Lidetu Abu Bedadi (219014961)Thesis.pdf

College of Science and Technology
Design and Optimization of Off-Grid Hybrid Renewable Power Plant with
Storage System for Rural Area in Rwanda
Thesis Number: ACEESD/PSE/20/12
By: Lidetu Abu Bedadi
Registration Number: 219014961
A thesis submitted to the African Center of Excellence in Energy for Sustainable
Development
College of Science and Technology
University of Rwanda
In partial fulfillment of the requirement of the degree of
MASTERS OF SCIENCE IN ELECTRICAL POWER SYSTEMS
Supervisor: Dr. Ir. Mulugeta Gebrehiwot
October 2020

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APPROVAL OF BOARD OF EXAMINERS
This is to certify that this Thesis has passed through the anti-plagiarism system and found compliant and this
is the approved final version of the Thesis:
Design and Optimization of Off-Grid Hybrid Renewable Power Plant with Storage System for Rural Area in
Rwanda
Lidetu Abu Bedadi 11 October 2020
Name and Signature of the student Date
Mulugeta Gebrehiwot G. (PhD) 08 October 2020
Name and Signature of Supervisor Date
___________________________________________ ___________________
Name and Signature of Head of Department Date
__________________________________________ ____________________
Name and Signature of Director of the Center Date

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Declaration
I, the undersigned, declare that this thesis is my original work, and has not been presented for the award of any
other degree in the University of Rwanda or any other universities. All sources of materials that are used for
the thesis work have been fully acknowledged and this thesis work has passed through the anti-plagiarism
system and found compliant.
Student Name: Lidetu Abu Bedadi
Registration Number: 219014961
Signature: _
Date: 11 October 2020
Main Supervisor’s Name: Mulugeta Gebrehiwot G. (PhD)
Signature:
Date: 08 October 2020

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ACKNOWLEDGMENTS
First and foremost, I take this opportunity to give glory to the Almighty God, without whom the completion of
this thesis work would have been impossible.
Next, I would like to express my sincere gratitude to my Supervisor, Dr. Ir. Mulugeta Gebrehiwot
Gebremichael, for his expert guidance, suggestions, constructive comments, an advice concerning the thesis
work and for future better life, and general support for the successful completion of this thesis work.
I would also like to give thanks to Dr. Ir. Getachew Biru (an Associate Professor at Addis Ababa University)
for his support, expert guidance, and constructive comments regardless of his busy schedule from the beginning
of the thesis to the end.
It’s my pleasure to convey my special gratitude to Mr. Alsaad Ndayizenye, a staff member of the Rwanda
Water Resources Board (RWB), Kigali, Rwanda for having open doors to me and for providing the required
run-of-river data for the area of my concern.
I would like to thank the African Center of Excellence in Energy for Sustainable Development (ACE-ESD)
for giving me the opportunity of this MSc. study and the World Bank for supporting me financially during the
study.
Finally, my sincere thanks go to my family, friends, and everyone whose constant concern and support
reinforced my efforts, and inspiration I received from their love contributing to the completion of this thesis
work.

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ABSTRACT
Rwanda is one of the fastest-growing countries in Africa. The government envisions transitioning the country
to 100% electrified by 2024 from which 52% grid-connected and 48% are Off-grid systems. The current off-
grid coverage of the country is 13% only. The country is endowed with sufficient renewable energy resources.
These resources are mainly micro-hydropower, biomass, and sun which can be used individually or in hybrid
form. The application of a hybrid renewable energy system has become an important alternative solution for
the rural electrification program. To satisfy the load demand, solar photovoltaic (4kW) and micro-hydro
(15kW) energy were considered as the main source of energy to supply electricity to the load and to charge
the battery bank when there was excess energy generation. However, either in peak load times or low
generation of primary sources storage battery banks could also be discharged. The load has been suggested
for residential loads including the deferable load (water pumping). During the design of this power system set-
up, the simulation and optimization were done based on the load demand, climatic data, the economics of
integrated system components, and other parameters in which the total Net Present Cost has to be minimized
to select economically feasible and technically capable hybrid power system. Furthermore, to use the power
efficiently and economically Fuzzy Logic Controller is also used to control power produced and to take the
decision to charge and discharge the battery bank at the necessary time. The decision of fuzzy logic is based
on the instructional rule written on it. Well-known licensed HOMER and MATLAB simulating software tools
have been used to design optimal off-grid systems and energy management systems respectively. In this thesis,
solar PV/micro hydropower/battery bank/converter has been designed, modeled, optimized, and simulated for
the rural area of Wimana village among the village of Ruhango District in the Southern Province of Rwanda
which has 136 households. Based on the load profile of the data collected for the village was a daily energy
consumption of 180.99kWh/day with a peak load demand of 18.56kW. The Net Present Cost and the Cost of
Energy for the optimized power system were found to be $78,763.26 and $0.0757/kWh respectively.
Key Words: Hybrid, Micro-Hydro power, Solar, MATLAB/Simulink, Fuzzy Logic Controller, HOMER Pro

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ACRONYMS
Abbreviations Description
AC Alternative Current
COE Cost of Energy
DC Direct Current
kW/kWh kilowatt/kilowatt-hour
MW Mega Watt
GW Giga Watt
DG Distributional Generation
REG Rwanda Energy Group
PV Photovoltaic
HRES Hybrid Renewable Energy Sources
MHP Micro-Hydropower
MPPT Maximum Power Point Tracking
HOMER Hybrid Optimization Model for Electric Renewables
HDPE High-Density Polyethylene
REG Rwanda Energy Group
ESSP Energy Sector Status Profile
MCCB Molded Case Circuit Breaker
IGBT Insulated-Gate Bipolar Transistor
PLC Programmable Logic Controller
IGC Induction Generator Controllers
UV Ultra Violate

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PSH Peak Sun Hours
FLA Flooded Lead Acid
AGM Absorbed Glass Mat
STC Standard Testing Condition
RES Renewable Energy System
RWB Rwanda Water Resources Board
NASA National Aeronautics and Space Administration
DVD Digital Versatile Disk
CFL Compact Fluorescent Lamp
REPS Renewable Energy Power System
NOCT Nominal Operating Cell Temperature
SOC State of Charge
DOD Depth of Discharge
O&M Operating and Maintenance
IRENA International Renewable Energy Agency
GPS Global Positioning System
NPC Net Present Cost
GHI Global Horizontal Index

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TABLE OF CONTENTS
Declaration .........................................................................................................................................................ii
ACKNOWLEDGMENTS.................................................................................................................................iii
ABSTRACT ......................................................................................................................................................iv
ACRONYMS .....................................................................................................................................................v
TABLE OF CONTENTS .................................................................................................................................vii
LIST OF TABLES ...........................................................................................................................................xii
LIST OF FIGURES.........................................................................................................................................xiii
CHAPTER ONE.................................................................................................................................................1
1. INTRODUCTION......................................................................................................................................1
1.1 Background..........................................................................................................................................1
1.2 Off-grid PV-Micro Hydro Power Systems ..........................................................................................3
1.3 Rwanda Energy Sector Status..............................................................................................................4
1.3.1 Summary of current resource potential of the country.................................................................4
1.4 Statement of the Problem.....................................................................................................................5
1.5 Objectives ............................................................................................................................................5
1.5.1 General objective..........................................................................................................................5
1.5.2 Specific objectives........................................................................................................................5
1.6 Scope and Limitation of the Study ......................................................................................................6
1.7 Expected Outcomes and Significance of the Study.............................................................................6
1.7.1 Expected outcomes of the study...................................................................................................6
1.7.2 Significance of the study ..............................................................................................................7
CHAPTER TWO................................................................................................................................................8
2. THEORETICAL BACKGROUND AND LITERATURE REVIEW .......................................................8
2.1 Hybrid Renewable Energy Systems ....................................................................................................8

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2.2 Literature Review ................................................................................................................................8
2.3 Micro-Hydropower Generation System.............................................................................................10
2.3.1 Introduction ................................................................................................................................10
2.3.2 Classification of hydropower .....................................................................................................11
2.3.3 Micro-hydropower basics...........................................................................................................14
2.3.4 Principal components of micro-hydropower plant.....................................................................16
2.3.5 Hydraulic turbines ......................................................................................................................23
2.3.6 Types of hydraulics turbines ......................................................................................................23
2.3.7 Hydraulic turbine efficiency.......................................................................................................29
2.3.8 Selection of hydro-turbines ........................................................................................................31
2.4 Photovoltaic Technology and Solar Energy Resources.....................................................................33
2.4.1 Introduction ................................................................................................................................33
2.4.2 Photovoltaic cell and power system ...........................................................................................34
2.4.3 Classification of solar photovoltaic cells and PV technology....................................................38
2.4.4 Main components of photovoltaic solar system .........................................................................40
2.4.5 Photovoltaic rating at STC .........................................................................................................41
2.4.6 Factors affecting the PV cell efficiency .....................................................................................42
CHAPTER THREE..........................................................................................................................................47
3. ELECTRIC ENERGY DEMAND OF THE STUDY VILLAGE............................................................47
3.1 Profile of Wimana Village.................................................................................................................47
3.2 Data Collection ..................................................................................................................................48
3.2.1 Primary data................................................................................................................................48
3.2.2 Secondary data............................................................................................................................50
3.3 Energy Demand Assessment and Load Scheduling of the Village ...................................................51
3.4 Electric Load Profile..........................................................................................................................52

