Design and Analyzing of an Off-Grid Hybrid Renewable Energy System to Supply Electricity for ...

109 Pages·2013·2.72 MB·English

Design and Analyzing of an Off-Grid
Hybrid Renewable Energy System to Supply
Electricity for Rural Areas
(Case Study: Atsbi District, North Ethiopia)

Solomon Teklemichael Bahta
(810609-T377)

Master of Science Thesis
KTH School of Industrial Engineering and Management
Energy Technology EGI-2013-115MSC EKV976
Division of Heat and Power Technology
SE-100 44 STOCKHOLM
Master of Science Thesis EGI-2013-115MSC EKV976
Design and Analyzing of an off-grid Hybrid
Renewable Energy System For Rural
Electrification in Ethiopia

Solomon Teklemichael Bahta
Approved Date Examiner Supervisor
19/09/2013 Associate Professor Reza Fakhraie Associate Professor Reza Fakhraie (PhD)
(PhD)

Commissioner Contact person

Abstract
Off the grid hybrid systems have been attracting to supply electricity to rural areas in all aspects like,
reliability, sustainability and environmental protections, especially for communities living far in areas
where grid extension is not appropriate. Hybrid renewable set-up indicates that various combinations
based on the renewable sources could be applied simultaneously to cater energy in the form employed in
an off-gird supporting with battery storage and diesel generator as backup systems. In this paper wind
turbine-photovoltaic-diesel generator-battery bank-converter have been simulated and optimized for the
rural community of Haressaw among the sub-districts of Atsbi district in the regional state of Tigray,
Ethiopia. Primary load demand of 1505kWh/day, peak load of 284kW, deferrable energy is about
17kWh/day, and deferrable peak load of 3.6kW was involved during optimization of the power system.
Well known freeware HOMER modeling tool have been used to design the off-grid system. Wind and
solar energy are considered as primary sources to supply electricity directly to the load and to charge
battery bank when excess generation is happened however in peak demand times diesel generator could
also be engaged. The community's load has been suggested for lighting, water pumping, school and health
clinic equipment load, television, radio, flour milling machines and local food (enjera) baking. During the
design of this power system set-up, the simulation and optimization was done based on the electricity
load, climatic data sources, economics of the power components and other parameters in which the NPC
has to be minimized to select an economic feasible power system. Moreover other parameters like capacity
shortage, renewable fraction, excess electricity, COE, diesel fuel consumption was also considered to
check the technical capability so as to select a system that is sound in techno-economic aspects. Two
approaches were used as comparison measurements to select one power system from the selected options
giving due merit to one of the measuring instruments (renewable fraction and low cost of energy). 12
sensitivity variables have been taken into account such as; 4 cases of diesel price, 4 cases of capacity
shortage, 2 cases of minimum renewable fraction and 2 cases of primary load variations.

Keywords: HOMER, Wind Speed sources, Solar Radiation, Off-grid power System, Wind/Solar
PV/battery/diesel generator, primary load, deferrable load, NPC, COE, Rural electrification, Renewable
energy fraction.
ii
Acknowledgment
It’s my pleasure to express my genuine appreciation for different people who provided me ideas and
support in different ways. My heartfelt special thanks take the opportunity to my scientific supervisor
Associate professor Reza Fakhraie (PhD) for his assistance, guidance, patience and time throughout the
lifelong of the thesis work. It would not have been finalized my thesis work without his patience,
moreover, he has been pillar of inspiration. My thanks goes to Mr. Bahram Saadatfar PhD student, for his
readiness and willingness for discussions. It’s my pleasure to convey my special gratitude to Dr. Mulu
Bayray staff member of Mechanical Engineering department, Mekelle University, Ethiopia for having a
free & open door to me and for providing me the climatic data's of solar radiation and wind speed sources
for the area of my concern which I was looking for Derra sub-district in Tigray Region, North Ethiopia.
Moreover I would like to thank my friend, Dr. Mulualem Gebregiorgis, associate research fellow & project
manager, University of Exeter, United Kingdom, for supporting and giving me valuable suggestions
throughout my thesis study. I also thank to Mr. Jhon for making his door open for discussions. At last but
not least my special appreciation goes to Lemlem Yihdego for her undisputable support throughout my
stay in Sweden. Above all my special gratitude goes to the most Gracious, the almighty God.

