wind energy ghana projetc msc

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PROSPECTS FOR THE APPLICATION OF LOW WIND SPEED

TURBINES FOR RURAL ELECTRIFICATION IN GHANA

By

Frederick Kenneth Appiah, BSc. Mech. Eng. (Hons.)

MASTER OF SCIENCE IN MECHANICAL ENGINEERING

Faculty of Agricultural and Mechanical Engineering

College of Engineering

Frederick Kenneth Appiah

September 2005


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PROSPECTS FOR THE APPLICATION OF LOW WIND SPEED

TURBINES FOR RURAL ELECTRIFICATION IN GHANA

By

Frederick Kenneth Appiah, BSc. Mech. Eng. (Hons.)

A Thesis submitted to the School of Graduate Studies, Kwame Nkrumah

University of Science and Technology, in partial fulfilment of the requirements for

the award of the degree of

MASTER OF SCIENCE IN MECHANICAL ENGINEERING

Faculty of Agricultural and Mechanical Engineering

College of Engineering

September 2005


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DECLARATION

I hereby declare that this submission is my own work towards the MSc and that,

to the best of my knowledge, it contains no material previously published by

another person nor material which has been accepted for the award of any other

degree of the University, except where due acknowledgement has been made in

the text.

APPIAH, FREDERICK KENNETH ...(Student ID No. 36804-03)

Certified by:

DR. JEROME ANTONIO ..... ...Supervisor

DR. FRANCIS K. FORSON .... ...Head of Department of Mechanical Engineering


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DEDICATION

In remembrance of my only brother who died less than a year of existence on earth, I

dedicate this work to Benjamin Appiah. May his soul rest in the bosom of the Almighty.


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ABSTRACT

Recent studies on wind resource in Ghana by Energy Commission and other bodies

indicate that there exists moderate wind resource potential in Ghana which could be

exploited for small wind applications, especially in the remote/rural areas where there

exist more than 46% of the countrys households without electricity.

This thesis assesses the prospects for the application of low wind speed turbine

technology in Ghana. Ghana has moderate wind speeds, especially, some areas along

the coast, of 4.8 to 5.5 m/s at 12 m a.g.l., that are suitable for small wind turbine

applications. It was observed that small wind turbines are mostly used in low wind

speed regimes because small wind turbines have the characteristics of starting at lowwind speed, thereby, extracting power from low speeds. The cut-in wind speed is

generally 3 m/s.

A wind energy project, Power to the Poor in Ghana project, is taken as a case study.

Data is collected and analysed both technically and economically with RETScreen and

Wind Energy Payback Workbook. The case study analysed revealed that the application

of the small wind turbine is mostly for lighting and powering of refrigerators,

computers, televisions, radio/cassette players, ceiling fans, and commercial battery

charging among other uses. In the economic evaluation, the annual worth and the unit

cost of electricity generation from imported and locally-made wind turbines are

analysed, and compared with solar photovoltaic and petrol generator, as alternative

sources for rural electrification. The levelised energy costs of electricity are $0.83,

$1.89, $0.86, $0.77 per kWh for solar PV, petrol generator, imported and locally-made

wind turbine, respectively. The unit cost of electricity, though very high for an average

peasant farmer and fisherman, can be a competitive option to grid connection which

cost between $0.32 and $0.79/kWh through a distance of 5 to 10 km.

The unit cost of a community project scenario is $0.1262 per kWh. However, it is noted

that, the community project will be economically viable if the avoided cost of energy is

at least $0.112/kWh. A hybrid system can be a better viable option, which should be

researched into.


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TABLE OF CONTENT

DECLARATION ........................................................................................................................ ii

DEDICATION ........................................................................................................................... iii

ABSTRACT

................................................................................................................................ iv

TABLE OF CONTENT .............................................................................................................. v

LIST OF APPENDICES ......................................................................................................... viii

LIST OF TABLES ..................................................................................................................... ix

LIST OF FIGURES ................................................................................................................... xi

SYMBOLS AND ABBREVIATIONS .................................................................................... xiv

ACKNOWLEDGEMENT ....................................................................................................... xvi

CHAPTER ONE ......................................................................................................................... 1

INTRODUCTION ........................................................................................................................ 11.1 BACKGROUND ..................................................................................................................... 1

1.1.1 Global Trend of Wind Energy ............................................................................................. 11.1.2 Energy Demand in Ghana ................................................................................................... 21.1.3 Schemes in place ................................................................................................................. 21.1.4 Wind as an Alternative Source ............................................................................................ 3

1.2 OBJECTIVESOFTHESIS .................................................................................................... 31.3 JUSTIFICATIONFOROBJECTIVES ................................................................ ................ 41.4 ORGANISATIONOFTHESIS ............................................................................................. 5

CHAPTER TWO ........................................................................................................................ 6

THEORETICAL FRAMEWORK ............................................................................................... 6

2.1 CHARACTERISTICSOFWIND ......................................................................................... 62.2 WINDRESOURCE ................................................................................................................ 6

2.2.1 Evaluation of Wind Resource .............................................................................................. 62.2.2 Classification of Wind Resource ......................................................................................... 72.2.3 Ghana Wind Resource Assessment ......................................................................... ............ 8

2.3 ENERGYINTHEWIND ....................................................................................................... 82.3.1 Lift and Drag Principle of Wind Energy Conversion .......................................................... 82.3.2 Blade Design ....................................................................................................................... 92.3.3 Small Wind Turbines for Low Wind Speed Regimes ......................................................... 162.3.4 Power in the Wind ............................................................................................................. 162.3.5 Available Power ................................................................................................................ 17

2.4 SMALLWINDTURBINETECHNOLOGY ...................................................................... 172.5 CLASSIFICATIONOFWINDTURBINE ................................................................ ......... 18

2.5.1 Rated Power Classification ............................................................................................... 182.5.2 Swept Area Classification ................................................................................................. 18

2.6 TYPESOFSMALLWINDTURBINE .................................................................. ............. 182.6.1 Horizontal Axis Wind Turbine (HAWT) ................................................................ ............ 182.6.2 Vertical Axis Wind Turbine (VAWT) ...................................................................... ........... 192.6.3 Modern Model ................................................................................................................... 20

2.7 TECHNICALCHARACTERISTICSOFSMALLWINDTURBINES ........................... 202.7.1 Power and Energy Curves ................................................................................................ 202.7.2 Power rating ..................................................................................................................... 212.7.3 Starting Torque ................................................................................................................. 212.7.4 Blade Radius ..................................................................................................................... 212.7.5 Capacity Factors/Efficiency .............................................................................................. 222.7.6 The Number of Blades ....................................................................................................... 23

2.7.7 Tip Speed ........................................................................................................................... 242.7.8 Operational Speeds ........................................................................................................... 25


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2.7.9 Pitch and Yaw Adjustment ................................................................................................ 252.7.10 Solidity .............................................................................................................................. 25

2.8 MATERIALS ........................................................................................................................ 26

CHAPTER THREE .................................................................................................................. 28

METHODOLOGY ..................................................................................................................... 28

3.1 SITESVISITANDDATACOLLECTION ................................................................ ........ 283.2 TECHNICALPARAMETERS ............................................................................................ 28

3.2.1 Energy Consumption ......................................................................................................... 283.2.2 Rated Power of Turbine .................................................................................................... 283.2.3 Daily Operating Hours ..................................................................................................... 29

3.3 ECONOMICANALYSISOFSMALLWINDTURBINE ................................................. 293.3.1 Cost Analysis of Small Wind Turbines ................................................................ .............. 293.3.2 Economic Indicators ......................................................................................................... 30

3.4 RENEWABLEENERGYTECHNOLOGY(RET)SIMULATOR .................................. 333.4.1 RETScreen Wind Energy Project Model ................................................................ ........... 343.4.2 Wind Energy Payback Period Workbook (v1.0) ............................................................... 353.4.3 Constraints and Limitations .............................................................................................. 35

CHAPTER FOUR ..................................................................................................................... 36

APPLICATIONS OF SMALL WIND TURBINES IN GHANA ............................................. 36

4.1 TYPICALAPPLICATIONOFSMALLWINDTURBINES ............................................ 364.2 WATERPUMPING .............................................................................................................. 37

4.2.1 Direct Coupling/Mechanical Pumping ................................................................ ............. 374.2.2 Electric Pumping .............................................................................................................. 38

4.3 OTHERAPPLICATIONS ................................................................................................... 394.3.1 Stand-Alone System ........................................................................................................... 394.3.2 Hybrid System ................................................................................................................... 394.3.3 Grid-Connected System ..................................................................................................... 40

4.4 SPECIFICAPPLICATIONINGHANA ................................................................ ............ 404.4.1

Commercial (DENG Ltd.)