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3.5 Forecasting of the Village Load Demand after 10 years ...................................................................56
CHAPTER FOUR ............................................................................................................................................62
4. MICRO-HYDRO AND SOLAR RESOURCE ASSESSMENT OF THE VILLAGE ............................62
4.1 Introduction........................................................................................................................................62
4.2 Solar Resources Assessment of Rwanda ...........................................................................................62
4.2.1 Solar resource assessment of the village ....................................................................................63
4.2.2 Solar radiation variation of the village .......................................................................................64
4.2.3 Solar radiation potential .............................................................................................................65
4.2.4 Estimation of PV output of the village.......................................................................................68
4.3 Micro-Hydro Resource Assessment of the Selected Village.............................................................69
4.3.1 Rating curve of the river.............................................................................................................70
CHAPTER FIVE..............................................................................................................................................73
5. SYSTEM MODELING AND DESIGN OF THE HYBRID SYSTEM...................................................73
5.1 Modeling of Hybrid Energy System Components.............................................................................74
5.1.1 Mathematical modeling of a micro-hydropower system............................................................74
5.1.2 Mathematical modeling of archimedean turbine........................................................................78
5.1.3 Mathematical modeling of PV system .......................................................................................81
5.1.4 Mathematical model of converter...............................................................................................82
5.1.5 Mathematical model of charge controller...................................................................................83
5.1.6 Mathematical modeling of battery bank.....................................................................................83
5.2 The Energy Optimization Model .......................................................................................................85
5.3 Hybrid System Designing and Sizing................................................................................................86
5.3.1 The methodology of the Design .................................................................................................86
5.3.2 Designing and sizing of micro-hydropower...............................................................................89
5.3.3 Designing and sizing of gearbox ................................................................................................91

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5.3.4 Designing and sizing of generator..............................................................................................92
5.3.5 Designing and sizing of solar PV ...............................................................................................96
5.3.6 Sizing of battery and specifying.................................................................................................99
5.3.7 Charge controller sizing and specifying...................................................................................102
5.3.8 Converter sizing and specifying ...............................................................................................102
5.4 Summary of Input Data to HOMER Pro .........................................................................................103
5.5 Performance Prediction of the Graphical Output of Power Generated over a year.........................105
5.6 Flow Chart Algorithm of System Power Management ...................................................................106
CHAPTER SIX ..............................................................................................................................................109
6. SIMULATION RESULTS AND DISCUSSIONS ................................................................................109
6.1 Optimization Results........................................................................................................................109
6.2 Time Series Detail Analysis of the System Energy Production and Consumption.........................113
6.2.1 Details of solar PV power output .............................................................................................115
6.2.2 Details of micro-hydro output power .......................................................................................116
6.2.3 Details of Energy in and out of the battery bank......................................................................118
6.2.4 Details of converter output power ............................................................................................120
6.3 Cost Summary of the Hybrid System ..............................................................................................122
6.3.1 Cost summary in terms of NPC by component type ................................................................122
6.3.2 Cost summary of the system by cost type ................................................................................122
6.4 Sensitivity Consideration.................................................................................................................123
6.5 MATLAB/Simulink Model and Simulation Results .......................................................................125
6.5.1 PV array components model on simulink ................................................................................125
6.5.2 Battey bank model representation on simulink ........................................................................128
6.5.3 Micro-hydro model representation on simulink.......................................................................130
6.5.4 Overall simulink model of the developed hybrid system.........................................................132

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6.5.5 Fault analysis and its effect on the system ...............................................................................137
6.6 Fuzzy Logic Controller for the Proposed Hybrid System ...............................................................137
6.6.1 Modeling of fuzzy logic controller for the hybrid system........................................................137
6.6.2 Fuzzy logic controller algorithm ..............................................................................................138
CHAPTER SEVEN........................................................................................................................................146
7. COST ANALYSIS OF THE HYBRID SYSTEM .................................................................................146
7.1 Equations Used for Cost Analysis in HOMER Pro.........................................................................146
7.2 Cost Assessment of Hybrid System Component.............................................................................147
7.2.1 Cost of hydropower turbine......................................................................................................147
7.2.2 Costs of solar photovoltaic .......................................................................................................149
7.2.3 Cost of battery ..........................................................................................................................150
7.2.4 Cost of bidirectional converter .................................................................................................152
7.3 Life cycle cost analysis....................................................................................................................153
7.4 Cost Analysis of the Present Worth of the Hybrid System..............................................................154
7.4.1 Initial costs for the system design ............................................................................................154
7.4.2 Present worth of replacement, operation and maintenance cost...............................................154
7.5 Summary of the Cost Analysis ........................................................................................................155
7.5.1 Electricity cost comparison with the grid cost .........................................................................156
7.6 Potential Impact of the Research .....................................................................................................157
7.7 Discussion........................................................................................................................................157
7.8 Conclusion .......................................................................................................................................158
7.9 Recommendations............................................................................................................................160
REFERENCES...............................................................................................................................................161
Appendix – I: Optimal Ratio Parameters of Archimedes Screw for Various Numbers of Blades ................166
Appendix – II: Table of all Fuzzy Logic Rules..............................................................................................167

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LIST OF TABLES
Table 2.1. Classification of hydropower by installed capacity ........................................................................12
Table 2.2. Impulse and Reaction turbines ........................................................................................................24
Table 2.3. Typical efficiencies of small turbines .............................................................................................30
Table 2.4. Hydropower turbines and their characteristics................................................................................32
Table 3.1. Primary data collected at the selected site.......................................................................................49
Table 3.2. Collected secondary data.................................................................................................................51
Table 3.3. Summary of energy demand of Wimana village.............................................................................53
Table 3.4. Forecasting public and commercial loads .......................................................................................58
Table 3.5. Daily energy demand of the village in weekdays............................................................................59
Table 3.6. Daily energy demand of the village in weekends............................................................................60
Table 4.1. Clearness Index and Daily Radiation of the selected village ..........................................................63
Table 4.2. Monthly average streamflow...........................................................................................................69
Table 5.1. Characteristics of REPS ..................................................................................................................73
Table 5.2. Total load consumption of the village.............................................................................................89
Table 5.3. General information data for selected PV .......................................................................................97
Table 5.4. Selected battery specifications ......................................................................................................100
Table 5.5. Specification of the selected bidirectional converter ....................................................................102
Table 5.6. Economic inputs to HOMER Pro..................................................................................................104
Table 5.7. Resource inputs to HOMER Pro ...................................................................................................104
Table 6.1. Overall optimization result of the hybrid system ..........................................................................111
Table 6.2. Categorized optimization result of the hybrid system...................................................................112
Table 6.3. Details of solar PV output information .........................................................................................115
Table 6.4. Details of micro-hydro output information ...................................................................................116
Table 6.5. The detail output information of the storage system.....................................................................118
Table 6.6. Worst day of the state of power variation for each component in 24-hours .................................120
Table 6.7. Details of inverter and rectifier output power characteristics .......................................................121
Table 7.1. Cost specification and characteristics of hydropower...................................................................148
Table 7.2. Initial cost summary hybrid energy equipment.............................................................................154
Table 7.3. Operation and maintenance cost and replacement costs summary ...............................................155
Table 7.4 Electricity tariff of the Rwandan grid.............................................................................................156

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LIST OF FIGURES
Figure 1.1. Hybrid of Renewable Energy System..............................................................................................2
Figure 2.1. Types of hydropower by the head..................................................................................................13
Figure 2.2. Structure of hydropower plant .......................................................................................................14
Figure 2.3. Head of a micro-hydropower system.............................................................................................15
Figure 2.4. Over-all arrangement of the MHP and its main components.........................................................16
Figure 2.5. Diversion weir and Intake..............................................................................................................17
Figure 2.6. Settling Basin .................................................................................................................................18
Figure 2.7. A typical spillway in Micro Hydropower System .........................................................................19
Figure 2.8. A typical forebay tank in Micro Hydropower System...................................................................19
Figure 2.9. Mechanisms of the penstock assembly ..........................................................................................20
Figure 2.10. Direct coupled drive system.........................................................................................................22
Figure 2.11. Pelton Turbine..............................................................................................................................25
Figure 2.12. Turgo Turbine ..............................................................................................................................25
Figure 2.13. Cross-Flow Turbine .....................................................................................................................26
Figure 2.14. Francis turbine and its main components.....................................................................................27
Figure 2.15. Kaplan turbine..............................................................................................................................27
Figure 2.16. Archimedes screw plant principle................................................................................................28
Figure 2.17. Archimedes screw turbine............................................................................................................29
Figure 2.18. Typical small hydro turbines efficiencies ....................................................................................30
Figure 2.19. Typical Archimedean Screw hydro turbine efficiency curve ......................................................31
Figure 2.20. The operating ranges for hydraulic turbines in terms of head and flow rate ...............................33
Figure 2.21. Worldwide installed capacity of solar PV from 2010-2030. .......................................................34
Figure 2.22. Solar photovoltaic components configuration .............................................................................35
Figure 2.23. Basic solar cell operating principle..............................................................................................36
Figure 2.24. Shows the relative amounts of power in different wavelengths of the solar spectrum................37
Figure 2.25. Relationship between solar irradiance and solar insolation.........................................................38
Figure 2.26. Classification of photovoltaic cell based on PV material ............................................................38
Figure 2.27. Monocrystalline silicon PV module.............................................................................................39
Figure 2.28. Polycrystalline silicon PV............................................................................................................39
Figure 2.29. Thin-Film PV cell ........................................................................................................................40

