizing circuit protection between Inverter and Grid 69

6.4.3 AC Isolation/Disconnect 69

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6.4.4 Earth and Lightning Protection 70

CHAPTER 7 DISCUSSION

7.1 Introduction 71

7.2 HOMER Optimization 71

7.3 HOMER Simulations 73

7.4 Selection of PV modules and Inverter 74

7.5 Outline of Inverter technology 75

7.6 Incentives and Subsidies for PV 76

7.7 Issues with Feed-in Tariffs 78

7.8 Climate Change Mitigation 79

CHAPTER 8 CONCLUSION and RECOMMENDATIONS

8.1 Conclusions 81

8.2 Recommendations 82

BIBLIOGRAPHY 83

APPENDIX 88

xii

LIST OF TABLES

PAGE

Table 1.1 Electricity Generation in Fiji excluding IPPs 3

Table 1 .2 Electricity Generation and Projections 4

Table 2.1 Grid connected PV capacity 9

Table 3.1 Recorded solar data 24

Table 3.2 PVSYST PV array designs 30

Table 3.3 HOMER input details 32

Table 4.1 HOMER Techno-Economic results 43

Table 4.2 Net present costs (NPC) for 5 kW PV and 3 kW Inverter system 43

Table 4.3 Net present costs for 5 kW PV and 5 kW Inverter system 44

Table 4.4 Annualized costs for 5 kW PV and 5 kW Inverter system 44

Table 4.5 Annualized costs for 5 kW PV and 3 kW Inverter system 45

Table 4.6 Monthly electricity budget for 5 kW PV and 3 kW Inverter 45

Table 4.7 Monthly electricity budget for 5 kW PV and 5 kW Inverter 46

Table 5.1 Comparison of 5 kW PV system with 3 kW and 5 kW inverter 52

Table 5.2 Comparison of nominal and discounted cash flows of system I

and system II 53

Table 6.1 Copper cable characteristics- Dicksmith 65

Table 6.2 Copper cable characteristics- Olex 66

Table 7.1 Net Present Cost of electricity 72

xiii

LIST OF FIGURES

PAGE

Figure 1.1 Electricity consumption trend 5

Figure 1.2 Aerial view of the project site 7

Figure 2.1 PV installations in IEA member countries 8

Figure 2.2 Carbon dioxide emissions from fossil fuel

consumption in Fiji 11

Figure 2.3 Earth revolving around the sun 14

Figure 2.4 Schematic of a solar cell 18

Figure 3.1 Efficiency graph of Energrid Inverter 29

Figure 3.2 PVSYST design of 9 x 3 PV array 30

Figure 3.3 PVSYST design for 10 x 3 PV array 31

Figure 3.4 HOMER schematic of grid connected PV system 33

Figure 4.1 Graph showing the average daily radiation data 35

Figure 4.2 Solar paths at FNU - Samabula. 35

Figure 4.3 Graph showing the load profile for a weekday 36

Figure 4.4 Graph showing the load profile for weekend 36

Figure 4.5 Graph showing the average monthly load profile 37

Figure 4.6 I-V curve of Conergy, P 180M 37

Figure 4.7 Efficiency vs. Cell temperature graph of Conergy 180M 38

Figure 4.8 PVSYST design of 5 kW PV system 38

Figure 4.9 Graph showing the average electricity

generation and grid purchases 39

Figure 4.10 HOMER graph showing Global solar radiation vs. PV power 40

Figure 4.11 HOMER optimization results after sensitivity analysis 42

Figure 4.12 Graph showing the 5 kW Inverter output power 47

Figure 4.13 Graph showing the power output of 3 kW inverter 48

Figure 5.1 PV Array sizing 50

Figure 5.2 Summing the voltage and current of each PV module 51

Figure 5.3 Graph comparing nominal and discounted cash

flows of system I and system II 54

Figure 5.4 Graph comparing PV system II having 5 kW

Inverter with system I using 3 kW Inverter 55

xiv

Figure 5.5 Graph showing net present cost summary by components 55

Figure 5.6 Graph showing net present cost by cost type 56

Figure 6.1 Wiring layout of grid connected PV components 62

Figure 6.2 Wiring layout of PV modules and the inverter 63

Figure 6.3 Block diagram of grid connected PV system 63

Figure 6.4 Diagram of 5A ATC blade fuse and holder 68

Figure 6.5 Wiring diagram for the solar panels to the inverter 69

1

CHAPTER 1 INTRODUCTION 1.1 Research Background

Electricity generation is one issue that continues to occupy the minds of many

researchers, policy makers, planners and governments. Considering the depleting

petroleum resources and the costs involved, it is necessary for any country to

diversify its sources of energy and at the same time lower the carbon dioxide content

of electricity generation.

Electricity can be generated from various energy sources which include hydro,

nuclear, wind, solar, biomass, wave, tidal, geothermal and thermal. The different

sources of electrical energy can be grouped into two main categories; renewable and

non-renewable. Renewable energy is infinite and naturally regenerative while non-

renewable energy sources are unrecoverable once depleted or replaced very slowly

through natural processes. The choice of a particular source of energy depends on a

number of factors such as; availability of resources, cost of generation and

environmental effects.

With the global CO2 emissions rising at an exponential rate the world today is facing

twin energy related threats. Firstly, that of environmental harm caused by consuming

too much of non-renewable fuels and secondly that of not having adequate and

secure supplies of energy at affordable prices. While the use of renewable energy

helps mitigate effects of climate changes by stabilizing green house gas (GHG)

concentrations, its use is crucial for the sustainable development of any country.

Solar photovoltaic (PV) energy is the conversion of the solar energy into direct

current (DC) electricity through a phenomenon called the photovoltaic effect.

Photovoltaic energy utilization can be divided into three broad categories of

standalone systems, grid connected systems and PV pumping systems. Unlike PV

pumping systems, standalone PV systems usually have battery backup. The

utilization of solar PV energy offers many benefits over other energy sources

including securing energy supplies in both the long term and short term.

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1.2 Energy Needs of Fiji

A vital part of economic and social development for any country is the availability of

energy which is associated with several aspects of daily life. Of the different forms of

energy, electricity is the high-quality secondary energy and an important material

base of industrial production and people’s life.

The Fiji Islands Bureau of Statistics-Key Statistics report 2010 reports that since

1990, there had been a 12 % increase in total national electricity production. For the

same period, the population growth rate had been 7 % and the Gross Domestic

Product (GDP) growth rate had ranged between -2.7 % and 8.7 %.

The energy sector in Fiji has undergone significant changes with total electricity

consumption growing from 202.8 GWh in 1980 to 715.3 GWh in 2009, an increase

of 252.9%. With this change, our dependency on non renewable energy sources has

now reached an unprecedented level. This dependency is making our country

vulnerable to external shocks. Fiji is losing substantial amount of money in importing

fossil fuels (Reddy, 2010).

According to the Fiji Census of population and housing report, 2008 the increased

demand for electricity in Fiji is due to factors such as expanding economy with the

growing population, urbanisation and introduction of modern and new electrical

appliances. Fiji’s population was 588,068 in 1976, 715,375 in 1986, 775, 077 in 1996

and 837, 271 in 2007. It is projected to reach one million just after 2030.

Fiji’s present renewable energy based power plants operated by the Fiji Electricity

Authority are Wailoa hydro, Wainiqeu hydro, Wainikasau hydro, Nagado hydro and

Butoni wind farm. In addition to these, FEA operates many thermal generators

especially to power the outer islands and also to meet the power demands during

times of low outputs from the hydro power plants.

3

Table 1.1 Electricity Generation (MWh) excluding IPPs (FEA Annual Report 2009, pg 60)

Year Hydro Thermal Wind Solar Total FEA

generation

% Hydro

contribution

% Thermal

contribution

1999 449,850 78,611 - 9 528,470 85 15

2000 414,383 109,511 - 11 523,905 79 21

2001 462,957 106,517 - 14 569,488 81 19

2002 450,198 153,501 - 10 603,709 75 25

2003 343,729 284,621 - 9 628,359 55 45

2004 367,357 282,189 - 6 649,552 57 43

2005 338,739 346,032 - 2 684,773 49 51

2006 341,255 394,363 - 4 735,622 46 54

2007 508,486 255,989 3,351 1 767,827 66 33

2008 495,090 269,745 4,604 0 769,439 64 35

2009 460,192 309,924 7,211 0 777,327 59 40

In the last decade while the population grew by slightly over 62000 (8%), the total

FEA generation had increased by 147%. For the same period, as shown in table 1.1,

thermal based generation increased by almost four folds while the total electricity

generated from renewable based resources dominated by hydro had not experienced

any significant increases.

Since 2007, combined contribution of wind and solar had remained constant at 1 %

of the total electricity generation although wind generation continued to increase

after its commissioning in 2007. But electricity generation from the only grid

connected PV system kept decreasing from 2001 to 2007, except 2006 and then

stopped since 2008.

The increasing demand and the delays in harnessing additional renewable energy

resources into Fiji’s electricity sector, has resulted in significant increases in fossil

fuel imports for electricity generation. For 60:40 ratio of renewable sources to fossil

fuel electricity generation, FEA spends around $70 to $90 million in fuel bill in a

year (Natuva, Fiji Sun 12/11/2010).

4

Table 1.2 Electricity Generation and Projections (GWh), 2008 – 2015

Year 2008 2009 2010 2011 2012 2013 2014 2015 Total Generation required made of: 774.6 785.6 820.4 898.9 968.7 1035.1 1096.8 1150.5

Wailoa (FEA) 400.0 400.0 360.0 400.0 400.0 400.0 400.0 400.0 Nagado (FEA) 18.0 18.0 18.0 18.0 18.0 18.0 18.0 18.0

Wainikasau (FEA) 18.0 18.0 18.0 18.0 18.0 18.0 18.0 18.0

Waniqeu (FEA) 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 FSC Lautoka

(IPP) 15.0 15.0 15.0 15.0 15.0 40.0 40.0 40.0 FSC Labasa (IPP) 7.0 7.0 7.0 7.0 15.8 15.8 15.8 15.8

Tropik Drasa (IPP) 0.0 0.0 24.0 72.0 72.0 72.0 72.0 72.0

Nadarivatu (FEA) 0.0 0.0 0.0 0.0 101.0 101.0 101.0 101.0 Vuda Biomass

(IPP) 0.0 0.0 0.0 0.0 71.0 141.9 141.9 141.9 Wainisavulevu

(FEA) 0.0 0.0 0.0 0.0 7.0 7.0 7.0 7.0 Labasa Biomass

(IPP) 0.0 0.0 0.0 0.0 15.8 15.8 31.5 31.5 Savusavu

Geotherm (IPP) 0.0 0.0 0.0 0.0 0.0 15.8 31.5 31.5 Wailoa

Downstream (FEA) 0.0 0.0 0.0 0.0 0.0 0.0 35.6 35.6

Qaliwana (FEA) 0.0 0.0 0.0 0.0 0.0 0.0 43.8 43.8 FSC Rarawai

(IPP) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 87.6 VLIS Biomass

(IPP) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Diesel & HFO

(FEA) 314.4 325.4 376.2 366.7 233.1 187.7 138.4 104.6

Renewable Energy - - 444.2 532.2 735.7 847.4 958.3 1045.9

Non Renewable Energy 376.2 366.7 233.1 187.7 138.4 104.6 % of Non

Renewable Energy 37.0 43.0 45.9 40.8 24.1 18.1 12.6 9.1

% of Renewable Energy 63.0 57.0 54.1 59.2 75.9 81.9 87.4 90.9

(Source: Fiji Commerce Commission Press release 21/10/2010)

The data in table 1.2 indicates that with the entry of independent Power Producers

(IPPs) at the planned times, FEA could reach its target of using 90 % renewable

5

sources for electricity generation by 2015. The magnitude of electricity generation

and the entry of IPPs into the energy market are expected to increase strongly given

the revised electricity tariff structure by the Fiji Commerce Commission (FCC)

setting minimum tariff for IPPs at $0.27/kWh. The upward revision of electricity

tariff from 8 – 13 cents before June 2010 to $0.23/kWh thereafter and then setting

the minimum rate of $0.27/kWh applicable from 21/10/2010 provides a good

stimulus for the growth in the renewable energy sector in Fiji. At the same time the

FCC is encouraging FEA to consider higher tariff rates for investors in the high cost

areas such as the outer islands.

1.3 Electricity Consumption in Fiji

Fiji’s electricity consumption is mainly divided into three main sectors namely

Domestic/ Residential

Commercial

Industrial

Figure 1.1 Electricity consumption trend (source: FEA annual report 2009)

The graph shows an overall increase in electricity consumption of all three sectors

but the industrial sector consumption had been the greatest. In 2003 the electricity

consumption declined in all sectors but then increased steadily until 2006 and

thereafter there has been a gradual increase in consumption. In 2009 the industrial

6

sector consumed almost three times the amount of electricity consumed by the

residential sector and about 1.5 times the commercial sector.

The Fiji Department of Energy (DOE) together with FEA is undertaking demand

side management by advising consumers to become more energy efficient by

providing; technical advice, energy saving tips and billing data. Energy audits are

also carried out providing in-depth knowledge of energy consumption and

recommendations for reducing the electricity bills.

1.4 Objectives

This study is undertaken to investigate the technical, economic and environmental

suitability of installing a grid connected PV system at the C–Block at Fiji National

University Samabula campus, Suva, Fiji Islands. The C-Block has 6 classrooms, 3

science laboratories, and 4 staff rooms. The current electricity supply is from the

main power lines of the Fiji Electricity Authority (FEA) but there is also a backup

diesel generator for times of power shutdown by the FEA. The electrical appliances

used are one hundred sixty 36W fluorescent lights, forty 51W electric fans, twenty

five 40W computers, six 1000W air conditioners and some laboratory apparatus as

per use.

