DESIGN OF A HYBRID SOLAR PV-DIESEL GENERATOR SYSTEMS FOR REMOTE

MOBILE BASE TRANSCEIVER STATIONS

(A CASE STUDY OF MILE-9 SCANCOM (MTN) CELL SITE)

By

Abednego Ofori Akonnor, BSc (Hon)

A Thesis submitted to the School of Graduate Studies,

Kwame Nkrumah University of Science and Technology, Kumasi–Ghana, in partial

fulfillment of the requirements for the degree of

MASTER OF SCIENCE, Renewable Energy Technologies

Department of Mechanical Engineering

College of Engineering

December, 2018

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DECLARATION

I hereby declare that this thesis submission is my own research work towards the MSc.

programme under the supervision of the undersigned, that all other works consulted have been

referenced and it contains no material previously published by another person nor material which

has been accepted for the award of any other degree of the University except where due

acknowledgement has been made in the text.

Akonnor, Abednego Ofori (PG 9807413) ……………………….. …………………..

Signature Date

Certified by:

Prof. Albert K. Sunnu ……………………….. …………………..

Supervisor Signature Date

Certified by:

Prof. G.Y Obeng ……………………….. …………………..

Head of Department Signature Date

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DEDICATION

This thesis is dedicated to God Almighty for His grace and mercies throughout this project work

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ACKNOWLEDGEMENT

Thanks to the almighty God for His grace and mercies to be able to put this work together and

appreciate the proof reading and encouragement of family especially my wife, Mrs. Vera Adwoa

Asiraa Akonnor and colleagues. I also acknowledge the guidance and patience of my supervisor

Prof. Albert K. Sunnu, in bring this work to a successful completion, May the Almighty God

richly reward him.

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ABSTRACT

Mobile Telephony and access to data for communication through telecommunications forms a

central part of Ghana's economy which affects productivity in all sectors of the economy. The

days of manual letter writings, use of telegram systems, etc., has become a thing of the past with

the introduction of modern telecommunication system which seeks to facilitate messaging, fax,

voice, data, mobile money services, etc., thereby boosting the economic productivity across

various sectors within the country. To ensure universal access to these services in the country,

telecommunication companies install mobile cell sites at urban and rural areas. The mobile cell

sites are named based on their physical location; some include Kumasi-1, Knust Hostile, Mile-9,

Obuasi-1, Ayigya-2, etc. Access to the national grid to powering these sites pose serious

challenges due to its erratic supply of the grid power, low voltage and absence in some rural

areas. In some rural areas where the national grid is not accessible, diesel generators are used to

address this short fall in the grid supply. The operations of these diesel generators come with

high cost of running due to high fuel prices, fuel theft, lack of qualified technical personnel,

transportation losses and environmental impacts such as air and sound pollution. This thesis

designed a hybrid solar PV-Diesel generator system to power remote mobile transceiver station

(BTS) focusing on Mile-9 Scancom (MTN) indoor cell site as a case study. A load profile of this

site was determined and simulated in HOMER using various power supply technology scenarios

and economic and technical analyses made to find the best choice of power supply. The result

shows that the optimized standalone PV system had a total net present cost of $ 575,327 whereas

the hybrid (PV and Diesel Generator) had $429,351 and diesel generator alone had $834,437.

The levelised cost of energy was lower for hybrid system compared with standalone solar PV

and Diesel alone; meaning the cost of energy is lower. Standalone solar PV shows operating cost

of $11,805/yr. ($ 9,135/yr. for Hybrid system and $ 33,754/yr. for diesel generator alone) which

was higher than the hybrid systems due to replacement cost associated with batteries serving

high consuming AC equipment such as air-conditioner. It is worth noting that, standalone solar

PV systems are not economical for high loads. The $33,754/yr. operational cost for powering a

site with Diesel generator alone is due to continuous purchase of fuel, frequent servicing and

repairs due to wearing of parts. Thus the order of preference for this site is hybrid solar PV-

diesel, standalone PV and generator alone. Technically and economically, the combination of

Solar PV and diesel generator to form a hybrid system was the best choice.

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TABLE OF CONTENTSDECLARATION....................................................................................................................................... ii

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

ACKNOWLEDGEMENT........................................................................................................................iv

ABSTRACT...............................................................................................................................................v

TABLE OF CONTENTS………………………..…………………………….………………………..vi

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

LIST OF FIGURES...................................................................................................................................x

LIST OF ABBREVIATIONS...................................................................................................................xi

CHAPTER 1

INTRODUCTION

1.1 Background............................................................................................................................1

1.2 Problem Statement.................................................................................................................2

1.3 Aim and Objectives................................................................................................................3

1.4 Justification of Project...........................................................................................................3

1.5 Organization of the thesis......................................................................................................4

CHAPTER 2

LITERATURE REVIEW

2.0 Introduction............................................................................................................................5

2.1 Solar Energy...........................................................................................................................5

2.1.1 Main use of Solar Energy....................................................................................................5

2.1.2 Role of solar energy in current and future energy systems.................................................6

2.2 Photovoltaic Technology.......................................................................................................8

2.2.1 Nomenclature......................................................................................................................8

2.2.2 Photovoltaic Cell.................................................................................................................8

2.3 Solar PV Configuration Systems...........................................................................................9

2.3.1 Direct Coupled..................................................................................................................10

2.3.2 Standalone System............................................................................................................10

2.3.3 Grid Connected PV System..............................................................................................11

2.3.4 Hybrid System...................................................................................................................11

2.4 Review of Earlier Works......................................................................................................12

2.4.1 Review One:......................................................................................................................12

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2.4.2 Review Two:.....................................................................................................................13

2.4.3 Review Three:...................................................................................................................15

2.4.4 Review Four:.....................................................................................................................16

2.5 Technical consideration of Hybrid Solar PV-Diesel generator Systems.............................17

2.5.1 Ghana’s Electricity supply and its challenges...................................................................17

2.5.2 Government policies to promote renewable energy use...................................................19

2.5.3.1 Power requirements of Telecom Sites...........................................................................20

2.5.3.2 Load profile....................................................................................................................21

2.5.3.3 Mile-9 Scancom (MTN) Site Power Supply and Site Layouts......................................22

2.5.3.4 The Diesel Generator Component..................................................................................24

2.6 Total Net Present Cost.........................................................................................................25

CHAPTER 3

METHODOLOGY

3.0 Introduction..........................................................................................................................27

3.1 Loads Assessment Profile of Mile 9 MTN cell site.............................................................27

3.2.1Hybrid Solar PV-Diesel Generator System Design Architecture......................................29

3.2.2Sizing of Components........................................................................................................30

3.2.2.1 Inverter sizing................................................................................................................30

3.2.2 Proposed Case Daily Energy Demand Estimation............................................................31

3.2.3Battery Bank Capacity (CBB)............................................................................................32

3.2.2.4 Photovoltaic Array Peak Power (Wp) Sizing................................................................34

3.2.2.5 Charge Controller Sizing...............................................................................................35

3.2.2.6 Diesel Generator Sizing.................................................................................................36

3.3 Design of the Solar PV-Diesel Generator System with HOMER Software........................36

3.4 Technical and Financial Viability of the PV-Diesel System Design...................................37

3.4.1 Solar PV............................................................................................................................37

3.4.2 Diesel Generator...............................................................................................................38

3.4.3 Battery bank......................................................................................................................38

3.4.4 Inverter with Rectifier.......................................................................................................38

3.4.5 System Wiring Network....................................................................................................39

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CHAPTER 4

RESULTS AND DISCUSSIONS

4.1 Load profile of Mile 9 cell site.............................................................................................40

4.1.1 Load Profile Estimation....................................................................................................40

4.1.2 Daily load demands estimation.........................................................................................41

4.2.1 Hybrid Solar PV-Diesel Design Architecture and Schematics.........................................42

4.2.2 Cost Investment Estimation of Various Components of the Design................................44

4.3 Projects in HOMER software results and discussions.........................................................44

4.3.1 Battery Bank state of Charge of system............................................................................45

4.3.2 Electricity Usage...............................................................................................................46

4.4.1 Financial Viability of the Hybrid Solar PV-Diesel design...............................................47

4.4.2 Total Net Present Cost (TNPC)........................................................................................49

4.4.3 Cash flows – PV/Diesel Power System............................................................................50

4.5 Summary – Homer Simulation Result.................................................................................51

CHAPTER 5

CONCLUSION AND RECOMMENDATIONS

5.1Conclusion ...........................................................................................................................53

5.2 Recommendations................................................................................................................54

REFERENCE..........................................................................................................................................55

APPENDIX 1..........................................................................................................................................58

APPENDIX 2..........................................................................................................................................58

APPENDIX 3..........................................................................................................................................58

APPENDIX 4.........................................................................................................................................586

LIST OF TABLES

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Table 3.1 Mile 9 cell site load assessment.....................................................................................29

Table 3.2 Daily Energy Demand...................................................................................................31

Table 3.3 Characteristics of PV module for the Study..................................................................34

Table 4.1 Load estimation of Mile_9 MTN Cell site (900/1800/3G-2100) site............................40

Table 4.2 Daily Load demand estimation Mile_9 Indoor (900/1800/3G-2100) site.....................41

Table 4.3 PV/Diesel system Architecture......................................................................................43

Table 4.4 Items, average cost of installation and operation and maintenance (O&M).................44

Table 4.5 Electricity Usage in hybrid and Diesel generator system..............................................46

Table 4.6 Net Present Cost of the Hybrid System.........................................................................47

Table 4.7 Net Present Cost of Components for Diesel generator alone on site.............................48

Table 4.8 Cost summary................................................................................................................49

LIST OF FIGURES

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Figure 2.1: From PV cell, Module, Panel to Array. .......................................................................8

Figure 2.2 Photovoltaic cell (Source: ENGINEERING.com, 2014)...............................................9

Figure 2.3 Direct coupled system symbols and connection..........................................................10

Figure 2.4 Standalone System symbols and connection................................................................10