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Figure 2.30. Temperature effects on I-V curve of a polycrystalline silicon solar cell.....................................42
Figure 2.31. Simplified equivalent circuit of a photovoltaic cell.....................................................................43
Figure 2.32. The I-V and P-V curves of a photovoltaic device........................................................................45
Figure 2.33. I-V diagram showing ISC, VOC, Pmax, and Fill Factor (FF). .......................................................46
Figure 3.1. Map of Ruhango District and location of the villages ...................................................................47
Figure 3.2. Geography allocation of Wimana site village................................................................................48
Figure 3.3. Site survey and gross head measurement for Ururumanza river ...................................................50
Figure 3.4. Daily peak demand of the village ..................................................................................................56
Figure 3.5. Daily energy demand of the village in weekdays ..........................................................................59
Figure 3.6. Daily energy demand of the village in weekends ..........................................................................60
Figure 4.1. Global Horizontal Radiation of solar energy of Rwanda...............................................................62
Figure 4.2. Selected village solar resources .....................................................................................................64
Figure 4.3. The relationship between Daily Radiation and Stream Discharge Rate of the selected village ....65
Figure 4.4. Monthly average stream flow of Ururumanza river.......................................................................70
Figure 4.5. Rating curve for the river of Ururumanza......................................................................................70
Figure 4.6. Net Head after the pipe loss is reduced from the Gross Head .......................................................72
Figure 5.1. Archimedean screw turbine ...........................................................................................................78
Figure 5.2. Block diagram of the proposed system..........................................................................................87
Figure 5.3. HOMER Pro representation of the designed system .....................................................................87
Figure 5.4 Designed model of the Archimedes Screw turbine.........................................................................91
Figure 5.5. Compound gearing system.............................................................................................................92
Figure 5.6. Single-line equivalent circuit diagram of 3-phase induction generator .........................................94
Figure 5.7. Parallel and series configuration of the proposed PV Array..........................................................99
Figure 5.8. Series and parallel configuration of the battery bank...................................................................101
Figure 5.9. Flow chart of power management for PV-micro hydro with energy storage hybrid system.......107
Figure 6.1. Average of monthly solar energy resources.................................................................................110
Figure 6.2. Average of monthly discharge of the run-of-river at the site.......................................................110
Figure 6.3. System architecture and monthly average electric production of the selected hybrid system.....113
Figure 6.4. Annual time series detail analysis of the system energy production and consumption...............114
Figure 6.5. LONGi Solar LR6 – 72PH power output.....................................................................................115
Figure 6.6. Solar PV power production..........................................................................................................116

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Figure 6.7. Monthly detail of output power for a micro-hydro system..........................................................117
Figure 6.8. Micro-hydropower production details in a year...........................................................................117
Figure 6.9. The battery bank state of charge and input power .......................................................................118
Figure 6.10. The worst case of battery charge and discharge in 24-hours .....................................................119
Figure 6.11. Inverter and rectifier output power indication ...........................................................................121
Figure 6.12. Cost summary in terms of NPC by component type..................................................................122
Figure 6.13.Cost summary of the system by cost type...................................................................................123
Figure 6.14. Yearly cash flow summaries by cost type..................................................................................123
Figure 6.15. All components of sensitivity results in tabular form................................................................124
Figure 6.16. Total Net Present Cost and Cost of Energy vs. Nominal Discount Rate...................................124
Figure 6.17. The sensitivity of converter capacity (kW) and Surrette S-260 battery (#) at variable Total Net
Present Cost and Cost of Energy....................................................................................................................125
Figure 6.18. Simulink model of the PV side components in the system........................................................126
Figure 6.19. I-V and P-V curve of the proposed PV array.............................................................................126
Figure 6.20. Average irradiance for 24-hour in February month...................................................................127
Figure 6.21. Hourly PV array output voltage.................................................................................................127
Figure 6.22. Hourly PV array output current .................................................................................................127
Figure 6.23. Hourly PV array output Power...................................................................................................128
Figure 6.24. Simulink model of the battery bank and charge controller........................................................129
Figure 6.25. Battey bank discharging time.....................................................................................................129
Figure 6.26. Battery bank charging time........................................................................................................130
Figure 6.27. MATLAB/Simulink model of a hydropower.............................................................................131
Figure 6.28. Stator current and load angle (pu) of the system at normal operation .......................................132
Figure 6.29. Mechanical input power and output active power of the generator...........................................132
Figure 6.30. Overall MATLAB/Simulink model of the developed hybrid system........................................133
Figure 6.31. Immediate output voltage, current, and power of the inverter...................................................134
Figure 6.32. Output voltage, current and power of the inverter after filtering...............................................134
Figure 6.33. System power quality represented in THD................................................................................136
Figure 6.34. Active and Reactive power production and consumption with power factor at load ................136
Figure 6.35. Fault occurrence and its effect on the system ............................................................................137
Figure 6.36. Fuzzy Interface Model ...............................................................................................................139

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Figure 6.37. Membership function of Generated Power ................................................................................140
Figure 6.38. Membership function of Demand Power (PDem) .....................................................................140
Figure 6.39. Membership function of Battery State of Charge ......................................................................141
Figure 6.40. Membership function of the Water Pump..................................................................................142
Figure 6.41. Membership function of Battery Status .....................................................................................142
Figure 6.42. Real-time modeling of fuzzy logic rules....................................................................................143
Figure 6.43. Rule evaluating for scenario 1 ...................................................................................................144
Figure 6.44. Rule evaluating for scenario 2 ...................................................................................................144
Figure 6.45 Surface representation of Ppv+Pgnr, PDem, and Water-pump on X, Y, Z plane.......................145
Figure 6.46 Surface representation of Ppv+Pgnr, PDem, and Battery Status on X, Y, Z plane ....................145
Figure 7.1. Micro-hydro cost and input data details.......................................................................................149
Figure 7.2. PV panel cost and input data details ............................................................................................150
Figure 7.3. Battery cost and technical input data ...........................................................................................151
Figure 7.4. Cost curve of the battery storage..................................................................................................152
Figure 7.5. Converter and Charge Controller cost and technical input data ..................................................153

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CHAPTER ONE
1. INTRODUCTION
1.1 Background
Energy is among the principal elements that are needed for the development of the socio-economic pace of a
country. It's the main way to achieve goals such as the health of the people with a high standard of living
conditions, a maintainable economy status, and a hygienic atmosphere. A countries’ resources of energy are
the essential key aspects indicating their growth and management place in the rivalry. Hence, the wise
utilization of energy turns out to be more of a big task for the countries. The efficiency scaling the relation
between inputs and outputs of energy through evaluation recognizes energy efficiency [1].
Energy resources are classified as renewable energy or non-renewable. Renewable energy resources are
frequently biomass-based and are accessible in infinite quantities in nature since these can be rehabilitated or
regenerated in natural processes over comparatively short periods. Renewable energy sources are limitless
which means they can be substituted after they are being used and they can generate energy repeatedly. The
various fossil fuel non- renewable energy resources like petroleum products, coal, natural gas, and nuclear
energy are likely to be finished at some time as a result of limitless utilization [2]. Among different types of
Energies, electrical energy is one of the most vital and backbone for the growth and prosperity of a country
and human well-being that is generated from both renewable and non-renewable energy resources.
Recently, renewable energies have minimized the gap between the demand raise of electricity and produced
power in consideration of upright alternative to the common sources of energy because population growth is
a reason for the lessening of conventional energy sources. In most growing countries, about thirty percent of
the total population stays in rural areas from them the majority of rural villages are situated in distant and
mountainous areas [3]. In Rwanda, as of December 2019, the off-grid access rate to the households is 14.3%
[4]. The Population which is connected to the grid accounts for around 51% of the whole population [4]. The
remaining population in the rural areas of Rwanda is not in access to electricity. In addition to this, the density
of the population in these areas is a lesser amount as related to the municipal areas. This shows us to fulfill the
need for electricity to the remotely located areas with electricity is a big challenge in technical and economical
way. So, the best option to overcome this challenge over conventional generations is the appropriate selection
of renewable energies can generate electricity sustainably. Even though single sources of renewable energy
have low efficiency and dependent on weather, but the hybrid of these renewable sources give more efficiency
and produce enough electricity to fulfill electricity demand of the area.