The specific objectives of the research are to:

i. Design a grid connected PV system using the software PVSYST (version

5.21).

ii. Carry out a techno-economic analysis of the PV system designed using the

software HOMER (version 2.68).

iii. Determine the cost of energy using different economic analysis methods and

compare the costs of electricity.

iv. Outline wiring and installation procedures for the PV system designed.

v. Undertake an environmental comparative analysis between grid connected

PV and thermal based electricity generation.

vi. Identify the various policies, incentives and initiatives for integration of

renewable energy into the existing national electricity grid in Fiji.

7

Figure 1.2 Aerial view of the project site (source: Google Earth)

1.5 Outline of Thesis

A brief structure of this thesis is as follows:

(a) Chapter 1 presents the research background, energy needs of Fiji, electricity

consumption trend in different sectors in Fiji and the research objectives.

(b) Chapter 2 is the review of literature and it presents the, global status of grid

connected PV systems, PV systems in the pacific, carbon emissions scenario

and sustainable development energy plans for Fiji. Some mathematical

formulas used for energy calculations and economic analysis are also

discussed.

(c) Chapter 3 presents the methodology adopted for the research. It includes

methods of solar data collection, selection of inverter and PV modules,

PVSYST preliminary and project design of grid connected PV system and

the use of HOMER for techno-economic analysis.

(d) The results of the research are presented in chapter 4.

(e) Chapter 5 presents the analysis of the results.

(f) Chapter 6 is about the wiring of the PV system. It presents type and size of

cables to be used for connecting different components of the system and also

includes sizing of fuses and circuit breakers.

(g) Chapter 7 is a general discussion of the research. It explores scenarios at

different electricity tariffs, outlines the inverter technology, benefits of using

solar energy and the various incentives and subsidies relevant to PV systems.

(h) Finally the conclusions and suggestions for future work are presented in

Chapter 8.

8

CHAPTER 2 LITERATURE REVIEW 2.1 Global Solar PV Trends

The use of photovoltaics technology for electricity generation differs substantially

from country to country. This is due to different energy policies and public support

programmes for renewable energy projects and especially photovoltaics, as well as

the varying grades of liberalization of domestic electricity markets. According to the

European Union PV Status report, (2009), between 2001 and 2008, installations of

PV systems in the European Union increased more than ten times and reached 9.5

GW cumulative installed capacity at the end of 2008. In 2009 alone, 4590 MW of

new PV capacity was constructed which were majority grid-tied.

Figure 2.1 PV installations in IEA member countries (IEA PVPS status

report, 2009)

These figures are indicative of the progress in the photovoltaic industry in terms of

research and development, support measures for PV projects by governments and the

much wider agreement and acceptance by people that renewable energy is part of the

solution for sustainable development.

Foster, (2008) states that “for the past decade photovoltaics have enjoyed an average

of 30 % growth across the global spectrum with certain hot spots in Europe, the

United States and Japan.” This has been mainly due to prudent government policies,

the fluctuations in fossil fuel prices and decrease in availability, and also

enhancements in the technology due to research and development. Thus, the market

development of solar energy is strongly dependent on the policy, technology

development and transfer, and economics of solar energy products.

Tota

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9

2.2 Grid Connected PV systems in the Pacific

While small PV stand-alone systems are common in the Pacific Islands, grid-

connected PV power systems are very few. The main determinant factor for

implementation of grid connected PV power projects in the Pacific Islands is the lack

of financial support for the energy sector. High capital costs of PV technologies

compared with non-renewable based technologies often limit investments in PV

systems unless funded by donor agencies e.g. the European Union Development

Fund multi-country initiative ACP-EU (REP–5) five Pacific Island countries (PICs)

has resulted in the installation of over 300 kWp of PV systems. Through the REP 5

programme, Niue, Nauru, Federated States of Micronesia (FSM) and Palau have grid

connected PV systems except Marshall Islands where off grid PV systems range

from 6 to 13 kWp for a total of 55.6 kWp.

Table 2.1 Grid connected PV capacity

(Source: www.rep5.eu/Project_Countries)

Similarly through the ‘Tuvalu e8 solar power project’ funded by the Italian

government, a total of 86 kWp of grid connected PV systems were installed in

Tuvalu; 40 kWp at Funafuti soccer stadium roof and the surrounding area and 46 kWp

system at Vaitapu Secondary school. Tokelau also has a 10 kWp PV system integrated

to the diesel supplied grid at Fakaofo which was jointly funded by UNESCO, UNDP

and the governments of New Zealand and France. Likewise, Fiji has a 10 kWp grid

connected PV project at Navutu, Lautoka funded by the Australian government and a

Japanese government funded hybrid mini-grid, 37.4 kWp solar PV and 536 kWp wind

turbines at Nabouwalu. However, due to a variety of reasons both the PV projects in

Fiji are currently non-functional. Overall, all PIC’s has shown strong interest in

Country Total cumulative installed

capacity (kW)

Niue 52

Federated States of Micronesia 52.5

Nauru 40

Palau 100

10

shifting their energy policies and energy sector initiatives towards the promotion of

renewable energy resources and diversification of the electricity production mix.

2.3 Roof Mounted Grid Connected PV systems

Solar photovoltaic systems mounted on buildings are becoming increasingly popular

as prices decrease and the installation infrastructure becomes increasingly mature.

The integration of large scale renewable energy projects into the main grid can

therefore bring down the cost of electricity and provide some financial relief to the

consumers.

Natano (2009) argues that as the cost of solar power technology, which has not

reached an optimal competitive level yet, continues to decrease over the next decade,

the spread of grid-connected power systems holds the potential to improving local

communities’ access to clean and reliable energy services. This in turn could

considerably contribute to improving the standards of living in the long run.

Siegfried, (2009) stresses that in the long term, an ecologically sustainable energy

supply can only be guaranteed by the integration of renewable resources. The

objective of a forward looking energy supply policy must therefore be to utilize the

existing grid as well as possible for the supply of clean, cheap and reliable power.

The traditional concepts of centralized power stations and very long distance

transmission of energy coupled with energy losses and high costs associated with

transmission lines needs to be reconsidered. Masters (2004), “there are compelling

reasons to believe that the traditional system of large, central power stations

connected to their customers by hundreds or thousands of miles of transmission lines

will likely need to be supplemented and eventually replaced with cleaner, smaller

plants located closer to their loads. Not only do such generation systems reduce

transmission losses and costs, but the potential to capture and utilize waste heat on

site greatly increases their overall efficiency and economic advantages.” Building

integrated generation systems offer increased reliability and reduced threat of

massive and widespread power failures.

11

Thus, there are huge opportunities for solar photovoltaic power systems especially

grid-tied PV systems but people need to overcome barriers such as perceptions,

regulatory frameworks, limitations of the existing transmission and distribution

structures and the biggest barrier of high PV capital cost.

2.4 Carbon Emissions and Climate Change

Increasing amounts of carbon emissions to the atmosphere and the changes in

climate, arising in great part from energy-producing processes, demand the reduction

of ever-increasing environmentally damaging emissions. The generation of

electricity, particularly by the use of renewable energy offers considerable scope for

the reduction of such emissions. Boxwell, (2009) emphasizes that in the context of

climate change, the immense potentials of solar and wind energy, in addition to the

world wide use of hydro, are of great importance.

Figure 2.2 Carbon dioxide emissions from fossil fuel consumption in Fiji.

(Source: Energy Information Administration (EIA) CO2 scenario, US DOE)

Figure 2.2 shows that between 1980 and 1990, on average one million metric tonnes

of CO2 per year was emitted to the atmosphere. However, the emissions had

drastically increased since 1998. In 2004 the CO2 emissions were slightly over 2.5

million metric tonnes compared with 1 million metric tonne in 1994. Emissions

declined slightly from 2004 to 2006 but then continued to increase with 2008 being

the year of highest carbon emissions in the past 28 years. The carbon emissions do

12

not only harm the environment but the use of fossil fuel results in great import bills

for Fiji, adding external pressure on our economy.

As instability in the world's oil producing countries increases, it is becoming ever

more important for nations to reduce reliance on fossil fuels. Of the sustainable

energy technologies that currently exist, solar power has the most potential for

growth in the long term, and if it is adopted at considerable levels, solar power could

have significant impact on the reduction of CO2 emissions and increased energy

security (Bradford, 2006).

Foster, (2008), “as climate change is emerging as a manageable and predictable

global problem, several industries are shifting the focus of their business to include

the reduction of greenhouse gasses. This is seen in most power generation

technologies, but solar PV systems have shown the most sustained level of growth.

Year over year the photovoltaic industry continues to expand tremendously.”

2.5 Sustainable Energy Development

The bewildering array of new options available today for sustainable energy

production offers great promise, but also an increasingly difficult challenge in

deciding how much to invest in which technologies, how to integrate these

technologies, and how to optimize the overall new energy economy. Our success as a

society, in addressing fundamental issues such as climate change and economic and

environmental sustainability in general, may well depend on our ability to meet this

challenge (Luce et. al, 2008). This suggests that for sustainable energy development,

every country should reduce their carbon footprints and effectively engage all sectors

in low carbon economic growth, while fostering inclusive economic development.

Masters, (2004) shares similar views on sustainable development in Renewable and

Efficient Electric Power Systems. “Engineering for sustainability is an emerging

theme for the twenty-first century and the need for more environmentally benign

electric power systems is a critical part of this new thrust. Renewable energy systems

that take advantage of energy sources that won’t diminish over time and are

13

independent of fluctuations in price and availability will be playing an ever

increasing role in modern power systems”.

For the sustainable development of the Fiji energy sector, the FEA policy in line with

the government policy is that by 2015, 90 % of the total electricity generated in Fiji

should be from renewable resources.

2.6 Solar Energy Principles

The global solar radiation recorded for this project was on a horizontal surface but to

calculate the power output from PV modules, solar radiation incident on the PV

surface should be considered. The Orientation of a PV array can be described using

two important parameters;

Tilt angle or slope (β). This is the angle formed between the panel and the

horizontal surface.

Azimuth (γ). It is the angle measured clockwise from North towards the

projected sunlight path on local horizontal plane. At solar noon, the sun is

directly south in the northern hemisphere and directly north in the southern

hemisphere. At sunrise it corresponds to 900 and 2700 at sunset. Thus for this

project azimuth was taken as 1800 which corresponds to north facing PV

modules.

Angle of Incidence (θ) is the angle between the beam radiation to the surface of the

PV array and the normal to that surface. When the earth revolves around the sun its

axis remains fixed in space at an angle 00 45.23�� away from the normal (figure

2.3) to the plane of revolution. (Twidell and Weir, 2006).

14

Figure 2.3 Earth revolving around the sun.

HOMER uses equation 2.1 to calculate the solar declination angle ( )� , the latitude at

which the sun's rays are perpendicular to the earth's surface at solar noon (Duffie and

Beckman, 1991).

�

���

����

��� �

�365

284360sin45.23 00 n� 2.1

Where; n is the day of a year.

The location of the sun in the sky at any time is described by the hour angle ),(� the

angle through which the earth has rotated since solar noon. Since the earth makes one

revolution in average time interval of 24 hours; ./1524360 0

0

hh�

� �hth s 12150

��� 2.2

Where; st is the solar time in hour. HOMER uses the convention whereby the hour

angle is negative before solar noon, zero at solar noon, and positive after solar noon.

Electrical load data and solar radiation data which are both time dependent are

considered as data in the local standard time or the civil time. However, HOMER

uses equation 2.3 to calculate the solar time for the respective time-dependent datas.

EZh

tt ccs ����/150

2.3

Where:

ct is the civil time in hours corresponding to the midpoint of the time step(h).

is the longitude ( 0 )

15

Zc is the time zone in hours East of Greenwich Mean Time, GMT (h)

E is the equation of time (h)

West longitudes and time zones west of GMT are taken as negative. The equation of

time accounts for the effects of obliquity (the tilt of the earth's axis of rotation

relative to the plane of the ecliptic) and the eccentricity of the earth's orbit. HOMER

calculates the equation of time as follows:

�

���

���

���

BBBB

E2sin04089.02cos014615.0

sin032077.0cos001868.0000075.082.3 2.4

B is given by: � �365

13600 ��

nB

Where: n is the day of a year.

The angle between the incident beam and the PV collector surface i.e. angle of

incidence (θ) (Duffie and Beckman, 1991) is calculated using

���������������������

sinsinsincoscoscossinsincoscoscoscoscoscossincossincossinsincos

�����

2.5

Where: θ is the angle of incidence ( 0 )

� is the slope of the surface ( 0 )

� is the azimuth of the surface ( 0 )

� is the latitude ( 0 )

� is the solar declination ( 0 )

� is the hour angle ( 0 )

The zenith angle � �Z� and the elevation/altitude angle are also important to consider

with the angle of incidence. Zenith angle is the angle formed between the vertical

and the suns ray and is zero when the sun is overhead and 900 when the sun is at the

horizon. Zenith and elevation angle are complementary.

� �elevationZ �� 090� 2.6

16

Using equation 2.5 and taking slope as zero )0( �� for a horizontal surface:

������ sinsincoscoscoscos ��z 2.7

2.6.1 Solar Radiation at top of the Earth’s atmosphere

The solar radiation striking the top of the earth’s atmosphere varies with time

because of the changes in distance between the Earth and the Sun due to the

eccentricity of the earths orbit. At mean distance of the earth from the sun, the solar

radiation striking a surface oriented perpendicular to the sun’s rays is called the solar

constant. It has a value of 1367 W/m2 but fluctuates during a year. Thus to calculate

the extraterrestrial normal radiation (Gn) at the top of the atmosphere equation 2.8 is

used.

���

��� ��

365360cos033.01 nGG scn 2.8

Where: Gsc is the solar constant

n is the day of the year.

The extraterrestrial solar radiation incident )( 0G on a horizontal surface is given by:

znGG �cos0 � 2.9

To calculate the average value of extraterrestrial solar radiation incident )( 0G on a

horizontal surface, equation 2.9 is integrated because HOMER does time step by step

analysis with the solar resource data.

� � � �� �

��� �

��� �����

�����

sinsin180

sinsincoscos12 12120 nGG 2.10

Where; 1� is the hour angle at the beginning of the time step and 2� at the end.