................................................................................................. 40

4.4.2 Private Residence .............................................................................................................. 414.4.3 Power to the Poor in Ghana Project ...................................................................... ........... 42

4.5 POWERTOTHEPOORINGHANAPROJECT ............................................................. 434.5.1 Background and Objective ................................................................................................ 434.5.2 Project Sites ...................................................................................................................... 444.5.3 Residential House ............................................................................................................. 444.5.4 Salt Production Unit ......................................................................................................... 454.5.5 Primary School ................................................................................................................. 464.5.6 Research Centre ................................................................................................................ 474.5.7 Battery Charging Centre ................................................................................................... 484.5.8 Chief Palace and Pub ....................................................................................................... 484.5.9 Church .............................................................................................................................. 48

4.5.10 Battery Charging Centre & Pastors Residence ............................................................... 494.5.11 Residential House ............................................................................................................. 494.5.12 Beach Resort ..................................................................................................................... 50

4.6 TECHNICALDATAOFTHEIMPORTEDWINDTURBINEANDLOCALLY-MADEWINDTURBINE .................................................................................................................. 51

CHAPTER FIVE ...................................................................................................................... 52

VIABILITY OF VARIOUS SMALL WIND TURBINE APPLICATIONS ............................. 52

5.1 DATATAKEN ...................................................................................................................... 525.1.1 Analysis of Data ................................................................................................................ 525.1.2 Energy Consumption ......................................................................................................... 55

5.2 PERFORMANCEOFSYSTEM .......................................................................................... 555.2.1 Wind Speed ........................................................................................................................ 555.2.2 Performance of a Wind Turbine Technology ................................................................... . 56


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5.3 ECONOMICANALYSISOFPOWERTOTHEPOORINGHANAPROJECT ....... 635.3.1 Cost Analysis ..................................................................................................................... 645.1.2 Annual Worth .................................................................................................................... 645.1.3 Levelised Energy Cost of Electricity ...................................................................... ........... 675.3.2 Affordability ...................................................................................................................... 705.3.3 Sensitivity Analysis ............................................................................................................ 71

5.4 COMMUNITYELECTRIFICATIONPROJECT ............................................................ 735.4.1 Energy Consumption and Required Wind Turbine ........................................................... 735.4.2 Life Cycle Cost Analysis ................................................................................................... 755.4.3 Economic Analysis ............................................................................................................ 765.4.4 Environmental Benefits ..................................................................................................... 785.4.5 Analysis of Scenario .......................................................................................................... 78

CHAPTER SIX ......................................................................................................................... 82

CONCLUSION AND RECOMMENDATIONS ....................................................................... 82

6.1 CONCLUSION ..................................................................................................................... 826.2 RECOMMENDATIONS ...................................................................................................... 83

REFERENCES .......................................................................................................................... 85

APPENDICES ........................................................................................................................... 90


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LIST OF APPENDICES

Appendix A: Technical Characteristics and Application of Small Wind Turbines in

Ghana.............................................................................................................. 90

Appendix B: Energy Consumption for the Sites Under the "Power to the Poor in Ghana"

Project............................................................................................................. 94

Appendix C: Data Taken from Taxe and Kpenu Sites.................................................... 99

Appendix D: Cost Analyses of the Power to the Poor in Ghana Project .................. 105

Appendix E: Sensitivity Analyses ................................................................................ 107


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LIST OF TABLES

Table 2.1: Beaufort Scale showing different Scales of Wind ........................................... 6

Table 2.2: Classes of Wind Power Density and Wind Speeds at 10m and 50m ............... 7

Table 2.3: Classification of Wind Turbines and typical Dimensions ............................. 18

Table 2.4: The Dependence of Important Parameters on Blade Radius ......................... 22

Table 2.5: Net Capacity Factors for Various Classes of Wind Speeds at 10 m and 50 m

........................................................................................................................ 23

Table 2.6: Technical Characteristics of Horizontal and Vertical Small Wind Turbines26

Table 2.7: Proportion of Materials used for the Components of Wind Turbines ........... 27

Table 4.1: Specifications of Imported and Locally-made Wind Turbines...................... 51

Table 4.2: Energy Output of Locally-made Wind Turbine............................................. 51

Table 5.1: Wind Generator Average Daily Operating Hours ......................................... 52

Table 5.2: General relationship between economic viability and wind speed ................ 56

Table 5.3: Evaluation of the Sites under Power to the Poor in Ghana Project............ 58

Table 5.4: Total Capital Cost of Imported and Locally-made Wind Generators............ 64

Table 5.5: Cost of Rural Electrification .......................................................................... 70

Table 5.6: Energy Consumption for Community Project Scenario ................................ 73

Table 5.7: Technical Characteristics of 50 kW Atlantic Orient AOC 15/50 Turbine .... 74

Table 5.8: Life Cycle Cost Analysis for Community Project ......................................... 75

Table 5.9: Economic Parameters and Assumption made................................................ 76

Table 5.10: Summary of Community Project Scenario .................................................. 77

Table 5.11: Summary of Economic Performance of Scenarios ...................................... 77

Table 5.12: Details of Cost Analysis .............................................................................. 79

Table A-1: Technical Characteristics and Application of Small Wind Turbines in Ghana

........................................................................................................................ 90Table B-1: Energy Consumption for the Sites under Power to the Poor in Ghana

Project............................................................................................................. 94

Table C-1: Data from a Residential House at Taxe-Anloga for March 2005 ................. 99

Table C-2: Data from a Residential House at Taxe-Anloga for April 2005................. 101

Table C-3: Data from Kpenu Primary School for March 2005 .................................... 102

Table C-4: Data from Kpenu Primary School for April 2005 ...................................... 104

Table D-1: Organization of the Excel Worksheet used for the Energy Generation Cost

Estimate ........................................................................................................ 105


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Table E-1: Unit Cost of Electricity Variation with Discount Rate ............................... 107

Table E-2: Percentage Change in Unit Cost of Electricity at Different Discount Rates

...................................................................................................................... 107

Table E-3: Unit Cost of Electricity Variation with Specific Investment ...................... 107

Table E-4: Percentage Change in Unit Cost of Electricity at Different Discount Rates

...................................................................................................................... 108

Table E-5: Unit Cost of Electricity Variation with Average Daily Load ..................... 108

Table E-6: Percentage Change in Unit Cost of Electricity at Different Average Daily

Loads ............................................................................................................ 108


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LIST OF FIGURES

Fig. 2.1: Lift and Drag acting on a Turbine Blade ............................................................ 9

Fig. 2.2: Force Diagram of Forces acting on the Blade of a Wind Turbine ................... 10

Fig. 2.3: LIFT versus Angle of Attack............................................................................ 11

Fig. 2.4: Blade section showing the variation of the Blade Setting Angle at different

Stations ........................................................................................................... 12

Fig. 2.5: Variation of Chord Width along the span of the blade..................................... 13

Fig. 2.6: Blade Twist and Chord Distribution of the Blade ............................................ 14

Fig. 2.7: Lift and Drag at High Incidence ....................................................................... 14

Fig. 2.8: Chord-pitch Integral for two Blades ................................................................. 15

Fig. 2.9: A graph of Speed and Power Output with a range of Rotor Sizes ................... 16

Fig. 2.10: Horizontal Axis Wind Turbines ..................................................................... 19

Fig. 2.11: Vertical Axis Wind Turbines.......................................................................... 19

Fig. 2.12: Spiral Blade Horizontal Axis Wind Turbine .................................................. 20

Fig. 2.13: The Power and Energy Curve of a 10 kW Wind Turbine .............................. 21

Fig. 2.14: Coefficient of Performance of Wind Turbine ................................................ 23

Fig. 2.15: Effect of Tip Speed Ratio and Lift/Drag on the Performance of the Blade ... 24

Fig. 4.1: A Boat powered by AIR X marine Wind Turbine ........................................... 36

Fig. 4.2: Recreational Vehicles powered by Small Wind Turbines................................ 37

Fig. 4.3: Diaphragm windpump being used for Irrigation .............................................. 38

Fig. 4.4: Whisper H40 mounted on top of DENG building ............................................ 41

Fig. 4.5: A Small Wind Turbine mounted in front of a residence at Anlo ..................... 41

Fig. 4.6: Bergey XL 1 mounted at a Residence at Taxe ................................................. 45

