HYBRID POWER SYSTEM USING SOLAR, WIND AND SERVICE LINE

Transcription

1 UNIVERSITY OF NAIROBI SCHOOL OF ENGINEERING DEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERING HYBRID POWER SYSTEM USING SOLAR, WIND AND SERVICE LINE PROJECT INDEX: PRJ 044 BY AMBUTU AMUKONGO ACADIUS F17/1462/2011 SUPERVISOR: PROF M.K. MANG OLI EXAMINER: DR. CYRUS WEKESA PROJECT REPORT SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE OF BACHELOR OF SCIENCE IN ELECTRICAL AND ELECTRONIC ENGINEERING OF THE UNIVERSITY OF NAIROBI 2016 SUBMITTED ON: 13 TH MAY, 2016

2 DECLARATION I hereby declare that I carried out the work reported in this report in the Department of Electrical and Information Engineering, University of Nairobi, under the supervision of Prof M.K. Mang oli. I solemnly declare that to the best of my knowledge, no part of this report has been submitted here or elsewhere in a previous application for award of a degree. All sources of knowledge used have been duly acknowledged. (Signature & Date)... AMBUTU AMUKONGO ACADIUS F17/1462/2011 i

3 APPROVAL This is to certify that the project titled Hybrid Power System Using Solar, Wind and Service Line carried out by Ambutu Amukongo Acadius, has been read and approved for meeting part of the requirements and regulations governing the award of the BSc. Electrical and Electronic Engineering degree of University of Nairobi, Nairobi, Kenya..... PROF M.K. MANG OLI DATE (PROJECT SUPERVISOR)... PROF H.A. OUMA DATE (HEAD OF DEPARTMENT) ii

4 DEDICATION This project is dedicated to my parents Mr. B.A Sensah and Mrs. S.L Ondiso, my siblings G. Khabukwi, C. Mukunda, B. Shinyeka and A. Ayidi for their love and support in life, studies and in my project. Duly appreciated. iii

5 ACKNOWLEDGEMENTS I thank the almighty God for the favors bestowed upon me. I thank my supervisor Prof. M.K. Mang oli for not only the support he gave me throughout the project but also for the commitment he showed towards the project success. I appreciate the guidance provided to me by Eng. Onditi and Mr. Onsare James from Kenya Power who also ensured that I had all the relevant information to successfully complete the project. I would like to thank Mr. Lomulen and Mr. Muchisu Albert who were of great help due to their vast experience with PV Systems. To my group members Khaemba, Hilda, Koki and Mokeira you will always be acknowledged. Finally, I thank all my classmates (class of 2016) for being a family to me. iv

6 TABLE OF CONTENTS Contents DECLARATION... i APPROVAL... ii DEDICATION... iii ACKNOWLEDGEMENTS... iv TABLE OF CONTENTS... v LIST OF FIGURES... viii LIST OF TABLES... x LIST OF ABBREVIATIONS AND SYMBOLS... xi ABSTRACT... xii Chapter 1 INTRODUCTION Background Problem Statement Objectives Methodology Project Scope Expected Results Hybrid Power System... 3 Chapter 2 LITERATURE REVIEW Introduction Overview of the Keywords Renewable Energy Why Renewable Energy Shortcomings of Renewable Energy Solar Energy Why Solar Power Shortcomings of Solar Power How PV Cells Generate Electricity... 7 v

7 2.4.4 Components of a PV Array Wind Energy Why Wind Energy Shortcomings of Wind Power Wind Power Generation Components of a Wind Turbine Hybrid Power System Electricity Generation Coupled at DC Bus Line Electricity Generation Coupled At AC Bus Line Auxiliary Components Batteries Rectifier Inverter Charge Controllers Service Line Conclusion Chapter 3 DESIGN Introduction Wind and Solar Resource Assessment Load Assessment Design of Solar PV System Design of Wind Turbine System Coupling of Wind Turbine and Solar PV System MPPT Solar Charge Controller Wind Charge Controller Phase Bidirectional Dual Mode Hybrid Inverter Battery Bank DC Cable Sizing AC Cable Sizing System Protection and Mechanical Considerations System Protection Mechanical Considerations vi

8 3.8 Conclusion Chapter 4 RESULTS AND ANALYSIS Introduction Solar System Power and Energy Output Wind Turbine Generator Power and Energy Output Hybrid Power System Power and Energy Output Financial Analysis Conclusion Chapter 5 CONCLUSION Conclusion Recommendations REFERENCES APPENDIX A: CLIMATIC DATA OF SHINAKOTSI AREA APPENDIX B: CONDUCTORS AND CABLES MANUAL APPENDIX C: TROJAN T-105 DATA SHEET APPENDIX D: APOLLO MPT-SERIES DATA SHEET APPENDIX E: SERAPHIM SRP-315-6MA DATA SHEET APPENDIX F: DEMING SOLAR CONTROLLER SERIES (120V84A) DATA SHEET APPENDIX G: ECO VANE (ev600 10kW) WIND TURBINE DATA SHEET APPENDIX F: DEMING POWER FKJB-10KW WIND CONTROLLER DATA SHEET APPENDIX G: MIDNITE SOLAR COMBINER BOX (MNPV-6) DATA SHEET APPENDIX H: ELECTRICITY COST IN KENYA vii

9 LIST OF FIGURES Figure 2.1 Solar Array... 8 Figure 2.2 Wind Speed Increases with Height Figure 2.3 Structure of a Wind Turbine Figure 2.4 Electricity Generation Coupled at DC Bus Line Figure 2.5 Electricity Generation Coupled at AC Bus Line Figure 3.1 Line Graph of Wind Speeds at 10m, 20m and 50m above Ground Figure 3.2 Solar Radiation at Different Tilt Angles Figure 3.3 Shinakotsi Load Profile Figure 3.4 Summary of Sizing Solar PV System Figure 3.5 Daily Output of a Module Figure 3.6 Minimum Number of Modules Required Figure 3.7 Design of Wind Turbine Generator Figure 3.8 Coupling of the Hybrid Power System Figure 3.9 The Hybrid Power System Figure 3.10 Calculation of Usable Capacity Figure 3.11 Calculation of the Minimum Number of Batteries Figure 4.1 Solar Power Output Figure 4.2 Solar Array Energy Output Figure 4.3 Wind Generator Power Output Figure 4.4 Wind Generator Energy Output Figure 4.5 Hybrid System Power Curve viii

10 Figure 4.6 Hybrid System Energy Figure 4.7 Annual Energy of the System ix

11 LIST OF TABLES Table 3.1 Site Details Table Year Average Monthly Wind Speed (m/s) at 10m 20m and 50m above Ground.. 20 Table 3.3 Monthly Averaged Insolation Incident on a Horizontal Surface (kwh/m 2 /day) Table 3.4 Monthly Averaged Daylight Hours Table 3.5 Monthly Averaged Incident on an Equator-Pointed Tilted Surface (kwh/m 2 /day) Table 3.6 Air Temperature ( 0 C) Table 3.7 Shinakotsi Daily Energy Demand Table 3.8 DC Conductor Sizes Used Table 3.9 Summary of System Protection Table 4.1 Solar Array Power Output Table 4.2 Solar Array Energy Output Table 4.3 Wind Generator Power Output Table 4.4 Wind Generator Energy Output Table 4.5 Hybrid Power System Power Output Table 4.6 Hybrid System Energy Table 4.7 Cost Estimate x

12 LIST OF ABBREVIATIONS AND SYMBOLS RES RE PV WEO MPPT TSR ABC ACSR AAC AAAC DOD SoC VDI RAE RET AEP WTG HAWT NEC THHN I Renewable Energy Systems Renewable Energy Photovoltaic World Economic Outlook Maximum Power Point Tracker Rotor Tip Speed Ratio Aerial Bundled Cable Aluminium Core/Conductor Steel Reinforced All Aluminium Conductor All Aluminium Alloy Conductor Depth of Discharge State of Charge Voltage Drop Index Reference Annual Energy Renewable Energy Technology Annual Energy Production Wind Turbine Generator Horizontal Axis Wind Turbine National Electric Code Thermoplastic High Heat resistant Nylon coated Current xi