2.6.2 Solar Radiation at the bottom of the Earth’s atmosphere

Solar data for projects are normally collected at a horizontal surface on the ground or

calculated using the clearness index (KT) which is as a ratio of surface radiation )(G

to the extraterrestrial radiation )( 0G . Monthly clearness index values were calculated

in this project.

17

0GGKT � 2.11

Solar data recorded at the earth’s surface usually referred as global solar radiation

(G) has two main components. It is the sum of diffuse (Gd) and direct or beam (Gb)

radiation.

db GGG �� 2.12

However, when calculating the solar radiation incident on an inclined surface, the

effect of the surface inclination on beam and diffuse radiations are considered. Beam

component is affected the most because it is incident from one direction only at a

particular time whereas diffuse radiation is multidirectional. Thus, the diffuse

fraction calculated as a function of the clearness index (Duffie and Beckman, 1991)

follows:

2.13

80.022.08.0;165.0

336.12638.16388.41604.09511.0

22.0;09.00.1432 !

"#

"$

%

&'����

�

� T

T

TTTT

TTd K

KforKKKK

KforK

GG

2.6.3 Global Radiation incident on PV

The global radiation incident on the PV array surface is calculated using the

following equation. 2.14

� � � � ���

��� �

��

���

����

�����

��

��� �

����2cos1

2sin1

2cos11 3 ����

gidbidbT GfAGRAGGG

Where:

g� is the ground reflectance.

zbR

��

coscos

� is the ratio of beam radiation on tilted surface to horizontal surface.

0GGA b

i � is the anisotropy index, a measure of beam radiation transmittance

GGf b� is the horizon brightening factor to account for the majority diffuse

radiation from the horizon in the sky.

18

2.6.4 PV Operation Principle

Photovoltaic is a technology that converts solar energy into electricity. The

individual photovoltaic elements, named cells are made of semiconductor materials.

The choice of semiconductor material for photovoltaic applications depends mainly

on its band gap and absorption coefficient. However, other important factors are

contact resistance, abundance of material, stability of junctions and materials,

toxicity of materials and radiation resistance. The greatest efficiencies for absorption

of solar energy and conversion into electrical energy are for those semiconductors

that have band gap near the infrared region of around 1.5 eV. The most commonly

used semiconductor material is Silicon with band gap of 1.1 eV and absorption

coefficient of 14101 �( cm at room temperature (Zeghbroeck, 2007).

In its pure state, crystalline silicon is a poor conductor at low temperatures, due to the

fact that all of the electrons in the outer orbit are bonded and cannot move freely. To

change this behaviour, pure silicon has to go through a process called ‘doping’. In

this process some “impurities” (eg. As, B) are added to the material (Zweibel, 1990).

Semiconductors are classified as p-type or n-type depending on the type of doping.

When energy applied to the free electrons in the valence band, exceeds the band gap

of the material, the electrons move to the conduction band where they start

conducting electricity. The energy required for this transition of electrons is provided

by sunlight or particles of sunlight known as photons.

Figure 2.4 Schematic of a solar cell (Source: Luque, 2002)

19

Figure 2.4 illustrates the photovoltaic process when a solar cell is exposed to

sunlight. The incident solar energy is absorbed by the electrons in the valence band

and if the solar energy provided by the photons is more than the band gap, the

electrons migrate to the conduction band. The electrons in the excited state are

collected by the n-type semiconductor and driven to an external circuit to generate

electricity. Then through a return circuit using a p-type semiconductor, the electrons

are restored in the lower energy valence band. When the energy provided by the

photons is lower than the band gap, it is absorbed as heat by the solar cells. This

results in rise in cell temperature and thus decreases the efficiency of the electricity

generation process. The voltage at which electrons are delivered to the external

circuit is slightly lower than the band gap and for materials with band gap of around

1 eV, the output per cell is usually in the range of 0.5 – 0.7 V. Thus, multiple cells

are connected together and encapsulated to form a PV module.

2.6.5 PV array power output

Real power output from PV panels is generally lower than their rated power because

in real life applications they hardly operate at standard test conditions. This is called

the derating factor ( pvf ) and it usually ranges from 0.8 to 0.9 for modern PV panels

over their lifetime of 20 to 25 years.

PV power output is also dependent on the cell temperature and the output decreases

with increase in cell temperature. The temperature coefficient of power ( p� ) is

usually around -0.5 % / 0C. Thus, taking the derating factor and the cell temperature

into consideration, the actual power output of PV array is:

� �) *STCccpSTCT

TpvRpv TT

GGfPP ,

,1 �����

����

�� � 2.15

Where:

RP is the rated power of the panel.

cT is the cell temperature.

STCcT , is the cell temperature at standard test conditions

20

p� is the temperature coefficient of power

TG is the global radiation incident on the PV array surface

2.6.6 PV cell Temperature

PV cell temperature is calculated using the energy balance of a PV panel from Duffie

and Beckman (1991), solar energy absorbed equals the sum of electrical output and

the heat loss to the surroundings.

� �acLTcT TTUGG ������ 2.16

Where:

� is the solar transmittance of PV cover surface (%)

� is the absorptance of the PV cover surface (%)

c� is the electrical conversion efficiency of the PV (%)

LU is the coefficient of heat transfer to the surroundings [kW/m2°C]

aT is the ambient temperature [°C]

From equation 2.16, it follows that; ���

��� ����

����

���

����� c

LTac U

GTT 1 2.17

However, PV manufactures usually report the Nominal Operating Cell Temperature

(NOCT) instead of cell temperature. NOCT refers to the surface temperature that a

PV cell would reach if exposed to 800 W/m2 of solar radiation at a surrounding

temperature of 200C, wind speed of 1 m/s and at no load ( c� = 0). Thus, substituting

these values into equation 2.17 yields;

NOCTT

NOCTaNOCTc

L GTT

U ,

,, ��

�� 2.18

Where: NOCTaT , is the ambient temperature at which the NOCT is defined [20°C]

NOCTTG , is the solar radiation at which the NOCT is defined [0.8 kW/m2]

NOCTcT , is the cell temperature at which the NOCT is defined [200C].

Substituting equation 2.18 into 2.17;

21

���

��� ����

����

� ���

���c

NOCTT

NOCTaNOCTcTac G

TTGTT 1

,

,, 2.19

Assuming that majority of the time the PV array operates at its maximum power

point, then cell efficiency is equal to maximum power point efficiency, mpc �� � .

Thus cell temperature ���

����

���

��

����

� ���

���mp

NOCTT

NOCTaNOCTcTac G

TTGTT 1

,

,, 2.20

However, mp� is dependent on cT because efficiency of PV array decreases with

increase in cell temperature. Thus, HOMER uses the following linear relationship:

� �) *STCccSTCmpmp TTp ,, 1 ��� ��� 2.21

Where:

STCmp,� is the maximum power point efficiency under standard test conditions [%]

p� is the temperature coefficient of power [%/ 0C]

STCcT , is the cell temperature under standard test conditions [25 0C]

Substituting 2.21 into 2.20 and solving for cell temperature, cT (K) yields:

� � � �

� � ���

����

����

����

���

�

���

� ���

��

����

���

�

����

����

STCmp

NOCTT

TNOCTaNOCTc

STCcSTCmp

NOCTT

TNOCTaNOCTca

c pG

GTT

pTG

GTTTT

,

,,,

,,

,,,

1

11

2.22

2.6.7 Economic Analysis

The annual interest rate is related to annual inflation rate and the nominal interest

rate and is given by:

ffii

��

�1

'

2.23

22

Where:

i = real interest rate 'i = nominal interest rate or the rate at which loan is secured

f = annual inflation rate

Capital recovery factor (CRF) is used to calculate the present value of a series of

annual cash flows and is given by:

1)1()1(),(��

�� N

N

iiiNiCRF 2.24

Where: i = real interest rate and N = number of years.

The future value of a series of annual payments is calculated using the Sinking Fund

Factor (SFF) and is given by the equation:

1)1(),(

��� Ni

iNiSFF 2.25

Annualized capital cost over the project life time is calculated from the initial capital

cost as follows:

),(, projcapcapa RiCRFCC (� 2.26

Where:

capC is the initial capital cost of a component

),( projRiCRF is the capital recovery factor with real interest rate i , and project

lifetime ., projR

The value of a system component remaining at the end of a project lifetime is called

the salvage value, S and is given by:

���

����

��

comp

remrep R

RCS 2.27

Where:

�repC replacement capital cost of a component

�compR component lifetime.

�remR Remaining life of a component at the end of project lifetime and is given by;

� �repprojcomprem RRRR ��� .

23

The replacement cost duration, repR , is calculated using the equation;

���

����

�(�

comp

projcomrep R

RINTRR . INT is the integer function, returning the integer portion

of a real value.

HOMER calculates the Annualized replacement cost using the equation:

� � � �) *projcomprepreparep RiSFFSRiSFFfCC ,, (�((� 2.28

Where: � �+ � � 0,,/, &� reprepprojrep RRiCRFRiCRFf and 0�repf for 0�repR .

24

CHAPTER 3 METHODOLOGY 3.1 Solar Resource Data

Solar data used for this research was the recorded global horizontal radiation at

Laucala bay area for 2008 and 2009. The research project site is less than 3 km away

from the data collection site and thus the data collected is a fair representation of the

solar data at the project site.

The scaled annual average irradiation was 3.94 kWh/m2/day and the scaled annual

average temperature was 25.8°C. The global meteorological coordinate for the

project site is:

� Latitude: 18.1 degrees South

� Longitude: 178.3 degrees East

� Time zone: GMT +12:00

Month

Clearness

Index

Average Daily

Radiation

(kWh/m2/d)

Average

Temperature

(°C)

January 0.381 4.38 27.1 February 0.448 4.98 27.6

March 0.447 4.56 27.4 April 0.459 4.08 26.8 May 0.326 2.49 24.8 June 0.347 2.43 25.0 July 0.453 3.29 24.4

August 0.402 3.34 25.0 September 0.422 4.07 25.1

October 0.411 4.42 26.0 November 0.388 4.41 26.1 December 0.422 4.88 27.2

Table 3.1 Recorded solar data

(Source: University of the South Pacific Energy Laboratory)

25

3.2 Software used for the project

3.2.1 Software for Photovoltaic Systems (PVSYST)

PVSYST is useful for designing PV systems for applications such as grid connected,

standalone, pumping and DC grid. It has three step design process comprising of a

preliminary system design, project design and tools menu.

The preliminary design offers a basic and quick way to determine PV component

sizes by defining the location for the project and system parameters. In the pre-sizing

process, PVSYST evaluates the monthly production and performances using a few

general system characteristics and provides a rough estimate of the costs of the PV

system. For building integrated grid connected systems, the design is architect

oriented as the input requirements are; available roof area, desired nominal power or

the desired energy yield. Other features like mounting of the solar modules and

ventilation are also considered.

Project design mode, is engineer oriented and offers a large database for PV

components, locations and meteorological sites. However, other meteorological data

can also be used. It has tools for adjusting the orientation of PV modules and the user

only has to choose a PV module, inverter and desired nominal power. PVSYST

provides the number of inverters and possible array layouts. It takes into account the

number of modules in series that would provide the maximum power point voltage

compatible with the inverter and also displays warnings if PV system configuration

is not satisfactory. It also has three dimensional (3-D) feature to analyze effects of

near and far shading on PV modules.

The tools menu of PVSYST has meteorological database for over 330 sites over the

world and also allows user to import meteorological data from other sources such as

Meteonorm, NASA-SSE and RETScreen etc. It holds components data of over 1750

PV modules, 650 inverters and data about many pumps, batteries and regulators. The

tool menu provides many graphical and tabular forms of results under various

conditions and offers features to extensively study the solar resource geometry, PV

array behavior and helps optimize the operating voltage. Thus, PVSYST is used for

detailed technical designs of PV systems.

26

3.2.2 Hybrid Optimization Model for Electric Renewables (HOMER)

HOMER is a micro power optimization model, which simplifies the task of

evaluating designs of both grid-connected and off-grid power systems for a variety

of applications. Homer’s optimization and sensitivity analysis algorithms make it

easier to evaluate many possible system configurations and to identify the most

economical power system (Lilienthal, 2005).

HOMER performs three principal tasks: simulation, optimization, and sensitivity

analysis. In the simulation process, HOMER models the performance of a particular

micro power system configuration for each hour of the year to determine its technical

feasibility and life-cycle cost. In the optimization process, HOMER simulates many

different system configurations in search of the one that satisfies the technical

constraints at the lowest life-cycle cost. In the sensitivity analysis process, HOMER

performs multiple optimizations under a range of input assumptions to gauge the

effects of uncertainty or changes in the model inputs.

Optimization determines the optimal value of the variables over which the system

designer has control such as the mix of components that make up the system and the

size or quantity of each. Sensitivity analysis helps assess the effects of uncertainty or

changes in the variables over which the designer has no control, such as the average

wind speed, average solar radiation or the future fuel price etc.

HOMER models a particular system configuration by performing an hourly time

series simulation of its operation over one year. HOMER steps through the year one

hour at a time, calculating the available renewable power, comparing it to the electric

load, and deciding what to do with surplus renewable power in times of excess, or

how best to generate (or purchase from the grid) additional power in times of deficit.

When it has completed one year’s worth of calculations, HOMER determines

whether the system satisfies the constraints imposed by the user on such quantities as

the fraction of the total electrical demand served, the proportion of power generated

by renewable sources, or the emissions of certain pollutants.

27

HOMER also computes the quantities required to calculate the system’s life-cycle

cost, such as the annual fuel consumption, annual generator operating hours,

expected battery life, or the quantity of power purchased annually from the grid. The

quantity HOMER uses to represent the life-cycle cost of the system is the total net

present cost (NPC). This single value includes all costs and revenues that occur

within the project lifetime, with future cash flows discounted to the present.