Figure 2.5 Grid connected system symbols and connection..........................................................11

Figure 2.6 Hybrid system symbols and connection.......................................................................11

Figure 2.7 Site Overview and Equipment layout (a-i)...................................................................23

Figure 3.1 Typical power layouts to all loads at Mile 9 base station............................................28

Figure 3.2 Hybrid PV design architecture for Mile 9……………………………...…………….30

Figure 3.3 Amara Raja 2V 500ah Batteries (Amaron Volt publication, 2017).............................32

Figure 4.1 Hourly Load Profile for the cell site.............................................................................41

Figure 4.2 Schematic diagram of the Solar PV-Diesel Power System..........................................42

Figure 4.3 Battery Bank state of Charge of Generator system to power indoor site…………….44

Figure 4.4 Battery Bank state of Charge of Hybrid system to power indoor site……………….44

Figure 4.5 Net Present Costs of the Components..........................................................................47

Figure 4.6 PV/Diesel Design Cash Flows.....................................................................................49

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LIST OF ABBREVIATIONS

AC Alternating CurrentAVR Automatic Voltage RegulatorBSS Base Station SubsystemBTS Base Station TransceiverCWh Storage Capacity of Battery BankCOE Cost Of EnergyDC Direct Current ECG Electricity Company of GhanaEIA Environmental Impact AssessmentFCG Fuel Consumption of diesel GeneratorFLA Full Load AmpGHG Green House GasHOMER Hybrid Optimization Model for Electric RenewableHRES Hybrid Renewable Energy SystemICT Information and Communication TechnologyKVA Kilo Volt AmpereLRA Locked Rotor AmpNASA National Aeronautics and Space AdministrationNEs Network ElementsNPC Net Present CostNREL National Renewable Energy LaboratoryO&M Operations and MaintenancePMG Permanent Magnet GeneratorPSH Peak Sunshine HoursPV Photovoltaic RRU Remote Radio UnitTHD Total Harmonic DistortionTNPC Total Net Present CostVRLA Valve Regulated Lead Acid

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CHAPTER 1

INTRODUCTION

1.1 Background

The emergence of information and Communications Technologies (ICT) has become an integral

part of today’s global economy. ICT infrastructural development in Ghana is progressing

comparatively faster to other low income countries and above the 1.1% average for Sub-Saharan

Africa (GIPC, 2014). The increase in this sector has made the telecom industries such as

Vodafone, Milicom, Glo, Espresso, Scancom (MTN) etc. to invest massively in their

infrastructure for better service delivery. The demand for information and transmission of data

across various institutions within the country has propelled the telecom companies to install a

number of Base Stations across the length and breadth of the country.

The power supply to these installed Base Stations has become a vital economic and

environmental concern. Supply of uninterrupted power to the base stations is one of the crucial

issues for mobile communication system due to increase demand for services provision and

quality of services to its customers. Base stations consume about 50% of the operator’s power

consumption (Deruyck, et al. 2010), and determines the design of base station which is key to

both the environmental impact and the operational expenditure.

Currently most base transceiver stations (BTS) rely solely on the national grid and use diesel

generators as an alternative power supply. In remote areas including islands, base transceiver

stations (BTS) are normally operated with diesel generators as lengthy grid extensions may not

be cost effective. In addition to the cost operation of these generators, maintenance of the

generators can also be expensive that is spare parts replacement and labour time. The diesel

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generators also contribute substantially to environmental pollution which is also a major concern.

Photovoltaic technology converts solar energy into electricity using no fossil fuels, no moving

parts, no noise and pollution, and with many years of lifespan on little maintenance. These

advantages together with the reliability and availability of power make it an attractive option.

Ghana, being a few degrees north of the equator, is enriched with abundant solar energy resource

spread across the length and breadth of the country. It has a daily solar radiation values ranging

from 4kWh/m² to 6kWh/m² with an annual sunshine duration between 1800 to 3000 hours giving

very high prospect for grid connected and off grid applications (Ministry of Energy, Ghana

2014). Before the actual installation of the PV system to the base transceiver station, it is

necessary to get an estimated number of photovoltaic (PV) cells, size of inverters and batteries

needed and also the cost of energy per unit to be produced. HOMER simulation tool will be used

in the simulation of cost efficient installation of the solar PV-Diesel powered base transceiver

stations (BTS).

1.2 Problem Statement

Rural electrification implementation across the country has been very low over the years making

business and livelihood within the remote areas including islands very difficult. Currently most

base transceiver stations (BTS) depend mainly on the national grid for their power requirement,

with diesel generators as backup power supply. In remote areas including islands, base

transceiver stations (BTS) are normally operated with diesel generators as lengthy grid

extensions may not be cost effective. In addition to the cost of operation of these generators,

maintenance of the generators can also be expensive in relation to spare parts replacement and

labour time. The diesel generators also contribute substantially to environmental pollution which

is also a major concern. In view of these challenges posed to the telecom companies, there is a

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need to seek for alternative power supplies which will be cost effective and environmentally

friendly. Solar PV Technologies over the years have provided various alternative powers to

remote areas where electricity expansion is not cost effective and has met the needs of various

businesses across the country and the world at large. This thesis seeks to Design hybrid Solar

PV-Diesel Generator system at Mile-9 for Scancom (MTN) cell site in a remote community

within the Obuasi Municipality in the Ashanti Region of Ghana.

1.3 Aim and Objectives

The main aim of this thesis is to design a hybrid Solar PV-Diesel Generator system for mobile

base transceiver stations (BTS) located in a remote area such as Mile 9, Scancom (MTN) cell site

in Ashanti Region within the Obuasi Municipality where it is not cost efficient to run power

transmission lines or have alternative generation such as diesel generators.

To pursue this aim the following specific objectives will be considered;

To develop a load assessment profile for Mile 9 Scancom (MTN) cell site

To design an appropriated hybrid Solar PV-Diesel Generator system to power the BTS

using Homer Simulation Tool

To perform a technical viability analyses of hybrid Solar PV-Diesel Generator system

verses the existing Diesel generator power system using Homer Simulation Tool

To perform technical and financial viability of the hybrid Solar PV-Diesel design

1.4 Justification of Project

The advancement of information technology across the globe, has propelled telecom industries in

Ghana to install numerous number of mobile cell site across the length and breadth of the

country over the last decade. These telecom cell sites experience constant power interruption due

to unstable power supply from the national grid and its limited access for some remote areas

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including islands across the country. Conventionally in these areas, diesel generators are used

which are not environmentally friendly due to green-house gas emissions and high operational

cost for running them on site. Greenhouse gas emissions reduction is of global importance.

Human activities across the globe also contribute to the increase of global warming. The effects

of global warming have negative effects on people, plants, and animals whose existence is

threatened. Majority of the greenhouse gases can be in the air for a long time after their released

and the effects of these gases will be in the atmosphere for many years (US-EPA, 2013). This

project seeks to help stakeholders to appreciate and understand the benefits of integrating solar

PV into the energy mix for telecom sites to reduce the greenhouse gases emission and its effects

on the environment as well as their cost-to-benefit analyses for running diesel generators on site.

1.5 Organization of the thesis

The thesis is structured into five chapters. Chapter 1 deals with the introduction of the thesis

comprising of the background, problem statement, objectives, justification and organization of

the thesis. Chapter 2 presents the literature review of similar hybrid solar-diesel electric power

projects around the world. It presents the basic principles of Solar PV components and

technologies as well as the technical and financial model of the various components used.

Chapter 3 presents the methodology of the various objectives and the steps used to achieve the

objectives.

Chapter 4 discusses the results and analysis while the chapter 5 deals with the conclusion and

recommendations of the thesis.

CHAPTER 2

LITERATURE REVIEW

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2.0 Introduction

This chapter focuses on the literature review of solar photovoltaic technology, consideration of

other journals, articles, reports, case study, and the implementation of similar projects across the

globe. It also looks at the technical considerations of hybrid solar PV- diesel generator systems in

relation to the project designs.

2.1 Solar Energy

The energy received from the sun’s radiation (solar radiation) for use is referred as solar energy.

Approximately the earth receives 1400 W/m² of the sun’s energy at the upper of the earth’s

hemisphere. A percentage of 30 % estimated sun’s radiation is reflected into the atmosphere with

the remaining 70 % absorbed by clouds, oceans and land masses. Solar energy received on earth

is assumed to be from 0 to 1000 W/m² ranges with respect to the location and period of the day

and year. The mean value for the earth is 200 W/m². Solar energy potential of about 5

kWh/day/m² is recorded within Africa’s atmosphere which is considered as the highest solar

energy potential across the globe.

2.1.1 Main use of Solar Energy

Solar technologies are mainly categorized as either passive or active according to the way the

sun’s energy is received, converted and distributed for useful purposes. The active solar method

uses PV panels or solar concentrating systems to convert sunlight into useful electricity for

various purposes whilst passive solar techniques include selecting materials with special thermal

characteristics, provisioning spaces that naturally circulate air, and proper alignment of an

infrastructure to the Sun position. Active solar methods are used as the supply side techniques as

they increase the supply of energy, whilst passive solar technologies reduce the need for other

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resources and are usually considered demand side technologies. Solar energy is predominantly

used in Africa in remote areas for electrification, pumping of water, cooking and other

commercial activities.

2.1.2 Role of solar energy in current and future energy systems

Fossil fuels have served the energy needs of the world for over a century but proven reserves of

fossil fuels indicates 46 years, 58 years and almost 150years for oil, natural gas and coal

respectively for usage at prevailing rates (IEA, 2010). This has created the awareness for a more

sustainable clean source of energy. About 885 million terawatt hours (TWh) of solar energy

reach the earth’s atmosphere in a year, that is 6200 times the commercial primary energy used by

humankind in the year 2008and 4200 times the energy that mankind would use by 2035 (IEA,

2011). An estimated time of one hour and 25 minutes is used by the sun to send the amount of

energy the world would use in a year. Solar energy unlike gas, oil or coal energy is non-

polluting. It is sustainable and helps for the protection of our environment. It does not release

carbon dioxide, nitrogen oxide, sulphur dioxide, etc. into the atmosphere as compared with

conventional forms of energy. Hence solar energy is not associated with global warming, acid

rain, etc. contribution to the earth. Solar energy systems have lower operations and maintenance

cost. They operate silently; do not produce strong smells and no additional fuel needed. These

have made solar energy emerge as one of the most rapidly growing renewable energy source in

the world. The growth of the global PV industry has been very appreciable since 2003; an

average annual growth rate of 40% and 136% in 2009 and 2010 respectively.