13 ABSTRACT Energy is fundamentally the ability to do work. The society came about to be as complex and modernized as it is due to evolutionary paths taken in energy conversion from one form to another. The world is however majorly concerned of the utilities to reduce the emissions from electricity generating plants by employing renewable energy and to supply and at a low cost electricity to remote areas. Hybrid power systems provide such solutions due to the employment of renewable energy (RE) that are freely available in nature, readily available and environmental friendly reducing greenhouse emissions. A remote area in western Kenya, Shinakotsi, is selected as a case study. The stand-alone hybrid power system employs solar and wind energy to generate electricity and batteries as a back-up system. The system components and specifications are arrived at after load assessment is done and the solar insolation and wind speed data are obtained. The micro grid is expected to provide stable electricity supply to the area throughout the year at minimal cost and be environmental friendly. xii

14 Chapter 1 INTRODUCTION 1.1 Background Kenya s economic growth depends on the country s ability and capacity to explore its energy stores. Efforts have been made to explore the renewable energy sources with geothermal power plants in Naivasha, Nakuru County which have significantly contributed to energy count in the country. Assessments by the Ministry of Energy shows that the country on average receives 4.5 kwh per square meter per day in solar energy and the Wind Resource Assessment carried out by WinDForce shows that 73% of Kenya s total area experiences annual wind speed of more than 6 m/s at 100 m above ground. To achieve universal electricity access by 2030, it is estimated that 40% of new capacity will need to be provided by Mini Grids (WEO 2010). Wind and solar energy are largely untapped in the country despite its immense potential to generate electricity and therefore the need to do more research in the RES to hit the vision 2030 target where the estimated power demand is projected at 15000MW. 1.2 Problem Statement With rising concerns of greenhouse effect and fuels prices there is need to come up with a system that will generate electricity at low costs and significantly reduce greenhouse emissions. A hybrid power system based on renewable energy sources of wind and solar is to be designed. A remote area in western Kenya is selected and based on data on wind speeds and solar insolation and load profile in the area, the system is designed to meet the demands. The hybrid power system is expected to be reliable, efficient and cost effective. 1

15 1.3 Objectives 1. To design a hybrid power system based on wind and solar 2. To design a battery back-up system for the plant 3. To size the conductors used in the system 4. To provide reliable and affordable electricity supply 1.4 Methodology 1. Wind and solar resource assessment 2. Determination of system load and energy input required 3. Design of PV system 4. Design of WTG system 5. Determination of the battery storage required 6. Coupling of the PV and WTG systems 1.5 Project Scope 1. Study the solar radiation and wind speeds of the projected neighborhood 2. Load assessment of the area 3. Design a hybrid power system using wind and solar energy and batteries as back-up 4. Sizing of the conductors used in the system 5. Provide reliable and affordable electricity supply 1.6 Expected Results It is expected that the hybrid power system will be able to provide the area with stable electricity supply throughout the year, run at minimal cost and be environmental friendly. 2

16 1.7 Hybrid Power System Hybrid power systems are designed for the generation and use of electrical power. They are most cases independent of the large centralized electrical grid and in-cooperate more than one power source. This system may range from a number of megawatts to individual household power supplies of 1 kw. They deliver alternating current at a fixed frequency and observe the voltage variation of plus or minus 6%. Usually has a major control system which enables the system to supply electricity in the required quality. A "hybrid" electric system that combines wind and solar technologies offers several advantages over either single system. Even during the same day, in many regions worldwide, there are different and opposite wind and solar resource patterns. Where power is to be transported over long distances the power may be transformed to higher voltages to minimize losses but rarely is this the case. Inverters and battery systems are applied for frequency and voltage stabilization in small systems of less than 100 kw. Such a system is found on Mageta Island in Lake Victoria, Kenya. 3

17 Chapter 2 LITERATURE REVIEW 2.1 Introduction In this chapter, a detailed and thorough review of the literature in the area of hybrid power systems is presented. The literature includes journals, technical books and websites. The literature has been divided into seven sections in view of the project objectives as follows: 1. Overview of keywords 2. Renewable energy 3. Solar energy 4. Wind energy 5. Hybrid power system 6. Auxiliary components 7. Service line The first section looks at the key words of the project and defines them to come up with project definition. The second section looks at renewable energy in definition and its significance. The third and fourth sections look at solar and wind energy and their use in electricity generation. The fifth section looks at the hybrid power system as a whole using wind and solar as the energy sources. The sixth section gives a brief overview of the auxiliary components in the hybrid power system. Finally service line and conductors adopted for supply of electrical power are looked at. 4

18 2.2 Overview of the Keywords Hybrid; is the product of mixing two or more different things. Power system; is the generation, transmission, distribution and utilization of electric power and the electrical devices connected to such systems including generators, motors and transformers. Solar; is relating to or denoting energy derived from the sun's rays. Wind; is the perceptible natural movement of the air, especially in the form of a current of air blowing from a particular direction. Service Line; the line conductor that connects the consumer to the distributor. The project therefore covers the generation of power from more than one source, solar and wind, its distribution, electrical devices used in the system, their choice, and their operation as a system, system stability and system protection. 2.3 Renewable Energy Energy exists freely in nature. Some of them exist infinitely (never run out, called RENEWABLE) the rest have finite amounts (they took millions of years to form and will run out one day, called NON-RENEWABLE). Water, wind, sun and biomass (vegetation) are all available naturally and were not formed. The others do not exist by themselves, they were formed. Renewable energy resources are always available to be tapped and will not run out. This is why it is referred to as Green Energy. Renewable energy can be converted to electricity which is transported to industries and homes for use Why Renewable Energy Renewable energy is important and has a great future in the energy world because of the following fundamental reasons; 1. It is a clean form of energy and therefore reduces the greenhouse effect 5

19 2. It is free in nature and therefore offers a cheap alternative energy source 3. Since it will never run out it gives energy security and assurance hence the name energy for our children s children Shortcomings of Renewable Energy The main disadvantage is that these sources are seasonal and therefore leads to fluctuations in electricity generation from one season to the other and therefore the need to back-up the system. 2.4 Solar Energy Solar energy is energy from the Sun. It is renewable, inexhaustible and environmental pollution free. Kenya, like most other countries is blessed with large amount of sunshine all the year with an average sun radiation of 4.5 kwh/m 2 /day. Solar charged battery systems provide power supply for complete 24 hours a day irrespective of bad weather Why Solar Power Solar energy is slowly being embraced in Kenya because of the following fundamental reasons; 1. Sunlight is practically infinite, free and easily accessible 2. Cost of maintaining the system is low even in harsh weather conditions 3. The system is versatile as it can be used to supply a wide range of loads 4. Clean energy source and since it does not involve moving parts it does not contribute to noise pollution Shortcomings of Solar Power Solar power has a few shortcomings namely; 1. The output is variable depending on the availability of solar radiation 6

20 2. The efficiency of the photovoltaic modules is low being less than 23% depending on the technology used [1] How PV Cells Generate Electricity Under the sun, a photovoltaic cell acts as a photosensitive diode that instantaneously converts light but not heat into electricity Cell Layers A top, phosphorus-diffused silicon layer carries free electrons un-anchored particles with negative charges. A thicker, boron doped bottom layer contains holes, or absences of electrons, that also can move freely. In effect, precise manufacturing has instilled an electronic imbalance between the two layers Sun Activation Photons bombard and penetrate the cell and activate electrons, knocking them loose in both silicon layers. Some electrons in the bottom layer sling-shot to the top of the cell. These electrons flow into the metal contacts as electricity, moving into a circuit through an n-cell module. Electrons flow back into the cell via a solid contact layer at the bottom creating closed loop or circuit. The solar cell is the basic building of the PV power system and it produces about 1 W of power. To obtain high power, a great number of such cells are connected in series and parallel circuits on a panel, also known as a module. The solar array is a group of a several modules electrically connected in series parallel combination to generate the required current and voltage [2]. Fig.2.1 shows an example of PV array. 7