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The cost of electricity has decreased abruptly in the last ten years as a cause of improved technology, the scale
of economies, modest progressive supply chains, and improving designers’ experience. Consequently, in all
parts of the world, the technologies used for the generation of power from renewable energies have become
the least-cost option for new capacity [5].
Figure 1.1. Hybrid of Renewable Energy System
The hybrid energy system is represented as an altogether of single or number of energy sources as a single unit
to supply the electricity demand. It involves Renewable Energy Resources (RES) like solar photovoltaic,
biogas, micro-hydro, and conventional energy systems (like distributed generator sets or central grid) for the
supply of consumer loads. It can provide energy efficiency and in a consistent way. In this thesis work, the
off-grid combination system of PV and Micro-hydro with storage systems practices renewable energy sources
that are available at a selected location in Rwanda's rural area. Solar PV systems and micro-hydro are taken as
key sources of renewable energy but due to the intermittent of these sources, the battery is used as an energy
storage device to store energy. When there is insufficient generation from these sources, then the battery
supplies stored energy to the load demand [3].
According to Rwanda’s plan of economic development, the country has an envision to meet 100% access to
electricity by the end of 2024 [4] as it is the main driver for the growth of the country’s economy and
development. The energy sector strategic plan believes that the utilization of off-grid systems has an advantage

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over the grid which takes more time by stipulating the usage of solar home systems and mini-grids as a feasible
alternative to grid connections.
1.2 Off-grid PV-Micro Hydro Power Systems
To increase the access of electricity worldwide, implementation of the off-grid system is now observed
universally as significant means that incorporates mini-grids and solar home systems fitted to individual
houses.
According to Rwanda Energy Group (REG), a detailed national electrification plan mapping has developed to
electrify all places and technologies to be applied either off-grid or on-grid. It is anticipated that 48% [4] of the
households will get electricity that is supplied by off-grid solutions by 2024 while 52% [4] remaining
households will be linked to the grid.
Off-grid can be grounded on a series of innovations and knowledge. The off-grid of Solar PV and hydro are
advantageous in operating at a very low cost but have high initial costs and the power gained is intermittent.
In contrast to this, diesel generators have high operating costs and can generate power when necessary but have
some complexities related to purchasing and environmental issues [6].
The advantage of a generation consisting of renewable energies is that it can be constructed in a rural area that
is detached from the main grid, and where there is a necessity for off-grid electricity. The drawbacks are some
variable output because of their irregular output which depends on weather and environment, and low
efficiency for PV and wind energy systems. As a result, the generation fails to meet the load required at the
required time. Therefore, developing a hybrid system of PV-Wind Turbine Generator-Micro- Hydro, and
Biomass are applied as the best solution [7].
This study deal with the design and optimization of a Micro-hydro and PV hybrid system with a storage system
that can be executed in one of the countryside areas of Rwanda in the Western province where most
communities are not having access to electricity. This kind of design is to ensure that the hybrid energy source
can still supply the load if the load side demand shows some increment in the future. A well-regulated voltage
at the load can be found but at no guarantee to the reliability of the power supplied. Therefore, battery banks
are extensively used to advance the reliability of the standalone hybrid system. HOMER Pro and MATLAB
software will be used to do the optimization analysis and design configurations.
The expected outcome of this study is to power non-electrified villages with hybrid renewable power plants to
its maximum load demand with less cost and efficient power generation and consumption by implementing
controlling units and modern power electronics technologies in enhancing the reliability of the plant.

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1.3 Rwanda Energy Sector Status
Electrical energy is a crucial motor for modern technology and socio-economic development for the country.
It powers small appliances, such as mobile phones and lighting, which advances the living style of the citizens,
also for processing activities in industries.
The installed electricity generation capacity in Rwanda is 218MW of which 212.5MW connected to the grid
and 5.5MW is imported. This is an increment from the 160MW installed capacity at the same time as the
previous Energy Sector Status Profile (ESSP). The technology mix has also been diversified. Hydropower
takes 45% of installed capacity, Methane gas 14%, diesel & Heavy Fuel Oil (HFO) 27%, Peat 7%, and Solar
6% [8].
1.3.1 Summary of current resource potential of the country
Hydropower – hydropower covers the bulk of electricity since the 1960s. Its total potential is assessed at
up to 400MW, with the present installed hydro capacity is 218MW. Hydropower is the cheapest electricity
generation in the long run as a result of its enormously low operational costs [8].
Methane – Kivuwatt, a 27MW generation capacity that has verified the commercial and technical viability
of extracting methane from Lake Kivu. Further utilization of methane resources is planned, with significant
stakeholder interest. The resource potential of methane in the country ranges from 140-180MW [9].
Peat – The master plan was first established in 1993. Approximations of potential capacity have been revised
downwards from the initial 700MW to 121MW-161MW in 2016. Peat reserves about 77% are near the
Rwabusoro plains and Akanyaru and Nyabarongo rivers. At this time, generating electricity of 15MW is from
Gishoma which is primarily used in the dry season. Hakan, 80MW station is under construction [8].
Geothermal – Geothermal resources in Rwanda needs to be verified. Though 47.3MW of generation have
been identified at Kinigi, Karisimbi, Gisenyi, and Bugarama as a promising area, further study is needed to
confirm this [9].
Solar Energy – The variation of solar radiation in Rwanda is between 4.3 to 5.2kWh/m2
/day. The solar
installed capacity is 12MW. There is high interest from the private sector in on-grid solar power development.
Peak demand in Rwanda occurs between 19:00 – 21:00, meaning storage must be used for solar to contribute
[8].

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Biomass – Small-scale power generation using agricultural residues or biomass briquettes is feasible at low
levels of capacity. A private power plant of 0.7MW has been developed in the Eastern Province of the country
[9].
Wind Energy – Commercially in Rwanda, wind power resources are not anticipated to be substantially
based on past resources assessments and modeling work [8].
1.4 Statement of the Problem
Rwanda is among the fastest-developing countries in Africa. The government envisions transitioning the
country to 100% electrified by 2024 from which 52% are connected to the and 48% are off-grid or standalone
systems [4]. The current off-grid coverage of the country is 13% only [9, 3]. Some rural areas in the districts
of the country have not been electrified. To electrify the remote areas, it is necessary either by extending power
from the grids or by building up off-grid (standalone) power systems. Extending the existing grid to all regions
where there is energy demand is not economical due to the geographical location, dispersed population, and
due to the limited capacity of the grid energy.
Hence, to give all that it takes to achieve the country’s goals towards electrification, exploring the potential of
distributed energy systems through harvesting renewable energy sources is the way forward. This thesis
particularly takes the Southern Province as a study area since there is a huge number of populations living there
with energy poverty. Considering all the possible scenarios and with the appropriate engineering concepts to
design a hybrid renewable energy generation plant, this thesis will come up with a possible solution to the
existing problem of the rural community.
1.5 Objectives
1.5.1 General objective
The main objective of this thesis is to design and optimize a micro-hydro-photovoltaic system and energy
storage for hybrid electrification of remote village in Rwanda to give access to clean, affordable, and
reasonably stable stand-alone electricity supply.
1.5.2 Specific objectives
To achieve the main goals, the study has the following specific objectives:
- To determine the present and near future electrical energy demand of the community living in the rural
area under study.
- To evaluate the renewable energy resource of the area; solar energy potential and micro-hydro.

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- To design a standalone hybrid system to meet the electrical energy demand of the community.
- To evaluate the economic and technical performance of the micro hydro-PV hybrid System and make
sensitivity analysis by using appropriate software tools.
- To estimate a cost analysis of the system and study the energy management of the designed hybrid
power generation plant.
1.6 Scope and Limitation of the Study
The scope of this study is to design and optimize a standalone PV-Micro hydropower hybrid energy system
with a battery storage system to supply the rural community detached from the national grid in Rwanda. An
investigation will be carried out starting from knowing the total electric demand in one of selected remote rural
area of Rwandan district building up to the design of solar photovoltaic and micro-hydro power hybrid energy
system and sizing of stand-alone hybrid components like PV module, batteries, inverter, charge controller,
turbine and generator necessary to the system and finally simulate using the renewable energy software
HOMER Pro and MATLAB/Simulink.
This study intends to gather and examine relevant information and data to examine and select the configuration
of the most suitable system, endorse essential actions, compulsory actions that arrange a system to
accommodate the current and near-future electrical energy demand for the village. This thesis study is limited
to PV and micro-hydro combined with the battery storage system. It doesn’t consider wind as part of the hybrid
system. The study will not deal with the whole real-time arrangement of the systems in the selected area. Good
practices of this work can be reproduced and be applied to other off-grid regions of Rwanda.
1.7 Expected Outcomes and Significance of the Study
1.7.1 Expected outcomes of the study
The design and optimization of hybrid systems of PV and Micro-hydro would enable electrification of remotely
located areas that are detached from the main grid and costly to stretch a transmission line from the substations.
The expected outcome of this thesis work is to come up with a feasible off-grid hybrid renewable energy source
plant combined with a battery storage system to fulfill the energy demand of a rural community in Rwanda.
This will be realized by considering the nature of the load at the consumers’ side, the efficiency of power
generation, cost, and reliability of the plant.