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Table of Contents
Abstract ........................................................................................................................................................................... ii
Acknowledgment .......................................................................................................................................................... iii
List of Figures .............................................................................................................................................................. vii
List of Tables............................................................................................................................................................... viii
Nomenclature ............................................................................................................................................................... ix
1 Chapter One: Introduction ................................................................................................................................. 1
1.1. Background .................................................................................................................................................. 1
1.2. Problem Statement and Motivation of the Study .................................................................................. 2
1.3. Thesis Layout ............................................................................................................................................... 3
2 Chapter Two: Literature Review ........................................................................................................................ 4
2.1 Review of Related Works .......................................................................................................................... 4
2.2 Specific Objectives ...................................................................................................................................... 5
2.3 Methodology ................................................................................................................................................ 6
2.4 Boundaries .................................................................................................................................................... 6
2.5 Renewable Energy Potentials in Ethiopia ............................................................................................... 6
2.5.1 Wind Energy Sources ............................................................................................................................ 7
2.5.2 Solar Energy Sources ............................................................................................................................. 7
2.5.3 Hydro Energy sources ........................................................................................................................... 7
2.5.4 Geothermal Energy sources ................................................................................................................. 7
2.5.5 Liquid Biofuel Sources ........................................................................................................................... 8
2.6 Case Study Area ........................................................................................................................................... 8
3 Chapter Three: Solar Photovoltaic Systems ................................................................................................... 10
3.1 Types of Solar PV Cells ...........................................................................................................................10
3.2 The PV Module and PV Array ...............................................................................................................11
3.3 Solar PV Installation Methods ................................................................................................................12
3.4 Solar Terminologies ..................................................................................................................................12
3.5 Incident Radiation .....................................................................................................................................13
3.6 Solar Energy Potential of the Site...........................................................................................................17
3.7 Solar PV Modeling ....................................................................................................................................19
3.7.1 Equivalent Electrical Circuit of PV Cell ...........................................................................................19
3.7.2 Mathematical modeling ...................................................................................................................21
4 Chapter Four: Wind Energy Converters Basics ............................................................................................ 23
4.1 Wind Energy Converters and Regulation Mechanisms ......................................................................23
4.1.1 Classification of Wind Turbines .........................................................................................................24
4.2 The Physics of Wind Energy ...................................................................................................................25
4.3 Wind Shear .................................................................................................................................................30
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4.4 Autocorrelation .........................................................................................................................................31
4.5 Wind Energy Potential of the Site ..........................................................................................................32
4.5.1 Weibull Distribution ........................................................................................................................33
5 Chapter Five: Hybrid Power System and HOMER Tool............................................................................ 35
5.1 Classification of Hybrid Configuration .................................................................................................35
5.1.1 AC/DC-Coupled Configuration Systems ........................................................................................35
5.1.2 Series/Parallel Hybrid Power System ...........................................................................................38
5.2 Auxiliary Components of the Hybrid System ......................................................................................39
5.2.1 Backup Diesel Generator ...............................................................................................................39
5.2.2 Converters .........................................................................................................................................40
5.2.3 Energy Storage Types and Selection Criteria's ............................................................................41
5.3 Overview of HOMER Software .............................................................................................................44
6 Chapter Six: Electricity Load Estimation of the Village .............................................................................. 46
6.1 Estimation of Primary Load ....................................................................................................................46
6.1.1 Domestic Load .....................................................................................................................................46
6.1.2 Commercial Load .................................................................................................................................47
6.1.3 School Load ...........................................................................................................................................47
6.1.4 Health Clinic Load ...............................................................................................................................48
6.2 Estimation of Deferrable Load ...............................................................................................................50
6.2.1 Water Supply Load ..........................................................................................................................50
6.2.1 Irrigation System Load ....................................................................................................................51
7 Chapter Seven: Optimization of Inputs of the Hybrid System .................................................................. 52
7.1 Electricity Load Input ..............................................................................................................................52
7.2 Solar and Wind Energy Sources .............................................................................................................53
7.3 Cost Data and Size Specifications of Each Component ....................................................................54
7.3.1 Solar PV Size and Cost ........................................................................................................................54
7.3.2 Wind Turbine Size and Cost ...............................................................................................................55
7.3.3 Cost and Size of Batteries ...................................................................................................................55
7.3.4 Diesel Generator Size and Cost .........................................................................................................55
7.3.5 Power Converter Size and Cost .........................................................................................................56
7.4 Other Inputs that Affect Power System Optimization .......................................................................56
7.4.1 Economic Inputs ..................................................................................................................................56
7.4.2 Constraint Inputs ..................................................................................................................................56
7.4.3 Emission and System Control Parameters .......................................................................................57
7.5 Sensitivity Variables ..................................................................................................................................57
8 Chapter Eight: Results and Discussions ......................................................................................................... 58
8.1 Systems Optimization and Selection Scenarios ....................................................................................58
v
8.2 Comparison of Scenarios for Economic Power Systems ...................................................................58
8.3 Optimization Analysis of the Selected Scenario ..................................................................................61
8.3.1 First Approach to Select Techno-Economic System .....................................................................69
8.3.2 Second Approach to Select Techno-Economic System .................................................................74
8.4 Sensitivity Analysis ....................................................................................................................................77
9 Chapter Nine: Conclusion and Recommendation ........................................................................................ 82
9.1 Conclusion .................................................................................................................................................82
9.2 Recommendation ......................................................................................................................................83
9.3 Suggestions for Future Work ..................................................................................................................83
Bibiliography ................................................................................................................................................................ 84
Appendices ................................................................................................................................................................... 88
Appendix A1 ...........................................................................................................................................................88
Appendix A2 ...........................................................................................................................................................88
Appendix A3 ...........................................................................................................................................................89
Appendix A4 ...........................................................................................................................................................89
Appendix A5 ...........................................................................................................................................................95