21 Figure 2.1 Solar Array Powering Homes Current leaving a module, or array of modules, passes through a wire conduit leading to an inverter. This device, about the shape of a waffle iron, inverts direct current, which flows with a fixed current and voltage, into alternating current, which flows with oscillating current and voltage. From the inverter, the solar-generated power feeds into circuitry of a household, business or power plant and onto the region s electrical grid. A remote, or independent, power system also can form a self-contained circuit without connecting to the grid. The off-grid system, however, requires batteries to store power for times, such as night, when modules do not capture enough light energy from the sun. Power output from a PV module can be obtained using equation (2.1) P PV (t) = I ns (t) A Eff(PV) (2.1) 8

22 Where; I ns (t) insolation data at time t (kw/m 2 ), A is the area of a single PV panel (m 2 ) and Eff(PV) is the overall efficiency of the PV panels and DC/DC converters Components of a PV Array A photovoltaic array consists of multiple photovoltaic modules, casually referred to as solar panels, to convert solar radiation into usable direct current electricity. A photovoltaic system for residential, commercial, or industrial energy supply normally contains an array of photovoltaic (PV) modules, one or more inverter, a tracking system, electrical wiring and interconnections, and mounting for other components. A photovoltaic system may include any or all of the following: renewable energy credit revenue-grade meter, maximum power point tracker (MPPT), battery system and charger, GPS solar tracker, energy management software, solar concentrators, solar irradiance sensors. The number of modules in the system determines the total DC watts capable of being generated by the solar array; however, the inverter is what governs the amount of AC watts that can be distributed for consumption. This means that the rating of the inverter determines the available AC watts available for use by the consumer. 2.5 Wind Energy Wind energy is derived fundamentally from solar energy via a thermodynamic process. Sunlight warms the ground causing air above it to rise. The ensuing pressure differential causes air from elsewhere to move in, resulting in air motion (wind). Different regions on earth are heated differently than others, primarily a function of latitude. Air motion is also affected by the earth s rotation. The net effect is that certain parts of the world experience higher average winds than others. The regions of highest winds are the most attractive for extracting its energy: 9

23 Theoretically, the power which can be extracted from the wind is proportional to the cube of the velocity Why Wind Energy Wind energy is key to the future of the energy sector because of the following fundamental reasons; 1. It is a free energy source and renewable hence giving cheap and secure power 2. It is a clean form of energy hence does not contribute to the greenhouse emissions 3. It is versatile in that it can supply a wide range of loads Shortcomings of Wind Power 1. Winds are seasonal hence leads to fluctuations in generated power 2. Wind turbines may be noisy leading to noise pollution Wind Power Generation Wind power systems convert the kinetic energy of the wind into other forms of energy such as electricity. Although wind energy conversion is relatively simple in concept, turbine design can be quite complex. Most commercially available wind turbine uses a horizontal axis configuration (HAWT) with two or three blades, a drive train including a gearbox and a generator and a tower to support the rotor [3]. Typical sizes for a wind turbine range from KW with electricity produce within a specific range of wind speed. Cooperative research done by manufacturing companies is aimed at increasing the aerodynamics efficiency and structural strength of wind turbine blades, developing variable speed generation and electronic 10

24 power controls and using taller tower that allow access to the stronger wind found at greater height. An important factor in how much power your wind turbine will produce is the height of its tower. The power available in the wind is proportional to the cube of its speed. This means that if wind speed doubles, the power available to the wind generator increases by a factor of 8. Since wind speed increases with height an increase in the tower height can mean enormous increase in the amount of electricity generated by a wind turbine. Figure 2.2 shows the relationship between height above ground and wind power. Figure 2.2 Wind Speed Increases with Height The fundamental equation governing the mechanical power capture of the wind turbine rotor blades, which drives the electrical generator, is given by equation (2.2) P win = 1 ρ A 2 V3 C p (2.2) Where ρ = air density (kg/m 3 ) A = area swept of rotor (m 2 ) 11

25 V = wind speed (m/s) The theoretical maximum value of the power coefficient C p is 0.59 (Betz Limit) and it is often expressed as function of the rotor tip-speed to wind-speed ratio (TSR). Whatever maximum value is attainable with a given wind turbine, it must be maintained constant at that value for the efficient capture of maximum wind power. Power is directly proportional to wind speed, as the wind speed increases the power delivered by a wind turbine also increases. If wind speed is between the rated wind speed and the furling speed of the wind turbine, the power output will be equal to the rated power of the turbine. Finally, if the wind speed is less than the cut-in speed or greater than the furling speed there will be no output power from the turbine. Power output from practical turbine; the fraction of power extracted from the power in the wind by a practical wind turbine is usually given the symbol C p, standing for the coefficient of performance. Using this notation the actual mechanical power output can be given by equation (2.3) P m = 1 ρ A 2 V3 C p (2.3) Where; C p is the performance coefficient and other symbols retain their initial meanings Components of a Wind Turbine Wind turbine has the following components two or three blades, a drive train including a gearbox and a generator and a tower to support the rotor. Fig. 2.3 shows the components of a wind turbine. 12

26 Figure 2.3 Structure of a Wind Turbine 2.6 Hybrid Power System A typical hybrid system combines two or more energy sources, from renewable energy technologies, such as photovoltaic panels, wind or small hydro turbines; and from conventional technologies, usually diesel or LPG gensets (though biomass fed gensets are also a feasible option, if locally available). In addition, it includes power electronics and electricity storage batteries. The hybrid system can be designed following different configurations to effectively use the locally available renewable energy sources and to serve ALL power appliances (requiring DC or AC electricity). The technological configurations can be classified according to the voltage they are coupled with; this is, using DC, AC and mixed (DC and AC) bus lines. DC bus line and AC bus line are considered. 13

27 2.6.1 Electricity Generation Coupled at DC Bus Line All electricity generating components are connected to a DC bus line from which the battery is charged. AC generating components need an AC/DC converter. The battery is controlled and protected from over charge and discharge by a charge controller, then supplies power to the DC loads in response to the demand. AC loads can be optionally supplied by an inverter. DC bus coupling is illustrated in Fig. 2.4 where the electricity generated is coupled to a DC bus line to charge the batteries, supply DC loads and AC loads supplied through an inverter. The total wind and PV generated power during each hour is computed by equation (2.4) P gen (t) = N wind P wind (t) + N PV P PV (t) (2.4) Where; P wind (t)is power from wind turbine, P PV (t)is power from PV panel, N PV is the number of PV panels and N wind is the number of wind turbines Figure 2.4 Electricity Generation Coupled at DC Bus Line 14

28 2.6.2 Electricity Generation Coupled At AC Bus Line All electricity generating components are connected to an AC bus line. AC generating components may be directly connected to the AC bus line or may need an AC/AC converter to enable stable coupling of the components. In both options, a bidirectional master inverter controls the energy supply for the AC loads and the battery charging. DC loads can be optionally supplied by the battery. Fig. 2.5 illustrates AC bus coupling. Figure 2.5 Electricity Generation Coupled at AC Bus Line 2.7 Auxiliary Components These components are referred to as auxiliary by the fact that they support the main components to function according to the system requirements. 15

29 2.7.1 Batteries Batteries are used for storage of DC power in a system. Important specifications include battery capacity (Ah) and battery energy (Wh). Battery life measured in cycles is mainly determined by depth of discharge (DOD) and operating temperature. Lead-acid batteries are the most common battery type in hybrid power systems. Flooded lead-acid batteries are usually the least expensive, but require adding distilled water occasionally to replenish water lost during the normal charging process. Equation (2.5) converts AC power (VA) to DC power (W). Watts = VA inverter PF inverter efficiency (2.5) Rectifier Rectifiers are used to convert the AC power from the wind turbine to DC power to be used in the charging of batteries and supplying DC loads [4]. These are normally in cooperated in the wind turbines designed for off-grid operation Inverter Power inverters are used in the hybrid power system to convert the generated power from direct current (DC) to alternating current (AC) for grid connection or for powering AC loads [5]. Most inverters are of the variable voltage, variable frequency design. Inverters are basically the pure sine wave and modified sine wave types. The modified sine wave inverters are much cheaper than their counterpart but have bounded use in AC applications. The pure sine wave inverter types are expensive but find use in any AC application. With the world heading towards high voltage DC transmission these systems find great role to play in the success of the system which has numerous advantages over the high voltage AC transmission. 16