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1.7.2 Significance of the study
The combination of the two renewable sources photovoltaic and hydropower have the advantage that they
complementary to each other because the peak power generation hours of the two systems occur at different
periods of the day and year. The power generation of such kind of hybrid plants is more constant and experience
less fluctuation than each of the two components subsystem and it also increases the reliability and feasibility
of the power generation. The system provides a high level of energy security through the combination of
generation methods and often integrates a storage system (battery bank) to ensure maximum supply, reliability,
and security. The benefit of hybrid power generation from the renewable energy source to the rural community
is to supply reliable, sustainable, and low-cost electricity and to start modern life i.e. creating a job opportunity
and extending average working hours in the community. In addition to this, the wide use of renewable energy
sources decreases the possibility of pollution of the environment from pollutant gases that are released from
thermal power generations.

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CHAPTER TWO
2. THEORETICAL BACKGROUND AND LITERATURE REVIEW
2.1 Hybrid Renewable Energy Systems
Hybrid Renewable Energy Systems (HRES) have become another possibility for the generation of power and
has opened the eyes of designers and researchers to explore the available potential of conventional and
renewable energy resources in the last ten years. Usually, battery storage systems are integrated into HRES to
supply the demand efficiently at a peak load or when a failure of generation occurs by the renewable energy
resources because of their intermittency. Another advantage of the storage system is leveling the gap of energy
demand during peak hours and maximum power generation. The performance of an individual system model
is required to be modeled independently in the design of HRES. Next to modeling individual component
performance, then the combination of each model is evaluated that helps in the prediction of the system
performance and the sustainable supply of energy to meet the demand. Researchers have adopted that power
can be delivered at a lower cost from the resultant combination of each component if the predicted output
power is accurate enough from the individual component [11].
Improper prediction of the output energy from the hybrid system results in a complex optimal design of a
hybrid energy system. There are several reasons for the appraisal of these complex optimization. The first one
is multiple of variables involving in the optimization problem of the energy design. The second one, the
existence of objectives that conflict with each other which makes the optimization problem complex such as
performance, cost, management of demand/supply, limitation of the grid, and so on. Also, coupled non-
convexities, non-linearity, and mixed-type variables, frequently disregard the opportunity of using
conventional optimization methods to solve such problems [12]. This research paper aims at designing the
HRES regarding solar and Micro-hydro energy in the existence of a battery bank.
2.2 Literature Review
Tremendous research has been conducted in off-grid and grid-connected hybrid power generation systems in
Rwanda and the whole world. Diverse researches used dissimilar technology selections and approaches to
assess the various formations of resources of renewable energy, such as wind energy, biomass, solar energy,
micro-hydropower, and hybrid arrangements [13]. Several study results have been published, some of the
research works which have been done related to the topic of this work were reviewed in this chapter.

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The author in [3] conducted a system of hybrid energy for a remote and rural village in India combining PV
and micro-hydro with a storage system for a grid-connected system. In the work, HOMER software is utilized
to optimize the best mixing of sources of renewable energies that were accessible at the remote rural
community and decrease the cost of energy. The output result shows that 47.8 % of energy demand was met
by the PV, 11.1 % by micro-hydro. The total of it fulfills 58.9% of the energy requirement, but if they would
have calculated the percentage met correctly, the load would have covered by more percentage from their
result.
The thesis work in [14] investigated on Fuzzy Logic Controller based hybrid renewable power generation for
Fogera woreda (Northern Ethiopia) by assessing PV-micro hydro and biomass capacity of Fogera woreda to
generate electricity. The author investigated that micro-hydro is one of the hybrid components from which
50% of the village electricity demand is covered. Finally, in the thesis, Fuzzy Logic Controller and
MATLAB/Simulink based Solar/Micro-hydro/Biomass hybrid renewable power generating system was
designed to solve the scarcity of electricity in the selected village.
The closely related work in [15] proposed and studied about a hybrid system model comprising of micro-
hydro and PV with a battery bank for the Ethiopian rural village of Mogno Keshenbel using HOMER software.
In the study, the feasibility of a micro-hydro/PV with a battery hybrid electric supply scheme to the village is
examined employing the HOMER software (Hybrid Optimization Model for Electric Renewable). In this
thesis, the author is mainly focused on a renewable energy generator (PV), and an inverter (DC/AC converter),
a back-up unit generator set (Generator), and a storage system (batteries), and uses renewable energy resources
of solar radiation and water resources as the main energy source. The total power demand and energy
consumption in the village were 341.55 kW and 1925.35 kWh/day was met with the NPC of $394,819 and
the LCOE 0.044$/kWh. But control mechanism of renewable energy resources is not discussed in detail.
A hybrid model in [16] was analyzed a case study of a rural remote village in Rwanda and used HOMER
software to analyze the power system possibilities for electrifying Rwanda’s rural areas. To supply the villages,
the author proposed a study of micro-hybrid power system selections to reach the finest techno-economic and
best formation of Renewable Energy Technologies (RETs). According to the thesis, the maximum demand
accounted for is 38kW. Therefore, to meet this demand the author designed a hybrid system that comprises a
system configuration of 20kW micro-hydro power, diesel generator of 10kW, 10kW capacity of Inverter, and
8 Surrette 6CS 25P batteries. The cost of energy produced by these systems typically varies from 0.28 – 0.30
$/kWh. The Cost of Energy the author proposed was greater than the grid electricity price and the system is
not environmentally friendly because of the diesel generator.

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A paper in [17] proposed an off-grid photovoltaic, small hydro, diesel generator hybrid power system for a
detached village in Nigeria. In this paper, three converters of which two DC-DC (battery and PV side) and one
AC converter (Diesel Generator side) were used. According to this paper, the average energy demand required
for the community was 6831kWh/day while the average power demand was 285kW with a peak of 791 kW
and the load factor was 0.360. As the results and conclusion, the optimization of the Hybrid Power System
(HPS) was 954 kW of small hydropower, 290kW of PV array with battery storage of 9,500 sets of battery
strings, and 350 kW of a diesel generator at a Levelized Cost of Energy $0.185/kW/hr. Even if the energy price
is low, the system which is modeled in the paper is not environmentally friendly due to the high emission of
carbon gas to the surrounding environment.
The author in [18] optimized and simulated an off-grid combination of wind turbine and solar PV with a battery
bank for the rural area found in the Amhara region of Ethiopia applying HOMER and MATLAB simulating
software tool. According to the author, solar PV and wind energy were considered as primary sources to supply
electricity directly to the load and to charge battery banks when there was excess energy generation to use it
back either in peak load times or low generation of primary sources.
2.3 Micro-Hydropower Generation System
2.3.1 Introduction
Currently, hydropower has a wide coverage of meeting the load demand and it is regarded as the best electricity
source. It generated electricity from the falling or moving energy of water from a hilly height. Previous
literature examined that its cost of electricity has remained constant for over the year. Most countries have
hydropower as the main source of electricity due to its several advantages. The reason why hydropower has
many advantages is that it is green energy, which means that no pollutants of air are produced from it, also it
does not produce greenhouse gases such as carbon dioxide and nitrous oxide. These reasons make it an
environmental-friendly source of energy. It also has a great role in fighting the growth of global warming [19].
Why Hydropower plants are said to be sources of clean energy is that they convert the potential energy of the
water to electrical energy without emitting pollutant gases. The water used to hit the turbine and generate
electricity is used back for irrigation and other useful purposes. To generate electricity from moving water, the
waterwheel on the Fox River was the first used in 1882 [20]. At the early time of this century, hydropower
continued to expand the electricity coverage around the world. They generate electrical power from a few kW
capacities to hundreds and thousands of MW. Hydropower plant with a generating capacity range from 5kW
to 100kW is named as Micro-hydropower [20].