vi
List of Figures
Figure 1-1: Comparison of Utility Grid and PV Power Schemes by Capital Cost [52] .................................... 1
Figure 2-1: Map of Atsbi [25] ..................................................................................................................................... 9
Figure 3-1: Typical PV Cell [75] ...............................................................................................................................10
Figure 3-2: Schematic Diagram for Cell, Module and PV Array [26] ................................................................11
Figure 3-3: Orientation and Slope of Solar PV Module [30] ...............................................................................14
Figure 3-4: Monthly Solar Radiation Sources and Clearness Index ...................................................................18
Figure 3-5: Diurnal Variation of Global Horizontal Solar Radiation Source ....................................................18
Figure 3-6: Data Map of daily solar energy resource pattern ...............................................................................18
Figure 3-7: Equivalent Circuit of Solar PV Cell [38] ............................................................................................19
Figure 3-8: Variation of I-V Characteristic Curve of PV Cell with Categories of Different Losses [41] .....21
Figure 4-1: Architecture of Typical Wind Energy Converter [44] ......................................................................23
Figure 4-2: Wind Turbine Power Control Mechanisms [45] ...............................................................................24
Figure 4-3: Block diagram Showing Classification of Wind Turbines ................................................................25
Figure 4-4: Lift & Drag based Wind Turbines Blade Profile [50] ......................................................................26
Figure 4-5: Air Flow Across the Wind Rotor [53] ................................................................................................27
Figure 4-6: Power Coefficient Versus Tip Speed Ratio for Various Wind Turbines [49] ..............................29
Figure 4-7: Characteristic Curve of Typical Wind Turbine [50] .........................................................................29
Figure 4-8: Wind Speed Variation with Height Above Ground Surface [31] ...................................................31
Figure 4-9: Wind Resources Data .............................................................................................................................32
Figure 4-10: Diurnal variation of wind speed for each month ............................................................................32
Figure 4-11: HOMER Generated Probability Distribution Function of Derra Wind Speed .........................34
Figure 5-1: Hybrid System Configuration ...............................................................................................................35
Figure 5-2: Centralized AC-Coupled Hybrid Power System [57, 59, 60] ..........................................................36
Figure 5-3: Distributed AC Hybrid Power System [52, 65] .................................................................................37
Figure 5-4: DC-Coupled Hybrid Power System [57, 59, 60] ...............................................................................37
Figure 5-5: Series Hybrid Power System [52, 65] ..................................................................................................38
Figure 5-6: Parallel Hybrid System [52, 65] ............................................................................................................39
Figure 5-7: Interactions between Simulation, Optimization and Sensitivity Analysis [31] ............................44
Figure 6-1: Daily Primary Load Profile of the Village ...........................................................................................50
Figure 6-2: HOMER generated Monthly Average Deferrable Load of the Village .........................................51
Figure 7-1: Architecture of the Selected Technologies of the Hybrid System Produced by HOMER ........52
Figure 7-2: Diurnal Variation of Primary Load Profile .........................................................................................53
Figure 7-3: Data-Map of the Monthly Primary Load Profile ...............................................................................53
Figure 8-1: Comparison of Scenarios Based on NPC ...........................................................................................59
Figure 8-2: Comparison of Scenarios Based on COE ...........................................................................................60
Figure 8-3: Comparison of Scenarios Based on Diesel Fuel Consumption ......................................................60
Figure 8-4: Comparisons Based on Capacity Shortage and RF ...........................................................................61
Figure 8-5: Comparison of Scenarios Based on Excess Electricity .....................................................................61
Figure 8-6: Share of Electricity Generation from the Optimum System with a 76% RF ...............................63
Figure 8-7: Power Generation Percentage Share from Each System Components 76% RF .........................63
Figure 8-8: Capacity Shortage, Unmet Load, and Share of Excess Electricity for 76% RF ...........................64
Figure 8-9: Wind Turbine Power Output with 76% Renewable Contribution .................................................64
Figure 8-10: PV Power Production with the 76% Renewable Contribution .....................................................65
Figure 8-11: Diesel Generator Power Production .................................................................................................66
Figure 8-12: Diesel Generator Power Production .................................................................................................66