30 2.7.4 Charge Controllers Charge controllers are used to prevent the batteries from getting overcharged or over drained in order to extend their lifetime operation. They also regulate the rate of charging and discharging of a battery bank and maintain it within a predetermined rate. A wind charge controller is different in design to the solar charge controller in that it switches from charging the batteries when full to the dump load. This is because a wind turbine has to constantly be on load to avoid overspinning and getting damaged due to high centrifugal forces. On the other hand a solar charge controller simply isolates the PV array from the batteries when full. 2.8 Service Line Service line is the conductor that links the consumer to the distributor. Here the ratings of overhead and underground conductors used in the distribution network are also briefly looked at. There is a voltage drop along all cables carrying a current because the wires in a cable have a small resistance. The voltage drop should be kept below a certain limit otherwise the appliances may not function properly. The size of a conductor is chosen according to the acceptable voltage drop. The cable cost is also important and cables used should only be as large as required for a low voltage drop in order to keep the total cost down. There are various cable designs and configurations which include; Aerial Bundled Cable (ABC), Aluminium Conductor Steel Reinforced (ACSR), All Aluminium Conductor (AAC), All Aluminium Alloy Conductor (AAAC). Service line connections are made by the use of the single core concentric cable with PVC insulation of Uo/U 0.6/1 kv. 16 mm 2 aluminium cable is used for overhead whereas 10mm 2 copper cable is used for underground service lines [B2]. 17

31 2.9 Conclusion The literature has provided an insight into solar, wind and hybrid systems in details but as brief as possible to be precise. It has given details on wind and solar energy separately then coupling them to form a hybrid power system. The hybrid power system was discussed as a whole including the auxiliary components such as charge controllers and converters. This gives an opportunity to therefore look at the design of the hybrid power system. 18

32 Chapter 3 DESIGN 3.1 Introduction In this chapter the design of the hybrid power system is done in six stages namely; 1. Wind and solar resource assessment 2. Determination of system load and energy input required 3. Design of PV system 4. Design of WTG system 5. Coupling of the PV and WTG systems 6. System protection and mechanical considerations The first section looks at the data for monthly wind speed and solar radiation [A] using 10 year and 22 year average respectively of Shinakotsi area whereas the second section looks at the load and load profile of the area. The third and fourth sections look at the design of the solar PV and wind turbine systems using the solar radiation data, wind speed data and load. The fifth section looks at combining the two systems into a stand-alone hybrid power system that includes battery back-up system. Finally the sixth section looks at the system protection and mechanical systems of the plant. 3.2 Wind and Solar Resource Assessment Shinakotsi area is located at latitudes N and longitudes E in Kakamega County, Kenya. The details of Shinakotsi area are given in Table 3.1 whereas the 10 year monthly average wind speed is given in Table 3.2. The line graph of the wind speeds at 10 m, 19

33 20 m and 50 m above ground is given in Figure 3.1. A twenty two year monthly average solar radiation of the area is given in Table 3.3 and Table 3.4 shows the monthly average sunlight hours. Table 3.1 Site Details UNIT CLIMATE DATA LOCATION Latitude 0 N 0.23 Longitude 0 E Elevation M 1503 Heating design temperature 0 C Cooling design temperature 0 C Earth temperature amplitude 0 C Frost days at site Day 0 [6] Table Year Average Monthly Wind Speed (m/s) at 10m 20m and 50m above Ground M Jan Feb Mar April May Jun July Aug Sept Oct Nov Dec Anl [7] The data shows that there is reasonably favorable wind speed at 20 m and 50 m above ground to generate electricity that meets the load. 20

34 wind speed (m/s) line graph of wind speeds at 10m 20m and 50m jan feb mar april may june july aug sept oct nov dec 10m m m month of the year 10m 50m 20m Figure 3.1 Line Graph of Wind Speeds at 10m, 20m and 50m above Ground Table 3.3 Monthly Averaged Insolation Incident on a Horizontal Surface (kwh/m 2 /day) Jan Feb Mar April May Jun July Aug Sept Oct Nov Dec 22yr [7] Table 3.4 Monthly Averaged Daylight Hours Jan Feb Mar April May Jun July Aug Sept Oct Nov Dec avg [7] Table 3.5 shows the area s radiation data at different tilt angles and Table 3.6 gives data for the air temperature of the area of study. The data shows sufficient grounds for solar power generation. Figure 3.2 shows the area s radiation data at different tilt angles. 21

35 solar radiation (kwh/m 2 /day) Table 3.5 Monthly Averaged Incident on an Equator-Pointed Tilted Surface (kwh/m 2 /day) Jan Feb Mar April May June July Aug Sept Oct Nov Dec Annual SSE HRZ K Diffuse Direct Tilt Tilt Tilt OPT OPT ANG K clearness index [7] Table 3.6 Air Temperature ( 0 C) Jan Feb Mar April May Jun July Aug Sept Oct Nov Dec Avg [7] comparison of radiation at different tilt angles Jan Feb Mar April May Jun July Aug Sept Oct Nov Dec month of the year averaged direct tilt 0 tilt 15 tilt 90 OPT Figure 3.2 Solar Radiation at Different Tilt Angles 22

36 3.3 Load Assessment Shinakotsi area s load was assessed and relevant data collected and analyzed. Table 3.7 shows the area s daily energy consumption with its corresponding load curve shown in Figure 3.3. Table 3.7 Shinakotsi Daily Energy Demand AC LOAD DESCRIPTION QTY HOURS PER DAY WATTS EACH TOTAL KILOWATTS ENERGY (kwh/day) HOUSEHOLDS bulbs security lights radio television set iron box HEALTH bulbs CENTRE security lights refrigerator water heater portable fan well water pump SHOPS bulbs security lights freezer PRIMARY bulbs SCHOOL security lights desktop inkjet printer POSHO MILL machinery security lights TOTAL SYSTEM LOSSES (10%) TOTAL ENERGY DESIGN

37 Load (kw) Load Curve hour of day Figure 3.3 Shinakotsi Load Profile From the load data in Table 3.7 and Figure 3.3 it is possible to calculate the system s capacity that will supply the area with electricity. 3.4 Design of Solar PV System The design of the solar PV system essentially is done using the steps outlined in Figure 3.4. The daily electrical requirement is as shown in Table 3.7, kwh/day. This is to be shared between solar and wind power generating units as; 1. Solar PV system kwh/day 2. Wind generator system kwh/day Daily Electrical Requirement of Appliances supplied by solar arrays = kwh The calculation of the daily output of a module is summarized in Fig. 3.5 and equation (3.1) shows the conversion of daily insolation from kwh/m 2 to daily insolation in peak-hours per day (Conversion factor is one) [8]. Hence it can be concluded as shown in equation (3.2) that daily insolation in kwh/m 2 equals daily insolation in peak-hours per day. 24

38 [8] Figure 3.4 Summary of Sizing Solar PV System Equation (3.3) shows the daily output of a single module. The daily insolation in peak-hours per used in the calculations is 5.25 peak-hours per day for the worst month of the year (July). Figure 3.5 Daily Output of a Module daily insolation(peak hours day) = daily insolation(kwh m 2 ) conv. factor (3.1) 25

39 With the conversion factor of 1; daily insolation (kwh m 2 ) = daily insolation (peak hours per day) (3.2) The solar modules used are the SERAPHIM SRP-315-6MA [E] which have an optimum operating current of 8.55A and a nominal voltage of 24 V. It is desired to employ temperature derating at the highest ambient temperature of 27 o C be 1.36% (0.04%/ o C), dirt derating factor of 5% and manufacture s tolerance of 5% for an overall factor of daily output (Wh day) = ( )A 5.25 ((peak hours)/day) 120 V (3.3) = Wh/day The calculation of the minimum number of modules needed to supply the given load is summarized in Figure 3.6. Since the solar system is to be divided into two arrays of equal outputs for flexibility then load is to be shared as in equations (3.4) and (3.5). Equation (3.6) shows the calculation of the minimum number of modules required. PV Array 1 = ( ) Wh (3.4) = Wh PV Array 2 = ( )Wh (3.5) = Wh 26