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From renewable energy sources hydropower plant is more efficient, reliable and source of clean energy, unlike
the fossil fuel power plant. For the location where there is enough flow of water and demand for electricity,
the above characteristics of hydropower result in the growth of the plant from small to medium size hydropower
generation stations [20]. Micro-hydro plants are more feasible and cost reductive for off-grid systems at a place
where it is detached from the grid with an area of lower population density [20].
2.3.2 Classification of hydropower
The Hydropower Plants can be categorized based on the type of operational feature, by demand of electrical
power, by installed capacity, available head at the inlet, discharge through the vanes, and specific speed.
2.3.2.1 Classification of hydropower by operational feature
Any researcher who is interested in studying about the engineering of hydropower should require to understand
the development of different hydropower types. In this thesis they are classified as follows:
● Run-of-river hydropower: it is a facility that diverts the flowing of water from its originated river via
a penstock or a canal to rotate the turbine. Usually, the development of run-of-river may have small or
no facilities for storing water. The facility regulated the flow of the water depending on the daily
demand fluctuation where the hydropower providing continuous electricity supply at baseload with
some operational flexibility [21].
● Diversion and canal developments: This type of hydropower changes the natural flowing channel of
the river into a penstock or a canal by changing the water flow in the stream for some reasonable
distance.
● Storage hydropower: Typically, it is a large hydropower system that stores water at the upper
reservoir. The stored water in the upper reservoir will gain potential energy and when it is released
through a penstock to the turbine it hits the turbine and the turbine rotates the generator. Then electricity
is produced as the generator start rotating. Such hydropower meets the baseload and can shut-down and
start-up in a short period to meet the peak load demand. It can operate for a long time independently
because of the ability that can offer enough capacity of storing water [21].
● Pumped-storage hydropower: Mostly it is used to provide peak-loads by cycling water between the
upper and lower reservoir using excess energy generated at minimum load demand by pumps. When
the demand for electricity goes maximum, the water stored in the upper reservoir is released to the
lower reservoir through the turbine to generate electricity. Mostly, since demand during the night is

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lower, the water is pumped to its upper artificial lake and released during the day when the demand
rises to its peak [21].
2.3.2.2 Classification of hydropower based on the demand for electrical power
● Base-load developments: the energy available necessarily all the time is called firm-power. Base-load
plants are functional when the power generated by the hydropower plant meets the firm power and all
or portion of the continual electrical load.
● Peak-load developments: Plants whose generation capacity is relatively large and the amount of the
water discharged can be varied are used to sufficiently meet the load at peak demand. A storage system
or a reservoir is necessarily required to store and discharge enough water when demand is at peak.
2.3.2.3 Classification of hydropower by its installed capacity
Classification of hydropower by its Installed Capacity is different from countries to countries, for instance, in
some countries like Spain, Portugal, Greece, Ireland, and Belgium 10 MW is accepted as the installed capacity
for the upper limit. In Italy, plants should sell energy at low prices if the installed capacity of the plant exceeds
the fixed limit at 3 MW and 1.5MW in Sweden too. In France, the 12MW limit has been established recently
not as an explicit limit of micro-hydro power, but as the maximum value of installed power for which the grid
should purchase electrical energy from renewable energy sources [22]. Many countries have their classification
criteria to classify hydropower plants, a universal classification of hydropower plants is as given below in
Table 2.1.
Table 2.1. Classification of hydropower by installed capacity
Type Capacity
Large-hydro Greater than 100 MW and often supplying a large electricity grid
Medium-hydro 15-100 MW grid-connected
Small-hydro 1-15 MW – usually feeding into a grid
Mini-hydro Between 100kW – 1MW; either standalone scheme or often
feeding into the grid
Micro-hydro Between 5kW – 100kW; often providing a community or an
industry in a remotely located area detached from the grid.
Pico-hydro Between a few hundred – 5kW

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2.3.2.4 Classification of hydropower based on the availability of water head
The hydraulic head is a key specific factor that affects the selection of the turbine, components required, and
the cost of construction for the hydropower plants. Therefore, reference models should be developed for
different ranges of head and matching turbine categories:
⮚ Low head (2 - 30 m): Archimedean Screw, cross-flow, Francis, axial flow (AF) Kaplan/propeller,
[20, 11].
Low head hydropower plants use the above types of turbines for the referenced range of head as shown in
figure 2.1 (a). The water resource such as the river or the pond is just directed to the dam, and it flows through
the penstock just after the water coarse to the turbine [24].
⮚ Medium head (30 - 100 m): conventional Kaplan/propeller, Francis [20, 11].
Forebay is constructed for this power plant mainly for water storage purposes. They serve as a storage tank
and they tap the water from the river then sends it to the turbine through the penstock [24].
⮚ High head (100-m and above): Pelton, Turgo, and Francis [21, 11]
This type of dam is usually constructed to store a big amount of water at the top reservoir as shown in Figure
2.1 (c). at peak load demand an extra amount of water is required to supply to the turbine, so the surge tank
releases the water it has stored at normal operation [24].
Figure 2.1. Types of hydropower by the head [25]
The net head and the gross head are important during head determination. The distance in vertical from the
top point of the penstock that sends the water under pressure and tailrace where the water leaves the
powerhouse is named as the gross head. The difference in gross head and head loss created from the friction
in the penstock gives net head. (net head = gross head – losses in the penstock) [25].

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2.3.3 Micro-hydropower basics
For electrical power output from 5kW – 100kW, the micro hydropower is the prospective solution for the
generation of electricity. Among the benefits and reasons for the practical application of MHP compared with
traditional hydropower, one is a small impact on the environment, low cost, serviceability, no need of
relocating people, and the ability to construct the plant nearby the consumers [26].
Figure 2.2. comprises of a water turbine, generator, gearbox, and electrical unit, that can be a converter,
capacitor bank, static reactive power compensator, or others.
Figure 2.2. Structure of hydropower plant
The modest micro-hydro power plant is constructed on the run-of-river water coarse; no storage proficiency is
required to store the water. It produces electricity only when the water starts running or due to other civil work
components, it might have a small capacity for water storage. Rural areas that are remotely located and
detached from the grid that is in a need of electricity, micro-hydropower is an exciting outlook to supply power
for those areas [15].
There is also a possibility for this type of plant to be connected to the grid directly or indirectly of connection.
The voltage quality and the frequency are a concern in the advancement of the plant which could supply several
consumers.
2.3.3.1 General principles of micro-hydropower plant (MHP)
Head and flow are the foremost significant parameters for the generation of electricity from water. Both are
necessarily needed to produce hydroelectric. Water is subjected to the conduit of penstock from the height of
the head of the plant to downhill through the mechanical device called the turbine. The water flowing in the
pipeline gets pressurized by the head of the site. This pressurized water creates a force which makes the turbine

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to rotate. The hydro turbine is coupled to the generator’s shaft with a coupling device so that the generator
rotates to produce electrical power as the turbine starts rotating. However, because of the inefficiency of the
generator and the turbine, always the produced electrical output power is a little bit less than the input power
from the water.
Figure 2.3. Head of a micro-hydropower system [24]
The elevation created between the intake of the water and the turbine is named as head or water pressure. The
vertical height (head) measured by meters or feet, or as pressure, pound per square inch. The net head is always
less than the pressure or gross head that is the pressure obtainable at the turbine the minute water is flowing.
The diameter of the pipeline also affects netload.
Flow is the amount of water obtainable and is articulated as ‘volume per unit of time’, such as cubic meters
per second (m3
/s), gallons per minute (GPM), or liters per minute (lpm). Design flow is the all-out flow for
which the hydro system is calculated [24].
2.3.3.2 Power from a micro-hydropower plant
Knowing the quantity of flow of water accessible from the watercourse for power production and the existing
head are the essential elements to know the power potential of water in a stream. The amount of water that is
used at the powerhouse for the generation of power is the volume of water in m3
/s or liters/sec that is subjected
to the penstock’s intake. Therefore, the total power that can be produced from the water in hydroelectric power
plant due to its head is specified by:
P = η ‧ ṁ ‧ g ‧ h = η ‧ ρ ‧ Q ‧ g ‧ h (2.1)

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Where: P – is the total power that could be produced, ṁ - is the mass flow of water falling = Q ‧ ρ, η – is the
overall efficiency of power stations, ρ – is the density of water, Q – is the flow rate of water= Volume V per
unit time, g – is the acceleration due to gravity (9.81 m/s2
), h – is the height of the waterfall.
Equation (2.1) represents the direct relationship of hydropower output power and the two natural parameters
which are the head of the waterfall and the flow quantity of the water. The efficiency is the subsequent
significant parameter which can be enhanced through appropriate assortment and operation of apparatus. The
overall efficiency is denoted by (η) which is a product of the efficiency of the turbine and generator neglecting
losses in the pipe.
Based on the design and type of the turbine used, usually, the efficiency of the turbine ranges from 0.85 to
0.95, including efficiency losses from friction and turbulence between the entrance of the turbine and the end
of the draft-tube. The losses due to losses in the generator result in heating and noise in the machine and
powerhouse dropping the efficiency 98%, increasing the number of installed units can raise the overall station
efficiency, especially when flows are fluctuating [27].
2.3.4 Principal components of micro-hydropower plant
The main components of a basic Micro Hydropower System (MHS) are shown in Figure 2.4.
Figure 2.4. Over-all arrangement of the MHP and its main components [28]

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All those represented and used the main components of a micro-hydro power in Figure 2.4 could be categorized
under components of civil work and components of powerhouse groups. The following section explains all
these components classified into three.
2.3.4.1 Civil work components of micro-hydropower unit
The water that is flowing through the micro-hydropower system is controlled by the civil work constructions
and conveyances take the largest part of the work. The construction of civil structures must be at a feasible
location and should be designed at optimum performance and stability. To reduce the cost and to make sure
the system is reliable factors such as fitting technology, selection of structures that are cost-effective and
environmentally friendly, wise usage of local material and labor, drainage area treatment and landslide area
treatment should be considered [25].
⮚ Diversion weir and intake
It is a barrier civil work built along the river that drives the water into the settling basin via an opening in the
riverside [28].
Figure 2.5. Diversion weir and Intake [29]
⮚ Headrace
The water in the micro-hydropower is transported from one point to another point using the headrace. So, the
function of the headrace in this system is to transport the designed discharge from the intake to the forebay.
Commonly, all micro hydropower plants use canal systems, pipe systems are applicable only for difficult
terrains. A canal can be stone masonry or concrete (lined) or earthen (unlined). Mild steel or HDPE pipes can
be used in micro-hydropower and it can be either open or buried [29].