The total NPC includes the initial capital cost of the system components, the cost of

any component replacements that occur within the project lifetime, the cost of

maintenance and fuel, and the cost of purchasing power from the grid. Any revenue

from the sale of power to the grid reduces the total NPC.

3.3 Design of PV System

The grid connected PV system was designed using the software for photovoltaic

systems, PVSYST. The software has features of preliminary system design and

project design.

3.3.1 Preliminary Design

PVSYST preliminary design could be done in three different ways using the array

specification features of:

� Active area (m2)

� Annual yield (MWh/y)

� Nominal power (kWp)

Firstly a grid connected PV system was designed using the total available north

facing roof area of approximately 320 m2. A 75 kW PV system was required to cover

the whole roof area but this design was not economically viable as it would have

required huge capital investments.

Therefore, a grid connected PV system was designed by specifying the desired

nominal power as 5 kWp because the daily power demand which was greatest during

28

weekdays was 4.5 kW. This design was based on a standard monocrystalline Silicon

cell technology solar module mounted on tilted roof with free ventilation properties.

The total roof area required for a 5 kW system was 36 m2. Following the preliminary

system design, a 5 kW grid connected PV system was designed using the ‘project

design’ feature of PVSYST.

3.3.2 Project Design Strategy

The meteorological and project site data were first specified under the ‘project

design’ tool of PVSYST. The values used were; 18.10 South latitude, 178.30 East

longitude and site elevation above the sea level as 64 m. PV module orientation was

specified as; fixed tilted plane at 180 from the horizontal and at an azimuth of 1800.

Following that, in the ‘system’ tool of PVSYST, 180Wp 30 V Conergy PV module

and Energrid El 5000 pure sine wave 5 kWp inverter were selected.

3.3.2.1 Selection of Project Site

The building proposed to be used for this project has a north facing gable roof with

pitch angle of 15 degrees, making it suitable for installation of solar panels. The

building is a 3 storey concrete structure and the roofing profile is also quite strong,

capable of withstanding addition weight of the PV modules. The project site (C-

block) is also free of any shading effects from the surrounding structures and plants.

3.3.2.2 Selection of Inverter

A Tenesol manufactured Energrid El 5000 model grid connect inverter was selected

for this project. Its features include; Maximum Power Point (MPP) voltage range of

150 to 450 V, absolute maximum PV voltage of 540 V, nominal MPP voltage of 270

V, nominal AC power of 5 kW, maximum AC power of 5.24 kW, nominal AC current

of 22 A, maximum AC current of 27.2 A, maximum efficiency of 95.6 % and

monophased output on AC grid side at frequency of 50 Hz.

29

P in (DC) [kW]

Figure 3.1 Efficiency curve of Energrid Inverter

(Source: Energrid El 5000 technical data sheet - PVSYST)

The efficiency curve indicates that there is very little decrease in efficiency when the

DC input power decreases from 5 kW to 1 kW making the inverter highly suitable

for periods of both high radiation levels and low radiation levels.

3.3.2.3 Selection of PV module

The PV modules selected were silicon monocrystalline technology based 30 V

Conergy P180M model which has 72 cells in series. Its nominal power at STC is 180

Wp. At reference temperature of 25 0C and reference solar radiation of 1000 W/m2,

the short circuit current is 5.20 A and open circuit voltage is 45 V. The maximum

power point (MPP) voltage is 36 V with MPP current of 5 A.

Basic model parameters include; 900 Ω shunt resistance, 0.134 Ω series resistance

(model), 0.60 Ω series resistance (apparent), 37 nA diode saturation current, 1.30

diode quality factor, voltage temperature coefficient of CmV 0/3.142� and

temperature coefficient for power = C0%/5.0� . Each module dimension is 1580

mm x 808 mm x 45 mm with an area of 1.277 m2 and module mass of 15 kg.

There are 4 by-pass diodes per module with reverse characteristics of -0.7 V diode

direct voltage, quadratic factor of 2/2.3 VmA and absorptivity coefficient for

temperature of 0.9.

30

3.4 Array Sizing

The optimum array configuration was determined using ‘design the array’ feature of

PVSYST which provided the different possibilities of number of modules and strings

and the array power at different operating conditions. After selecting the PV

modules, inverter and specifying other parameters such as orientation of modules

and site solar resource data, a PV array design of 4 parallel strings, each with 7

modules in series, occupying maximum roof area of 36 m2 was obtained (figure 4.8).

The maximum operating power from a 7 x 4 array was 4.6 kW. The maximum power

point voltage of the 7 x 4 PV array at average cell temperature of 20 0C (Vmpp = 268

V) and at the highest possible cell temperature of 60 0C (Vmpp = 227 V) are within

the inverter input voltage range of 150 – 450 V.

Figure 3.2 PVSYST design of 9 x 3 PV array.

Other possible configurations of the PV array which had between 6 and 10 modules

in series was modeled in PVSYST and the maximum power point voltage and

maximum operating power of each array design was compared with the 7 x 4 array

design. A 9 x 3 PV array design (figure 3.2) yielded the closest nominal power to a 7

x 4 PV array but the inverter was marginally oversized with respect to PV array.

Modules in series

No. of strings

Vmpp at 20 0C (V)

Vmpp at 60 0C (V)

Pmax (kW) Pnom (kW)

7 4 268 227 4.6 5.0 8 4 307 260 5.3 5.8 9 4 345 292 5.9 6.5 7 3 268 227 3.5 3.8 9 3 345 292 4.4 4.9 10 3 383 324 4.9 5.4

Table 3.2 PVSYST PV array designs

31

Increasing the PV modules in each series string to 8 resulted in the array nominal

power exceeding the desired nominal array power of 5 kW (table 3.2). Similarly,

when each series string had 9 PV modules with 4 in each parallel string, the array

nominal power exceeded the desired nominal array power by 1.5 kW and also the

array ( Pmax = 5.9 kW) was oversized with respect to the inverter.

Figure 3.3 PVSYST design for 10 x 3 PV array. PV array configuration of 10 x 3 yielded maximum operating power of 4.9 kW,

closest of all designs but the nominal power exceeded by 0.4 kW. Moreover, a

technically challenging and difficult task in this particular design was to integrate 3

strings from the PV array with only 2 maximum power point tracking inputs of the

inverter.

After sizing the different PV array configurations and comparing its compatibility

with the inverter, the optimum design achieved for a 5 kW grid connected PV system

had an array of 4 parallel strings with 7 modules in series. Further analysis based on

the technology and economics was carried out using HOMER.

3.5 HOMER Techno-Economic Analysis method

Firstly, a new file was created under HOMER and a schematic was built which

consisted of primary load, photovoltaic panel, converter and AC / DC bus. Then the

hourly load details for each month and the component details such as technology

options, component costs, and the sizes and numbers of each component (Inverter

and solar panels) that HOMER used for simulations was specified.

32

Table 3.3 HOMER input details

Photovoltaic Modules

Slope = 180 Azimuth = 1800

Lifetime = 25 years

O&M cost = $10/y

Capital cost = $12/W

Replacement cost = $10/W

Tracking system: none (fixed)

Derating factor = 90 %

Efficiency at STC = 15 %

Ground reflectance = 20 %

Coefficient of power = -0.5 % /0C

NOCT = 45 0C

Sizes to Consider (kW) = 0.02, 0.03,

0.04, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 10,

13, 16, 17, 20, 25, 40, 41, 42, 70, 75, 80,

85

Grid No Interconnection cost

Purchase capacity (kW) = 10, 11, 12, 13,

14, 15

Net metering: monthly accumulation

C02 emissions factor = 632 g/kWh

S02 emissions factor = 2.74 g/kWh

NOx emissions factor = 1.34 g/kWh

Power price = $0.3484/kWh

Sellback rate = $0.27/kWh

Demand rate = $0.3484/kWh

Rates applicable – Jan to Dec- All week

00:00-24:00

Sale capacity (kW) = 5, 10, 11, 12, 13,

14, 15, 16, 17, 18, 19, 20, 25, 30, 40, 50,

60, 70, 80, 85

Inverter

O&M cost = $10/y

Lifetime = 15 years

Capital cost = $1700/kW

Replacement cost = $1600/kW

Efficiency at full load = 95.6 %

Rectifier capacity relative to inverter =

100 %

Rectifier efficiency = 97.7 %

Sizes to consider (kW) = 0.05, 0.1, 0.2,

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 16, 19,

20

Economics

Annual real interest rate = 6 %

Project lifetime = 25 years

System fixed capital cost = $1000

System fixed O&M cost = $200/y

Capacity shortage penalty = $0/kWh

Constraints

Maximum annual capacity shortage =

10, 15, 20 %

Minimum renewable fraction = 30, 40,

50, 60, 70, 80 %

Operating reserve as percentage of solar

power output - 100 %

Operating reserve as percentage of

hourly load - 100 %

33

Figure 3.4 HOMER schematic of grid connected PV system.

The recorded solar resource detail for every hour of the year including two year

monthly average ambient temperatures were input as HOMER data. The average

value of solar irradiation obtained was 3.94 kWh/m2/d. The cost of buying electricity

($0.3484/kWh) from FEA grid and the selling price to the grid ($0.2700/kWh) was

also specified into HOMER. The software used these inputs to simulate different

configurations of system components and generated results that were viewed as a list

of feasible solutions sorted by net present cost. HOMER also displayed simulation

results in tables and graphs that helped compare configurations and evaluate them on

their economic and technical merits.

HOMER simulations were done using the sensitivity variables of; minimum

renewable energy contribution (30, 40, 50, 60, 70 and 80 %), maximum capacity

shortage of (10, 20 and 30 %), grid sale capacity of (5 kW to 75 kW) and finally an

optimum solution was achieved. From the list of feasible solutions, a 5 kW grid

connected PV system contributing 31 % renewable energy to the electric load at a

cost of $0.698/kWh was obtained.

3.6 Economic Analysis methods

A detailed economic analysis of the 5 kW PV system designed was carried out

manually with the following economic analysis methods:

1. Simple payback period analysis

2. Cost of energy analysis

3. Life-cycle costing analysis

34

Hence, the production cost of a unit of electricity ($/kWh) from the solar system

designed was compared with the present cost of a unit of electricity supplied by the

Fiji Electricity Authority.

Energy policies of the Fiji government and various incentives for the integration of

grid connected renewable energy technologies are also studied. Finally, the

environmental impacts of the use of solar power systems were discussed and a report

was compiled as the mini-thesis.

35

CHAPTER 4 RESULTS 4.1 PV system Results

Figure 4.1 Graph showing the average daily radiation data.

The results show that the average daily global horizontal radiation for the first four

months is 4.50 kWh/m2/d, 2.89 kWh/m2/d for the months of May to August and 4.45

kWh/m2/d for the last four months of a year. The average daily irradiation over a year

is 3.94 kWh/m2/d whereas from September to April the average is 4.47 kWh/m2/d.

Overall the available solar resource at this site is not very good as on average the

solar irradiation is below 5 kWh/m2/d.

Figure 4.2 Solar paths at FNU - Samabula.

Aver

age

Dai

ly R

adia

tion

(kW

h/m

2 /d)

36

The solar path diagram is for latitude 18.10 South, longitude 178.30 East at an altitude

of 64 m. From January (path 6) to June (path 1) the Sun moves towards the North and

then back towards path (7) in December. It shows that majority of the time the solar

radiation is received towards the equator, hence the solar modules to be mounted

would be equator facing and tilted at 180 above the horizontal.

Figure 4.3 Graph showing the load profile for a weekday.

The graph shows that there is actually very low demand for power from 7 pm to 7

o’clock in the morning but the demand is about 4.5 kW from 8 am to 7 pm in the

evening. This is because of the normal teaching hours at the Fiji National University

(FNU) campus whereby almost all the six classrooms, the staff room, computers and

the three laboratories are in use. The electric fans would normally be used during the

hot hours of a day (depending on the weather) but its usage is taken as an average

over a day. The power demand is still 4.5 kW from 5 pm to 7 pm because of the

evening classes at the campus. The low demand of about 0.5 kW from 7 pm to 7

o’clock in the morning is because of the exterior lights that are switched on around

the building.

Figure 4.4 Graph showing the load profile of weekend.

37

The demand for electricity in the weekends is low but some students and staff

members come and work in the C-Block, usually during day times of Saturdays and

Sundays. The load of 0.5 kW from 6 pm to 6 am represents the lighting needs during

the dark hours.

Figure 4.5 Graph showing the average monthly load profile.

The results show that except for the months of June and December, every other

month the maximum daily electrical load is around 4 kW and the average load for

each day of every month is about 2 kW. These values indicate that the average power

demand is reasonably constant over a year except for June and December due to the

semester breaks. The scaled annual average is 40 kWh/d or 1.67 kW and the peak

load is 8.09 kW with a load factor of 0.206. Day-to-day electrical load variation of

15 % was considered for HOMER optimization.

Figure 4.6 I-V curve of Conergy, P 180M.

(Source: Technical data sheet Conergy P 180M module-PVSYST)

38

The power output of PV modules is dependent on the cell temperature as well as the

incident irradiation. At the project site the average recorded irradiation was 3.94

kWh/m2/d, which corresponds to power density of 394 W/m2 at 10 hours of radiation

per day. Hence each module would produce on average 60 W (figure 4.6). For the

solar modules temperature effects were also taken into account with nominal

operating cell temperature (NOCT) of 45 oC and temperature coefficient of power as -

0.5 % / oC.

Figure 4.7 Efficiency vs. Cell temperature graph of Conergy, P 180M.

(Source: Technical data sheet Conergy P 180M module-PVSYST)

The rated efficiency of Conergy P 180M modules at STC is 14.5 % but efficiency

decreases with increase in PV cell temperature. Therefore, an efficiency of 13 % was

considered for calculations at NOCT of 45 0C.

Figure 4.8 PVSYST design of 5 kW PV system. The optimum array size of the 5 kW PV system designed using PVSYST, consisted of

7 modules in series and 4 parallel strings, providing maximum operating power of 4.6

39

kW without any overload losses. There was only one possibility for the number of

strings (4 in parallel) but it was possible to have between 6 and 10 modules in series.