Cumulatively the global PV installed capacity increased from 0.1 GW in 1992 to 40 GW at the

end of 2010 fiscal year, with 42% installed capacity recorded in 2010 alone (IEA, 2011). In

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2011, renewable energy contributed 208 GW of electric capacity globally with solar PV

accounting for almost 30% of the new renewable capacity (REN21, 2011).The International

Energy Agency predicts that we will produce 662 GW of solar energy by 2035.

One reason for the rapid deployment of solar technologies is that prices of solar energy

technologies continue to fall. Averagely since 1998, the price of installed PV system has been on

the decline of about 6-7% per year. Between 2011 to 2012, price of the installed PV system

declined by $0.88/W(14%) for PV systems less than 10 kW and $0.3/W (6%) for PV systems

greater than 100 kW(NREL, 2014). Technological advancement and investments will drive the

price of solar technologies further. Occasionally, the initial investment cost of installation is very

high due to the cost of assembling the PV system. This poses a greater disadvantage on large

scale installation. For larger scale of production, quit a substantial area for installation is required

to achieve the intended energy needed. The efficiency of the system also depends on the location

of the sun, although this problem can be overcome with the installation of a higher number of

components. Solar energy generation is affected by the existence of clouds and the level of air

pollution in the atmosphere. Again, solar energy during night is zero but the presence of backup

battery helps to sustain power until the sun’s energy takes over during the day. The quest for a

cleaner, very abundant and inexhaustible energy resource for mankind means solar energy will

be a vital energy source for generation unborn.

2.2 Photovoltaic Technology

2.2.1 Nomenclature

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Cells - Semiconductor device that converts sunlight into direct current (DC)electricity

Modules - PV modules consist of PV cell circuits.

Panels - PV panels include one or more PV modules assembled as a pre-wired, field.

Arrays - PV array is the complete power of any number of PV modules

Figure 2.1: PV cell, Module, Panel and Array.(Source: Florida Solar Energy Center, 2014)

2.2.2 Photovoltaic Cell

A solar cell is a semiconductor that can convert solar energy into Direct Current electricity

through the photovoltaic phenomenon. Energy from solar cell is dependent on the amount of

solar irradiation accessible by the cell. A solar cell comprises of at least double layered

semiconductor devices. The first layer has a positive doping, the second is doped negatively.

When light enters the cell, some of the photons of the light are received by the semiconductor

atoms, freeing electrons from the negative layer of the cell to move through an external circuit

and return into the positive layer. This movement of electrons constitutes an electric current. The

photocurrent that is internally produced in a solar cell is equal to the irradiance.

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Figure 2.2 Photovoltaic cell (Source: ENGINEERING.com, 2014)

The main types are amorphous, polycrystalline and mono-crystalline silicon cells.

Monocrystalline silicon cells constitute a greater percentage of purity of the material and

enhance the best performance with respect to efficiency. Polycrystalline silicon cells have a

lower purity and involve less efficiency than the mono-crystalline type. Amorphous Silicon cell

is the deposition of a thin layer of silicon crystal (1-2 microns) on the surfaces of other materials,

such as glass or plastic ones. It has the lowest efficiency.

2.3 Solar PV Configuration Systems

Photovoltaic power systems are usually categorized in relation to their functional and operational

necessity, component configurations, and their connection to other power sources and electrical

loads. The two main configurations are stand-alone PV systems and grid-connected or utility

interactive PV systems. Photovoltaic systems can be designed as a stand-alone or a hybrid

system where other energy sources can be connected to provide DC and or AC power service.

2.3.1 Direct-Coupled

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The direct-coupled system has its output power from the PV module connected directly to a DC

load as shown in figure 2.3. To better utilize the availability of the output power from the array a

maximum power point tracker (MPPT) device is sited in between the array and load. The direct-

couple system design does not have backup batteries included and as such only suitable to

electrical load that does require over-night operation. Water pumping devices is a typical

example of such loads.

Figure 2.3 Direct-coupled system symbols and connection

2.3.2 Standalone System

The standalone system use a charge controller connected directly to the PV array to regulate the

backup battery charging and also provides power to the DC loads and the inverter in figure 2.4.

The backup battery provides alternative power to the loads in the night and in period where the

solar radiation is low or unavailable while the inverter converts direct current (DC) into

alternative current (AC) for other AC loads on site.

Figure 2.4 Standalone System symbols and connection2.3.3 Grid-Connected PV System

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The grid-connected system has an electric grid integrated in its design through an inverter as

shown in figure 2.5. Excess electricity from the PV system is feed into the grid and the grid also

provides power to the loads in the events where the PV module energy is low or unavailable.

Figure 2.5 Grid-connected system symbols and connection

2.3.4 Hybrid System

In a hybrid system, PV is combined with other forms of generation as shown in figure 2.6. The

other form of generation may be a type which is able to modulate power output as a function of

demand. Another form of power generation maybe a diesel generator or wind source.

Figure 2.6 Hybrid system symbols and connection

2.4 Review of Earlier Works

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This section reviews existing journals, articles, reports and case studies on similar projects across

the globe touching on hybrid solar PV design technology, methodology adopted and

implementation as well as shortcoming and omissions of their work.

2.4.1 Review One:

Optimization of Hybrid PV/Diesel Power System for Remote Telecom Station by Dr.

Kareem K. Jasim and Dr. Mahdi A. Abdul-Hussain (2016)

Dr. Kareem K. Jasim al et. publication on Optimization of Hybrid PV/Diesel Power System for

Remote Telecom Station dealt with the design of PV system for electrification of remote

communication towers in a mobile company in Algazalia- Iraq. The hybrid system is composed

of photovoltaic system, diesel generator, power flow controller, power electronic converter and

the tower loads.

Homer Software was used to perform a techno-economic analyses looking at different measured

values over the collection period, such as: variation of solar radiation in Baghdad, variation of

electrical loads, and output energy vs. solar radiations. This analysis gave an appropriate

justification for the PV sizes as the optimum design for electrification of these towers by using

solar energy. The average daily energy used for the BTS cell site is 32.25 kWh/day and the total

max demand is 2.288 kW.

The analyses gave PV-diesel-battery system as the proposed system for the site with 8 kW solar

PV systems and a 5.5 kW diesel generator system. These components are connected together to

improve the output power for the system to cater for the unpredictable variations in the weather

changes. The converter is included in the design to maintain the movement of energy between

the AC and DC components, while the batteries numbering 64 pieces are used as a backup in

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order to ensure uninterrupted power and to maintain the desired power quality at the load point.

The combination of the two energy sources with the backup batteries helps to provide

uninterrupted power supply to the load on site. This makes the hybrid system more reliable and

efficient. It was highly recommended to implement the design suggested in this research in oil

companies for economic and environmental savings.

This research covers most of the areas to be considered in our design, touching on the technical

implementations and the environmental aspects but the terrain of implementation is different

from our solar PV-diesel generator system design. These will eventual give differential results

and analyses to be focused.

2.4.2 Review Two:

Simulation and Optimization of Hybrid Diesel Power Generation System for GSM Base

Station Site in Nigeria by Ani Vincent Anayochukwu and Emetu Alice Nnene (2013)

Ani Vincent et al. research work considers the simulation and optimization of a hybrid system

for a GSM base station site situated in Abuja (FCT), Nigeria with a daily load of 318 kWh dˉ¹.

HOMER simulation tool was used to design the power system for the base station transceiver

(BTS). Load profile from various loads on site was taken and an estimated load profile demand

was established. The loads included are radio equipment, power conversion equipment,

transmission equipment and among others. Load profile estimation from daily energy

consumption collected and analyzed show that 13,334 W hˉ¹ power requirement is needed to

operate the BTS site. HOMER software sizes various components and also makes comparison

analyses of two simple dispatch methods. These dispatch methods are Load Following and Cycle

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Charging. An energy consumption of 318 kWh dˉ¹ with a 13.3 kW peak demand load was

released from HOMER simulations.

The results from the simulation as an optimum energy combination of 18 kW of diesel generator,

36 kW of solar PV array, 192 Surrette 6CS25P of backup batteries, and a 25 kW AC/DC

converter. Two different cost estimations that are the annual cost and total cost of operation were

used to compare the diesel alone and PV-diesel hybrid system only. From the simulation results,

the proposed system has total NPC and amount of carbon dioxide (CO2) as $995,774; 65.270

tonnes, and saves $716,397; 57.835 tonnes when compared with the diesel only system

$1,712,171; 123.105 tonnes.

PV/diesel hybrid system was considered as a better power system for the BTS site especially in

remote areas. The results indicated that even though the hybrid PV/diesel system has a high

initial cost of installation, the overall costs is lower over the project’s 20 years lifespan.

The study was conducted in Abuja township where climatic changes varies from the remote

settings and also captured various power parameters of the telecom devices which depict an

outdoor cell site with power variations on site compared to indoor site. The hybrid system design

focuses on indoor site where air-condition units are also factored in analyzing and design of the

solar PV-diesel generator system with specific concentration on remote setting at Mile-9,

Kumasi-Ghana.

2.4.3 Review Three:

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Cellular Base Station Powered by Hybrid Energy Options by Raees M. Asif and

Fahimullah Khanzada (2015)

Raees M. Asif et al. research work addresses the energy consumption problem of a typical base

transceiver station (BTS) and also propose the possibility of a hybrid energy system for the site.