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When building the headrace canal the slope of the canal should be slightly elevated to avoid a higher velocity
of water that causes erosion on the surface of the headrace canal [30].
⮚ Settling Basin
The settling basin that might be built at the intake of the forebay is used to trap sand or suspended silt from the
water earlier ingoing the penstock [28].
To reduce the sediment density, which hurts other components of the MHP de-sanding basins are used to catch
remains by letting the particles settle down by dropping the speed of the water and clearing them out earlier
they go in the canal. Hence, they are regularly constructed at the head of the canal [30].
Figure 2.6. Settling Basin [29]
● Spillway
Spillways are required in the case where there is a flooding problem of water to remove excess water from the
flood that helps to lessen the adverse effects on the components of the micro hydropower. Often, spillways are
built in the de-sanding basin and the forebay from which the surplus water is without harm sidetracked to the
water basis.

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Figure 2.7. A typical spillway in Micro Hydropower System [29]
⮚ Forebay
The Forebay is a tank pool that is found at the termination of the headrace canal where the penstock is
connected to it. The forebay is mainly used to decrease the entry of air bubbles into the penstock pipe, to avoid
cavitation or explosion occurs due to the trapped air bubbles in the penstock and at the turbine under high
pressure. The head of the micro-hydro is determined from this level, so it is also essential to govern the water
level at the forebay [30]. Figure 2.8. demonstrates a forebay tank in the micro-hydropower System.
Figure 2.8. A typical forebay tank in Micro Hydropower System [30]
⮚ Penstock
Water is conveyed from a state of free-flow (at a forebay or a settling basin) to a pressurized state of flow to
the turbine through a penstock. The potential energy of the flow of the water at the forebay or the settling basin
is converted to kinetic energy at the turbine by the penstock [29]. For this reason, it is among the utmost

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significant components of the micro hydropower with different flow rates based on the size and is every so
often located at a slope over 45 degrees [30].
The penstock is an important constituent of the micro-hydropower system of which it takes the one-third budget
of the total expense in the installation of the plant and should be selected carefully and specifically designed.
Head loss and capital cost are the main aspects to consider are when selecting a penstock because when the
pipe diameter increases the head loss from friction decreases but in a reverse way the cost of the pipe increases
as the diameter increases. Therefore, there should be a compromise between performance and cost during the
selection of a penstock.
Figure 2.9. Mechanisms of the penstock assembly [30]
⮚ Tailrace
The tailrace is the downstream part of the civil work components where the seized water re-enters back to the
source after use. It is the latter part of the micro-hydropower plant construction earlier the water goes in the
downriver. The tailrace is wider as moved towards its end for the reduction of energetic losses. The loss of this
energy at its water outgoing helps to reduce the pressure created back on upstream thus helps the turbine to
operate efficiently [27].
2.3.4.2 Powerhouse components
The powerhouse is the part of the components of micro-hydropower where the mechanical power is converted
to electrical power. Powerhouse comprises electro-mechanical equipment such as turbines, generators, drive
systems, and electrical load controllers.

21 | P a g e
⮚ Turbine
The turbine in the hydropower generation is the foremost important component of the part of the powerhouse
component. It is a mechanical device that converts the flow of the kinetic energy of the water flowing from the
height of ahead through the penstock to rotational mechanical energy through the runner rotation. The selection
of the appropriate turbine depends on the head of the site and the flow rate of the river or the water flowing
technical parameters. Also, maintenance costs and availability of a person who maintains the turbine are
another practical consideration. The rotor speed of a turbine at its best performance is regarded as the optimal
speed of the turbine. The turbine desires to work at this optimal speed to get the maximum conceivable output
at entirely loading circumstances. Turbines have been generally differentiated based on their functionality into
two parts: impulse turbine and reaction turbine [30].
Impulse turbines include Pelton, Turgo, and Cross-flow turbines. Their rotor is not submerged in the water like
the reaction type of turbines but they rotate freely in the atmospheric pressure. The high-velocity of water
creates an impulse force that affects the bucket mounted on the periphery of the runner and makes the runner
and the shaft to rotate. The water under pressure is converted to kinetic energy by the jet type nozzle headed
to the turbine [30].
Unlike impulse turbines, Reaction turbines are different in that it operates by the reaction force of the prevailing
water and the water that is acting on the wheel is greater than the atmospheric pressure because of the
submersion of the rotor of the turbine in the water. At the vent, a draft tube is tailored to the turbine. Both the
potential and kinetic energy of the water are being utilized [30].
⮚ Generators
Generators are an electrical machine that are the main power components of a micro-hydropower system that
converts a mechanical form of energy into electrical energy. Different types of generators are available based
on their applications, construction, and power generation.
In hydroelectricity, generally, two types of generator types are available named as synchronous or
asynchronous (Induction generators). Synchronous generators are extensively applicable on a large scale and
in a system where constant rotation of the rotor is required. But the asynchronous or the induction generators
applicable in a situation where the level output power is lower (< 10MW) [30]. Induction generators are
correspondingly the chosen type of generators in Micro Hydro Project because they can work at inconstant
speeds with constant frequency, are accessible cheaply, and need less maintenance than the synchronous
generators. Both generators can be applicable allied to the grid or just grid-unconnected operation.

22 | P a g e
⮚ Drive systems
The drive system is useful to transfer rotational kinetic energy from the turbine to the shaft of the generator at
multiplied or the same rotation speed and required direction to produced electrical energy at stable frequency
and voltage. The following types of drive systems are used in micro-hydropower systems.
Direct drive: this type of drive system is required when only the rotor of the generator is needed to rotate at
the same speed as the rotation speed of the turbine because it directly connects the generator and turbine. This
coupling is advantageous in low cost, higher efficiency, and lower maintenance [25].
“V” or wedge belts and pulleys: it is the most commonly used drive system in the micro-hydro system and
they are widely available and used in all kinds of machinery in the industry [25].
Timing belt and sprocket pulley: they are toothed belts and pulleys commonly used on the camshaft drives
for vehicles. They are clean-running and efficient especially for very small drive systems less than 3kW where
efficiency is significant [25].
Gearbox: For larger types of machinery where the belt is cumbersome and inefficient, the gearbox is used.
they have challenges related to alignment, specifications, cost, and maintenance and this does not allow them
for use in micro-hydropower systems except they are specified as part of generator and turbine [25].
Figure 2.10. Direct coupled drive system [25]
⮚ Electrical Load Controllers
In rural settings, micro-hydro power systems are designed to operate at its full capacity to reduce the cost of
the electromechanical controller. The flow of the water passing through the turbine is regulated by the
electromechanical control systems that control the generator's electrical energy output. Though operating the
generator at full output power, it strains the generator and the generated power fails to match the load demand.
Consequently, micro-hydro systems suffer from an increased failure rate. As a result, the mismatching of the

23 | P a g e
electric supply and the electric load deviated the system frequency. When supply is greater than demand the
generator speeds up with increasing frequency and slows down when the electric load demand is greater than
the supplied power with decreasing frequency.
Nowadays, programmable logic controllers (PLC) are widely used in the implementation of an electrical load
controller that makes them feasible in the application of micro-hydropower because of the ability to withstand
dirt, high levels of dust, and moisture [25].
The type of generator built in the system is a base for the selection of an electronic load controller. For instance,
Induction Generator Controllers (IGC) are essentially mounted when the induction generator is installed in the
MHS [31].
2.3.5 Hydraulic turbines
Hydro turbines are mechanical devices coupled to a generator which is rotated by different types of mechanical
energy to generate electricity as a result of the rotation of the shaft of the generator. From the general formula
represented by Equation 2.1 above, for any hydro system’s power, the available power is power available is
relative to the product of flow rate (Q) of the water flowing and the pressure head (H).
The finest turbines can have hydraulic effectiveness in the range from 80% to over 90% [32] in advanced to
other prime movers.
2.3.6 Types of hydraulics turbines
In Table 2.2, hydro turbines are roughly classified relative to their size as high, medium, and low head. The
higher head for a smaller turbine can be a lower head for a larger. For instance, maybe a Pelton turbine is used
at 50m head at a 10-kW system but may require a minimum head of 150 m to be well-thought-out for a 1 MW
system. In Figure 2.20, the precise range of the flow, range, and the power applied to various turbine are
presented. These are assessed and reliant on the detailed design of each producer [32].