Fig. 4.7: Locally-made Wind Turbine mounted at a Salt production unit ...................... 46

Fig. 4.8: Bergey XL 1 mounted at Kpenu Primary School ............................................. 46Fig. 4.9: Primary School Children and community members watching a Television

powered by the Wind Turbine ........................................................................ 47

Fig. 4.10: A Locally-made Wind Turbine mounted at Institute of Industrial Research

(IIR), CSIR, Accra.......................................................................................... 47

Fig. 4.11: A Computer with Internet Facility being powered by the Wind Turbine at IIR,

CSIR, Accra.................................................................................................... 48

Fig. 4.12: The Beneficiary enjoying clean Lighting and TV at his Residence ............... 49

Fig. 4.13: 1 kW Bergey XL1 mounted at Tobloku for Residential use .......................... 50


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Fig. 5.1: Variation of Voltage at Residential House at Taxe for March 05................... 53

Fig. 5.2: Variation of Voltage at Residential House at Taxe for April 05..................... 53

Fig. 5.3: Variation of Voltage at Kpenu Primary School for March 05 ........................ 54

Fig. 5.4: Variation of Voltage at Kpenu Primary School for April 05 .......................... 54

Fig. 5.5: Daily Average Energy Consumption for various Sites .................................... 55

Fig. 5.6: Total Capital Cost for Solar PV, Petrol Generator and Imported and Locally-

made Wind Turbines ...................................................................................... 64

Fig. 5.7: Total Life Cycle Cost for Solar PV, Petrol Generator and Imported and

Locally-made Wind Turbines......................................................................... 65

Fig. 5.8: Life Cycle O&M Cost for Solar PV, Petrol Generator and Imported and


Fig. 5.9: Annualised Life Cycle Cost of Solar PV, Petrol Generator, Imported and


Fig. 5.10: Annualised Capital Cost of Solar PV, Petrol Generator, Imported and


Fig. 5.11: Annualised O&M Cost of Solar PV, Petrol Generator, Imported and


Fig. 5.12: Monthly O&M and Replacement Cost of Solar PV, Petrol Generator,

Imported and Locally-made Wind Turbines .................................................. 67

Fig. 5.13: Annualised Replacement Cost of Solar PV, Petrol Generator, Imported and


Fig. 5.14: Comparative Levelised Energy Cost of Electricity from Solar PV, Petrol

Generator, Wind Turbines and Hydro (Grid) ................................................. 68

Fig. 5.15: Variation of Levelised Energy Cost within the 20 years Period of Analyses

for Solar PV, Petrol Generator and Imported and Locally-made Wind

Turbines .......................................................................................................... 69

Fig. 5.16: Cost Analysis for Supplying 50 kW Electricity to Rural Areas ..................... 70

Fig. 5.17: Sensitivity Results of Discount Rate Variations ............................................ 71

Fig. 5.18: Sensitivity Results of Specific Investment Variations ................................... 72

Fig. 5.19: Sensitivity Results of Average Daily Load Variations................................... 72

Fig. 5.20: Power and Energy Curve for 50 kW Atlantic Orient AOC 15/50 Wind

Turbine ........................................................................................................... 74

Fig. 5.21: Variation of Simple Payback Period with Avoided Cost of Electricity ......... 80Fig. 5.22: Variation of NPV with Avoided Cost of Electricity ...................................... 80


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Fig. 5.23: Variation of IRR with Avoided Cost of Electricity........................................ 81


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SYMBOLS AND ABBREVIATIONS

Amph Ampere hourAmps Amperesft FeetHz Hertzkg Kilogramkm KilometrekW KilowattkWh Kilowatt hourkWh/yr Kilowatt hour per yearlit. Litrem Metrem/s Metre per secondmph Miles per hour

MW MegawattR Radiusrpm Revolution per minuteV VoltsW WattW/m2 Watt per square metrei Inflation Rated Discount Rate

f Discount Factor

a Annualization Factor

n Period of Analyses

t Period of Replacementv Velocity

w Present Wortha.g.l. Above ground levelAC Alternating CurrentADB Asian Development BankB/W Black and WhiteCSIR Council for Scientific and Industrial ResearchDC Direct CurrentDNV Det Norske VeritasEC Energy CommissionEq. EquationEWW Enterprise Works WorldwideGMT Greenwich Mean TimeHAWT Horizontal Axis Wind TurbineIIR Institute of Industrial Research, CSIRKNUST Kwame Nkrumah University of Science and TechnologyLtd. LimitedMOE Ministry of EnergyMOFA Ministry of Food and AgricultureMSD Meteorological Service Department

NES National Electrification SchemeNREL National Renewable Energy Laboratory


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pcs. PiecesPM Permanent MagnetPV PhotovoltaicPWF Present Worth Factor

Re Reynolds Number

REES Rural Energy and Environment SystemsRep. ReplacementRET Renewable Energy TechnologySHEP Self-Help Electrification ProgramSNEP Strategic National Energy PlanSWERA Solar and Wind Energy Resource AssessmentTCC Total Capital CostTSR Tip Speed RatioTV TelevisionUSA United States of AmericaVAWT Vertical Axis Wind Turbine

VRA Volta River AuthorityWAsP Wind Atlas Analysis and Application Program


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ACKNOWLEDGEMENT

With heartfelt gratitude and appreciation I wish to acknowledge the immense

contribution, correction and motivation of my supervisor, Dr. Jerome Antonio, Senior

Lecturer, Mechanical Engineering Department, Kwame Nkrumah University of Science

and Technology, Kumasi, Ghana.

I also want to thank Prof. Fred Ohene Akuffo, Dr. D. M. Obeng, Dr. L. E. Ansong, Dr.

Francis K. Forson and Dr. Owusu-Achaw for investing in my education during my

second degree studies.

I wish to acknowledge the help from Mr. Wisdom Ahiataku-Togobo, Director, Rural

Energy and Environment Systems (REES), and also the Head-Renewable Energy,

Ministry of Energy, Dr. E. B. Hagan and Mr. Joseph Dzanie of the Institute of Industrial

Research (IIR) of the Council for Scientific and Industrial Research (CSIR), Mr. Atsu

Tittiati, Mr. Seth Agbeve and Mrs. Wilhemina Quaye of Enterprise Works Ghana and

Mr. Matt Knack-Baiden of Solarwinds Engineering Services.

My research fellows and roommates are not left out. S. O. Frimpong, Daniel Ofori

Dankyi and Kuanda Chiyembekeso, and Mr. Michael Awuah-Baah, Godsway Kwasi

Dzoboku and Timothy Adjettey; thanks for the love. I also appreciate all the persons

who directly or indirectly helped me to accomplish this research work.

Last but not the least, to my father, Uncle Kwesi Essuman, my mother, Auntie Joe and

my dear sisters, Mrs. Celestina Adusah-Poku, Irene Appiah and Rosetta Appiah. Thanks

for the unflinching financial and moral support. I can not measure.

I wish you all Gods blessings. May you live long to enjoy the fruit of your labour.

APPIAH, FREDERICK KENNETH

August, 2005


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CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND

1.1.1 Global Trend of Wind Energy

Wind Energy is the worlds fastest growing source of energy because of its economic

and environmental characteristics. Modern wind turbines are fuelling wind energys

current renaissance. The cost of production and generating power has been declining

and, in many applications, wind is already competitive with conventional options for

generating electricity. Wind technology also produces electricity without creating airpollution, water pollution, greenhouse gases, or hazardous wastes. The global wind

energy industry has shown an average cumulative growth of 29% over the past six

years. Total power production as at 2004 stood at 47,616 MW, a 20% increment over

the previous year [Global Wind Energy Council, 2005].

The global trend shows governments and institutions are going into assessment,

technical analysis, manufacturing techniques and economic feasibility of the

technology. Countries which benefit much from such technology for large scale

application, like electricity production, have substantial amount of wind speed, with

annual average wind speeds ranging from 6 to 8 m/s at 12 m a.g.l.

Another development in the wind energy sector is the small wind energy conversion

systems suitable for low wind speed regimes. Small wind turbines have been developed

for various applications in the rural and urban environment. Remote communities,

school and clinics derive much benefit from such application. Urban application ismuch focused on grid connection to supplement the energy from the utility providers.

Small wind turbine technology has been expanding. There are currently over 150,000

small-scale renewable energy systems in United States of America and they are growing

by 30% yearly. The small-scale use of wind power is growing at twice that amount--

over 60% per year [Gipe, 2003]. There are also more than 50 manufacturers of small

wind turbines worldwide producing over 100 different models. Altogether

manufacturers in western countries have built about 60,000 small wind turbines during


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the last two decades. And tens of thousands more have been manufactured in China for

use by nomads on the Mongolian steppes [Jones, 1999].