The study also seeks to find an optimum stand-alone hybrid energy system to power the mobile

BTS in an urban area such that its dependence on diesel fuel is minimized. The study considers

the Pakistan’s capital, Islamabad as a case study.

HOMER simulation tool was used to analyze various energy combinations for the BTS site.

Technical and economic possibility of using hybrid energy system is considered. Load profile

format of BTS sites were varied leading to variations in hourly weather sequence but for the

worst case scenario, a peak power value of constant load of 2.5 kW with 4.5 kW were used.

HOMER undertakes an hourly simulation for each of the given energy options based on

operational characteristics that is, the annual electricity production, renewable fraction, Cost Of

Energy (COE) and Net Present Cost (NPC) etc. HOMER categorizes the energy options

according to their lowest NPC value achieved from the analyses.

HOMER presents various scenarios of energy power combination but PV/Wind/Diesel/Battery

hybrid system of $ 0.839 /kWh was selected as the preferred power source for the BTS site. The

hybrid energy option is made up of 5 kW PV, 1 kW Wind Turbines, 3 kW Diesel Generator and

16 backup batteries.

The techno-economic analysis gave an optimal hybrid energy system made up of Solar PV,

Small-scale wind, diesel and batteries for urban areas typical of Islamabad. Besides, it is

environmentally friendly with the least CO2 emission. The use of renewable energy options in

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addition with conventional diesel and batteries can not only lower the energy cost but also lowers

the greenhouse gas emissions associated with it.

The article had four energy power combinations; Solar PV, Small-scale wind, diesel and

batteries to achieve an optimum power required for the BTS cell site which three energy power

sources; Solar PV, diesel and batteries in our thesis can achieve the same outcome and

advantages.

2.4.4 Review Four:

Optimization and Economic Analysis of Solar PV/Diesel Gen-Set Hybrid System of Nepal

Television Repeater Station in Ilam by SherHusai and Dinesh Sharma (2014)

SherHusai et al. conducted an optimization and economic studies of solar PV/diesel genset

hybrid system for Nepal Television station in Ilam. HOMER simulation tool was considered for

the system optimization. The load profile of 5 kW was obtained from the station using wattage

rating of the equipment for 24 hours period. Solar radiation data from the site is taken from the

online data of NASA meteorological department. The HOMER software simulates the various

energy options and gives a list of possible configuration depending on the total net present cost

(TNPC) representing the system life cycle cos. The sensitivity option of the solar radiations and

the cost of diesel fuel, gave a final optimized hybrid system with the lowest TNPC. The overall

optimal hybrid system has $ 140,681 as an initial cost of capital and $ 266, 892 of TNPC with

0.495 $/kWh cost of energy (COE) obtained. This system give a better option compared with

diesel generator alone system of $ 379,507 TNPC with cost of energy at 0.704 $/kWh.

Reliability of the optimum system is enhanced because it has both the renewable and non-

renewable generators. The inclusion of inverter in the system helps to produce amount of energy

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required from the PV without discharging the battery. It also has economic gains over the diesel

generator system alone.

Because the renewable energy option of the hybrid optimum system is 93 %, a long cloudy

weather implies longer operational hours for the genset and this result in high fuel usage with its

attendant cost and large amount of CO2 emission produced into the environment. Our project

work will also deal with optimizing Solar PV/Diesel system concentrating on the environmental

impact in relation the number of hours the diesel genset runs in the absence of the PV system and

also include detail technical analyses on adopting this system in remote BTS cell site at Mile 9 in

Ghana where the nation grid is not accessible.

2.5 Technical consideration of Hybrid Solar PV-Diesel generator Systems

This section of the project discusses current electricity conditions in Ghana, power requirement

and distribution at typical mobile base station within the telecom industry. It also considers the

economic ramifications of the project to the telecom industry.

2.5.1 Ghana’s Electricity supply and its challenges

Ghana’s energy sector before late 1990s was vertically operated as a monopoly power generating

and transmission system by Volta River Authority (VRA). Power distribution to the northern part

of Ghana was through Northern Electricity Department (NED) of its subsidiary company while

the southern sector energy distribution was through Electricity Company of Ghana. Power sector

reform in the late 1990s split Volta River Authority (VRA) into a separate generation and

transmission system operations which also made it possible for other Independent Power

Producers (IPP) to enter the market.

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Currently in Ghana, both renewable and non-renewable power stations are used for electricity

generation to meet the country’s load demands. The first hydroelectric plant was constructed in

Akosombo in 1965 with installed capacity of 1020 MW, followed later by the Kpong and Bui

power stations with installed capacity of 160 MW and 400 MW respectively. Ghana experienced

it first electricity crisis between 1982 and 1984 as a result of severe drought during which the

total inflow into the Akosombo Dam was less than 15 percent of the long term expected total.

Ghana’s power sector over the years has gone through several power crises which has affected

power supply to various regions in the aim of achieving its universal access to power. Ghana

suffered severe power rationing/load shedding in the years 1983–1984, 1997–1998, 2003, 2006–

2007, 2011–2017; a condition that could be mainly associated to fuel supply problems including

the low water level in the Akosombo dam and natural gas shortages. (Nyarko Kumi, 2017)

This challenge led to the implementation of Thermal Power Plants into power generation mix. A

550 MW installed capacity (Tapco and Tico) at the Takoradi Thermal Plant from by VRA was

the first thermal plant introduced into the power generation mix. The total installed capacity of

thermal power plants increased to 2,053 MW at the end of 2015 (Energy Commission of Ghana,

2016a). Electricity crisis became a household phenomenon in Ghana leading to the adoption of

the local word “Dumsor” to describe the situation. In December 2013, the 400 MW Bui

Hydroelectric Power Station was commissioned to provide electricity to support the peak load of

the country, which has been on an ever-increasing trajectory.

Before 2016, the only renewable energy introduced into the national grid was a 2.5 MW solar

photovoltaic plant by the Volta River Authority in Navrongo. A 20 MW solar plant from BXC

Ghana was commissioned in 2016 to increase the amount of renewable energy sources to the

country’s power generation mix. Also, a 100kW biogas electricity generation facility was

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introduced into the national grid in 2016. The Energy Commission of Ghana reports a total of

500 kW of installed solar PV systems (both grid connected and with battery backup) from

individuals and institutions (EADTF, 2014).

2.5.2 Government policies to promote renewable energy use

The objective of the strategic plan for energy for the commercial and service sector in Ghana's

Strategic National Energy Plan 2006-2020 report is to minimize the energy usage in general and

wood fuel consumption by providing energy efficiency programs and cleaner energy options

(Green power for Mobile, 2008).

The renewable energy policy direction for solar concentrates on enhancing the cost effectiveness

of the technology, creating conducive regulatory and fiscal regimes, encourage local research

and development of the technology to reduce cost and support the use of solar PV technology as

a decentralized off-grid alternative technology making them competitive with conventional

electricity supply (Ministry of Energy- Ghana, 2010) .

Furthermore, Ghana government commitment in the development of renewable energy is seen in

passing of the renewable energy Act 832. The act is to provide for the development,

management, utilization, sustainability and adequate supply of renewable energy for generation

of heat and power for related matters (Parliament of Ghana, 2011). This act details the

responsibility of various institutions in the energy sectors to achieve the act objective.

Institutions such as the Energy commission are to provide technical and licensing of renewable

electricity generation, transmission and distribution. The Public Utility Regulatory commissions

(PURC) assist in economic regulation and setting tariffs for electricity including renewable

energy feed-in-tariff. The impacts of the environment are checked and regulated by the

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Environmental Protection Agency (EPA). Incentives to assist and facilitate private sector

investments are available at the Ghana Investment Promotion Centre (Emmanuel Armah Kofi

Buah, 2014).

2.5.3.1 Power requirements of Telecom Sites

Competition is keen among telecom companies which have resulted in innovative services at a

low rate. However, the prices of power keep increasing thereby increasing operational cost for

telecom sites. Telecom sites are usually classified into exchange, hub and terminal. Exchanges

house more equipment hence more power consumption. These equipment include but not limited

to; Switch, Media gateway, Base Station Controller, Add Drop Multiplexer, Base Transceiver

Station, fiber and microwave equipment, cooling system and power systems. Hub sites serve as

relay sites; they send signals to terminal sites and exchange sites. Equipment typically found are

fiber or Microwave radios, Base Transceiver Station, Add Drop Multiplexer, cooling system and

power system. Terminal sites are last point sites with fewer equipment and lower power

consumption. A Base Transceiver Station and a link (fiber or microwave radio), cooling system

and a power unit are usually found in hub sites.

The Base station subsystem (BSS) has the highest energy consumption of cellular networks

which amount to 50% of the total energy consumption on site (Deruyck, 2010), and it is

important to identify those elements which contribute most to the overall energy consumption.

BSS is the section of a traditional cellular telephone network which is responsible for handling

traffic and signaling between a mobile phone and the network switching subsystem. The higher

the traffic the more the power consumed.

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Modern telecom terminal sites are outdoor cabinet with inbuilt cooling system serving as

compartment for BTS, radio/ fiber equipment and battery cabinet. These outdoor cabinets use

fans for cooling of equipment hence reduced power consumption. Indoor sites have a shelter that

needs to be cooled with air conditioners. Huawei Technologies, Alcatel lucent and ZTE are

example of manufacturers of outdoor cabinets for telecom companies in Ghana.

2.5.3.2 Load profile

A load profile gives a graph of the variation in the electrical load versus time usually hourly. A

load profile depends on customer energy usage pattern. Energy providers utilize this information

to design how much electricity they will need to make available at given period. For efficient

performance of the BSS, a voltage ran of – 43 V to – 56 V DC power is required. Consequently,

most electrical safety regulations consider DC voltage lower than – 50V to be a safe low-voltage

circuit. It is also practical, because this voltage is easily supplied from standard valve regulated

lead acid (VRLA) batteries by connecting four 12V batteries in series, making it a simple system

(Wissam, 2011).