40 Figure 3.6 Minimum Number of Modules Required The charging efficiency of the flooded lead acid batteries used in the system (Trojan T-105) [C] is taken to be 85% even though it is a function of many factors as rate of charge and discharge and the state of charge i.e. not a constant figure. minimum number of strings = Wh Wh 0.85 (3.6) = 5 From equation (3.6) 5, 120 V solar modules are required. The solar modules used are rated at nominal voltage of 24 V hence to get 120 V, 5 modules are connected in a string as shown in equation (3.7) number of modules in a string = system voltage module voltage (3.7) 120 V 24 V = 5 Hence the total number of modules in array 1 is given by equation (3.8) total number of modules = no. of modules in a string no. of strings (3.8) 5 5 = 25 27

41 Therefore Array 1 has 25 modules and since there is equal sharing of the load between the two arrays, Array 2 also has 25 modules. It can therefore be concluded that the PV system is implemented in 2 arrays of 25 modules each. To calculate the current output of a PV module the derating factor of 0.89 is used. Equation (3.9) calculates the corrected current output of a module. The current output of a module equals the current output of a string. corrected current output of module = A (3.9) A = A Equation (3.10) is used to calculate the corrected current output of a PV Array [9]. currected I output of array = number of strings corrected string I(A) (3.10) A = A The current output of PV Array 1 = current output of PV Array 2 To obtain the corrected power output of the module, 14.62% temperature derating factor (maximum ambient temperature of 27 o C at 0.43%/ o C), 5% dirt derating factor and 5% manufactures tolerance are used. The corrected power output is calculated in equation (3.11). power output of a module = ( ) W (3.11) W = W Therefore the expected power output of a PV Array is calculated in equation (3.12) using the corrected power output. This is true for solar insolation of 1000 W/m 2. power output of a PV Array = W (3.12) 28

42 = W The two arrays are similar hence the same output of W is expected at solar insolation of 1000 W/m Design of Wind Turbine System The wind turbine is expected to supply at least Wh/day. The operation of wind generator system is simple but its design is complex due to trying to find the balance in system efficiency, rotor diameter and tower height to match the wind speeds of the area of study [10]. Most commercial wind turbines work with a cut-in speed of at least 3.5 m/s which possess a great challenge in designing the appropriate wind turbine for the site that will operate efficiently. The area has low wind speeds but sufficient to install wind turbine(s) to work with the PV system. With the right choice of a low speed off-grid wind turbine and tall enough towers and appropriate positioning the right combination can be found. The power output from a WTG is given by equation (3.13). The symbols used carry the initial meanings used in equation (2.2). Figure 3.7 shows the design process of a WTG system for the site. P = 1 2 ρ A V3 C p (3.13) Figure 3.7 Design of Wind Turbine Generator The power coefficient C p is specific to each turbine and varies from one wind speed to another in a non-linear manner. Hence it is important that it is obtained from the wind turbine datasheet 29

43 for appropriate calculations of expected power output from the wind turbine to be carried out. One way of choosing a wind turbine is by using the Reference Annual Energy (RAE) of the WTG mostly at 5 m/s or using the energy curve or power curve which can be matched to the particular site of interest. Equation (3.14) gives the minimal annual energy expected from the wind turbine. minimal annual energy output = minimal daily energy output 365 (3.14) = Wh/year = kwh/year Using the annual energy demand obtained from equation (3.14) and look-up tables for various wind turbines the appropriate wind turbine was found to be the Eco Vane ev kw wind turbine for off grid applications with an approximate annual energy production (AEP) of kwh at 4 m/s. This makes this wind turbine an appropriate solution for the low wind speeds of the area. Some desirable characteristics include; the low start-up speed of 1.8 m/s and low engage speed of 2.5 m/s and availability of the used system voltage of 120 VDC output. 3.6 Coupling of Wind Turbine and Solar PV System After the sizing of the PV system and the wind turbine system they are coupled through appropriate charge controllers, DC bus, bidirectional inverter and batteries to constitute a hybrid power system. The system DC voltage chosen is 120 VDC to keep the voltage drop in the recommended range of plus minus 6%. High voltage is used to keep the currents low for the various benefits as low percentage voltage drops and small cross-sectional area conductors. Figure 3.8 shows the coupling of the PV system and WTG system into a hybrid power system whereas Figure 3.9 shows the hybrid power system. 30

44 Figure 3.8 Coupling of the Hybrid Power System MPPT Solar Charge Controller The solar charge controller is expected to support 125% of the array short circuit current as shown in equation (3.15) charge controller current rating = I sc 1.25 number of strings (3.15) = A Hence the nearest controller rating is the 120V/84A model from Deming Power which can handle a maximum of 10 kw solar power. The two MPPT charge controllers used are the Deming Solar Charge Controller 120V/84A model [F]. Its features include; MPPT charging, multi-protection functions such as over-charge, over-discharge, electronic short circuit, overload and reverse connection. LED display for the state of charge (SoC) and prevents charging/discharging from the storage battery to the solar panel during the night. 31

45 Figure 3.9 The Hybrid Power System 32

46 3.6.2 Wind Charge Controller The wind turbine used ev600 10kW has a nominal rated power of 10 kw, peak power of 10.5 kw and an output of 120 VDC hence to obtain the maximum DC current from the turbine equation (3.16) is used. For the site of interest this is a theoretical maximum as the wind speeds are much lower than the rated wind speeds. maximum output current = peak output power nominal output voltage (3.16) W 120 V = 87.5 A The PWM maximum current is obtained using the PWM constant voltage as shown in equation (3.17) PWM maximum current = peak output power PWM constant voltage (3.17) W 138 V = A Using the current, voltage and power limitations the wind charge controller used is the Deming Power FKJB-10kW wind controller [F] with maximum charging current of 100 A and maximum PWM current of 80 A. some of the stand out features include; LCD display for working status of the wind turbine, battery and controller (wind turbine voltage, current, power, battery charging current and voltage). Two sets of control systems, PWM constant voltage system and 3-phase dump load system. In case of exceeding the PWM s capacity or battery disconnect the dump load will automatically start immediately to ensure safe running of the overall wind turbine system. Protection function for battery reverse polarity and overcharging (125% of nominal voltage). Auto recharging of battery at 108% of nominal voltage and equipped with surge arrestor. 33

47 Phase Bidirectional Dual Mode Hybrid Inverter The total wattage of all the equipment (connected load) is kw but the peak load is kw. Calculation of the demand factor is as in equation (3.16) which is a measure of spare capacity. demand factor = maximum demand connected load (3.16) kw kw = The maximum DC current into the inverter is obtained using equation (3.17). max. current I = solar arrays max. current I + wind max. current I (3.17) A W 120 V = A The maximum battery current is obtained using equation (3.18) maximum battery current = total wattage system voltage (3.18) W 120 V = A The AC current output is calculated using equation (3.19). The inverter is rated at unity power factor but using the worst case of 0.98 and an assumption of all appliances are connected to the system at the same time (demand factor of 1) i.e. connected load is used. AC current output = real power (3 phase voltage power factor) (3.19) W (3 240 V 0.98) = A The sizing of the inverter is done to match the system load. This is done with the assumption that all the appliances are on at the same time i.e. demand factor of 1 hence the load used is kw. Therefore the Leonics MPT-412E 3-phase bidirectional dual mode hybrid inverter 34

48 [D] which is a 15 kw inverter is used. This inverter has a nominal DC voltage of 120 V, maximum battery current of 170 A, maximum AC current of 22.7 A and 240 V/415 V AC voltage. Some desirable features include; it is capable of using multi-renewable energy sources in both DC coupling and AC coupling, automatic battery equalization, battery temperature compensation, IP65 protection (protection against contact and infiltration of water and dust- IP65-complete protection), outdoor enclosure and efficiencies greater than 94% Battery Bank The battery bank is the most expensive equipment of the system and should be handled with utmost care. The battery bank is chosen to be a back-up for the health center and primary school. This gives a value of kwh/day (plus 10% losses) hence the battery bank is designed to supply the same daily requirement. Inverter efficiency is >94% which was factored in system losses hence no need to be factored in sizing the battery bank and operates at unity power factor. Figure 3.10 shows the calculation of total usable capacity. Figure 3.10 Calculation of Usable Capacity 35