1.1.2 Energy Demand in Ghana

In the year 2000, 6777 GWh of electricity was consumed constituting about 11% of the

total energy consumed in the country. Household electricity consumption also increased

from 688.03 GWh in 1990 at an average annual growth rate of 11% to 2373.8 GWh in

2000, and further increased to about 3250 GWh in 2003. Out of this, rural household

consumed a meagre 123.6 GWh of electricity in 2000 which accounted for 5.2% of total

household consumption. Ghanas electricity supply is mainly obtained from hydro and

thermal sources. Ghana also relies on some level of imports from neighbouring La Cote

d'Ivoire to supplement domestic supply especially during peak hours. The existing

installed electricity generation capacity is 1,652 MW made up of 1,072 MW of hydro

and 550 MW of thermal. In addition to these, there is a 30 MW diesel plant at Tema,

which is currently operated only during contingencies [Asante, 2004].

The electricity supply mix in the country is expected to change by the year 2010 from

the largely hydro-based system to a largely thermal-based one relying on natural gas as

the main source of fuel. This transition would be made possible by the West African

Gas Pipeline Project, which is expected to transport natural gas from Nigeria through

Benin and Togo to Ghana [Asante, 2004].

1.1.3 Schemes in place

Effort has been made and various schemes structured by governmental agencies and

institutions to ensure that electricity supply covers all parts of the country over a 30-

year period from 1990-2020 [Asante, 2004]. Schemes like the National ElectrificationScheme (NES) and Self-Help Electrification Program (SHEP) have been introduced to

stimulate and promote economic activities and raise the standard of living of people.

Though 2,900 communities were linked to the national grid between 1989 and 2000 and

a total of 1,179 communities connected between 2001 and 2004, there exist 46% of the

households which do not have access to electricity [Asante, 2004].

Although schemes like the NES and SHEP are put into place to ensure that the whole

country had access to electricity by 2020, renewable energy experts foresee that it


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would be unlikely that all communities be connected by 2020 if electricity supply is

based on grid extension only.

1.1.4 Wind as an Alternative Source

Most of the communities which do not have access to electricity are far away from the

electricity grid and therefore the development and application of renewable energy

technologies, especially, wind generating technologies, can play an important role to

alleviate poverty as well as promote economic and small business activities in these

areas.

Though Ghana has low wind speeds throughout the country, the annual average wind

speed for the identified potential sites ranges from 4.8 to 5.5 m/s at 12 m a.g.l. [Energy

Commission, Ghana, 2003], which is suitable for power generation, especially, with low

wind speed machines.

1.2 OBJECTIVES OF THESIS

The main objective of this research is to explore small wind turbine technology and

assess the prospects for application of the technology in Ghana.

The specific objectives are as follows:

1. To explore the design and performance characteristics of low wind speed turbine

technology.

2. To explore the application of low wind speed turbines in rural environment in

Ghana.

3. Assess the performance of existing small wind turbine applications.

4. With the aid of a Renewable Energy Technology (RET) simulator, assess the

economic viability of various small wind energy technology applications in

Ghana.


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1.3 JUSTIFICATION FOR OBJECTIVES

Over the years, much concentration and analysis have been on power generation to

supplement the national grid in Ghana.Recent studies by the Energy Commission (EC)

of Ghana and other private concerns at potential sites indicate that the monthly average

wind speed measurement at 12 m a.g.l. varies in the range of 4.8 to 5.5 m/s [Energy

Commission, Ghana, 2003]. Assessment tools such as RETScreen software (which is

used for preliminary evaluation of renewable energy projects) also suggest that sites

with wind speeds less than 5 m/s are not likely to be economically viable [Nkrumah,

2003].

In order to achieve its vision that the whole country has access to electricity by 2020,the Ghana Government has recently initiated programmes and structures to promote

Small Wind Energy Technology, which is suitable for low wind speed regimes, as an

alternative to the traditional hydro and thermal electricity sources. These programmes

are geared towards poverty reduction and energy conservation across the country.

1. The Ministry of Energy in 2004 launched a wind energy project dubbed, Wind

Power to the Poor in Ghana. The projects target was existing businesses or well-

run private service providers in isolated, low-income communities. Under the

programme, 17 local artisans were trained to build 500 W capacity wind turbines

from materials available on the local market. The trained artisans were to build

and install 10 turbines to demonstrate the feasibility of wind-generated electricity

at selected sites across the country [Gobah & Taylor-Amoah, 2004, p. 27].

2. The Ministry of Agriculture also has initiated wind pump installation projects for

water supply for agriculture, livestock and human consumption. It was anticipatedthat about 30 wind pumps would be installed throughout the country by the end of

the year 2004, but ultimately, the number increased to 50 [Yeboah, 2004, p. 27].

However, only limited work has been done in Ghana on the exploitation of Small Wind

Energy Conversion Systems, and thus there is the need to investigate the prospect and

its viability in low wind speed regimes like Ghana.


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This thesis, thus, focuses on the technical and economic viability of the small wind

energy conversion system and its relevant application in Ghana.

1.4 ORGANISATION OF THESIS

The first chapter of this thesis gives the background to the thesis, including the growth

in wind energy technology, the energy trend in Ghana and the role of small wind turbine

technology for rural development. The chapter also introduces the objectives of the

project and the significance of the study.

The theoretical framework which deals with the design of small wind turbines and its

underlining principles is the focus in the second chapter. Wind characteristics and

resource in Ghana are also reviewed. Various types of wind turbines are classified and

their characteristics described, but the focus is on small wind turbines from various

manufacturers. The economic principles and the Renewable Energy Technology

software used for economic analysis are also discussed.

The third chapter deals with the methodology used for this thesis

The fourth chapter describes various small wind turbine applications both in the urban

and rural environment. A wind energy project currently running in Ghana is taken as a

case study and its application assessed.

In the fifth chapter of this thesis, the viability of small wind turbine applications is

discussed. The focus is mainly on the economic analysis of the case study. Other

scenarios are created and their economic viability analysed.

The conclusions and recommendations are given in Chapter Six.


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CHAPTER TWO

THEORETICAL FRAMEWORK

2.1 CHARACTERISTICS OF WIND

The different scales of wind have been described by the Beaufort scale in Table 2.1.

Low wind speed can be said to be of Beaufort Scale 3 and below.

Table 2.1: Beaufort Scale showing different Scales of Wind

BEAUFORT SCALE OF WIND FORCE @ 10m a.g.l.

Scale Rating miles/h km/h m/s knot

0 Calm 1 1.6 0.45 0.87

1 Light Air 1 - 3 1.6 - 5 0.45 - 1.34 0.87 - 2.61

2 Light Breeze 4 - 7 6 - 11 1.79 - 3.13 3.48 - 6.08

3 Gentle Breeze 8 - 12 13 - 19 3.58 - 5.36 6.95 - 10.43

4 Moderate Breeze 13 - 18 21 - 29 5.81 - 8.05 11.30 - 15.64

5 Fresh Breeze 19 - 24 31 - 39 8.49 - 10.73 16.51 - 20.86

6 Strong Breeze 25 - 31 40 - 50 11.18 - 13.86 21.73 - 26.94

7 Moderate Gale 32 - 38 51 - 61 14.30 - 16.99 27.81 - 33.02

8 Fresh Gale 39 - 46 63 - 74 17.43 - 20.56 33.89 - 39.97

9 Strong Gale 47 - 54 76 - 87 21.01 - 24.14 40.84 - 46.93

10 Whole Gale 55 - 63 89 - 101 24.59 - 28.16 47.80 - 54.75

11 Storm 64 - 75 103 - 121 28.61 - 33.53 55.62 - 65.18

12 Hurricane 76+ 122+ 33.97+ 66.04+

Source: Beaufort Scale, www.galeforce.nireland.co.uk

2.2 WIND RESOURCE

2.2.1 Evaluation of Wind Resource

Evaluation of wind resource data at a site is essential since it is the first step in assessing

the potential for wind power and projecting turbine performance at that particular site of

interest. The energy available in a wind stream is proportional to the cube of its speed,

which means that doubling the wind speed increases the available energy by a factor of


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eight. Furthermore, the wind resource itself is seldom a steady, consistent flow. It varies

with the time of day, season, height above ground, and type of terrain. Places near the

coast usually have higher wind speeds than those inland; the wind speed 100 km inland

is around two-thirds of the wind speed near the coast [Hulscher & Fraenkel, 1994].