However, for other possibilities of the number of modules in series except 7, the PV

array maximum operating power was lower than 4.6 kW in each case (table 3.2).

The maximum power point operating voltage (Vmpp) for each module was 32.4 V at

60 0C and the open circuit voltage (Voc) at -10 0C was 49.9 V. Thus for the PV array,

Vmpp at 60 0C was 227 V and 268 V at 20 0C (figure 4.8) i.e. the PV output decreases

with the increase in cell temperature. Since each series string had 7 modules the array

Voc was 350V. The roof area needed for the optimum array size of 28 solar modules

was 36 m2 and the total weight of the panels would be 420 kg i.e. 11.67 kg/m2.

Figure 4.9 Graph showing the average electricity generation and grid purchases. For every month of a year, majority of the power demand is met from the grid. The

minimum energy productions from the PV system are during the months of May and

June, generally the cooler months of a year. It also corresponds to the lowest clearness

index values for the solar resource during these months.

Annual PV production based on the average daily irradiation of 3.94 kWh/m2/d

(assuming 10 hours of radiation) was 6135 kWh/y while the grid purchases are

13,674 kWh/y. The PV array production would meet 31 % of the electricity demand

of C Block at FNU. Of the total renewable energy generated from the PV system, 92

% would be consumed and the remaining could be sold to the FEA grid.

40

The PV array output is usually lower than the rated output due to the power losses

during DC to AC conversion, decrease in efficiency of PV modules with increase in

temperature and also because of losses arising from system wirings and connections.

Figure 4.10 HOMER graph showing Global solar radiation vs. PV power.

For solar radiation values around 1000 Wm-2 (figure 4.10), the maximum operating

PV power as calculated by HOMER is slightly less than 4.5 kW which is less than the

rated power of 5 kW. This is because for Conergy modules the nominal operating cell

temperature is 45 0C and the temperature coefficient of power is -0.5 %/ oC. Therefore

a 25 oC temperature rise from STC corresponds to 12.5 % (0.625 kW) decrease in PV

power. Cell temperature rise above 45 0C during periods of low wind speeds coupled

with high irradiation values account for further power losses. Therefore, proper

ventilation for solar modules is an integral part of the design process.

41

4.2 HOMER Techno-Economic Results

HOMER techno-economic analysis was done using sensitivity variables of grid sale

capacity, maximum annual capacity shortage and minimum renewable fraction.

Annual capacity shortage is the ratio of the total capacity shortage and the total

electrical load. Specifying a capacity shortage value means that the power system is

designed not to meet peaks which occur over short times. Otherwise, the system

designed would include large and expensive equipments which would remain unused

majority of the time but increase the system total cost. An annual capacity shortage

factor enables HOMER to design a smaller and less expensive power system to meet

all loads except the peak. Generally, power systems with higher capacity shortage

are considered infeasible.

Grid sale capacity is the amount of electricity that can be fed into the power utility

grid and it was taken as 5 kW to 75 kW to allow for any future expansion of the PV

project. The Net Present Cost (NPC) which considers time value of money is the sum

of present values of all cash-flows associated with a project and is strongly

dependent on the discount rate. Thus, for this project a discount rate of 6 % over 25

year period was used for HOMER simulations.

The optimum solution achieved was a 5 kW grid connected PV power system (fig

4.11) with renewable energy contribution of 31 %. The list of feasible solutions had

many different configurations of the PV and inverter sizes. Based on the lowest cost

of energy of $0.678/kWh the optimum solution was a 5 kW PV system utilizing a 3

kW inverter. The NPC for this system was $126,627.00. This was considered as the

base case system.

However, to ensure that inverter and PV were neither under nor over sized relative to

each other, the optimum solution for the power system was 5 kW PV with 5 kW

inverter i.e. the current system. The cost of energy was $0.698/kWh, which was

$0.02/kWh higher than the base case system and the NPC was $130, 211.00.

42

Figure 4.11 HOMER optimization results after sensitivity analysis.

As shown in figure 4.11, the grid sale capacity does not have any effect on the cost

of energy. Similarly, when the annual capacity shortage sensitivity values of 10 %,

20 % and 30 % were used in HOMER simulations, the capacity shortage was always

zero as shown in the list of feasible solutions in figure 4.11. This is because the PV

system is grid connected and even at times of high peak load, the demand would be

met from the FEA grid.

Results for simulations with the sensitivity variable of minimum renewable energy

fraction are summarized in table 4.1

43

Renewable

Fraction

PV System

Size (kW)

Initial

Capital

Cost ($)

Operating

Cost

($/y)

Total NPC

($)

COE

($/kWh)

0.31 5 69,500 4749 130,211 0.698

0.40 7 96,900 4137 149,790 0.803

0.53 10 138,000 2971 175,979 0.943

0.62 13 177,400 1755 199,834 1.071

0.71 17 232,200 437 237,786 1.274

0.81 25 335,000 -1326 318,050 1.704

Table 4.1 HOMER Techno-Economic results

The operating cost of the PV system decreases as the system size increases because

of higher grid sales with bigger power systems. For PV systems with renewable

energy contribution of 71 % and less, the operating cost represents annual electricity

bill payment to FEA whereas the operating cost for 25 kW system represents the

revenue generated from annual grid sales of electricity. The NPC of a 25 kW system

is lower than the initial capital cost as a result of revenue generated from grid sales.

Component

Capital

($)

Replacement

($)

O&M

($/y)

Salvage

($/y)

Total

($/y)

PV 60,000 0 639 0 60,639

Grid 0 0 55,662 0 55,662

Inverter 5,100 2,003 38 -373 6,768

Other 1,000 0 2,557 0 3,557

System 66,100 2,003 58,897 -373 126,627

Table 4.2 Net present costs (NPC) for 5 kW PV and 3 kW Inverter system.

The capital cost of the power system represents 52 % of the NPC. Grid O&M cost is

reasonably high in comparison with O&M of other components because HOMER

calculates grid O&M costs as difference of the cost of purchasing electricity from the

grid and the revenue generated from grid sales.

44

Component

Capital

($)

Replacement

($)

O&M

($/y)

Salvage

($/y)

Total

($/y)

PV 60,000 0 639 0 60,639

Grid 0 0 54,734 0 54,734

Inverter 8,500 3,338 64 -621 11,281

Other 1,000 0 2,557 0 3,557

System 69,500 3,338 57,994 -621 130,211

Table 4.3 Net present costs for 5 kW PV and 5 kW Inverter system.

Comparing the base case system with the current PV system utilizing 5 kW inverter

shows that although the initial capital cost increases, the grid operation and

maintenance cost decreases. The grid O&M cost for a system using 5 kW inverter is

$903.00 lower than a system using 3 kW inverter because a 5 kW inverter would be

able to feed more electricity into the FEA grid and hence generate more revenue.

Component

Capital

($/y)

Replacement

($/y)

O&M

($/y)

Salvage

($/y)

Total

($/y)

PV 4,694 0 50 0 4,744

Grid 0 0 4,282 0 4,282

Inverter 665 261 5 -49 882

Other 78 0 200 0 278

System 5,437 261 4,537 -49 10,186

Table 4.4 Annualized costs for 5 kW PV and 5 kW Inverter system

It can be deduced from table 4.4 that the operation and maintenance cost of the solar

panels, inverter, and the balance of system (BOS) is $255.00/y or only 5.6 % of the

system annual O&M costs. When the grid operation and maintenance costs of

$4282.00/y are included then the system O&M cost increases to $4537.00. The total

annualized cost is $4749.00 greater than the annualized capital cost because this

system will not meet the full electricity demand of the building.

45

Component

Capital

($/y)

Replacement

($/y)

O&M

($/y)

Salvage

($/y)

Total

($/y)

PV 4,694 0 50 0 4,744

Grid 0 0 4,354 0 4,354

Inverter 399 157 3 -29 529

Other 78 0 200 0 278

System 5,171 157 4,607 -29 9,906

Table 4.5 Annualized costs for 5 kW PV and 3 kW Inverter system

The O&M cost of using 3 kW inverter (table 4.5), excluding the grid O&M cost is

$253.00/y i.e. $2.00 less than a system utilizing 5 kW inverter. When grid O&M

costs is included the system O&M cost increases by $70.00 because a 3 kW inverter

would feed less electricity to the FEA grid than a 5 kW inverter for the same PV

array output hence increase in electricity bill.

Month

Energy

Purchased

(kWh)

Energy

Sold

(kWh)

Net

Purchases

(kWh)

Peak

Demand

(kW)

Energy

Charge

($)

Jan 1,320 100 1,220 7 425

Feb 1,126 123 1,004 8 350

Mar 1,293 130 1,162 8 405

Apr 1,241 100 1,141 7 397

May 1,275 83 1,193 7 415

Jun 605 82 523 4 182

Jul 1,266 84 1,182 8 412

Aug 1,405 94 1,311 7 457

Sep 1,197 111 1,085 8 378

Oct 1,304 116 1,189 7 414

Nov 1,235 130 1,105 7 385

Dec 503 194 309 3 108

Annual 13,770 1,347 12,424 8 4,326

Table 4.6 Monthly electricity budget for 5 kW PV and 3 kW Inverter system.

46

Table 4.6 assumes that FEA prices for buying and selling electricity do not change

over the project life. It can be interpreted from the results in table 4.6 that on yearly

basis the PV system can feed-in a total of 1347 kWh of electricity to the FEA grid

which would be savings of $469.29/y in terms of the electricity bill. This generally

accounts for the weekends when the power demand for the building is low compared

with the weekdays and hence the PV electricity generated is fed into the grid.

On the other hand, the PV system alone cannot meet the average annual power

demand and hence 13,770 kWh of electricity needs to be purchased from the FEA

grid. The difference between the demand and surplus corresponds to 12,424 kWh of

net purchases from the FEA grid. In economical terms it translates to the FNU

paying the FEA $4326.00/year as the total cost of its electricity bill for the C-Block.

The lowest values for the net energy purchases are during the months of December

(309 kWh) and June (523 kWh) because of the semester breaks during these months.

Month

Energy

Purchased

(kWh)

Energy

Sold

(kWh)

Net

Purchases

(kWh)

Peak

Demand

(kW)

Energy

Charge

($)

Jan 1,320 108 1,212 7 422

Feb 1,112 134 978 8 341

Mar 1,285 140 1,145 8 399

Apr 1,231 104 1,127 7 392

May 1,275 88 1,187 7 413

Jun 605 90 515 4 179

Jul 1,245 88 1,158 8 403

Aug 1,398 102 1,296 7 451

Sep 1,189 121 1,068 8 372

Oct 1,295 125 1,169 7 407

Nov 1,215 145 1,071 7 373

Dec 503 214 290 3 101

Annual 13,674 1,459 12,215 8 4,253

Table 4.7 Monthly electricity budget for 5 kW PV and 5 kW Inverter system.

47

The peak demand of electricity ranges from 3 kW to 8 kW (table 4.7). The results

show that a PV system utilizing 5 kW inverter can feed-in a total of 1459 kWh of

electricity to the FEA grid; 112 kWh more compared with 1347 kWh if a 3 kW

inverter is used. Using 5 kW inverter in the PV system would reduce the electricity

bill from $4326.00 to $4253.00 per annum; a reduction in the electricity bill by

$73.00/y. However, the initial capital cost of having a 5 kW inverter will be

$3400.00 more than a 3 kW inverter but it will ensure the available solar energy is

fully harnessed by the PV system.

The highest grid sales of 214 kWh is in December and the lowest grid sales are in the

months of May (88 kWh), June (90kWh) and July (88kWh), generally the cooler

months of a year.

4.3 Inverter Output

At 10 h/d of operation for the 5 kW inverter, yearly mean output is 0.67 kW. This is

due to the generally poor solar resource. The maximum output is 4.41 kW and at full

capacity it operates for 1278 hours in a year. The capacity factor which is the ratio of

average output to the nominal output is 13.4 % and losses account for 110 kWh/y

(4.4 %) of the total energy input of 2495 kWh/y.

Figure 4.12 Graph showing the 5 kW Inverter output power.

The optimum solution provided by HOMER with lowest cost of energy of $0.678/kWh

was a 5 kW PV system with 3 kW inverter (figure 4.11).

48

Figure 4.13 Graph showing the power output of 3 kW inverter.

If 3 kW inverter is used then the capacity factor is 20 % with mean output of 0.6 kW.

It would operate for 1251 hours per year and the energy output will be 2176 kWh/y

with energy losses accounting for 100 kWh/y (4.4 %). However, if 3 kW inverter is

used then the PV system will be undersized relative to the PV array capacity during

times of good solar irradiation.

49

CHAPTER 5 ANALYSIS 5.1 PV system analysis

There are several characteristics of PV power systems which bear considerable

examination because they have direct impacts on how an investor values the worth of

the technology. Three such basic analyses of investment in PV systems include; the

system capital cost, cost per kW and cost per unit area. The total capital cost of the 5

kW PV system designed was $69,500.00.

./00.900,13$5

00.500,69$ kWkWPowerRated

CostCapitalkWperCostSystem ���

./56.1930$36

00.500,69$ 22 m

mAreaArrayPVCostPowerRatedAreaunitperCost ���

Despite the availability of renewable energy equipments at duty free rates in Fiji, PV

system capital costs in common with other countries are quite high and do not

compare favourably with the capital costs of fossil fuel based power systems of

similar power ratings. The high costs are because PV modules and inverters are not

manufactured locally and therefore the prices are driven by overseas market prices

and freight costs associated with the supply of equipments.

Apart from the technological and economic aspects of PV systems, their performance

analysis is heavily dependent on the local climatic conditions. Thus, two technical

terms of interest are the specific yield and the specific output both of which are a

function of the energy produced annually.