49 Equation (3.20) shows the calculation of total usable capacity. Storage days are usually between 2-5 days. For the regions around the equator the storage days is taken to be 2 due to availability of the sun all-round the year. (21087Wh 2) 120 V = Ah (3.20) Figure 3.11 shows how to obtain the minimum number of batteries needed for the system. Figure 3.11 Calculation of the Minimum Number of Batteries Equation (3.21) shows the calculation of the minimum number of batteries. For the deep cycle flooded lead acid batteries T-105 6V C20 = 225 Ah [C] used, the depth of discharge is between 50-80% in order to obtain many discharge cycles from the battery as recommended by the manufacturer. 52.6% is used in the design to obtain a large number of cycles from the batteries Ah 225 Ah = 3 (3.21) Therefore 3, 120 V batteries are required. To obtain the number of batteries to be connected in a string to get a 120 V battery bank system equation (3.22) is used. number of batteries in a string = system voltage single battery voltage (3.22) 120 V 6 V = 20 batteries 36

50 Hence the total number of batteries in the battery bank is given by equation (3.23) total number of batteries = no. of bat. in a string no. of strings (3.23) 20 3 = 60 batteries Hence the number of flooded lead acid batteries required is DC Cable Sizing Cable sizing is required to link; 1. PV Array to combiner box to solar charge controller and controller to DC bus 2. Wind turbine to wind charge controller and controller to DC bus 3. Wind charge controller to dump load 4. DC bus and DC bus to inverter 5. Battery to inverter battery terminal and controller In this sizing the voltage drop is restricted to 3% and maximum currents used in order to prevent the cables from heating up. The currents used in calculation of the DC wiring are maximum conductor currents since it is recommended in DC wiring the conductor sizes are slightly over-estimated taking the financial constraints into consideration. The 120 VDC system used helps to minimize the currents but is still lower than the 240 V/415 V on the AC side hence larger conductors are required on the DC side. The NEC (Articles , , and ) conductor sizing standards require that the conductor be sized to handle 125% of continuous current. To obtain the cable size for combiner box to controller and to DC bus the solar charge controller current rating is used as shown in equation (3.24) controller cond. sizing I = solar controller I rating 1.25 (3.24) 37

51 A = 105 A To calculate the sizing currents between the wind turbine and wind charge controller equation (3.25) is used. wind turbine cond. sizing I = ( W) 120 V (3.25) = A To obtain the sizing current between the wind charge controller and the dump load equation (3.26) is used. dump load cond. sizing I = (wind turbine rated power 1.25) system voltage (3.26) (10000W 1.25) 120 V = A The DC bus sizing current is given by equation (3.27) DC bus sizing I = total array sizing I + wind turbine sizing I (3.27) = A The sizing current between the DC bus and the inverter used is the 125% of inverter input current rating which gives A (170 A by 1.25). To obtain the current between the battery bank and the inverter battery terminal equation (3.28) is used. The conductor between the battery and inverter battery terminal is usually the most over-estimated to avoid overheating that will kill the batteries exponentially. Maximum battery bank current rating is used. battery cond. sizing I = A (3.28) = A 38

52 The PV string sizing current is A i. e. (8.55A 1.25). The voltage drop index (VDI) is used in the calculation of the wire sizes according to equation (3.29) and Tables B 1 and B 3 used to obtain the wire gauge together with the recommended current carrying capacity of each wire gauge (continuous current at 75 o C). A voltage drop of 3% is used. The results then summarized in Table 3.8 VDI = {current (A) length(feet)} {%voltage drop voltage} (3.29) Table 3.8 DC Conductor Sizes Used Connection L (feet) VDI AWG Rated I (A) PV string Combiner Box #12 25 C. Box-Solar Charge Controller #2 115 Wind Turbine-Wind Charge Controller #3/0 200 DC Bus kcml Cu 335 Wind Charge Controller-Dump Load #2 115 DC Bus-Inverter #4/0 230 Battery-Inverter Battery Terminal #4/0 230 REMARKS 1. Stranded THHN Copper conductors are used AC Cable Sizing Per phase maximum current is A, we adopt the Kenya Power distribution standards [12] which also gives room for additional load and/or future grid connection. Conductors are made of aluminium and are referred to as AA. The size used is AA 50mm 2 [Table B 2] with rated current of 181 A and rated capacity of 125 kva. All phase conductors and neutral are aluminium. Insulated conductors used are PVC insulated and are used in the following 39

53 situations; to obtain clearance from buildings, passing through forested areas, in cases where it is not possible to use underground cables and as per the designer s choice. Service line connections are made by the use of the single core concentric cable with PVC insulation of Uo/U 0.6/1 kv. 16mm 2 aluminium cable are used for overhead whereas 10mm 2 copper cable are used for underground service lines each with a rated current of 80 A and capacity of 18 kva [Table B 2]. Since the generating plant is in the load center there is no need to step up the voltage since no transmission is required. The distribution is therefore radial which helps to maintain high voltage regulation and easy isolation of lines to supply sensitive loads in times of inadequate generation. 3.7 System Protection and Mechanical Considerations System Protection The system must be properly protected to ensure safety of both the users and the equipment. Protection is done using fuses, circuit breakers and proper grounding of equipment. Fuses will be used between the combiner and solar charge controller, solar charge controller and DC bus, wind generator and wind controller, wind controller and the DC bus and DC bus and the inverter. The circuit breakers are employed between the inverter and AC load. Equation (3.30) shows the calculation of solar string fuse rating to be installed in the combiner box for each of the 5-strings. NEC (Articles , 215-3, and ) recommends 156% of the module short circuit current and 125% of rated current for controller fuse ratings. string fuse rating = 1.56 module short cct current (3.30) 40

54 A = A With a short circuit in a single module it is possible that all the array current can flow in a single string. It is recommended by the solar module manufacturer that the maximum series fuse rating be 20 A. The overall array fuse is calculated using equation (3.31) where the string short circuit current is multiplied by the number of strings. array fuse rating = string fuse rating number of strings (3.31) A 5 = A Therefore the standard 80 A fuse is used between the combiner and the solar charge controller. The solar charge controller is an MPPT type and therefore the output fuse does not have the same rating as the input fuse. The rated output current is used to calculate the fuse rating as per equation (3.32) solar charge controller fuse rating = 1.25 current rating (3.32) A = 105 A Therefore the standard 110 A fuse is used. The wind generator has a maximum current output of 87.5 A. The wind controller is a PWM type which uses the same fuse rating for input and output. Which invites the use of the 125 A fuse (wind controller fuse rating) between the wind generator and the wind controller. The inverter has a rated DC input current of 170 A (215 A DC disconnect) and 22.7 A (per phase) for AC system and has its own protection in the panel which includes; over-current (30 A per phase), over-voltage, short-circuit, over-temperature, over-voltage and under-voltage protection. Summary of the protection is shown in Table 3.9. The equipment are put as close to 41

55 each other as possible and common grounding is done. This single point grounding greatly reduces the potential for lightning damage to electrical equipment. Table 3.9 Summary of System Protection PROTECTION FUSE RATING (A) String combiner box 20 Combiner box solar charge controller 80 Solar charge controller DC bus 110 Wind generator wind controller 125 Wind controller DC bus 125 DC Bus Inverter 215 Battery Inverter 215 Inverter AC Load AC Breaker Panel REMARKS 1. Fuses used are gpv and gg types 2. Circuit breakers are adjustable amp + trip 3-phase Mechanical Considerations Since the modules are much greater than four, ground mounting is done. It is ensured that no object should shade any part of the modules at any time of the year during daytime. The modules are secured on racks fixed on concrete and tilted at 5 o facing south which also allows water to run-off washing away the dust. The modules are therefore off the ground (out of dust, run-off water and animals) and can be cooled naturally by wind. The racks are made of corrosion resistant weather proof stainless steel. 42