In telecom sites, the main equipment operates 24 hours and others such as aviation lights and

premises lighting comes on when there is darkness. AC plugs are also available to power laptops

and measuring instruments. The voice and data traffic intensity at a site has an effect on the

power usage of network elements (NEs). Designing a PV system takes into account the load

demand of the site in order to meet it. The voice and data traffic at site should be considered and

an optimum value used to prevent over sizing or under sizing; the more the demand, the more the

backup battery, thereby increasing cost. Finding the load profile involves making a list of all

equipment that will be fed by solar PV system with their power rating, efficiency and operational

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hours. The product of the rectified power and duration of use gives the energy demand. Terminal

sites do not retransmit traffic to serve other sites whereas hub sites can have more links to serve

other sites via radio or fiber links. More radios increase the energy demand of the site.

The general site elements are as follows;

1) Radio link / fiber link

2) BTS

3) Aviation lights

4) security lighting

5) plugs

6) cooling system( Air Condition Unit)

7) Remote Radio Unit (RRU)

8) Node B

2.5.3.3 Mile-9 Scancom (MTN) Site Power Supply and Site Layouts

Mile-9 is a small village located 38 km from Obuasi Municipality located on latitude 6.221452

and longitude 1.7901 with a total estimated population of 15,000 inhabitants. Currently Mile-9

Township is not on the national grid, making economic activities within the area very difficult.

Mile-9 MTN cell site runs on twin diesel generator system which alternates concurrently with

backup batteries. In the event of a major failure where the twin generators are unable to work, a

total network failure in and around the environs of Mile-9 occurs making communication to

other parts of the villages very difficult. Figure 2.7 shows the photography of devices and

equipment layout within the MTN cell site.

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a. General Tower Overview b. Site Front view c. Site Environs

d. DC plant with Batteries e. Indoor House Overview f. Air-condition system

g. BTS Cabinet h. Transmission Cabinet i. Indoor Lighting System

Figure 2.7 Site Overview and Equipment layout (a-i)

2.5.3.4 The Diesel Generator Component

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Sizing diesel generator systems are of paramount importance since it has a direct impact on the

cost of the system. A poorly sized diesel generator might not adequately serve the load or be

oversized. All equipment on site which are to be powered by diesel generators total steady-state

requirements must be known so as to match it with the required alternator to supply the locked

rotor amp (LRA) needed for starting cooling system (Air conditioning units) in the Shelter (for

indoor installations). The locked Rotor Amp (LRA) might be sized as high as Six (6) times the

rated Full Load amp (FLA) output of 3-phase motors. It could be up to twelve (12) times the

FLA in the case single-phase motors. The steady state reactive power requirements must be met

by the alternator for loads at site. Therefore alternators are usually oversized up to about 150%-

200% of the actual power required to power telecom sites. The transient voltage dip caused by

starting air conditioners is improved by the over sizing of the alternators and further minimizes

the total harmonic distortion (THD) on the voltage output of the generator set caused by the

rectifiers. The bigger prime mover or engine required to drive alternator during sizing makes it

easier to allow growth of the load at site when expansion if needed. In cases where expansion

does not occur during the lifespan of the generator, this solution will not be energy-efficient with

higher capital cost and operation and maintenance (O&M) cost (Wissam, 2011). More particulate

matter (PM) would be emitted by such big engines from their exhaust into the atmosphere

thereby causing air pollution and increases in greenhouse gas (GHG) effect. Sound pollution can

be curbed in residential areas using generators with sound attenuator enclosure and not simply by

specifying a critical muffler since there are other sources of noise apart from the exhaust

(Example radiator fan). Telemesis (remote monitoring system) are required in rural areas to

check fuel levels and general state of operation of generators, this prevents fuel theft. Provision

of at least eight input/output dry contacts and relays should be available for this connection.

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Heavy-duty air filters should be used in sandy and dusty areas to ensure efficient operation of

generators, however, specify aluminum enclosures and anti-condensation heaters to prevent

insulation failures and short circuits between the windings in the alternator stator in wet and

humid environments. Cold climates would require engine block and oil heaters when they are

used as standby. Specify a permanent magnet generator (PMG) excited system for generator sets

above 25 kW. Distortion of voltage output caused by nonlinear BTS rectifier loads on the

generator’s automatic voltage regulator (AVR) is prevented by the use of Permanent magnet

generators (PMG) and with better field-forcing capabilities for air conditioning motor starting

than a self-excited generator would provide (Wissam, 2011).

2.6 Total Net Present Cost

Economics is a science that deals with people and the society for survival. Using these economic

principles in engineering solves problems such as comparing the cost of two alternative projects

(Paul, 1985) is resourceful. The net present cost of a system is the present value of all the cost of

installing and operating the system over its lifetime, minus the present value of all the revenue

that it earns over its lifetime from selling power to the grid. Costs may include capital costs,

replacement costs, operating and maintenance costs, fuel costs, the cost of buying electricity

from the grid, and other costs such as penalties resulting from pollutant emissions. The net

present cost (NPC) is the negative of the net present value (NPV). It is the same as the lifecycle

cost (Tom, 2008). Revenues include salvage value and grid sales revenue. With the NPC, costs

are positive and revenues are negative. This is the opposite of the net present value (NPV). As a

result, the NPC differs from NPV only in sign (Kayako, 2010).

The total net present cost (CNPC) is calculated in HOMER using the following equation:

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CNPC = Cann ,tot

CRF (i , R proj) where;

Cann,tot= Total Annualized Cost ($/yr)

CRF (I,R proj) = Capital Recovery Factor

I = Interest Rate (%)

R proj = Project Lifetime (yr)

CHAPTER 3

METHODOLOGY

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3.0 Introduction

This chapter focuses on methodology adapted for the Hybrid PV-diesel design. The PV-diesel

system design involves;

1. Load Assessment profile of Mile 9 MTN cell site

2. Hybrid Solar PV-Diesel System Design Architecture

3. Design of the Hybrid Power with HOMER Software

4. Financial and Technical viability for the Hybrid Solar PV-Diesel Components

3.1 Load Assessment Profile of Mile 9 MTN cell site

A typical mobile cell site is composed of a base transceiver station, a microwave transmission

medium and a number of power related equipment for site monitoring including Fluorescent

lamps, Aviation lights, Air-condition unit and AC Plugs or sockets for on-site activities. These

equipment are mainly powered by electricity either from the national grid or diesel generator

installed at the site. Mile 9 MTN cell site is currently powered by two diesel generators because

of the absence of the national grid to the site and its environs. Figure 3.1 illustrates a typical

power layout of all loads at Mile 9 MTN base station.

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Automatic Transfer Switch

Distribution Panel

SMPS Unit

Diesel Genset

Diesel Genset

Figure 3.1 Typical power layouts to all loads at Mile 9 base station.

Power supply to the various loads on site by the diesel generator runs for 24 hours daily with

backup batteries supplying power to the loads when the diesel generator is unable to start on

auto. The Microwaves Transmission equipment, Base transceiver Station (BTS) and the Air-

condition unit consume DC power while other lightings within the site and the aviation light

together with some receptacles consume AC power. The Automatic Transfer Switch (ATS)

alternates the AC power supply from the two generator feed into the AC distribution panel. The

Switch-Mode power supply (SMPS) converts the AC power into DC power which is feed into a

DC power distribution board (DCPDB) on which the DC loads on site take their power source.

The Backup batteries are also connected to the DCPDB for charging the batteries on site.

Alternatively, in the event where the two generators are unable to work or function, the backup

battery discharges to feed the DC loads on site. The peak period where all equipment are in their

full operation is recorded between the hours of 6:30pm to 5:30am. Due to the variable nature of

the DC load, the study will use the highest of the daily peak loads recorded during the period

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Lighting and Receptacles

Backup Batteries

Air-Condition Unit

under study. Table 3.1 shows Mile 9 MTN cell site load assessment indicating power

consumptions recorded of the various components on site.

Table 3.1 Mile 9 cell site load assessmentLoads Voltage Power Time

V W Hours/Day2 CFL Lamp 220V AC 20 12Aviation Light 220V AC 25 122 Plugs/Sockets 220V AC 25 4BTS 48V DC 620 24Microwave 48V DC 194 24

The BTS system is seen to have the highest power consumption with Air-condition unit closely

following. Load determination on site currently is done by the diesel generator set supply system

which operates alternately depending on the run hours.

3.2.1 Architectural Design of the Hybrid Solar PV-Diesel System

In the PV-Diesel Design system, the BTS receives power from two different power sources that

is solar PV system and diesel genset. The BTS receives its power from the solar PV system

during the day whilst in the night and cloudy weather period power supply to the BTS is by the

diesel generator. The hybrid solar PV-diesel generator system consists of solar PV array and a

diesel generator system working alongside each other alternatively. An automatic transfer switch

(ATS) alternates power supply from the solar PV system and the diesel generator system to the

loads on site. A DC Bus line sends all the DC power generated to the rectifier backplane. The

Power supply units (PSUs) or the Switch-mode power supply (SMPS) converts alternative

current (AC) power to direct current (DC) power to be operated in the rectifier backplane while

the battery form units (BFU) control the charging and discharging of the backup batteries. The

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block diagram illustrated in figure 3.2 shows the Hybrid PV-Diesel system design architecture to

be implemented at Mile 9 cell site.

Figure 3.2 Hybrid PV design architecture for Mile 9

3.2.2 Sizing of Components

3.2.2.1 Sizing of the Inverter

Direct current (DC) energy is converted to an alternative current (AC) by the inverter installed

with the power design which is fed into the loads on site. The inverter rating must meet two

conditions:

1. Nominal power ≥ Power estimated x 1.1 …………………………………..(1)

2. Surge power ≥ Power estimated x 2 ……………………………………… (2)

The total AC power estimated from table 3.1 is 70W AC, therefore the following analogue can

be drawn from the AC power established:

Nominal power ≥ 70 x 1.1 = 77 W

Surge power ≥ 70 x 2 = 140 W

The inverter should therefore have a power rating of at least 77 W and a surge power of

at least 140 W. The chosen inverter has to be able to supply the required 220 V for

the CFL lamps, aviation lights and the sockets.