2.2.2 Classification of Wind Resource

There are several ways and parameters used for classifying wind resource.

a. Wind Power Class

Wind resources are often rated according to a Wind Power Class system which

corresponds to ranges of average wind speeds as shown in Table 2.2. Areas

designated Class 4 or greater are suitable for large-scale electricity generation withadvanced wind turbine technology. Power Class 3 areas may be suitable for large-

scale generation and are suitable for small-scale wind projects [Wind Resources].

b. Power Density

Wind Power Density is a useful way to evaluate the wind resource available at a

potential site. The wind power density, measured in watts per square meter,

indicates how much energy is available at the site for conversion by a wind turbine.

Classes of wind power density for two standard wind measurement heights are listed

in Table 2.2 below.

Table 2.2: Classes of Wind Power Density and Wind Speeds at 10m and 50m

Classes of Wind Power Density at 10 m and 50 m(a)

. 10 m (33 ft) 50 m (164 ft)

Wind PowerClass

Wind Power Density(W/m2)

Speed(b) m/s (mph) Wind Power

Density (W/m2)Speed(

b) m/s (mph)

1 < 100 < 4.4 (9.8) < 200 < 5.6 (12.5)

2 100 - 150 4.4 (9.8) / 5.1 (11.5) 200 - 300 5.6 (12.5) / 6.4 (14.3)

3 150 - 200 5.1 (11.5) / 5.6 (12.5) 300 - 400 6.4 (14.3) / 7.0 (15.7)

4 200 - 250 5.6 (12.5) / 6.0 (13.4) 400 - 500 7.0 (15.7) / 7.5 (16.8)

5 250 - 300 6.0 (13.4) / 6.4 (14.3) 500 - 600 7.5 (16.8) / 8.0 (17.9)

6 300 - 400 6.4 (14.3) / 7.0 (15.7) 600 - 800 8.0 (17.9) / 8.8 (19.7)

7 > 400 > 7.0 (15.7) > 800 > 8.8 (19.7)

(a) Vertical extrapolation of wind speed based on the 1/7 power law

(b) Mean wind speed is based on the Rayleigh speed distribution of equivalent wind power density. Windspeed is for standard sea-level conditions. To maintain the same power density, speed increases 3%/1000 m

(5%/5000 ft) of elevation. (from the Battelle Wind Energy Resource Atlas) www.awea.orgSource: Wind Energy Resource (1998), www.awea.org


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In general, sites with a Wind Power Class rating of 4 or higher are now preferred for

large scale wind plants. Research conducted by industry and governments is expanding

the applications of grid- connected wind technology to areas with more moderate wind

speeds.

2.2.3 Ghana Wind Resource Assessment

From 1989 up to date, many studies have gone into Wind Energy assessment in Ghana

by renewable energy analysts and groups of researchers. Data has been compiled and

analysed by researching institutions such as Meteorological Service Department (MSD),

Energy Commission (EC) and Mechanical Engineering Department of Kwame

Nkrumah University of Science and Technology (KNUST). It has been observed that

wind energy generation may be possible in some parts of the country, especially, along

the coast, as an alternate supplement to the hydro-electric power and for off-grid

applications. The monthly average wind speed for the identified potential sites along the

coast ranges from 4.8 to 5.5 m/s at 12 m a.g.l. [Energy Commission, Ghana, 2003].

2.3 ENERGY IN THE WIND

The suitability of wind turbines for low wind speed regime is its ability to extract power

at that low speed. Therefore, the lowest wind speed at which the wind turbine starts to

produce power is of much interest.

2.3.1 Lift and Drag Principle of Wind Energy Conversion

There are two primary physical principles by which energy can be extracted from the

wind; these are through the creation of either lift or drag force (or through a

combination of the two), which are defined by Equations (2.1) and (2.2).

( ) 22/aL

AVCForceLift = (2.1)

( ) 22/aD

AVCForceDrag = (2.2)


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where, CL and CD are the lift and drag coefficients, respectively, which depend on the

cross section of the blade and on the angle of attack , at which the wind

strikes the blade and the Reynolds number, a measure of the size and speed of

the blade. Vais the apparent wind speed through the rotor of an area A.

Fig. 2.1: Lift and Drag acting on a Turbine Blade

The blade acts as an aerofoil, therefore, as the wind passes over the blade it moves more

rapidly over one side of the blade causing unequal pressure. This unequal pressure

produces a lift which in turn causes the blade to spin.

One important condition to satisfy when extracting energy from the wind is the Betz

criterion which states that the maximum possible value of the aerodynamic efficiency is

achieved when the turbine reduces the wind speed to one-third of the undisturbed,

upstream wind [DNV/Ris, 2002].

2.3.2 Blade Design

To create the design of the blade the chord width of the blade C, and the blade setting

angle , at each of a series of stations along the span of the blade need to be specified.

At each station the right shape of the blade to produce the right lift to satisfy Betz

criterion is created using finite element analysis.

A diagram of the forces acting on the blade is shown in Figure 2.2.

Direction of rotation LIFT

Chord line

Direction of wind

DRAG Va


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Fig. 2.2: Force Diagram of Forces acting on the Blade of a Wind Turbine

Blade Angle, From Figure 2.2, += (2.3)

where, is the angle at which the apparent wind strikes the rotor plane

is the blade setting angle

is the angle of attack

To satisfy Betz condition, is chosen to optimize the lift force. A typical graph of Lift

vs. angle of attack ,is shown in Figure 2.3. As

increases, so does the lift, until a

point is reached where the blade stalls. At stalling, lift fails and drag increases rapidly

because air flow separates from the back of blade. This principle is used to control the

blade from rotating beyond its allowable speed limit.

Real Wind= 2V/3 (For Betz Criterion)

Net Force

Lift Force

Apparent Wind= (r/R)V/ cos

Head Wind

= (r/R)V

Thrust Force= LIFT cos + DRAG sin

Drag Force

Driving Force= LIFT sin - DRAG cos

Wind Direction

Direction of Rotation

Chord line


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Fig. 2.3: LIFT versus Angle of Attack

The key to wind turbine performance is the ratio of the lift to drag, rather than their

individual values. In practice, most sections will produce their best LIFT/DRAG at =5, so as a general rule, where detailed data is not available, can be set to give thisangle of attack. [Piggot, 2004b]

Thus,5= (2.4)

Because the head wind varies along the span of the rotor blade, also changes alongthe span of the rotor.

From Figure 2.2,)3/(2tan rR= (2.5)

Therefore,

( ) 53/2tan, 1 = rRAngleBlade (2.6)

This means that the ideal shape for the blade is twisted at each station of the blade, as

shown in Figure 2.4.


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Fig. 2.4: Blade Section showing the variation of the Blade Setting Angle at differentStations

Chord Width, C

From Figure 2.2, the basic blade element equations are derived.

cosDRAGsinLIFTForceDriving =

)/1( kcossinLIFT =

))2/3(1( kRrsinLIFT = (2.7)

where kis LIFT/DRAG Ratio

sinDRAGcosLIFTForceThrust += (2.8)

To satisfy Betz condition, the wind in each part of the swept area of the rotor must be

slowed down to 1/3 of its upstream velocity, and this slowing is done by the Thrust

force, which is closely related to the Lift force.

Neglecting Drag (very small error), Equation (2.8) becomes,

cosLIFTForceThrust =

Let us consider a blade element of thickness r .

To satisfy Betz condition,

22 )2()9/4()9/4( VrrAVForceThrust == (2.9)

Trailing e

Blade angle at different stations

Leading edge

DropThickness

Chord width, C

Leading edge


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And from Equation (2.1),

2)/)/(()2/( cosRrVrBCCForceLift L = (2.10)

where C is the chord widthB is the number of blades

This leads to an approximate expression for the chord width C, which will produce the

right amount of thrust to meet the Betz condition:

( )B

rRRCWidthChord

29

/16,

= (2.11)

It should be noted that both CL and cos were assumed to be approximately one for

simplicity, and Equation (2.11) works best for the outer part of the blade. Figure 2.5

shows the chord width at different stations along the span of the blade.

Fig. 2.5: Variation of Chord Width along the Span of the Blade

A characteristic design curve of a three-bladed turbine to operate at a tip speed ratio of

10 is shown in Figure 2.9.