56 The wind generator is mounted on a 20 m tall tower secured on a concrete foundation. The area is clear of obstructions with care taken to ensure that the generator is 30 ft. above any object within 300 ft. The batteries are stored indoors in a well ventilated area on wooden battery boxes which helps minimize self-discharging of batteries. They are kept off highly used areas. The controllers and inverter are mounted on board then to the wall, not wall directly, in a secure but easy access area. The plant area is secured by a fence for security purposes and the equipment installed indoors in a well ventilated room. 3.8 Conclusion In chapter three the design of the hybrid power system based on solar, wind and battery as a back-up system is done. The battery bank is implemented in three strings which is in line with the manufacturer s recommendation of a maximum of three strings to ensure uniform charging and discharging of individual batteries. The required sizes of conductors for both DC and AC systems were also obtained. The protection of the system is done using majorly fuses and earthing, breaker panels were also employed for proper isolation. The distribution is done radially as the plant is located in the load center. Selection of the equipment used is based on performance, cost and availability. 43

57 Chapter 4 RESULTS AND ANALYSIS 4.1 Introduction In this chapter the system s results are looked at and analyzed in the following subsections; 1. Solar system power and energy output 2. Wind generator system power and energy output 3. Hybrid power system power and energy output 4. Financial Analysis In the first section the power and energy output of the solar array system is calculated, graphs plotted and relevant analysis made. In the second section the power and energy output of the wind generator is found by fitting the WTG energy curve into the area of study. Then contributions of the solar system, wind generator and battery back-up are looked at, analysis made and relevant conclusions drawn. Finally the financial viability of the system is looked at in the last section. 4.2 Solar System Power and Energy Output The power and energy output of the solar system are calculated using the solar insolation data module efficiency of 16.7 % and dimensions (1956 by 992 mm) for the 72 (6 by 12) cell module. To obtain the power output of a solar module equation (4.1) is used. P PV (t) = I ns (t) A Eff(PV) (4.1) Where PPV (t) is the power output of the module (kw), Ins. (t) is the insolation data at t (kw/m 2 ), A is the area of a single PV panel (m 2 ) and Eff (PV) is the efficiency of the module, converters 44

58 and conductors. Module efficiency of 16.2% is employed and default performance ratio of 0.75 for an overall efficiency of 12.15%. The energy output is calculated using equation (4.2) E PV (t) = I ns (t) A Eff(PV) (4.2) Where EPV is the energy output (kwh) and Ins. (t) is solar insolation in kwh/m 2 The power output of the solar arrays is captured in Table 4.1 and Figure 4.1. This was calculated using the 3-hourly day data for the worst month of July. Table 4.1 Solar Array Power Output TIME INSOLATION (kw/m 2 ) POWER OUTPUT (kw) Table 4.1 shows that solar insolation is available from about six in the morning to six in the evening. The power output is maximum at about noon where there is maximum demand as shown in the load profile. The energy output of the solar array is given in Table 4.2 and Figure

59 POWER (kw) SOLAR POWER OUTPUT TIME (24hrs) Figure 4.1 Solar Power Output Table 4.2 Solar Array Energy Output MONTH No. OF DAYS INSOLATION (kwh/m 2 /day) ENERGY OUTPUT ENERGY OUTPUT (kwh/month) (kwh/day) JAN FEB MAR APRIL MAY JUNE JULY AUG SEPT OCT NOV DEC ANNUAL

60 ENERGY (kwh) SOLAR ENERGY JAN FEB MAR APRIL MAY JUNE JULY AUG SEPT OCT NOV DEC MONTH OF THE YEAR Figure 4.2 Solar Array Energy Output 4.3 Wind Turbine Generator Power and Energy Output The energy and power output of the wind generator are estimated using the manufacturer s data sheet of the energy curve. Table 4.3 and Figure 4.3 give the power output of the wind generator. The 3-hourly data used is for the month of July. Table 4.3 Wind Generator Power Output TIME WIND SPEED 20m POWER OUTPUT (kw)

61 POWER (kw) WIND POWER OUTPUT TIME (24hrs) Figure 4.3 Wind Generator Power Output The wind generator energy output is given in Table 4.4 and Figure 4.4. Table 4.4 Wind Generator Energy Output MONTH NUMBER OF DAYS WIND SPEED (m/s) ENERGY (kwh/day) ENERGY OUTPUT (kwh/month) JAN FEB MAR APRIL MAY JUNE JULY AUG SEPT OCT NOV DEC ANNUAL

62 ENERGY (kwh) WIND ENERGY JAN FEB MAR APRIL MAY JUNE JULY AUG SEPT OCT NOV DEC MONTH OF THE YEAR Figure 4.4 Wind Generator Energy Output 4.4 Hybrid Power System Power and Energy Output The hybrid system power output is given in Table 4.5 and Figure 4.5. The battery is used to supply the peak load for a few hours at night as is evident in the results. Table 4.5 Hybrid Power System Power Output TIME SOLAR POWER OUTPUT (kw) WIND POWER OUTPUT (kw) WIND + SOLAR (kw) BATTERY POWER (kw) HYBRID SYSTEM OUTPUT (kw) AC LOAD (kw)

63 POWER (kw) HYBRID POWER TIME (24hrs) SOLAR POWER OUTPUT (kw) WIND POWER OUTPUT (kw) WIND + SOLAR (kw) BATTERY POWER (kw) HYBRID SYSTEM OUTPUT (kw) AC LOAD (kw) Figure 4.5 Hybrid System Power Curve The energy output of the hybrid system is given in Table 4.6 and Figure 4.6 Table 4.6 Hybrid System Energy MONTH NUMBER OF DAYS SOLAR ENERGY (kwh) WIND ENERGY (kwh) 50 BATTERY ENERGY (kwh) HYBRID ENERGY (kwh) AC LOAD DEMAND (kwh) JAN FEB MAR APRIL MAY JUNE JULY AUG SEPT OCT NOV DEC TOTAL

64 ENERGY (kwh) ENERGY (kwh) SYSTEM ENERGY JAN FEB MAR APRIL MAY JUNE JULY AUG SEPT OCT NOV DEC MONTH SOLAR ENERGY (kwh) WIND ENERGY (kwh) BATTERY ENERGY (kwh) HYBRID SYSTEM ENERGY (kwh) AC LOAD CONSUMPTION (kwh) Figure 4.6 Hybrid System Energy Figure 4.7 shows the annual energy output/consumption of the various sub-systems. ANNUAL ENERGY SOLAR ENERGY (kwh) WIND ENERGY (kwh) BATTERY ENERGY (kwh) SYSTEM HYBRID SYSTEM ENERGY (kwh) AC LOAD CONSUMPTION (kwh) CHARGE ENERGY (kwh) Figure 4.7 Annual Energy of the System 51

65 The hybrid power system is capable of meeting the load throughout the 24 hour period with battery back-up boosting the supply for night peak load. The system power output curve shows that there are times when power output from the system is greater than the demand, the extra power is used in the charging of battery bank simultaneously. The battery bank is a load and a source depending on the demand and its state of charge. Figure 4.7 shows that the charge energy is greater than battery energy output which means the batteries are able to recover all the charge delivered at night hence maintain a full state of charge increasing the number of cycles delivered by the batteries. For a good site a WTG operates on average between % of its rated capacity. Hence the WTG in the site operates to the required standards. The dump load serves to remove excess energy from the micro grid which helps to control the system frequency. Hence it is used as a fast acting stability control unit. 4.5 Financial Analysis The cost of the system is estimated using the current prices in the market. This is summarized in Table 4.7. To estimate the minimum cost of per unit generated equation (4.3) is used. The load factor is 0.4 with a maximum demand of kw. min. cost of per unit gen. = total annual charges units generated per annum (4.3) $ kWh = $ 0.201/kWh This translates to about Ksh ( ) = Ksh 20.41/kWh. This is the minimal cost of a unit of energy and depending on how fast one wants to recover ones capital this value is increased by a factor. 52