3.2.2.2 Proposed Case Daily Energy Demand Estimation

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The total daily energy demand is required to estimate the backup battery capacity and the solar

PV peak power capacity.

The daily energy demand (E) of each load is given by the formula:

E(Wh) =Power (W) of the load x hours (h) of use per day. …………………….. (3)

For the AC loads, the power used for computing the energy demand is the rectified power. The

rectified power for the AC load is the power taking into account the inverter efficiency. It is

defined by;

Rectified Power = Power

Inverter Efficiency …………………………… (4)

The inverter chosen has an efficiency of 95% for this study. The table 3.2 gives the energy

demand for the BTS site.

Table 3.2 Daily Energy Demand

Loads Power Time Rectified Power Daily EnergyW Hours/Day W Wh.

2 CFL Lamp 40 12 42.11 505.26Aviation Light 25 12 26.32 315.792 Plugs/Sockets 50 4 52.63 410.53BTS 620 24 2320 14880Microwave 194 24 194 4656 Daily Energy Demand 20767.58

The estimated daily energy demand is therefore 20767.58 Wh. In this study 11% of the

energy has been taken as margin of safety. Total daily energy demand to be considered

= 20767.58 x 1.11 = 23052.014 Wh. ………………………………………….. (5)

3.2.2.3 Battery Bank Capacity (CBB)

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The battery bank is sized to cater for supply to loads during night and instance where there is low

or no sunlight during the day. The following conditions are required in sizing backup battery on

site;

1. Daily energy demand Ed (Wh) = 23052.014 Wh.

2. Backup Battery Efficiency, Beff.

3. Battery Nominal Voltage VBB.

4. Depth of Discharge (DOD)

5. Number of days of autonomy (Taut).

The size of the battery bank CBB (Ah) = E (d) xT (aut )

V (BB) X B (eff ) x DOD ……………. (6)

The choice of backup batteries for telecom sites is very crucial since its ability to sustain loads

on site for immediate site down intervention is crucial. Amaron batteries are known batteries

used to support loads on most telecom mobile cell sites.

Specifications of the Amaron batteries are:

Design float life: 20+ years @ 27ºC

Self-discharge < 2% per month

Shelf life without recharge up to 6 months

Operating range: - 40ºC to + 60ºC

AH efficiency: >95% and WH efficiency: >85%

Recombination efficiency >98%

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Design Cyclic Life:

1. 5500 to 6000 cycles @ 20% DOD

2. 2700 to 3000 cycles @ 50% DOD

3. 1500 to 1800 cycles @ 85% DOD

Figure 3.3 Amara Raja 2V 500ah Batteries (Amaron Volt publication, 2017)

Note: All values & charging parameters are rated @ 27ºC (Amaron Volt publication, 2017)

The BTS and microwave transmission equipment require 48V DC power for their normal

operation which is common to most telecom equipment. Therefore the study considers a 48 V

backup battery (VBB) voltage and 3 days of autonomy (Taut) will also be assumed in this study.

The days of autonomy is the number of days the backup battery can hold the loads on site in the

absence of the mains power supply. From the battery specification a DOD of 85% and efficiency

of 95% will be considered. The energy demand to be considered is 23052.014 Wh. (Eq. 5)

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CBB (Ah) = 23052.014 Wh x348 V X 0.95 x 0.85 ……………………….. (7)

CBB (Ah) = 1784.21 Ah …………………………………………………… (8)

To release the nominal storage voltage value of 48 V and a total capacity of 1784.21 Ah, a

series-parallel battery connection combination must be adopted.

3.2.2.4 Photovoltaic Array Peak Power (Wp) Sizing

Characteristic of solar PV module varies depending on the manufacturer and the type of

technology used to produce those modules. Table 3.4 gives detailed characteristic of a solar PV

module from Sun Electronic, 2014.

Table 3.3 Characteristics of PV module for the StudyElectrical CharacteristicsWatts(STC) 300WWatts(PTC) NoMaximum Voltage(Vmp) 36.5VMaximum Current(Imp) 8.22AOpen Circuit Voltage(Voc) 45VShort Circuit Current(Isc) 8.74APower Tolerance 0 to +5%Module Efficiency 15.63%(Source: Sun Electronics, 2014)

PV array sizing requires below data specifications;

1. Daily energy demand Ed (Wh/d) = 23052.014 Wh.

2. Monthly average solar radiation Hi (kWh/m2/d)

3. PV Derating Factor Egen (Typically 80%)

4. Battery Efficiency Beff (%)= Typically 95%

Wp = E(d)

H (i) X B (eff ) x Egen ……………………………….. (9)

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The specified PV module has 300 W at STC as its peak power with a maximum voltage of 36.5

V and a current of 8.22 A as indicated in table 3.3.The PV array is sized to achieve the average

daily energy demand on site with the lowest solar radiation (Hi) of 3.78 kWh/m²/d considered in

table 4.1. This indicates that the solar energy is available during all periods within the year. Daily

energy demand (Ed) of 23052.014 Wh (Eq. 5) will be used in the design process. A derating

factor of 80% of the PV array and a battery efficiency of 95% is considered.

Wp = 23052.014 Wh

3.78 X 0.95 x 0.8 …………………………………….. (10)

Wp = 8024.23 W ……………………………………….. (11)

Total Number of modules needed to supply 8024.23W is given by

W = 8024.23W

300W = 26.75 ≈ 27 ……………………………… (12)

For an anticipated load increase, evenly distribution and arrangement of the PV modules, 28

modules are selected. Actual peak power to be installed = 28 ×300 = 8400 W. The PV modules

will be connected in 2 parallel strings and 14 series models connection.

3.2.2.5 Charge Controller Sizing

The Nominal current of the charge controller is sized to be greater than the PV array’s maximum

current of the load of which the same system voltage being the same as the nominal voltage.

PV array current = Current for one string x number of strings …………… (13)

Current for one string = 8.22 A (Table 3.3), Number of strings = 2

PV array current = 2 × 8.22 = 16.44 A ……………… (14)

Max Load current = DC load current + AC loads current …………………. (15)

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The total AC loads current Iac = Pr

Vac x pf = 70

240 x 0.8 = 0.23 A …………… (16)

The total DC loads current Idc = Pr

Vdc = 81448 = 16.96 A …………… (17)

Maximum load current = (16.96+0.23) = 17.19 A. The maximum load current is greater than the

PV array current, hence the controller must have at least a nominal current of 17.19 A.

3.2.2.6 Diesel Generator Sizing

The estimated daily energy demand of 20767.58 Wh clearly indicates that a 25 KVA generator

plant will be an adequate power supply to support the loads on site.

3.3 Design of the Solar PV-Diesel Generator System with HOMER Software

The Hybrid Optimization Model for Electric Renewable (HOMER) is a computer simulation tool

created by the U.S. National Renewable Energy Laboratory (NREL) to help in the design of

micro-power systems and to facilitate the comparison of power generation technologies for

various range of power applications. HOMER designs a power system considering its physical

behavior and the life-cycle cost, which is the total cost of installation and operation over the

system’s lifespan. HOMER allows for the comparison of several possible design options

according to their technical and economic advantages. It also helps in understanding and

quantifying the effects of uncertainty or changes in the inputs (Simoes, 2006).

HOMER tool uses the energy balance calculation hourly throughout the year in its simulation of

the system. It presents various energy configuration scenarios according to their Total Net

Present Cost (TNPC) values obtained. The total net present cost depicts the system life cycle

cost. The result determines all costs obtained within the project lifetime in addition to cost of

initial set-up, component replacement, maintenance and fuel. With respect to the TNPC the

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system configuration is varied based on the sensitivity variables that have been selected. These

processes are repeated for other scenarios of the sensitivity variables. The final optimal solution

of a hybrid renewable energy system is referred to the lowest TNPC (Girma, 2013).

3.4 Technical and Financial Viability of the PV-Diesel System Design

The HOMER software accepts inputs of cost of the various components for financial simulations

which includes the cost of initial installations, operating cost, maintenance cost, and cost of

replacement. Each of the various variables according to their market values is inputted into the

HOMER software for simulation. The market values of solar PV, diesel generator, backup

batteries, and inverters are entered into the HOMER simulation tool. An estimated cost of power

distribution for the design system is entered into the HOMER simulation tool. The costs of

various components that are entered into the HOMER simulation tool are described below.

3.4.1 Solar PV

In recent times, the unit cost of solar PV systems has been lower due to its current market values.

In this project, a solar PV system of 1 kW PV is estimated to cost $2400 and $1200 per kW as

the cost of replacement. An operating and maintenance cost of $10/year/kW is assumed. The

lifespan of solar panels is estimated to be 25 years with 80% derating factor. The simulation is

done for various energy combinations range from 1 kW to 15 kW to enhance the optimal sizing

of the system.

3.4.2 Diesel Generator

There are different types of diesel generators with various specifications in the current market.

HOMER tool has an hourly operation and maintenance cost already integrated in the software.

The HOMER chooses the number of times a particulate diesel generator works within the year

xlviii

and computes the cost of operating from the value. However, there is little civil work in

installing a diesel generator on site and as a result the generator cost entered into the HOMER

simulation tool is assumed as the overall investment cost including the civil work on site. The

initial cost of 1 kW of generator is estimated to be $500 and a $400 as cost of replacement. An

estimated $0.5/hr operating and maintenance cost of 15 kW diesel generator is assumed. Diesel

price is estimated as $0.5/litre according to the current market value in Ghana. It is estimated that

the diesel generator run hour is 15,000 h in its lifespan and a 10% rated capacity for a minimum

load is assumed. The diesel generator size ranges from 1 kW to 25 kW in relation to its fuel

usage is selected and entered into the HOMER simulation tool.