Leading edge

C

Trailing edgeStations

Chord width at different stations


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Blade Twist and Chord Distributions at =10;B=3

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.05 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

r/R

C/R

-10

0

10

20

30

40

50

60

(deg)

C/R

= 10B = 3

Fig. 2.6: Blade Twist and Chord Distribution of the Blade

Cut-in Wind Speed, UC

From the force diagram, the generated torque on each blade element is,

cosDRAGsinLIFTForceDriving =

Therefore, RcosCsin(CVBCTorqueDrivingDL

2

r )21 =

A number of authors have proposed that the lift and drag properties of any aerofoil at

high can be approximated by equations of the type [Wood, 2002]:

cos2sinCL = (2.12)

and

2D 2sinC = (2.13)

Figure 2.7 shows variation of lift and drag with the angle of attack .

Lift and Drag at High Incidence

0

0.5

1

1.5

2

2.5

10 20 30 40 50 60 70 80 90Angle of Attack, (deg)

Cl,Cd

Cl

Cd

Fig. 2.7: Lift and Drag at High Incidence


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Equations (2.12) and (2.13) are seen to be good fits to the data when is larger than

45, which is the range of interest for starting blades.

Small wind turbines use permanent magnet (PM) generators that have an open circuit

resistive torque that is lower than the static torque for all values of rotational speed r,

that would be expected during starting. This significant resistive torque must be

overcome aerodynamically before the blades will start turning. In the final analysis, it is

assumed that torque equals the resistive torque of the generator (T=TR). Turbines start

only when the aerodynamic torque generated on the stationary blades exceeds the

resistive torque in the generator.

21

3

2,

=

CP

R

CIRB

TUSpeedWindinCut

(2.14)

where ICP is the chord-pitch integral

Equation (2.14) is the main result of this analysis. The integrand iCP of the chord-pitch

integral performed for two wind turbines blades is shown in Figure 2.8. I CPis 2.36 x 10-

3 for the 2.5 m blades and 6.22 x 10-3 for the smaller blades.

Fig. 2.8: Chord-pitch Integral for two Blades


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2.3.3 Small Wind Turbines for Low Wind Speed Regimes

It is observed that the smaller unit has a better starting performance but this is achieved

at the expense of its power coefficient. Thus, smaller wind turbines operate well even at

very low wind speeds, though they have low power output performance as shown in

Figure 2.9.

A desirable cut-in speed generally used is 3m/s. Furthermore, the lower the wind speed

at which the blades start rotating, the sooner power will be extracted as the wind

increases. Starting is also improved by using lightweight blades to minimize the

rotational moment of inertia of the turbine. This has the possible disadvantage of

increasing the difficulty of preventing the blades from over-speeding in high winds. In

other words, a turbine that starts easily may be difficult to control in high winds.

Fig. 2.8: A Graph of Speed and Power Output with a Range of Rotor Sizes

2.3.4 Power in the Wind

The amount of kinetic energy which the wind transfers to the rotor depends on the rotor

area, the wind speed and the density of the air, which varies with altitude. The formula

used for calculating the power in the wind is shown below:

3

2

1VAP = (2.15)

where,P is power in watts (W)

= 5Rated speed = 12m/s


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is the air density in kilograms per cubic metre (1.2 kg/m3)

A is the swept rotor area in square metre (m2)V is the wind speed in metres per second (m/s)

The fact that the power is proportional to the cube of the wind speed is very significant.

It means that if the wind speed doubles then the power in the wind increases by a factor

of eight.

2.3.5 Available Power

Although the Equation (2.15) gives us the power in the wind, the actual power that we

can extract from the wind is significantly less than this figure suggests. The actual

power will depend on several factors, such as the type of machine and rotor used, the

sophistication of blade design, friction losses, and the losses in the pump or other

equipment connected to the wind machine. There are also physical limits to the amount

of power that can be extracted realistically from the wind. It can be shown theoretically

that any wind turbine can only possibly extract a maximum of 59.26% (16/27) of the

power from the wind (this is known as the Betz limit). This figure is usually around

45% (maximum) for large electricity producing turbines and around 25-40% for small

wind generators [Hulscher & Fraenkel, 1994]. Well-designed blades will typically

extract 70% of the theoretical maximum [Rai, 2001].

Thus, 3

2

1Available,Power VACP pa = (2.16)

where pC is the capacity factor of the wind machine.

It is also worth bearing in mind that a wind machine will only operate at its maximum

efficiency for a fraction of the time it is running, due to variations in wind speed.

2.4 SMALL WIND TURBINE TECHNOLOGY

Though it is not necessarily the case that the cut-in wind speed UC, shouldbe made as

low as possible, the lower the wind speed at which the blades start rotating, the sooner

power will be extracted as the wind increases. Small wind turbines are designed to

extract power from low speeds.


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2.5 CLASSIFICATION OF WIND TURBINE

Wind turbines in general can be classified in many ways; according to

1. the rated power of the turbine

2. the swept area of the rotor blades

3. the application (to be dealt with in Chapter Four)

2.5.1 Rated Power Classification

Wind turbines can be classified according to their power ratings, large or industrial and

small with rated output power of over 500 kW and below 100 kW respectively, as

shown in Table 2.3.

Table 2.3: Classification of Wind Turbines and typical DimensionsTYPE Rated Power Weight Rotor Diameter Height

Large Wind Turbine > 500 kW > 40,000 kg > 45 m > 50 m

Small Wind Turbine < 500 kW < 40,000 kg < 45 m < 50 m

- Midi < 100 kW < 9,000 kg < 20 m < 35 m

- Mini < 10 kW < 450 kg < 10 m < 20 m

- Micro < 1 kW < 50 kg < 3 m < 10 m

Source: Koenemann (2005)

2.5.2 Swept Area Classification

The International Electrotechnical Commission (IEC) Standard 61400-2 defines a small

turbine as having a swept area of less that 200 m2, which corresponds to a power output

of about 120 kW. The small wind turbines can be described as Mini and Micro, and

generally are wind turbines with rated power output below 10 kW [Wood, 2000].

2.6 TYPES OF SMALL WIND TURBINE

Basically, wind turbines can be divided into two categories, horizontal axis wind turbine

and vertical axis wind turbine.

2.6.1 Horizontal Axis Wind Turbine (HAWT)

A horizontal axis wind turbine is one in which the axis of rotation of the shaft of the

blade is in the horizontal plane. The horizontal axis wind turbine comes in different


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types: one-bladed, two-bladed, three-bladed and multi-bladed wind turbines are shown

in Figure 2.10.

One-bladed Two-bladed Three-bladed Multi-bladed

Fig. 2.9: Horizontal Axis Wind Turbines

2.6.2 Vertical Axis Wind Turbine (VAWT)

A vertical axis wind turbine is one in which the axis of rotation of the shaft of the blade

is the vertical plane. Vertical axis wind turbines are of three types: Savonius type rotors,

Darrieus type rotors and H-type rotors, as shown in Figure 2.11. They are omni-

directional but usually not self-starting and often require an electric motor to get them

starting [Koenemann, 2005].

Most of the designs are drag-based and have tip speed ratio (TSR) less than 1. Thus,

these designs turn relatively slowly, but yield a high torque. One might use a gearbox,

but then efficiency suffers and the machine may not start at all or with difficulty.

Darrieus wind turbines have tip speed ratio (TSR) between 5 and 7 [Rai, 2001].

Savonius type Darrieus type H-type

Fig. 2.10: Vertical Axis Wind Turbines


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2.6.3 Modern Model

2.6.3.1 Spiral Blade Type

This modern type wind turbine is a lift-based horizontal type. It has a pair of spiral

vanes which are made of glass fibre reinforced compound material. The vanes are

bending into axial and radial direction. This bow shape is independent of flow and, in

comparison with the conventional units, it is essentially more effective because its

induced resistance is very low, strongly reducing the losses of flow. High rotational

speed can also be achieved. Wind Converters, as shown in Figure 2.12, can be used in

almost any place, in industrial as well as in private areas because of portability and low

cut-in wind speed of 2.5 m/s.

Fig. 2.11: Spiral Blade Horizontal Axis Wind Turbine

2.7 TECHNICAL CHARACTERISTICS OF SMALL WIND TURBINES

There are several technical parameters that are used to characterise wind machines. The

following are characteristics of wind turbines:

2.7.1 Power and Energy Curves

The power curve of a wind turbine relates the power output of the turbine to its

operational wind speeds as shown in Figure 2.13. It depicts the characteristics of a

particular turbine such as the cut-in and cut-out and the rated wind speeds, and in what

suitable wind regime it will easily start generating power. The rated power output of the

wind turbine occurs at the rated wind speed. The energy curve provides the total amount

of energy a wind turbine produces over a range of annual average wind speeds.