./42.17036

6135Pr 22 mkWh

mkWh

AreaArrayPVoductionEnergyAnnualYieldSpecific ���

loadfullatoperationofhours

kWkWh

PowerRatedoductionEnergyAnnualOutputSpecific

1277

56135Pr

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��

%1587601277

,��hh

yearainhoursoutputspecificfactorcapacitysystemPV

50

5.2 PV Array sizing

Figure 5.1 shows how the inverter maximum power point (MPP) input voltage range

(150 – 450) V and the maximum DC power curve constraint the maximum array

size. At STC temperature of 25 0C, the inverter DC power curve and the I-V curve

for the array are closest (at maximum inverter efficiency) to each other at a nominal

MPP voltage (VmppNom) less than 270 V.

Figure 5.1 PV array sizing

At the maximum annual ambient temperature of 29 0C, the open circuit voltage of the

PV array would be close to 315 V and the VmppNom will be between 250 - 270 V with

the maximum power point current (Impp) close to 20 A. Thus, the number of PV

modules needed in series was determined by taking the average (260V) of the

nominal maximum power point voltage and dividing by the MPP voltage (Vmpp) of

36 V for the Conergy PV modules. The result was 7.2; therefore the optimum

PVSYST design was 7 modules in series (figure 5.2).

51

For the series string of 7 modules, the open circuit voltage (Voc) was 285 V, short

circuit current (Isc) was 4.2 A, Vmpp was 250 V and Impp = 4 A. Thus the maximum

power output from each series string is 1000 W.

Figure 5.2 Summing the voltage and current of each PV module

The series string of 7 solar modules provides the PV array output voltage compatible

with the minimum inverter input voltage of 150 V but results in increase of the series

resistance of the circuit. Therefore, to increase PV power production and to reduce

losses due to circuit resistance, 3 other parallel strings were added. Thus the PV array

consists of 7 modules in each of the 4 parallel strings and the open circuit voltage of

the array is 285 V with short circuit current of 16.8 A.

52

5.3 Economic Analysis

PV

(kW) Inverter.

(kW) Grid (kW)

Initial Capital

Total NPC

System I 5 3 10 $66,100 $126,627 System II 5 5 10 $69,500 $130,211

Table 5.1 Comparison of 5 kW PV system with 3 kW and 5 kW inverter.

The optimum solution obtained from HOMER analysis for 30 % renewable energy

penetration was 5 kW PV array with 3 kW inverter but the inverter would be

undersized relative to the PV array. Therefore, a power system with 5 kW PV array

and 5 kW inverter was designed.

The present worth, which is the difference between the net present costs of system I

and system II is -$3584.00

Present Worth = $126,627.00 - $130,211.00 = - $3584.00.

The negative sign of the present worth indicates that system II doesn’t compare

favourably as an investment option with system I. It indicates that system II would

cost more money over the project lifetime compared with system I.

Annual worth is the product of the present worth and the capital recovery factor

(CRF). At interest rate 6( �i %) and system lifetime )25( �N years;

1)1()1(),(��

�� N

N

iiiNiCRF

0782.01)06.01(

)06.01(06.0)25,06.0( 25

25

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��CRF

Annual worth = (CRF present worth

y/00.280$27.28000.3584$0782.0 �,���(�

53

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,537

-7

8,57

3 -4

,607

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5,31

5 71

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-7

7,81

8 -4

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4,54

7 63

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,271

3

-4,5

37

-83,

110

-4,6

07

-79,

922

71

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88

-3,8

09

-81,

627

-3,8

68

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415

59

-3,2

11

4 -4

,537

-8

7,64

7 -4

,607

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4,52

9 71

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,593

-8

5,22

0 -3

,649

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2,06

5 56

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,155

5

-4,5

37

-92,

183

-4,6

07

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136

71

-3,0

47

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90

-88,

610

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43

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508

53

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03

6 -4

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6,72

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3,74

4 71

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1,80

8 -3

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-8

8,75

6 50

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7

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1 71

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8

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02,9

58

71

-2,8

35

-2,8

46

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672

-2,8

91

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710

44

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9 -4

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10,3

30

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07

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71

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00,3

57

-2,7

27

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42

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20

10

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12,1

73

71

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94

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33

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00,0

10

39

-2,8

80

11

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37

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-4

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16,7

80

71

-2,6

23

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90

-105

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02,4

37

37

-2,8

43

12

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37

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21,3

87

71

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53

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55

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04,7

27

35

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13

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95

71

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82

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33

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71

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31

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15

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71

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28

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00

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71

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03

21

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60

71

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24

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75

71

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25

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82

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7 -3

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36

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-7

01

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26

5 -3

,584

Ta

ble

5.2

C

ompa

rison

of n

omin

al a

nd d

isco

unte

d ca

sh fl

ows o

f sys

tem

I an

d sy

stem

II.

54

System II minus System I

Figure 5.3 Graph comparing nominal and discounted cash flows of system I and

system II.

Both the nominal and the discounted cash flow values show significant increases in

cumulative cash flows in year 15 because of the cost of replacing the inverter which

has a lifetime of 15 years. The nominal cost increases from $2411.00 in year 14 to

$5541.00 in year 15 whilst the discounted cash flow increases from $2744.00 to

$4049.00 respectively. The increases are by 129.8 % and 147.5 % respectively. Over

the project lifetime of 25 years, the cumulative nominal and discounted cash flows

were at its lowest values in year 14. Although the cash flow would continuously

improve after the inverter replacement, the costs at the end of project lifetime are

higher than the costs before inverter replacement. But overall the cash flow over the

lifetime improves from $3400.00 initially to $3768.00 for nominal cost and $3584.00

for discounted cost.

The return on investment (ROI) calculated using the cumulative nominal cash flows is:

� �) * blifetimebaROI --��

Where: a is cumulative nominal cash flow in final year.

b is cumulative nominal cash flow in year zero.

� �) * 43.000.3400$2500.3400$00.3768$ ���--����ROI %.

55

The discount factor over the project lifetime is given by:

� �2329.0

06.011

)1(1

25 ���

�� Nd i

f . i.e. The nominal cash flow of $3768.00 in the

25th year has a present value of $877.57

System II Compared with System I - Discounted

Figure 5.4 Graph comparing PV system II having 5 kW Inverter with system I

using 3 kW Inverter.

For system II utilizing 5 kW inverter, the change in cash flow from the 14th to the

15th year is large and abrupt compared with system I utilizing 3 kW inverter because

of the higher cost of replacement of 5 kW inverter. The initial difference between the

current and the base case power system is $3400.00 but at the end of 25 years the

difference increases to $3584.00. The nominal costs of system II increases from

$69,500.00 to $130,211.00 over the 25 year period.

Figure 5.5 Graph showing net present cost summary by components.

56

High capital cost of $60,000.00 for the PV modules and the O & M costs of $639.00

represent 47 % of the total net present cost (NPC) of $130,211.00 for the PV power

system. The net present costs for the inverter represents 8.7 % of the total while the

balance of system (BOS) costs of $3557.00 represent 3 %. The grid NPC of

$57,734.00 is the difference between the cost of buying and selling electricity from

the FEA grid.

Figure 5.6 Graph showing net present cost by cost type.

The high capital cost of the PV system in common with high initial capital costs of

most of renewable energy technologies represents 53 % of the total NPC. The

replacement cost of the inverter is $3338.00 with a salvage cost of $621.00. The

O&M cost of all system components including the grid is $57,994.00 and excluding

the grid O&M costs is $3260.00 i.e. 2.5 % of the total NPC of $130,211.00.

5.4 Simple Payback Period Analysis This calculation compares revenue with costs and determines the length of the time

required to recoup the initial investment. The payback period in years is equal to the

total capital cost divided by the average annual return from the power produced.

� � � �� �AARturnAnnualAverage

CcCostCapitalSPPeriodPaybackSimpleRe

�

The current cost of buying electricity from FEA grid is $0.3484/kWh for domestic

households, educational institutes and faith based energy customers e.g. churches and

57

temples. The government however provides a subsidy of $0.1425/kWh towards

electricity bills of all primary and secondary schools but tertiary institutes like Fiji

National University pay $0.3484/kWh.

Simple Payback Period @ $0.3484/kWh

� �

43.2137$3484.0$6135

cosPr

�(�

(�

kWh

kWpertAEPoductionEnergyAnnualAAR

yearsSP 5.3243.2137$00.500,69$

��

It would take 32.5 years to recover the initial investment on the PV system against

the system lifetime of 25 years. Thus, the investment will not be a viable one to

consider.

Simple Payback Period @ $0.2700/kWh

� �

45.1656$2700.0$6135

cosPr

�(�

(�

kWh

kWpertAEPoductionEnergyAnnualAAR

yearsSP 4296.4145.1656$00.500,69$

,��

The minimum tariff payable to Independent Power producers (IPPs) feeding into the

FEA grid is $0.2700/kWh. If separate meters are used for grid sales and grid

purchases instead of using net-metering then the simple payback period of the project

is 42 years.

The simple payback period analysis ignores several factors such as loan costs,

depreciation in capital costs, operational and maintenance costs and variation in the

value of delivered electricity over time. All these factors have direct influence on the

economics of any energy generation system. Thus, at the current electricity tariffs,

investment on grid connected PV power system would not be a viable investment

because the payback period is more than the system lifetime.

58

5.5 Cost of Energy Analysis This analysis is based on a fixed charge rate over the loan period and it neglects the

most important factor of economics i.e. the time value of money. The fixed charge

rates used are 6 % and 13 % to account for the average loan interest rates charged by

development bank and commercial banks respectively.

The cost of energy (COE) is defined as the unit cost to produce energy (in $/kWh)

from the solar energy system.

oductionEnergyAnnualtsOperatingEnergyofCost

Prcos

�

� �tsMORateeChFixedtCapitaltsOperating cos&argcoscos �(�

Fixed Charge Rate (FCR) = 6 % O&M costs = $255.00/year

Case 1: Half of the capital cost is financed at FCR of 6 %.

FCR only applies to ($69,500.00 ÷ 2) = $34,750.00

� � � �) * kWhkWh

COE /38.0$6135

00.255$06.000.750,34$�

�(�

Case 2: Half of the capital cost is financed at FCR of 13 %.

FCR only applies to ($69,500.00 ÷ 2) = $34,750.00

� � � �) * kWhkWh

COE /78.0$6135

00.255$13.000.750,34$�

�(�

Case 3: If the total capital cost is financed at FCR of 6 %.

� � � �) * kWhkWh

COE /72.0$6135

00.255$06.000.500,69$�

�(�

59

Case 4: If the total capital cost is financed at FCR of 13 %.

� � � �) * kWhkWh

COE /51.1$6135

00.255$13.000.500,69$�

�(�

In all of the four cases above, the cost of energy is greater than the cost at which the

FEA provides the electrical energy ($0.3484 / kWh).

5.6 Life Cycle Cost (LCC) Analysis

This analysis is more comprehensive and is more realistic in evaluating the

feasibility of renewable energy projects. It includes the net present value of money

( cNPV ) and calculates the levelized cost of energy ).(COEL

oductionEnergyAnnualCRFNPV

COEL c

Pr(

�

Levelizing is a method for expressing costs or revenues that occur once or in

irregular intervals as equivalent equal payments at regular intervals. The net present

value is generally used as a measure of economic value when comparing different

investment options in the life cycle costing analysis.

���

�����

����

����

�� LriYfCN

rYPPNPV mocadc ,

11,

11

&

� � � � 1;1

,1

.��

��

kk

kkxkYx

Using: Loan interest rate b = 6 %

Discount rate r = 5 %

System lifetime L = 25 years

Period of loan N = 20 years

Down payment on the system �dP = $34,750.00 (i.e. 50 % of cC )

Capital cost cC = $69,500.00

Annual Operation and maintenance cost, O&M = $255.00

60

Assumption: The general inflation and energy inflation rates, ( i ) are constant at 2 %

over the system lifetime.

The capital recovery factor (CRF) based on the loan interest rate, ( b ) rather than

discount rate ( r ) is used to determine the amount of each future payment required to

accumulate a given present value when the discount rate and the number of payments

are known.

� �) * 0;11

.��

� � rr

rCRF N CRF for loan = � �) * 0872.0

06.01106.0

20 ��� �

CRF based on system lifetime = � �) * 0709.0

05.01105.0

25 ��� �

Annual payment on system costs, � � CRFPCP dca (��

� �20.3030$

0872.000.750,34$00.500,69$�

(��

For payment

���

�����

��

����

����

����

20,06.1120,

06.011,

11 YYN

rY �

���

����

���

�����

��

���

�

�

06.111

06.11

06.11 120

5.1967

For system lifetime

5278.17

05.102.11

05.102.1

05.102.1

25,05.102.125,

05.0102.01,

11

125

����

����

���

�����

��

���

����

�����

��

�����

����

�����

�

YYLriY

Annual operation and maintenance cost fraction, 3& 1066.3

00.500,6900.255$ �(��mof

61

� � � �

59.955,54$

55.4458$04.747,15$00.750,34$

5278.171066.300.500,69$1967.520.3030$00.750,34$

,11,

11

3

&

�

���

(((�(��

���

�����

����

����

��/

�

LriYfCN

rYPPNPV mocadc

kWhoductionEnergyAnnual

CRFNPVCOEL c /64.0$

61350709.059.955,54$

Pr�

(�

(�

The life cycle cost of $0.64/kWh is almost double the current cost at which FEA

provides the electricity. Though the environmental value of PV generated electricity

is great, economically it is not a viable option at current electricity tariffs.

HOMER came up with the cost of energy as $0.69/kWh which is slightly greater than the

Life Cycle Cost analysis of $0.64/kWh. The difference is because HOMER assumes the

loan is paid over the 25 year period whereas the LCC analysis considered loan repayment

in 20 years.

62

CHAPTER 6 SYSTEM WIRING 6.1 Introduction

Wiring of the different components of a PV system is equally important as the design

of the PV system itself because poor wiring usually results in significant power

losses and can lead to system failures. This chapter outlines the many wiring aspects

of each system component; the length of cables, diameter of cables, power losses in

each segment of wiring, suitable sizes of fuses and circuit breakers. The general

layout of the system and earthing and lightning protection is also discussed.