3.4.3 Backup Battery

The market price for backup battery varies depending on the source of supply and the market

values. The design considers $120 capital cost for each battery and $100 as replacement cost

which are entered into the HOMER simulation tool. Technically, the number of batteries and

types are selected in ranges from the HOMER interface for modeling.

3.4.4 Inverter with Rectifier

A multifunctional inverter with rectifier is chosen. The initial cost of $200/kW and $150/kW cost

of replacement are considered for the multifunctional inverter. Operation and maintenance cost is

of $20 per 10kW of inverter per year is assumed. The inverter is assumed a 10 years lifespan and

an estimated efficiency of 85%. Inverter size ranges from 1 kW to 15 kW are also chosen for the

modeling.

xlix

3.4.5 System Wiring Network

The system wiring considers the distances between the individual components on site with

respect to the PV system setup and the diesel generator orientation on site as illustrated in figure

3.2. An estimated distance of 15 km from the PV system set and the ATS in the equipment room

and 10 km distance between the diesel generator setup from the ATC. The distance between the

ATS and the SMPS is also estimated as 10 km. The distance between the SMPS and the backup

batteries is also estimated as 12 km apart. Specific cable type with their power ratings will be

considered depending on the nature of wiring within the PV-Diesel design system. As the

HOMER does not consider the cost of cable wiring differently, an initial cost of $2,000 towards

the cost of distribution network for the design system is used and $80 per year towards fixed

operating and maintenance costs.

l

CHAPTER 4

RESULTS AND DISCUSSIONS

4.1 Load profile of Mile 9 cell site

This section gives the results and discussions of loads estimated and illustrate the daily energy

consumption on site. The results will also look at the AC power consumption trend against the

DC power usage on site.

4.1.1 Load Profile Estimation

The Load estimation of Mile_9 MTN cell site varies based on the hour of operation of various

electrical devices within the premises. Table 4.1 shows the estimated power profile within the

cell site.

Table 4.1 Load estimation of Mile_9 MTN Cell site (900/1800/3G-2100) siteLoads Power Time Rectified Power Daily Energy

W Hours/Day W Wh.2 CFL Lamp 40 12 42.11 505.26Aviation Light 25 12 26.32 315.792 Plugs/Sockets 50 4 52.63 410.53BTS 620 24 2320 14880Microwave 194 24 194 4656 Total Daily Energy Demand 20767.58

The BTS as the main equipment for mobile signal transmission has the highest power

consumption from the load profile above and aviation warning light has the lowest power

consumption. The daily energy demand value is used to estimate the sizing of various

components within the PV-diesel generator design as illustrated in chapter three.

li

4.1.2 Daily load demands estimation

AC and DC power consumption on site are captured on hourly basis and observed within 7 days.

Load estimation values were observed and shown in table 4.2

Table 4.2 Daily Load demand estimation Mile_9 Indoor (900/1800/3G-2100) site  Hourly load demand

Tim

e (h

our)

of

the

day

Bas

e

Stat

ion

Tran

scei

ver(

BTS

)

Mic

row

ave

Rad

io

(ID

U)

Pow

er

supp

ly/R

ectif

ier-

Shel

ter

light

ing

-

Ener

gy s

avin

g tu

be

light

s

FL00

2A-

Secu

rity

lig

hts

-

Ble

nded

m

ercu

ry

lam

ps (A

C)

Avi

atio

n

war

ning

lig

hts-

at

las

elec

trica

l (D

C)

5%

tole

ranc

e (in

stru

men

t/pho

ne

char

ging

) (A

C)

Tota

l per

hou

r (A

C

load

)

Tota

l per

hou

r (D

C

load

)

00-01 2640 499.2 1170   250 15 291.86 1711.86 3154.201-02. 2640 499.2 1170   250 15 291.86 1711.86 3154.202-03. 2640 499.2 1170   250 15 291.86 1711.86 3154.203-04. 2640 499.2 1170 144 250 15 291.86 1855.86 3154.204-05. 2640 499.2 1170 144 250 15 291.86 1855.86 3154.205-06. 2640 499.2 1170 144 250 15 291.86 1855.86 3154.206-07. 2640 499.2 1170       291.86 1461.86 3139.207-08. 2640 499.2 1170       291.86 1461.86 3139.208-09. 2640 499.2 1170       291.86 1461.86 3139.209-10. 2640 499.2 1170       291.86 1461.86 3139.210-11. 2640 499.2 1170       291.86 1461.86 3139.211-12. 2640 499.2 1170       291.86 1461.86 3139.212-13. 2640 499.2 1170       291.86 1461.86 3139.213-14. 2640 499.2 1170       291.86 1461.86 3139.214-15. 2640 499.2 1170       291.86 1461.86 3139.215-16. 2640 499.2 1170       291.86 1461.86 3139.216-17. 2640 499.2 1170       291.86 1461.86 3139.217-18. 2640 499.2 1170       291.86 1461.86 3139.218-19. 2640 499.2 1170   250 15 291.86 1711.86 3154.219-20. 2640 499.2 1170 144 250 15 291.86 1855.86 3154.220-21. 2640 499.2 1170 144 250 15 291.86 1855.86 3154.221-22. 2640 499.2 1170   250 15 291.86 1711.86 3154.222-23. 2640 499.2 1170   250 15 291.86 1711.86 3154.223-00 2640 499.2 1170   250 15 291.86 1711.86 3154.2

            Total(W) 38804.64 75520.8

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At each hour of the day, all equipment in operation were added to give the load at that particular

hour of the day. It was observed that the DC loads were fairly constant throughout the 24 hours

because those telecom loads operate continuously. However, the AC load component of load

profile shows clear variation during night and day hours. This is because security lighting and

shelter lights are put-on at night and put-off during the day. HOMER replicated this profile

throughout the year in the simulation mode since it is assumed the load will not change. Figure

4.1 shows the graphical view of the hourly load profile for various power characteristic on site

respectively. The various colors depict the individual hourly loads captured with respect to AC

loads and DC loads accordingly.

Figure 4.1 Hourly Load Profile for the cell site.

4.2.1 Hybrid Solar PV-Diesel Design Architecture and Schematics

The optimized PV/diesel power system for the design is made up of solar PV system of 30 kW, a

diesel generator system of 25 kW alongside 48 Surrette 4 KS25P batteries, and a 12 kW

multifunctional inverter.

liii

Table 4.3 PV/Diesel system ArchitectureComponent Description UnitPV Generic flat plate PV 30 kW

Generator Generic 725 kW Prime Power 25 kW

Battery Surrette 4 KS25P 48 quantity

Multifunctional Inverter System Inverter 12 kW

The HOMER simulation tool gives the below schematic setup of the PV-Diesel generator design.

Various components for the design are arranged on the HOMER software with respect to source

of energy and the load demand.

Figure 4.2 Schematic diagram of the Solar PV-Diesel Power System

From the above schematic diagram, the diesel generator set produces AC power source which a

converter converts to DC for supply to the DC loads through the DC bus bar. In connection with

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the PV system, the DC power supply from the system is given to the DC loads while those with

AC load received their power supply with the aid of a converter.

4.2.2 Cost Investment Estimation of Various Components of the Design

The prices of solar PV components were taken from local suppliers together with their estimates

for installation. The costs installations were not limited to the prices given because of differences

in project locations; a site located at a clay soil area will require deeper foundation and more

concrete pavement which would directly increase the cost of installation. With this project, the

location is not clayed soil. General estimates from suppliers were used for this work. HOMER

uses dollar, which means that prices quoted in Ghana cedi were converted to dollar at prevailing

rates as at May 2018 (Gh₵1 to US$0.24). Table 4.4 gives the summary of sizes, cost of

installation, item price and O&M cost which were used in the simulation.

Table 4.4 Items, average cost of installation and operation and maintenance (O&M)

Item SizeCost of Capital Cost of Replacement O&MGH₵ US$ GH₵ US$ GH₵ US$

Diesel fuel  1 ltr  3.67 0.89  - -  -  -Generator 25 kW 68345.67 16564.47 64432.79 15425.47 13.5 2/hrBattery 1350 Ah 6340 1520 6340 1520 211.33 50/yrPV modules 30 kW 550 132.6 550 132.6 420.67 100/yrConverter 12 kW 958 230 958 230 1120.33 50/yr

4.3 Projects in HOMER software results and discussions

Homer simulation software takes inputs from the load profile generated and the cost associated

with components of the power system for simulations where various scenarios were considered

and optimized. Scenarios that met the specified loads with lower Total Net Present Cost were

taken.

lv

4.3.1 Battery Bank state of Charge of system

The battery bank plays an essential role in its ability to sustain the Telecommunication loads at

critical times where the main electricity power or Diesel generator power to the cell site is not

readily available. A short in this function would affect the ability to supply uninterrupted power

to equipment. The power system intended to charge these batteries should be able to adequately

charge them to be discharged later. After the simulation, the state of charge of batteries is

presented by Homer in a pictorial form in figure 4.3 and 4.4 respectively. Each hour is

represented by a pixel showing the state of charge of battery bank at that particular hour of the 24

hours of the day. The figures are made up of 24x365 = 8760 pixels representing each hour of the

year. The hybrid system’s batteries rarely got fully charged which means the charge/discharge

cycle would increase thereby affecting the life span of the batteries. The diesel generator

batteries rarely get charged above 76% which is bad for the batteries; these batteries will get

damaged before their designed lifespan under this condition. Figures 4.3 and 4.4 are the state of

charge of batteries in those power system scenarios.

Figure 4.3 Battery Bank state of Charge of Hybrid system to power indoor site

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Figure 4.4 Battery Bank state of Charge of Generator system to power indoor siteThe PV and battery size is important in power system choice due to limited space. More space

usage means more fencing cost and waste of land. Batteries are expensive and heavy which have

a major influence on system cost. Appendix 6 gives the details of battery used in the hybrid

system. The charging and discharging of batteries times can be adjusted and synchronized with

the Diesel generator to enable the batteries fully discharge to increase their lifespan.