66 Table 4.7 Cost Estimate EQUIPMENT MANUFACTURER/MODEL UNITS COST/UNIT TOTAL COST Solar Module Seraphim SRP-315-6MA 50 $ $11, Wind Turbine Eco Vane ev600/s 10kW 1 $10,500 $10, Battery Trojan T $ $7, Inverter Leonics MTP-412E 15kW 1 $2,400 $2, Solar Charge Controller Deming 120V/84A 2 $570 $1, Wind Charge Controller + Dumb Load Deming FKJB-10kW 1 $860 $ Combiner Box Sunny Central SCCB-12 2 $92.82 $ Cables East African Cables $2, Fuses and Circuit Breakers Schneider Company $ Product Cost $37, Services (10% of PC) $3, Others (4% of PC) $1, Capital Cost $42, Charges Taxes, wages, salaries, maintenance $1,500 Interest and Depreciation (8.5% of CP) $3, Total Charges $5, REMARKS The prices are in US Dollars with an exchange rate of Kshs as of 10:03:16 The Cost of Energy (COE) is the value of the energy produced by a system over the lifetime of the system. It is given by equation (4.4) COE = {(IC FCR) + LRC + O&M + FC} AkWh (4.4) Where COE is the Cost of Energy, IC is the Initial Cost, FCR is the Fixed Charge Rate, Levelized Replacement Cost, O&M is the annual Operations and Maintenance and FC is the Fixed Charge {( ) } = $ The payback period SP is given by equation (4.5) where the initials retain their initial meanings SP = IC [(AkWh $/kwh) (IC FCR) O&M] (4.5) 53

67 {( ) ( ) 1500} = 11.8 years The cost of energy is $ (Ksh.23.80) which has a slightly higher grid parity compared to the grid prices as of February 2016 of Ksh for domestic consumer and Ksh for small commercial. However these prices keep varying as is evident in July 2014 where the cost was Ksh for domestic consumer and Ksh for small commercial [H]. Hence the cost of per unit of energy should compare favorably. The cost of per unit of energy generated reduces for larger capacities hence the system has its place in the energy world. 4.6 Conclusion This chapter has provided detailed analysis of the performance of the hybrid power system. The system provides power throughout the day and night with minimal use of the battery bank at night. The system generates enough energy to keep the batteries in a full state of charge to prolong their lifetime. The prices of the equipment used quoted in Table 4.7 are worth investing in as the system is expected to run at low costs and generate affordable electricity for the village. 54

68 Chapter 5 CONCLUSION 5.1 Conclusion The objectives of the project have been achieved as a hybrid power system based on wind and solar energy has been designed to meet the load of Shinakotsi Area. The battery back-up system has also been designed for 2 days of autonomy for the health center and lighting system. Both DC and AC conductors used in the system have been chosen after appropriate calculations were made and matched to look up tables. System protection has been done to protect both the equipment in the system and the users. The physical and financial constraints have been taken into account in the design to come up with a well-balanced system presented. Through analysis it is evident that the system provides reliable electricity throughout the day and year. The slightly higher grid parity is reasonable enough relative to expenses to be incurred in connecting the area to the grid or use of diesel generators. The hybrid power systems tend to become cheaper for bigger capacities. The project has presented an insight into renewable based rural/remote power systems that can help supply energy to rural needs in a clean, inexpensive way that does not burden the national economy. To achieve universal electricity access by 2030, it is estimated that 40% of new capacity will need to be provided by Mini Grids (WEO 2010). Hybrid power system is the future. 5.2 Recommendations Majorly the low wind speeds provided the biggest challenge in the design of the system. This can be improved by the use of taller towers which come with extra costs. 55

69 The success of the stand-alone hybrid power systems is dependent on user being well informed. Many such systems have failed because the user thought they could get more than they could actually get from the system. Hence proper user education should be done to ensure the success of the system. The ministry of energy should work with the meteorological department to provide precise data on wind and solar resource that could help in designing of more such systems that can help elevate rural areas economies. Combination of improved technology and economies of scale has pushed down the cost of renewable energy technologies. Renewable energy technologies are already the least cost electrification option in rural areas even without internalizing environmental costs. The initial high costs are offset by the low operational and maintenance cost and the longer expected useful life of renewable energy technologies. The government should therefore do more investment in RE and provide incentives for clean energy to realize vision

70 REFERENCES 1. Bruno Burge and Klaus Keifer. (2015). Photovoltaic Report. A Journal of Fraunhofer Institute for Solar Energy Systems, ISE with support of PSE AG Freiburg. 2. Anurag Sharma and Ankush Kansal. vol. 2. International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering. (Issue 8, August 2013). 3. J F Manwell and J G McGowan. (2009). Wind Energy Explained. Washington, USA: John Wiley and Sons Ltd. 4. Edward Hughes. (2008). Hughes Electrical and Electronic Technology. Harlow, England: Pearson Education Limited. 5. R. A. Messenger and J. Ventre. (2010). Photovoltaic Systems Engineering. Boca Raton: CRC Press. 6. (2016, Jan. 13). NASA Surface meteorology and Solar Energy - Available Tables files [Online]. Available: ubmit&lon= (2016, Jan. 13). NASA Surface meteorology and Solar Energy - Available Tables files [Online]. Available: & =skip@larc.nasa.gov&p=grid_id&p=swvdwncook&p=swv_dwn&p=sol_noon& p=ret_tlt0&p=mnavail1&p=surplus1&p=day_cld&p=t10m&p=wspd50m0&p=gipe_wn d&p=rh10m&p=toa_dwn&step=2&lon= Simon Roberts. (1991). Solar Electricity. New York, Prentice Hall. 57

71 9. Dr. Justus Simiyu, Prof. Bernard Aduda, Prof. Julius Mwabora, Dr. Sebastian Waita and Dr. Robinson Musembi. (2012). Training Course on Solar Photovoltaic Sizing, Installation and Maintenance. Nairobi, University of Nairobi Press. 10. John W. Twidell and Anthony D. Weir. (1990). Renewable Energy Resource. London, Chapman and Hall. 11. (2016, March, 28). Electricity cost in Kenya-Historic electricity cost data for Kenya [Online]. Available: Distribution Standards & Guidelines Manual O & M Module. (Issue July 2010). 58

72 APPENDIX A: CLIMATIC DATA OF SHINAKOTSI AREA Table A 1: Monthly Averaged Insolation Incident on a Horizontal Surface (kwh/m2/day) Lat. 0.9 Lon Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 22-year Average Table A 2: Minimum Available Insolation over a Consecutive-day Period (%) Lat. 0.9 Lon Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Min/1 day Min/3 day Min/7 day Min/14 day Min/21 day Min/Month Table A 3: Monthly Averaged Wind Speed at 50 m above The Surface of The Earth For Indicated GMT Times (m/s) Lat 0.9 Lon Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Average Average@ Average@ Average@ Average@ Average@ Average@ Average@ Average@

73 APPENDIX B: CONDUCTORS AND CABLES MANUAL Table B 1: DC Wire Gauge Table WIRE SIZE (AWG) AREA (mm 2 ) VDI Table B 2: Rated Capacities of Cables and Conductors (240V/415V) 60

74 Table B 3: Electrical and Mechanical Characteristics of Bare and PVC Insulated Conductors 61

75 Table B 4: American Wire Gauge 62

76 APPENDIX C: TROJAN T-105 DATA SHEET 63

77 64

78 APPENDIX D: APOLLO MPT-SERIES DATA SHEET 65

79 APPENDIX E: SERAPHIM SRP-315-6MA DATA SHEET 66

80 APPENDIX F: DEMING SOLAR CONTROLLER SERIES (120V84A) DATA SHEET 67

81 APPENDIX G: ECO VANE (ev600 10kW) WIND TURBINE DATA SHEET 68

82 APPENDIX F: DEMING POWER FKJB-10KW WIND CONTROLLER DATA SHEET 69

83 APPENDIX G: MIDNITE SOLAR COMBINER BOX (MNPV-6) DATA SHEET 70