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Fig. 2.12: The Power and Energy Curve of a 10 kW Wind Turbine

2.7.2 Power rating

Typically small turbines are defined by their power-generating capacity, and rather

arbitrarily, considered as turbines less than 100 kW in size [Muir-Harmony, 2001]. The

rated power is at rated speed of the wind turbine: 13m/s for smaller wind turbines and

15m/s for larger wind turbines [Wood, 2002].

2.7.3 Starting Torque

Most small turbines do not have pitch adjustment and so the significant resistive torque

caused by generators of small turbines must be overcome aerodynamically at high

angles of attack before the blades will start turning. Since these turbines rely on

aerodynamic torque for starting, and because Reynolds numbers (Re) are typically

small, their operational efficiency is strongly dependent on performance at low wind

speeds [Clausen & Wood, 2000].

2.7.4 Blade Radius

The relationship of various properties important to wind machines is shown in Table

2.4, as they relate to the blade radius for a constant tip-speed ratio and blade density.

The minimum height of a wind machines tower is directly proportional to the radius of

the rotor R. Other important relationships to note from Table 2.7 which have significant


39/125

effects on wind turbine design are the starting torque, power output, and noise output

[Clausen, 1999].

Table 2.4: The Dependence of Important Parameters on Blade RadiusParameter Dependence on Blade Radius

Reynolds Number (Re) R

Minimum Tower height R

Power Output R2

Noise Output R2

Centrifugal Loads R2

Starting Torque R3

Inertia of Blades R5

It is clear from Table 2.4 that micro-turbines have the poorest starting performance

which is often worsened by the use of permanent magnet alternators, which can have a

significant cogging effect.

2.7.5 Capacity Factors/Efficiency

The efficiency of a wind turbine is defined by its capacity factor, C p, which relates theoutput of a turbine to the kinetic energy of the air, and depends on design and the tip-

speed ratio. By capacity factor, also known as coefficient of performance, we mean

turbines actual annual energy output divided by the theoretical maximum output, if the

machine were running at its rated (maximum) power during all of the 8760 hours of the

year.

OutputEnergylTheoreticaMaximum

OutputEnergyAnnualActualCP = (2.17)

The maximum, theoretically obtainable capacity factor is 0.5926. Well-designed wind

turbines will extract approximately 70% of this theoretical value [Weisman & Eckart,

1988; Rai, 2001]. Capacity factor is not strictly efficiency, even though it is sometimes

treated as one. However, capacity factor can be interpreted as efficiency when

comparing turbines of the same type [Wood, 2002].Capacity factor is sometimes called

the load factor. Wind energy technology has a lower load factor than many other

technologies such as coal and hydro.


40/125

Table 2.5 below shows capacity factors for various classes of wind speeds at 10 m and

50 m. Typical values of capacity factors of wind turbines are also shown in Figure 2.14.

Table 2.5: Net Capacity Factors for Various Classes of Wind Speeds at 10 m and 50 m

Net CapacityFactor

Class*Wind Speed

Range(mph)

*Wind SpeedRange(m/s)

**Wind SpeedRange(mph)

**Wind SpeedRange(m/s)

Not worth it 1


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2.7.7 Tip Speed

The tip speed ratio simply defines the rate at which the tip of the blade of a wind turbine

turns in comparison to how fast the wind is blowing.

That is,

0,

,,

UWindofSpeed

VSpeedTipBladeRatioSpeedTip

tip= (2.18)

Since tip speed is crucial to power generation, because most of a turbines power is

produced near the tip [Wood, 2002], small wind turbines must spin faster than their

larger counterparts. This fact strongly contributes to the relationship between noise

output and size. Drag devices which use aerodynamic drag to operate always have tip

speed ratios less than one and hence turn slowly, whereas lift devices which use

aerodynamic lift to operate can have high tip speed ratios (up to 13:1) and hence turn

quickly relative to the wind [Wind for Electricity]. Modern wind generators have tip

speed ratios of up to 8:1, therefore at wind speeds of 5 m/s, the tips of the blades move

at 40 m/s [Wind Power Basics]. Usually, the tip-speed ratio lies between 7 and 10

when a turbine is performing optimally [Wood, 2002], but the design value chosen is

between 6 and 12, and does not exceed a tip-speed of 100 m/s [Piggot, 2004b]. Figure

2.15 shows the effect of tip speed ratio and LIFT/DRAG on the performance of the

blade.

Fig. 2.14: Effect of Tip Speed Ratio and Lift/Drag on the Performance of the BladeSource: Piggot (2004b)

60

180

CP

0.5

0.4

0.3

0.2

0.1

0

0.593


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2.7.8 Operational Speeds

The following are the important operational wind speeds of wind turbine:

a. Start-up wind speed-- the wind speed that will turn an unloaded rotor

b. Cut-in wind speed the minimum wind speed at which energy is generated

c. Rated wind speed the wind speed at which the machine is designed to run

(This is at optimum tip-speed ratio)

d. Cut-out wind speed the wind speed at which the machine will be turned

out of the wind to prevent damage. (Also known as the furling speed)

e. Maximum design wind speed the wind speed above which damage could

occur to the machine

For a small application the wind has to blow at a speed of 3 m/s. For a large industrial

operation the wind speed must be 6 m/s [Schultz, 2004]. Most wind generators will

begin producing power at 3 - 4.5 m/s and will reach full output at 11 - 13 m/s. [Bergey,

2005] The cut-out speed for small machines is 15 m/s and 25 m/s for lager machines.

2.7.9 Pitch and Yaw Adjustment

Many small turbines are designed to furl at high speeds. This can be done by yaw

(motion in the horizontal plane) or by pitch (a vertical motion of the turbine)

adjustment. Mostly used method for furling is to displace the turbine axis horizontally

from the yaw axis. The tail fin is spring loaded to allow collapse at sufficiently high

wind speed. Pitch control is rarely used on small wind turbines because of cost. [Wood,

2002]

2.7.10 Solidity

Solidity is usually defined as the percentage of the area of the rotor, which contains

material rather than air. Low-solidity machines, such as wind turbines, run at higher

speed and tend to be used for electricity generation. High-solidity machines, such as

windpumps, carry a lot of material and have coarse blade angles. They generate much

higher starting torque than low-solidity machines but are inherently less efficient than

low-solidity machines. High solidity machines will have a low tip-speed ratio and vice

versa [Wind for Electricity]. Increasing the blade number at a given solidity has also

indicated higher power coefficients. A higher solidity and/or blade number could extract


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more energy at a lower speed and offer additional advantages of lower noise, lower cut-

in wind speed, and less blade erosion [Visser, 2004].

Table 2.6 below shows other technical characteristics of both horizontal and vertical

small wind turbines:

Table 2.6: Technical Characteristics of Horizontal and Vertical Small Wind Turbines

Type Speed Torque CpSolidity

(%)Use

Horizontal Axis

Multi-bladedAerofoil

Low High 0.25 0.4 50 80 Mechanical Power

Three-bladedAerofoil

High Low Up to 0.45 < 5 Electricity Production

Vertical Axis

Panemone Low Medium < 0.1 50 Mechanical Power

Savonius Moderate Medium 0.15 100 Mechanical Power

Darrieus Moderate Very low 0.25 0.35 10 20 Electricity ProductionSource: Wind for Electricity, www.itdg.org

2.8 MATERIALS

Material selection is very much important in the manufacturing of small wind turbine. A

wide range of materials is used in wind turbines. Mostly, aluminium alloy, stainless

steel and plastic materials are used for all external parts to prevent corrosion, backed up

by the comprehensive use of rubber seals. Rotor blades are either glass reinforced

plastic, wood-epoxy or injection moulded plastic with carbon fibres. The hub is made of

steel and aluminium. Aluminium is mostly used for the tower of small wind machines.

Small machines tend to use lighter weight castings in an effort to reduce costs. Many

parts are die cast aluminium in small turbines, while in large machines steel castings or

forgings are needed to meet strength and structural fatigue requirements [Ancona and

McVeigh, 2001]. Table 2.7 shows the proportion of materials used for the components.