6.2 Wiring layout of PV system components

A thorough knowledge of the PV system circuit wiring is vital to ensure connections

are correct and that system components do not get electrically damaged. The overall

PV system wiring is divided into three main sections comprising of the PV array, the

inverter and the user load with the grid backup.

Figure 6.1 Wiring layout of grid connected PV system with its components.

63

The PV array consists of 28 Conergy P180M solar modules. There are 4 parallel

strings and 7 PV modules are connected in each series string. Output from each

parallel string is connected separately to a common DC busbar from which only a

single negative and positive connection is made to the inverter. The DC busbar

incorporates a blocking diode which ensures that the PV array does not draw current

from the grid during non sun hours.

Figure 6.2 Wiring layout of PV modules and the inverter.

The arrows in the block diagram below indicate the generation and flow of electricity

through the various components of the grid connected PV system.

Figure 6.3 Block diagram of grid connected PV system.

5 kW PV Array with

DC fuse

Single Phase 5 kW Inverter With double

MPPT

Main distribution panel with

meter

Loads

Grid

AC

dis

conn

ect

Switc

h

64

6.3 Cable Sizing

Accurate sizing and selection of cables for component wirings is important to ensure

safe current handling capacity of cables is not exceeded and the performance of any

component is not compromised.

Ohm’s law states that the voltage drop across the ends of any conductor is equal to the

product of resistance and the current through it. i.e. .RIV � The resistance is given

by:

AR ��� 6.1

Where: �� resistivity of the cable / conductor � �m0

�� Length of the cable � �m

�A Cross sectional area of the cable � �2m

Thus, the voltage drop is given by: .IA

V (��� 6.2

Multiplying the length of the cable by 2 to account for the total loop wiring and

making cross sectional area, A, the subject of the equation yields:

� �V

IAIA

V (((�'(

(�

�� �� 2.2 6.3

Technical Information

� Copper cable resistivity, m0(� �8107.1�

� Standard maximum allowable voltage drop across cables in grid-tied systems

= 5 %

� Standard maximum allowable current for PV circuit = 125 % of the short

circuit current.

6.3.1 Cable sizing for PV array series connection

The following information was used for cable sizing:

� Nominal voltage rating of each Conergy module = 24 V DC.

� Short circuit current, .20.5 AIsc �

� Maximum cable length, 1�� m.

65

Maximum possible current .5.620.525.1 AA �(�

Maximum allowable voltage drop VV 2.124100

5�(�

Therefore the minimum cross sectional area required for the cable interconnecting the

PV modules is:

.18.01084.12.1

5.61107.122 2278

mmmV

IA �(�((((

�(((

� ����

However, cables with such low minimum cross sectional area and high current

carrying capacity are expensive as these are normally used in electronics. Therefore,

DC electrical cables for this project were selected using the table given below.

Number & Size of Strands

Conductor Area (sq.mm)

Current Rating (Amps)

Resistance per metre

(Ohms 35 0C)

Nearest Equivalent

AWG (B & S) 10 x 0.12 0.11 1.1 0.17 27 7 x 0.16 0.14 1.4 0.13 26 1 x 0.5 0.20 2.0 0.10 24

14 x 0.14 0.22 2.2 0.088 24 7 x 0.2 0.22 2.2 0.086 24 1 x 0.6 0.28 2.8 0.067 23 1 x 0.7 0.38 3.8 0.049 21

14 x 0.2 0.44 4.4 0.043 21 10 x 0.25 0.49 4.9 0.039 20 63 x 0.10 0.49 4.9 0.039 20 50 x 0.12 0.55 5.0 0.035 20 60 x 0.12 0.68 6.8 0.028 19 89 x 0.1 0.70 7.0 0.027 19 24 x 0.2 0.75 7.5 0.025 18

112 x 0.10 0.88 8.8 0.022 18 30 x 0.2 0.94 9.4 0.02 17 1 x 1.13 1.0 10.0 0.019 17 32 x 0.2 1.0 10.0 0.019 17

512 x 0.05 1.0 10.0 0.019 17 168 x 0.1 1.32 13.0 0.014 16

7 x 0.5 1.4 14.0 0.014 16 30 x 0.25 1.5 15.0 0.013 15 26 x 0.3 1.8 17.0 0.010 15

168 x 0.12 1.9 18.0 0.010 14 26 x 0.32 2.1 19.0 0.0091 14 7 x 0.67 2.5 22.0 0.0077 13 1 x 1.78 2.5 22.0 0.0076 13

252 x 0.127 3.2 29.0 0.0059 12 41 x 0.32 3.3 30.0 0.0057 12

315 x 0.12 3.6 30.0 0.0053 12 630 x 0.12 7.13 50 0.0027 9

1666 x 0.12 18.84 120 0.0010 5 Table 6.1 Copper cable characteristics

(Source: Dicksmith Electronics Annual catalogue 2009, pg 350)

66

Thus, for the series connection of the PV panels, 268.0 mm copper cable would be

used because it has current carrying capacity of 6.8 A, which is a slightly higher value

than the maximum possible current of the array.

6.3.2 Cable sizing from DC Busbar to Inverter

Cable sizing was done using the following information:

� Maximum cable length, 10�� m.

� Inverter voltage input range = 180 - 450 V DC

The maximum possible current from an the array of 28 PV modules (7 x 4) =

.26420.525.1 A�((

Average of the inverter input voltage range (180 – 450 V) = 315 V. Thus, maximum

voltage drop = 75.15315100

5�( V V

2278

56.01061.575.15

2610107.122 mmmV

IA �(�((((

�(((

� ����

Thus, a 22.3 mm cable would be used for the wiring from the DC Busbar to the

inverter because it has current carrying capacity of 29 A, which is a slightly higher

value than the maximum possible current of 26 A from the array.

6.3.3 Cable sizing from Inverter to main distribution panel

Alternating current cables are needed for wiring this section of the PV circuit. Thus,

Olex electrical data and current ratings as given in the table below were used.

Table 6.2 Copper cable characteristics

(Source: Olex Electrical handbook 2009, pg 72)

67

Cable sizing was done using the following information:

� Maximum cable length, 10�� m.

� Inverter rating = 5 kVA single phase.

When the inverter operates at full load, the maximum current .83.20240

5 AkVA��

Maximum allowable voltage drop VV 12240100

5�(�

Therefore the minimum cross sectional area required for the cable from the inverter to

main junction box interfacing the inverter, grid and the load is:

.59.01090.512

83.2010107.122 2278

mmmV

IA �(�((((

�(((

� ����

Thus, a 24 mm cable would be used for the wiring from inverter to main distribution

panel because in PVC circular form that is the appropriate size having current

carrying capacity of 25 A, which is also higher than current carrying capacity (20.83

A) of the cable needed.

The voltage drop rating of this cable isAmmV12 . Thus, for 20m of cable the voltage

drop would be ,6202512 VmAAmmV

�(( which is within the voltage drop limit as

%5.21002406

�(V

V .

6.3.4 Cable selection for wiring

The length, cross sectional area, temperature effects on resistance and insulation and

the current carrying capacity are some important factors to consider in selecting the

right cables for wiring the different components of the PV circuit. Generally, the

current carrying capacity of the cables selected should be slightly more than the over

current protection devices rating to ensure non burning or melting of the cables which

can result in fire.

68

6.4 Sizing of circuit breakers

Circuit breakers used in grid connected PV systems are bi-directional which provide

protection against over current. The standard current rating of the fuse must be

maximum of 125 % of the nominal current flowing in the cable.

6.4.1 Sizing circuit protection between PV array and Inverter

The four parallel strings from the PV array could be connected with circuit breakers

in two different ways.

Option 1

A fuse/circuit breaker could be installed on each string before the cable is connected

to the inverter.

Option 2

All four parallel strings could be fused together and then a circuit breaker installed

before the fused output is connected to the inverter.

Due to the simplicity and ease of circuit breaker connection in each parallel string, the

first option is used for this project.

Maximum possible current .50.620.525.1 AA �(� The lowest rated DC fuses

commonly available are 5 A and the next is 8 A. Therefore, a 5A fuse would be used

for each parallel string.

Figure 6.4 Diagram of 5A ATC blade fuse and holder.

(Source: www.digikey.com)

69

Figure 6.5 Wiring diagram for the solar panels to the inverter

6.4.2 Sizing circuit protection between Inverter and Grid

This circuit breaker would be part of the main distribution panel providing circuit

protection to the grid from the single phase output of the inverter in an over current

situation.

For the inverter operating at full load, the maximum current .83.20240

5 AkVA��

Therefore, the current rating for the bi-directional AC circuit breaker would be 20 A.

This circuit breaker would be protecting the inverter from over current situations

resulting from the grid as well as it will ‘trip’ in case of any over current situations

from the inverter to the grid.

6.4.3 AC Isolation/Disconnect

The disconnect switch would be placed between the inverter and the main distribution

box allowing provision for isolating the PV system from the grid during system

maintenance times or to rectify some faults in the circuit operation. The rating for the

70

disconnect switch can be the same or slightly greater than the rating for circuit

protection between the inverter and the grid i.e. 20 A.

6.4.4 Earth and Lightning protection

Grounding or earth is important in PV systems for electrical safety as well as

lightning protection. Improper earthing of PV systems could cause catastrophic

failures of PV systems and its components. Therefore, to provide the easiest path for

lightning to get to ground, all PV panel frames and the mounting structures would be

grounded through a single earth rod (~ 2.5 m) long. The ground for the earth rod

would be salted with copper oxide to improve conductivity.

.

71

CHAPTER 7 DISCUSSION 7.1 Introduction

Economic viability of grid connected PV systems depends mainly on electricity

generation potential of PV projects and electricity tariffs applicable for generating

renewable energy. Thus, HOMER analysis was carried out using grid sale tariff of

$0.27/kWh and $0.3484/kWh at average daily irradiation value of 3.94 kWh/m2/d.

7.2 HOMER Optimization

Case 1

Demand rate =$0.3484/kWh

Grid power price = $0.3484/kWh

Grid sales price = $0.27/kWh.

For a 5 kW grid connected PV system, five different configurations of PV power

system were obtained as feasible solutions i.e. with five different inverter sizes

ranging from 1 kW to 5 kW. The net present cost of energy (NPC), for the inverter

sizes from 1 kW up to 5 kW was: $0.683/kWh, $0.679/kWh, $0.678/kWh,

$0.686/kWh and $0.698/kWh respectively.

Based on the lowest NPC, HOMER optimization provided a base case optimum

system consisting of 5 kW PV array with 3 kW inverter. The inverter capacity was

undersized relative to the PV array capacity because HOMER calculates the

optimum size based on the average daily irradiation values. To account for

irradiation levels during the bright sun hours of a day, when the irradiation values are

usually more than the average value of 3.94 kWh/m2/d, a 5 kW PV array with 5 kW

inverter was considered despite the COE being higher than the base case system.

This power system would meet 31 % of the electricity needs of the C block at FNU.

The current grid sale tariff in Fiji, set by the Fiji Commerce Commission is a

minimum of $0.27/kWh. It is an incentive for IPPs to consider energy projects in

72

outer islands but for an IPP operating on any of the two main islands, the grid sale

tariff applicable is fixed at $0.27/kWh.

.

Case 2

Demand rate =$0.3484/kWh

Grid power price = $0.3484/kWh

Grid sales price = $0.3484/kWh

All educational and religious institutions in Fiji, connected to the FEA grid were

supplied electricity at special tariff of $0.2059/kWh until 21/10/2010 when it was

revised to $0.3484/kWh effective from 01/11/2010. Following the tariff alignment by

the Fiji Commerce Commission, the government announced that it will subsidise the

increases for primary and secondary schools but tertiary institutes. Thus, HOMER

analysis was performed considering the grid sale tariff is set equal with the grid

purchase tariff of $0.3484/kWh, which could be an incentive for IPPs.

The optimization results of a 5 kW PV system were five feasible solutions of

different inverter configurations with sizes ranging from 1 kW to 5 kW. The NPC of

energy, for the inverter sizes from 1 kW up to 5 kW were: $0.683/kWh, $0.679/kWh,

$0.679/kWh, $0.686/kWh and $0.698/kWh respectively. Other PV system sizes and

their contribution to the electricity demand is summarised in table 7.1

PV system

size (kW)

Renewable

Fraction

NPC($/kWh) @

grid sellback rate

= $0.27/kWh

NPC($/kWh) @

grid sellback rate

= $0.3484/kWh

5 0.31 0.698 0.698

7 0.40 0.803 0.803

10 0.53 0.943 0.941

13 0.62 1.071 1.055

17 0.71 1.274 1.257

25 0.81 1.704 1.651

Table 7.1 Net Present Cost of electricity

73

Comparison of case 1 and 2, shows that higher tariff for grid sales would only have

any significant impact on the PV cost of energy when larger PV systems are

developed. For the PV project to have any significant impact on the electricity

consumption of the C block at FNU, it was decided that the solar system must

contribute at least 30 % of the total electricity demand. The cost of energy in all the

different PV system sizes obtained from HOMER is more than the present cost of

supply from FEA ($0.3484 / kWh). The unit cost of electricity increases with the

increase in the PV system size mainly due to the following reasons.

� Prices of PV modules, inverters, cables and the balance of system

components are unreasonably high compared with fossil fuel based electricity

generators.

� Project site has a poor solar resource, resulting in the maximum capacity of

the system not fully realized.

� HOMER does not consider a discount rate in the initial capital costs when

systems with larger power ratings are considered.

The high capital costs and low irradiation levels, creates an economic imbalance

between the installed capacity of the system and the actual power output. Thus, when

larger systems are installed, the economic imbalance is having a multiplying effect

and hence the cost of energy increases.

7.3 HOMER Simulations

From the HOMER analysis it was calculated that the energy production from the PV

system was 6135 kWh/y while total purchases from the FEA grid was 13,674 kWh/y.