Figure 8-13: Pollutants Emitted to the Environment ...........................................................................................66
Figure 8-14: Cash Flow Summary in terms of NPC by Component Type ........................................................67
Figure 8-15: Capital Cost Percentage by Components ..........................................................................................67
Figure 8-16: Electricity Generation Share of 79% RF ..........................................................................................68
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Figure 8-17: Excess Electricity, Unmet Load, and Capacity Shortage ................................................................68
Figure 8-18: Cost breakdown of Components by Cost Type ..............................................................................69
Figure 8-19: Comparison of Power System Options based on COE .................................................................70
Figure 8-20: Comparison of Power System Options based on NPC .................................................................70
Figure 8-21: Comparison of Power System Options based on Fuel Consumption .........................................70
Figure 8-22: Comparison of Power System Options based on RF .....................................................................71
Figure 8-23: Electricity Generation Share with 86% Renewable Fraction .........................................................72
Figure 8-24: Electricity Generation and Consumption .........................................................................................73
Figure 8-25: Cost of Power System Components as Percentage of Capital Cost .............................................73
Figure 8-26: Cost Breakdown of Diesel Generator ...............................................................................................73
Figure 8-27: Electricity Generation Share with 45% Renewable Fraction .........................................................75
Figure 8-28: Electricity Generation and Consumption .........................................................................................75
Figure 8-29: Cash Flow Summary in terms of NPC by Component Type ........................................................76
Figure 8-30: PV Capacity and Wind Turbine Quantity Variations......................................................................77
Figure 8-31: PV Capacity and Wind Turbine Quantity Variations......................................................................78
Figure 8-32: PV Capacity and Wind Turbine Quantity Variations Varying Primary Load Only ...................78
Figure 8-33: Generator Capacity and Quantity of Battery Variations With Primary Load and Fuel Price ..79
Figure 8-34: Quantity of Battery Variations with Varying Primary Load and Fuel Price ................................80
Figure 8-35: NPC and COE with Respect to Primary Load ................................................................................81
Figure 8-36: Diesel Consumption and Renewable Fractions with Respect to Diesel Price ............................81
List of Tables
Table 3-1: Two years Average Monthly Global Solar Radiation for 2011 & 2012 ...........................................17
Table 4-1: The Power Law Exponent [38] ........................................................................................................30
Table 4-2: Surface Roughness Lengths [31] ...........................................................................................................31
Table 4-3: Average Monthly Wind Speed (2011 & 2012) .....................................................................................32
Table 5-1: Advantages and Disadvantages of the Different Energy Storage Technologies [39] ....................42
Table 6-1: Single Household Electricity Consumption Features During Weekdays ........................................47
Table 6-2: Electric Load Consumption Characteristics of Flour milling Machine ...........................................47
Table 6-3: School Electricity Load Consumption ..................................................................................................48
Table 6-4: Health Clinic Electricity Consumption .................................................................................................49
Table 6-5: Pump Power Consumption Characteristics for Household’s Water Supply ..................................51
Table 7-1: Size and Cost of PV Panel ......................................................................................................................54
Table 7-2: The Wind Turbine Parametric Inputs into HOMER .........................................................................55
Table 7-3: Sensitivity Analyses Variables .................................................................................................................57
Table 8-1: Categorized Simulation Result ..............................................................................................................59
Table 8-2: Truncated From the Overall Optimization Results for Scenario A .................................................62
Table 8-3: Wind Turbine Scheme Result .................................................................................................................64
Table 8-4: PV Scheme Simulation Result ................................................................................................................65
Table 8-5: Simulation Results of the Hybrid System With 79% RF ...................................................................68
Table 8-6: Extracted optimization result from table 8-2 based on percentage of RF ......................................69
Table 8-7: Extracted Optimization Result from Table 8-2 based on Less COE ..............................................74