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Table 2.7: Proportion of Materials used for the Components of Wind Turbines

Large Turbines and (Small Turbines1)

Component/Material

(% by weight)

PermanentMagneticMaterials

Pre-stressedConcrete

Steel Aluminum Copper GlassReinforced

Plastic4

WoodEpoxy4

CarbonFilament

Reinforced

Plastic4

Rotor

Hub (95) 100 (5)Blades 5 95 (95) (95)

Nacelle2 (17) (65) 80 3 - 4 14 1- (2)Gearbox3 98 (100) (0) 2 (


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CHAPTER THREE

METHODOLOGY

The methodology used for this thesis is illustrated as follows:

i. Data collection from sites where small wind turbines are used

ii. Analysis of the data

iii. Economic analysis with RETScreen, a renewable energy technology

simulator

3.1 SITES VISIT AND DATA COLLECTION

A visit to 13 sites where small wind turbine technology has been applied in Ghana was

done. The Power to the Poor in Ghana wind energy project, a rural wind energy

project, is taken as a case study and its applications described.Most of these sites lie

along the coast of Ghana where the wind speeds are moderate. Data is collected at some

sites and analysed. The technical characteristics, application and performance of the

turbines at the various sites at the time of visits are compiled.

3.2 TECHNICAL PARAMETERS

The following technical parameters are calculated for the various sites visited based on

the data from the sites:

3.2.1 Energy Consumption

The energy consumption of a household is calculated using Equation (3.1).

)( = usedHoursofNumberGadgetofRatedPowernConsumptioEnergy (3.1)

3.2.2 Rated Power of Turbine

A community project is analysed and the rated wind turbine capacity to satisfy the

required energy demand is calculated using Equation (3.2).


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8760C

OutputEnergyAnnualTurbineWindofPowerRated

P = (3.2)

3.2.3 Daily Operating Hours

The daily operating hours of a particular wind turbine at a household is determined by

observing the number of hours the wind turbine runs continuously in a day.

3.3 ECONOMIC ANALYSIS OF SMALL WIND TURBINE

The economic analysis is pivoted around the economic concept of levelised energy cost

which is based on the principle of cost recovery. The levelised energy cost or unit cost

of electricity of the wind power system is compared with other unit cost of electricity of

alternatives. Two sets of scenarios are also created and assessed economically: a

community project in which power is supplied to the whole community based on their

annual energy consumption, and projects based on different energy consumptions.

The following economic indicators are used to assess the viability of the wind energy

project:

Annual Worth

Levelised Energy Cost of Electricity

The Simple Payback Period (SPB)

Net Present Value (NPV)

Internal Rate of Return (IRR)

3.3.1 Cost Analysis of Small Wind Turbines

3.3.1.1 Life Cycle CostThe life cycle cost comprises the capital cost of the project, the operation and

maintenance cost and the replacement cost over the systems lifetime, suitably

discounted. The fuel cost of wind turbine is free.

3.3.1.2 Capital Cost

Costs of smaller systems (less than 1 kW) vary widely, with installed costs from $2,000

to $3,000 per installed kilowatt [Dodge, 2002] while a grid-connected residential-scale
mailto:[email protected]:[email protected]


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system (1-10 kW) generally costs between $2,400 and $3,000 per installed kilowatt

[Wind Energy Economics, 2000].

3.3.1.3 Operation and Maintenance (O & M) Cost

With wind energy, and many other renewable energy technologies, the fuel is free.

Therefore once the project has been paid for, the only costs are operation and

maintenance and fixed costs, such as land rental to keep the project running. Annual

maintenance and insurance costs are typically in the range of 2-3% of the capital cost

[Wind Energy Economics, 2000].

3.3.2 Economic Indicators

The following economic indicators, based on life cycle cost analysis as defined by

Gregory et al. (1997), are used to determine the annual worth and the unit cost of

generating electricity of the wind project:

3.3.2.1 Annual Worth

The annual worth is used to discount future values (total life cycle costs) into a series of

annual payments (annuities) of equal amount over the duration of a project.

Total Life Cycle Cost

Total life cycle cost (LCC) is the sum of all discounted cost or payments occurring

during the lifetime of the system. These include the total capital cost (TCC), life cycle

operation and maintenance cost (LCOMC), life cycle replacement cost (LCRC) and

savings over the lifetime of the system (LCS), as defined by Equation (3.3). The savings

are in the form of tax exemptions and avoided cost, which is the cost the consumer

would have paid for using an alternative technology, say, electricity tariff from the grid.

LCSLCRCLCOMCTCCLCC ++= (3.3)

Annualised Life Cycle Cost

Annualised life cycle cost (ALCC), the total life cycle cost expressed in terms of

constant average cost per year, is defined by Equation (3.4)


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)(nPa

TLCCALCC = (3.4)

where )(nPa is the annualisation factor or the present value factor which is used to

discount future values into a series of annual payments of equal amount, as defined byEquation (3.5)

a

aanPa

n

=

1

)1()( (3.5)

a - nominal discount factord+

=

1

1

n - period of analysis

d - nominal or real discount rate

Annualised Capital Cost

Annualised capital cost is defined by Equation (3.6)

)(nPa

TCCACC = (3.6)

Annualised O & M Cost

Annualised O & M cost is defined by Equation (3.7)

)(nPa

LCOMCAOMC = (3.7)

Annualised Replacement Cost

Annualised replacement cost is defined by Equation (3.8)

)(nPa

LCRCARC = (3.8)

3.3.2.2 Levelised Energy Cost

Levelised energy cost (LEC) which is the unit cost of generated electricity is most

useful figure for comparing energy systems. It expresses the average cost of generatinga unit of useful energy during the lifetime of the system, as defined by Equation (3.9)


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SuppliedEnergyAnnual

CostCycleLifeAnnualisedkWhCostEnergyLevelised =)/($ (3.9)

3.3.2.3 Simple Payback Period

The purpose of calculating the simple payback period is to determine the point in time

at which the capital invested in an investment project will be recovered by the annual

returns.

If 0F is the investment cost and Ft is the net cash flow in period t, then the simple

payback period (SPB) is defined as the smallest value of N that satisfies the expression

minN SPB

t

t 0

F 0

=

=

(3.10)

The SPB can also be determined by relating the capital invested to the annual returns:

0,

,

Investment Cost FSPB

Annual Return AR= (3.11)

where

( ) ( ) ( ) ( ) ( )SubsidyTaxesCostMOvenueReCostAvoidedARturnReAnnual ++= &,

(3.12)

The criterion is seldom used with discounting. The simple payback period is calculated

easily, but it has serious deficiencies because it does not consider the time value of

money and the performance of the investment after the payback period, including the

magnitude and timing of cash flows and the expected life of the investment.

3.3.2.4 Net Present Value

The Net Present Value (NPV) is also called the net present worth. It is the difference

between the present worth of all expenses and the present worth of all revenues,

including savings, during the life cycle of the investment (system). A general expression

for the Net Present Value (NPV) is:


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( )

Nt

tt 0 t

FNPV

1 d=

=+

(3.13)

where Ft is the profit or net cash flow (revenue + savings expenses) in year t.

Positive Net Present Value (NPV) indicates the economic viability of an investment

under the specified conditions of the discount rate d, and the economic life time of the

investment N. The greater the value the more profitable the investment. Where there are

several alternative investment possibilities, the NPV of the different projects are

compared with each other and the investment with the highest NPV is selected,

satisfying the minimum criterion of NPV > 0.

3.3.2.5 Internal Rate of Return

The Internal Rate of Return is defined as the interest rate that causes the present worth

of a series of expenses to be equal to the present worth of a series of revenues.

Alternatively, it is defined as the interest rate that will result in zero NPV. That is, the

internal rate of return of an investment is the market discount rate d, which satisfies the

equation:

( )

Nt

t*t 0

FNPV 0

1 d=

= =

+ (3.14)

Hence: IRR = d* (3.15)

When applying the internal rate of return method an investment is viewed favourably if

the IRR is either equal to or greater than the pre-determined cut-off discount rate, d. The

following must hold true:

IRR d (3.16)

3.4 RENEWABLE ENERGY TECHNOLOGY (RET) SIMULATOR

Two Renewable Energy Technology (RET) tools, RETScreen and Wind Energy

Payback Period Workbook, are used for the technical and economic analyses of the

projects discussed in the Thesis. They both have in-built models which take technical

and financial inputs for simulations.


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3.4.1 RETScreen Wind Energy Project Model2

The RETScreen Wind Energy Project Model is a clean energy project analysis software

developed by Natural Resources Canada (NRCan). It is mostly used for preliminary

evaluation of renewable energy projects, decision-support and capacity building. It is

also used to evaluate the energy production, life-cycle costs and greenhouse gas

emission reductions and performs financial analysis for various types of energy efficient

and renewable energy technologies. RETScreen has six worksheets (Energy Model,

Equipment Da

wind energy ghana projetc msc

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