24 | P a g e
Table 2.2. Impulse and Reaction turbines
Head Classification
Turbine Type High(>50m) Medium(10-50m) Low(<10m)
Pelton Cross-flow Cross-flow
Impulse Turgo Turgo
Multi-jet Pelton Multi-jet Pelton
Archimedes Screw
Reaction Francis (Spiral case) Francis (open flame)
Propeller
Kaplan
Generally, based on their principle of operation hydraulic turbines are divided into either reaction or impulse
turbines. Reaction turbines are submerged in the water surrounded by pressure casing to which lift forces are
imposed to it as a difference in pressure across them, like those on aircraft wings, which cause the runner to
rotate. On the other hand, an impulse turbine runner is driven by a jet of water in the air, and the water remains
at atmospheric pressure previously and later made contact with the runner blades [32].
2.3.6.1 Impulse turbine
Usually, the behavior of the simplest design of the impulse turbines makes them be the most common
application for high head MHP. The runner of an impulse turbine moves by the velocity of the water and
discharges to atmospheric pressure. For hydropower sites with high head and low discharge of water, impulse
turbines are the most efficient. As the height of the head increases the water required for a given amount of
power decreases. Generally, high head hydro offers the most cost-effective developments. Therefore, smaller,
and hence cost-effective apparatus is required. The water-driven from the forebay into the pipeline creates
kinetic energy at the nozzle that makes the blades of the turbine to rotate.
The three main types of impulse turbines are called the Pelton, the Turgo, and the Cross-Flow turbines.
⮚ Pelton Turbine: The Pelton turbine as shown in Figure 2.11 a larger velocity of a jet of water is
engaged tangentially to the wheel with a series of split buckets that are set around its rime. The water jet
knockouts individual bucket and it splits in half, so each half is turned and bounced back almost through 180°
by the splitter which splits the bucket into two halves. Just about all the energy of the water goes into driving
the bucket and the bounced waterfalls into a discharge channel below [32].

25 | P a g e
Figure 2.11. Pelton Turbine [29]
⮚ Turgo Turbine: The Turgo turbine shown in Figure 2.12 has similar characteristics with the Pelton
turbine but the runner plane is strike by the jet of the water at an angle of 20° that makes the water enter one
side of the runner and leaves on the other side. Hence, the discharged fluid interfering does not limit the flow
rate with the incoming jet as this is the case for Pelton turbines. As a result, the runner diameter of the Turgo
turbine is smaller than a Pelton can have a smaller diameter runner than a Pelton turbine for alike power [32].
Figure 2.12. Turgo Turbine [32]
⮚ Cross-Flow Turbine: A cross-flow turbine gets its name from the way the water flows through, or
more correctly ‘across’ the rotor as shown below in Figure 2.13 has a drum-like rotor with a solid disc at each
terminal and gutter-shaped ‘slats’ connecting the two discs. From the top of the rotor through the curved blades,
a jet of water enters, evolving on the far side of the rotor by passing through the blades a second time.

26 | P a g e
Figure 2.13. Cross-Flow Turbine [23]
The second name given as Banki-Michell for the Cross-flow turbine is characterized by simple structure but
low efficiency, applicable for small hydropower stations whose water head is in the range of 10m-150m, and
a power output that can reach up to 300kW [15].
The advantage of cross-flow turbines is they can be easily manufactured, cheap compared to other turbine
types, easy to repair. It can generate power even during low flow rate periods [15].
2.3.6.2 Reaction turbine
The power developed by a reaction turbine is a combined result of the action of the flow and pressure of water.
Unlike impulse reaction, the runner of the reaction turbine is directly immersed in the stream of water that
flows over the blades instead of hitting each blade individually. As compared to impulse turbines, reaction
turbines are applicable in the site where the high flow of water and low head are available even though there
is many overlapping between the two turbines [33] as depicted in Figure 2.20.
⮚ Francis Turbine: is one of the types of reaction turbines which is commonly applied in a hydroelectric
plant whose generation capacity is large or medium. A site head at a minimum of 2m and a maximum of 300m
can use a Francis turbine. In addition to this, Francis turbines are advantageous for horizontal and vertical
positioned installation of the turbine as they have the same performance of the operation. In hydropower plants,
Francis turbines are used frequently as they have a wide range of operational coverage. The reason why these
turbines are considered a reaction turbine is the water going thru the turbine stays at less or more the same
speed even if it loses its pressure [34].

27 | P a g e
The flow of water to the turbine is radial to its axis of rotation meaning that the axis of rotation of the turbine
and the flow of water is perpendicular. After striking the turbine it leaves axially or parallels to the axis of
rotation [34].
Figure 2.14. Francis turbine and its main components [34]
⮚ Kaplan and Propeller Turbine: they are axial flow reaction turbines. Commonly applicable for the
head of a site ranging from 2m to 40m [23]. The runner of the Kaplan turbine can be adjustable but guide-
vanes may or may not be. The Kaplan turbines are termed as ‘double regulated’ when both the guide-vanes
and the runner are adjustable and ‘single regulated’ when the only runner is adjustable. If the runner is fixed,
then the Kaplan turbine is called a Propeller turbine and be applicable for the constant flow and head of a
hydropower plant which makes them unpracticable in smaller hydropower plants [23].
Figure 2.15. Kaplan turbine [35]

28 | P a g e
⮚ Archimedes Screws
Archimedean Screw Turbines are used in hydropower where there are low head and high flow rates of water
and it is fish friendly. Though they are generally applicable for the head that is less than 1.5m, they still operate
efficiently on the head that is as low as 1m. On its own Archimedes screws can operate on 8m head height but
if the head is greater than this height another suitable turbine for the site can be implemented. In Archimedes
Screw Turbine the water is subjected at the top of the screw so that the weight of the water can push the turbine
to rotate and it leaves at the bottom of the turbine. Since the rotation of the turbine is slower as compared to
the generator, multiple gears of belts are used to connect the turbine with the generator [36].
Figure 2.16. Archimedes screw plant principle [37]
The maximum water flow rate is determined by the diameter of the screw-like for the smallest 1m diameter of
a screw that can pass quantity water of 250 liters/second. In most cases for a 5m screw diameter 14.5m3
/s of
the maximum flow rate of water is engaged to it. Mostly, 3 meters is taken as the maximum diameter that can
be delivered to a site whereas the 5-meter maximum is based on practical delivery limits. A number of screw
turbines can be implemented for the site where there is more flow rate [36].
Regarding the power output of the Archimedean screw turbine, it can generate the smallest of 5kW and the
largest of 500kW [38].
Typically, Archimedean screws rotate at a speed of around 26 RPM, so this speed of screw should be connected
to a gearbox to maximize to 750 and 1500 RPM of the generator speed. Though the screw is rotating at a
relatively slow speed, it still splashes water to the outside area of the power plant. This splash of water is
reduced by fixing a splash guard at the edge of the screw turbine as shown in Figure 2.17 [36].

29 | P a g e
Figure 2.17. Archimedes screw turbine [38]
Practically, for the cost-effective implementation of a screw turbine, it is normally constructed at 22 degrees
from the horizontal having a scope if necessary to adjust the angle slightly [36].
2.3.7 Hydraulic turbine efficiency
The performance of a turbine characterizes the capability of the turbine. It is important also to have an
understanding that its hydrodynamic behavior. It is essential to remember that the efficiency characterizes not
only the ability of a turbine to exploit a site optimally but also its hydrodynamic behavior. If the hydraulic
design is not at optimum then takes the term a ‘very average efficiency’ that can cause problems like cavitation
and vibration which highly reduces the annual production and shortens the life of the turbine [39].
Every generation operator is required to ask the manufacturer of the turbine for its efficiency that has
experimentally approved in the laboratory. Even the same for micro-hydropower turbines [39].
Table 2.3 indicates the efficiencies of different small hydraulic turbines.

30 | P a g e
Table 2.3. Typical efficiencies of small turbines [20]
Turbine type Best Efficiency
Kaplan single regulated 0.91
Kaplan double regulated 0.93
Francis 0.94
Pelton n nozzles 0.90
Pelton 1 nozzle 0.89
Turgo 0.85
Kaplan single regulated 0.91
Archimedes Screw 0.87
Figure 2.18 is used in Table 2.3 to indicate the efficiency of various turbines by the manufacturer's guarantee.
The efficiency of the turbine is multiplied with generator efficiency to obtain the overall efficiency.
Figure 2.18. Typical small hydro turbines efficiencies [23]
The curve shown in Figure 2.19 is an efficiency curve for variable-speed Archimedean screw.

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