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Nomenclature

A Rotor swept area [m2]
Anisotropy index

Area of single module [m2]

CC Cycle charging
COE Cost of Energy
CFL Compact fluorescent lumps
The scale parameter in [m/sec]
Fraction of wind power extracted by the wind rotor [%]

CAES Compressed air energy storage
Capacity of battery [Ah]

DOD Depth of discharge [%]
( ) Maximum depth of discharge of battery [%]

DC Direct current
EEPCo Ethiopian Electric Power Corporation
E Equation of time [hr]
Fuel curve intercept coefficient [units/hr/kW]

Rated Capacity in [kW]

Energy output per hour from inverter [kWh]
( )
Energy output per hour from PV generator [kWh]
( )
Energy consumed per hour by the load side [kWh]
( )
Energy output per hour from inverter [kWh]
( )
Energy stored in battery at t-1 [kWh]
( )
Energy output per hour from rectifier [kWh]
( )
Energy input per hour to rectifier [kWh]
( )
Excess energy from AC sources [kWh]
( )
Energy generated per hour by wind generator [kWh]
( )
( ) Hourly energy consumed by the load side [kWh]
Energy input per hour to charge controller [kWh]
( )
Energy output per hour from charge controller [kWh]
( )
Excess energy from AC sources [kWh]
( )
Energy generated per hour by diesel generator [kWh]
( )
The electrical load [kWh]

Load requirement at time ( )
( )
ix
The cloudiness index
G Irradiance [W/m2]
Solar constant [1.367kW/m2]

̅ Extraterrestrial horizontal radiation averaged over time intervals

[kW/m2]
Extraterrestrial normal radiation [kW/m2]

Global irradiance [W/m2]

̅ Global radiation incident on the inclined surface

̅ Beam radiation [kW/m2]

̅ Diffuse radiation [kW/m2]

̅ Global horizontal radiation reached the earth's surface averaged
over time interval [kW/m2]
GHG Greenhouse Gas
Reference height above ground level [m]

Hub height [m]

ha Hectare
HRES Hybrid Renewable Energy System
HOMER Hybrid Optimization Model for Electric Renewable
Site elevation [m]

Short circuit current [A]

Light current source [A]

Diode current [A]

Shunt-leakage current [A]

I The output current at the output terminal [A]
Io Diode reveres saturation current [A]
PV panels maximum current at standard conditions [A]
PV panels short circuit current at standard condition [A]
PV panels maximum current

k Shape factor
K Boltzmann's constant = 1.38*10-23 [J/k]
Clearness index

km2 Square kilometer
KW Kilowatt
KWh Kilowatt hour
KWh/day.m2 Kilowatt hour per day square meter
The lower heating value [MJ/kg]

LP Liquefied petrol gas
ix