The mean output from the panels was 0.7 kW or 7 KWh/d. The mean output is really

low compared with the rated capacity of 5 kW for the PV panels and hence it

translates to a low capacity factor of 15 %. The PV system would operate for a total

of 2555 h/y. However, the total energy provided over a year from the PV system

accounts for 31% of the demand from the building i.e. renewable energy contribution

of 31%.

74

The initial cost of the complete system would be $69,500.00 and the net present cost

(NPC) after a system lifetime of 25 years of $130,211.00. The levelized cost of

energy came to a value of $0.698/kWh which is quite high compared with the cost of

electricity supplied by the Fiji Electricity Authority. i.e. $0.3484 / kWh.

Although the cost is quite high, a major advantage of having PV power system is

that it produces totally green energy i.e. 100% renewable energy. The annual

operation and maintenance cost of the system excluding the O&M of the grid was

$255.00/y with system fixed O&M cost of $200/y.

Some of the assumptions made for HOMER techno-economic analysis were:

� grid is available majority of the time

� loan interest rate remains constant at 6 %

� energy and real inflation rate is constant at 2 %

� electrical load variation is not more than 15 %

� inverter is expected not to produce very significant harmonic distortions.

HOMER performed a total of 2484 simulations with 324 sensitivities. The sensitivity

variables were maximum capacity shortage, minimum renewable energy fraction and

energy sale capacity of the power system.

7.4 Selection of PV modules and Inverter

Conergy P180 model solar panels were selected because it is designed especially for

large electrical power requirements and the 72 monocrystalline cells of each module

are embedded in ethylene vinyl acetate (EVA) which ensure long term performance

with high efficiency. Presence of solar glass on the front side of Conergy modules

raises ultraviolet (UV) resistance and improves insulation. The Aluminium frames

provide high resistance from corrosion and other metallic reactions when exposed to

the environment. Conergy modules are provided with general 5 year warranty with

12 year warranty on 90 % of the minimum power and 25 year warranty on 80 % of

the minimum power. The modules also have power tolerance of 31 %.

75

Inverter selection was made from 3 common inverter models; Energrid, Sunny mini

central and Sunny boy. 5 kW Sunny boy was only available with 60 Hz output but

one with 50 Hz rating was required. Based on PVSYST designs, Energrid was

technically better option than Sunny mini central because for different array

configurations the maximum operating power was greater than Sunny mini central.

In addition to that, Energrid has DC input voltage range (180 – 450) V with

maximum voltage input of 500 V compared with Sunny mini central input voltage

range (246 - 480) V and maximum input voltage of 540 V. The lower bound for the

input voltage of Energrid would enable the conversion of solar energy to electrical

energy even during not much bright hours of a day. The inverter weight is 32 Kg

(410mm x 180mm x 510 mm) and can provide output at frequency of either 50 Hz or

60 Hz. It has 4 DC inputs suitable to cater for any future expansion of the PV array.

7.5 Outline of Inverter technology

In grid-connected photovoltaic power systems, the DC output power for the

photovoltaic array has to be converted into the AC power of the utility power system.

Under this condition, an inverter to convert DC power into AC power is required.

The two main types of inverter technology available are line commutated and self

commutated inverters.

A line commutated inverter uses a switching device like a commutating thyristor that

can control the timing of turn-on while it cannot control the timing of turn-off by

itself. Turn-off should be performed by reducing circuit current to zero with the help

of supplemental circuit or source. Conversely, a self-commutated inverter is

characterized in that it uses a switching device that can freely control the ON-state

and the OFF-state, such as Insulated Gate Bipolar Transistor (IGBT) and Metal

Oxide Semiconductor Field Effect Transistor (MOSFET).

Self-commutated inverters can freely control the voltage and current waveform at the

AC side, and adjust the power factor and suppress the harmonic current, and is

highly resistant to utility system disturbance. Due to advances in switching devices,

most inverters for distributed power sources such as photovoltaic power generation

now employ a self-commutated inverter.

76

Self-commutated inverters include voltage and current types. The voltage type is a

system in which the DC side is a voltage source and the voltage waveform of the

constant amplitude and variable width can be obtained at the AC side. The current

type is a system in which the DC side is the current source and the current waveform

of the constant amplitude and variable width can be obtained at the AC side. In the

case of photovoltaic power generation, the DC output of the photovoltaic array is the

voltage source, thus, a voltage type inverter is employed.

The voltage type inverter can be operated as both the voltage source and the current

source when viewed from the AC side, only by changing the control scheme of the

inverter. When control is performed as the voltage source (the voltage control

scheme), the voltage value to be output is applied as a reference value, and control is

performed to obtain the voltage waveform corresponding to the reference value.

Pulse width modulation (PWM) control is used for waveform control. This system

determines the switching timing by comparing the waveform of the sinusoidal wave

to be output with the triangular waveform of the high-frequency wave, leading to a

pulse row of constant amplitude and a different width. In this system, a waveform

having less lower-order harmonic components can be obtained.

A self commutated inverter was selected for this project so that the PV system can

continue to operate in isolation even if the grid is down. Its features include 240V

single phase AC output at 50 Hz, 2 maximum power point tracking (MPPT) high

frequency converters followed by a rectifier, capacitor storage, a DC link and a DC

to AC grid connected output stage.

Finally, though the inverter technologies nowadays are very advanced, the capital

cost is an important element when considering the economics of PV power systems.

7.6 Incentives and Subsidies for PV

Feed-in-tariffs (FiTs) which have fueled many energy markets over the world in the

recent years is an explicit monetary reward for producing PV electricity. It is a

77

payment for electricity which is greater than the standard price paid to non-

renewable resource based electricity generators.

In Germany, the “Feed-in-Law” of 2004 permits customers to receive preferential

tariffs for solar generated electricity depending on the nature and size of the

installation. The feed-in-law fixes tariff over a 20 year period from commissioning

of a project and for roof mounted grid connected PV systems it was initially 0.481

€/kWh in 2004. The FiT is based on annual reduction and for roof mounted PV

electricity it is a 5 % reduction per annum whereas for grounded mounted PV

systems it is 6.5 % per year (European Union PV Status report 2009).

Similarly, according to European Union PV Status report 2009, French government’s

intention to increase the use of solar generated electricity 400 times by 2020 to a

total installed capacity of 5.4 GW has resulted in general feed-in tariffs remaining at

0.30 €/kWh for the next 20 years. In addition to that, for building-integrated PV

installations, there is a supplement of 0.25 €/kWh. If similar incentives are provided

for the building-integrated PV projects in Fiji, then significant growth in the grid-tied

PV power systems can be anticipated. However, the FiT incentive does not help

directly with high capital costs of PV systems but it guarantees electricity tariff

above the standard tariff over a number of years and FiTs can be used in proposals to

more easily secure funding for PV projects.

FiTs in Fiji’s energy sector can be applied in different contexts. It can be applied to

all power produced by the PV system or only applied to any additional power above

the needs of the customer. FiT can also be based on the benefits that PV will add to

the FEA grid, peak demand of electricity or line support. For larger grid connected

PV systems government should even consider a standard reward that could be a

certain multiple of the retail electricity price, either fixed for few years or could be

based on annual reduction of the tariff.

The FiT itself can be funded sustainably, whereby it is paid by a tax levied to all

electricity users instead of being sourced from government budgets, which can

change subject to government policy changes and priorities. In this way, the FiTs will

not be a burden for the tax payers.

78

Introducing attractive FiTs based on reducing tariff amount over time e.g. Germany,

could well be a temporary mechanism to stimulate growth in electricity generation

from grid connected PV systems. But if prices for PV system components do not

come down as the technology expands, or if the subsidy program itself is not directly

helping the local economy and instead PV system equipments are bought from

overseas countries, then not much progress in PV system installation could be

realized.

On the other hand, annual reduction of FiTs will encourage investors to invest early

and will ensure that PV systems are of high quality and perform well since funding

for the system is guaranteed. It will also force PV power producers to improve

overall power system efficiency as the annual reduction of the benefit will encourage

investors to acquire the best technology that will give them the greatest return. This

incentive may be targeted at commercial entities and large scale IPPs.

To attract groups with limited capital flow such as households, community based

organisations, schools particularly tertiary institutes and small businesses to invest in

renewable energy projects, the government can consider FiT combined with some

direct capital subsidy. Alternatively, government can decide to use direct capital

subsidies, renewable portfolio standards, green electricity schemes, tax breaks or

some combination instead of the FiT. Generally, using a type of subsidy other than

the FiT, progress in the industry would generally be slow but more constant and

predictable e.g. Germany, Italy, Korea, France, Portugal, Spain and Netherlands.

7.7 Issues with Feed-in Tariffs

The issue of where exactly to set the FiT is a major problem. Setting the FiT too high

will result in overheated markets and if it is set too low the investment in PV will be

negligible. This had been the case in Fiji before June 2010 when the tariff offered to

IPPs was between 8 to 13 cents per unit only. However, the current tariff structure

allows a minimum tariff of $0.27/kWh and also provides the incentive to encourage

investments away from the usual business centres and where higher tariffs could be

offered by FEA.

79

Even with higher tariffs now offered to IPPs, the market share of grid connected PV

generated electricity in Fiji is not expected to change significantly because the capital

costs remain unchanged. One way to increase PV installations could be offering

higher FiT to a specific market segment such as grid-tied PV at the beginning, and

then later expand to other segments such as hydro and wind.

Furthermore, even high levels of FiT rewards may not be proportional to market size,

but are rather sensitive to an incentive threshold that investors can be comfortable

with. Other important features in a sound FiT plan should include longevity and

stability i.e. there should not be mistrust between the investor and the government,

regarding the support for a PV subsidy, especially because of the high initial cost and

predicted length of operation of PV system.

7.8 Climate Change Mitigation

Global carbon emissions are rising at an exponential rate and there is a need for a

shift in energy supply from fossil fuels to renewable energy. Uses of renewable

energy helps in mitigating effects of climate changes by stabilizing green house gas

(GHG) concentrations in the atmosphere. The principle GHGs are water vapor

(H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and sulphur

dioxide (SO2). Water vapor behaves rather differently from other GHGs and is better

regarded as part of the climate than an outside influence on it. Other less significant

GHGs include chlorofluorocarbons (CFCs), halocarbons (HFCs) and

perfluorocarbons (PFCs).

Carbon dioxide is the most abundant GHG but its Global Warming Potential (GWP)

is lower than other GHGs. Each tonne of CH4 contributes 21 times as much to

global warming as each tonne of CO2 i.e. GWP of methane is 21. The GWP of N2O

is 310 and for SO2 and other Sulphur fluorides e.g. Sulphur hexa fluorides (SF6) the

GWP is above 23900 (IPCC 4AR WG1 TS sec.TS2).

Thus, comparing this 5 kW PV project with a diesel generator, it would help

decrease carbon dioxide emissions to the environment by 7720 kg/y, sulphur dioxide

80

by 33.5 kg/y and nitrous oxides by an amount of 16.4 kg/y. The total reduction per

annum would be 7759.43 kg CO2eq per annum.

This project would provide emission reductions against what would otherwise occur

if a diesel generator is used and hence could qualify to earn Certified Emission

Reduction (CER) credits under the Clean Development Mechanism (CDM) projects

as defined in article 12 of the Kyoto protocol. Thus considering the value of 1 tonne

of CO2eq as USD30.00 (adapted from: http://cdm.unfccc.int/about/index.html), the

value of carbon credits from this PV project would amount to US$23.28 per annum.

This is indicative of the scope in Fiji for generating funds for the mitigation of

climate change under the CDM.

81

CHAPTER 8 CONCLUSION and RECOMMENDATIONS 8.1 Conclusions

Accurate and long term solar resource data is vital for assessing the site potential for

photovoltaic applications. The findings in this project are based on 2008 and 2009

solar data with an average irradiation of 3.94 kWh/m2/day. The software used for

design was PVSYST while HOMER was used for evaluating the techno-economic

viability of PV systems.

The optimum size of the power system for the C-Block at Fiji National University

Samabula Campus was a 5 kW grid-connected photovoltaic system at a cost of

$0.698/kWh. The power output from this 5 kW PV system represents 31 % of

renewable energy contribution to the total power demand of the building. The simple

payback period is 32.5 years, which is greater than the system lifetime of 25 years

because of the low feed-in-tariffs for renewable energy projects in Fiji. Therefore, it

is not an economically viable investment to consider.

Economic analysis of the PV system was also done using the net present cost of

energy (NPC) analysis method, cost of energy (COE) and cost of energy levelized

(COEL) method which yielded $0.698/kWh, $0.64/kWh and $0.72/kWh

respectively. The unit costs of electricity from all the three economic analysis

methods are similar and almost double the cost of electricity supplied by the FEA. In

common with other renewable energy sources the cost of electricity generated from

the PV system is dominated by the capital cost of the system making it non-

competitive with the present conventional forms of electricity generation.

The PV array designed has 7 modules in series and 4 parallel strings, occupying total

roof area of 36 m2. The weight of these 28 modules would be 420 kg i.e. 11.67 kg/m2.

Thus, the C block can withstand this weight as well as the additional weight of other

mounting structures. The solar panels will be facing north and mounted at 180 tilt to

optimise the use of available solar resource and also to control the economic costs

associated with maintenance of tracking mechanisms.

82

Finally, one of the major obstacles affecting the progress in the use of renewable

resources for power generation is the high capital costs of the technologies despite it

being available without any duty charges in Fiji. However, with the technological

advances of PV systems coupled with the escalating fossil fuel prices, grid tied PV

systems are becoming increasingly viable option for electricity generation. Thus, as

the era of cheap oil draws to a close with the global need to reduce carbon emissions,

other energy options must be developed which are sustainable and have minimum

ecological impact.

8.2 Recommendations

From the design and techno-economic analysis undertaken, the researcher

recommends that the implementation of grid connected PV systems should be

genuinely pursued in Fiji and research needs to be done on the electrical effects of

connecting small power producers directly to the FEA grid. It is also recommended

that further research be done on the introduction of feed-in tariffs and its impact on

the energy sector in Fiji.

83

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APPENDIX PVSYST Array Designs

Tenesol Inverter