4.3.2 Electricity Usage

Mobile BTS sites should be up and operational at 24/7 daily to ensure availability of service to

customers. A power system supply to these loads should be adequate and avoid wastage. For the

terminal MTN cell site loads at Mile_9, the electricity usage for the Solar PV-Diesel power

system is presented in Table 4.4.

Table 4.5 Electricity Usage in hybrid and Diesel generator systemHybrid system Diesel Generator only

Excess electricity (kWh/yr) 15,234 0

Unmet load (kWh/yr.) 0 0

Capacity shortage (kWh/yr.)

0 0

Renewable fraction 1 0

Clearly from the table excess electricity produced at 15,234Wh/yr. was achieved with the hybrid

power system whilst the diesel generator alone achieved a zero readings. On the same tables,

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both the hybrid system and the diesel generator system had unmet load of zero meaning for the

whole year the load was met.

The electricity usage of the diesel generator alone records no excess electricity, unmet load and

capacity shortage. This means that any addition of load will affect the entire design.

4.4.1 Financial Viability of the Hybrid Solar PV-Diesel design

The capital cost for the optimized power system from the simulation result gives $41,000 and

$97,448 net present cost with a levelised cost of $0.453/kWh of electricity generated. The net

present cost considers costs of the acquisition of components, installation, replacement, operation

and maintenance for the project. Table 4.10 shows the summary of the NPC for various

components.

Table 4.6 Net Present Cost of the Hybrid SystemComponent Capital Replacement O&M Fuel Salvage Total $Solar PV 20,800 0 496 0 0 21,296

Diesel Generator 16,564 15,425 1,480 34,575 -78 67,966

Battery 11,520 780 213 0 -850 11,663

Inverter 940 530 320 0 -79 1,711

System 41,000 14,732 12,178 31,448 -1,910 97,448

The net cost of components of operating diesel generator alone is also presented in the table 4.7

below.

Table 4.7 Net Present Cost of Components for Diesel generator alone on site

ComponentCapital Replacement O&M Fuel Salvage Total$ $ $ $ $ $

Generator 1 16,564 54,330 198,539 375,620 -11,324 633,729

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Surrette 4KS25P 54,000 92,840 40,381 0 -40,049 147,172

Converter 3,096 2,726 1,122 0 -835 6,109

System 77,087 179,897 254,041 375,620 -52,208 834,437

The result from the simulation above shows clearly that running diesel generator alone on site

has high operation cost with a system net cost of $834,437 and -$52,208 salvage value.

Compared with the solar PV-diesel system of $97,448 and -$1,910 salvage value, the hybrid

system projects a more cost effective operation over the project lifespan of 20 year.

The bar chart below in Figure 4.5 shows the hybrid system cost of the various components of the

design. The bar chart deduces that the diesel generator had the highest net present cost

component whilst the converter had the least. Therefore, any attempt to reduce the diesel

generator fuel usage can significantly reduce this cost component.

Figure 4.5 Net Present Costs of the Components

4.4.2 Total Net Present Cost (TNPC)

Economics contribute significantly in HOMER simulation process, wherein it runs the system in

order to reduce the total net present cost (TNPC). During the optimization procedure, it looks for

the lowest TNPC from the system configuration. It also estimates that every price from the

various scenarios of the system is known at the same rate over the project lifespan. In every

lix

parameter of the system, an initial capital cost is incurred in the first period. The cost of

replacement is incurred any time a component requires a replacement at the end of the project

lifespan. The cost of operation and maintenance (O&M) occurs every year in the project lifespan.

Table 4.8 show the cost summary of various scenarios that were considered.

Table 4.8 Cost summary

Projects Standalone PV – indoor hub site

Hybrid system – indoor hub site

Diesel Generator only – Hub site

Total net present cost (TNPC)

$ 575,327 $ 429,351 $ 850,741

Levelized cost of energy

$ 0.62/kWh $ 0.453/kWh $ 0.899/kWh

Cost of Operation

$ 11,805/yr. $ 9,135/yr. $ 33,754/yr.

The optimized standalone PV system for cell site had a TNPC of $ 575,327 whereas the hybrid

(PV and Diesel Generator) for cell site had $429,351. Running a cell site on solely diesel

generator has the highest TNPC. Furthermore, the levelised cost of energy was lower for hybrid

system meaning the cost of energy is lower. Standalone solar PV powering for a cell site shows

operating cost of $11,805/yr. which was higher than the hybrid systems due to replacement cost

associated with batteries serving high consuming AC equipment such as air conditioner. It is

worth noting here that, standalone solar PV systems are not economical for high loads. The

lx

Parameter

$33,754/yr. as operating cost for powering a site with Diesel generator alone is due to continuous

purchase of fuel, frequent servicing and repairs due to wearing of parts.

4.4.3 Cash flows – PV/Diesel Power System

The bar chart below illustrates the cash flow for operating the PV/Diesel system for the project

life span of 20 years.

Figure 4.6 PV/Diesel Design Cash Flows

A 20years lifespan of the project is considered for the project lifespan with the debt repayment

period. An initial capital cost of $41,000 with $7,000 salvage value is achieved as indicated from

the bar chart above at the end of the project lifespan. HOMER computes the salvage value of the

assets according to the remaining lifespan together with the cost of replacement of the asset.

Moreover, even though there are different components in the project lifespan, the cost of the

project is mainly associated to the lifespan of the project.

lxi

In conclusion, a reduced capital and operating cost of any of the component makes it more

desirable for the cost of generation to be reduced. Moreover, unrealistic cost reduces the

relevance of the analysis and distorts the optimal solution of the project.

4.5 Summary – Homer Simulation Result

HOMER simulation results are categorized into areas anticipated to be achieved. These include

power production, the capacity utilization of components, and the cost of each of the main

components of the design.

i. PV Component System: The PV system produces a mean energy output of

25.586kWh/day with an annual electricity generation of 9,339 kWh. The PV system

operates for 4,380 h in a year and had a levelized electricity cost of $0.14237 per kWh.

The capital cost of PV arrays comes to $20,800 and the PV system achieves a capacity

utilization of 17.768%. The PV system penetration is 40.899%.

ii. Diesel Genset Component: The diesel generator runs for 1,776 h/year of 20.15%

utilization capacity. It produces 17,655kWh/year and consumes 4,882.40 L of diesel. The

cost of diesel generator is $16,564 with an additional cost $34,575 for fuel over the

project lifespan. Considering the higher utilization of the generator with respect to the PV

system, its overall life reduces to 8.45years and to maintain the activeness of its operation

lxii

in the project, an approximately two replacements of the diesel generator is required

during the lifespan of the project with a replacement cost $15,425 on each count.

iii. Backup Battery Component: The nominal capacity of the battery system is 172.8 kWh

with autonomy of 46.4 h. The battery has an annual throughput of 7467 kWh/year. The

expected lifespan of the batteries is 10years and they have to be replaced once during the

project lifespan with an investment of $780. A capital cost of $11,520 of the battery

system is achieved with a net present value of battery-related cost of $11,663.

iv. Inverter/Converter Component: The capital cost of the inverter/converter is $ 940.

This inverter has to be replaced once during the lifespan of the project with an amount of

$ 530.

lxiii

CHAPTER 5

CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion

The analysis of the technical and financial implementation gave the following results;

The load profile of the various components of Mile 9 Scancom (MTN) cell site was

undertaken and a daily load estimation of 23.054 kWh obtained.

A diesel genset of a capacity of 25 kVA was used to support power supply loads on Mile

9 Scancom (MTN) cell site in the event of bad weather condition where the solar PV

power of a capacity of 30kW is unavailable. It also supports the site during night hours

when the backup batteries have discharged to an average of 70 percent of its rated

capacity. This brings down the operational hours and reduces the cost of operation of the

genset.

Analysis of the HOMER simulation indicates that technically it is possible to power Mile

9 Scancom (MTN) cell site using hybrid solar PV of 30 kW coupled with diesel generator

set of 25 kVA. Currently, Mile 9 cell site already has a diesel generator and storage

battery infrastructure in place and will have to add solar PV components to make it

lxiv

hybrid. The addition of solar PV will reduce the generator run time, O&M and fuel cost

to operators and eventually reduce service tariff, downtime due to replacement / repairs

of diesel generators and improve on coverage in Ghana.

The result shows that the optimized standalone PV system had a total net present cost of

$ 575,327 whereas the hybrid (PV and Diesel Generator) had $429,351 and diesel

generator alone had $834,437. The levelised cost of energy was lower for hybrid system

compared with standalone solar PV and Diesel alone systems, meaning the cost of energy

is lower. Standalone solar PV shows operating cost of $11,805/yr. ($ 9,135/yr. for Hybrid

system and $ 33,754/yr. for diesel generator alone) which was higher than the hybrid

systems due to replacement cost associated with batteries serving high consuming AC

equipment such as air conditioner. It is worth noting here that, standalone solar PV

systems are not economical for high loads. The $33,754/yr. as operating cost for

powering a site with Diesel generator alone is due to continuous purchase of fuel,

frequent servicing and repairs due to wearing of parts. Thus the order of preference for

this site is hybrid solar PV-diesel, standalone PV and generator alone. Technically and

economically, the combination of Solar PV and diesel generator to form a hybrid system

was the best choice.

5.2 Recommendations

Solar PV technology has a promising future in the telecommunication industry in Ghana but its

penetration into our energy mix has some questions left to be answered. Most of the giant

Telecom industries in Ghana have already piloted Solar PV projects either as standalone or

Hybrid (PV & Generator) but not in large quantities across the country. It is recommended that

lxv

further studies are conducted to determine the reason(s) for the low penetration of solar PV on

the side of operators and on policy issues from the appropriate institution(s).

REFERENCE

1. Ani, V.A. and Emetu, A.N. (2013). “Estimation of environmental impact of power generation at GSM base station site.” Electronic Journal of Energy andEnvironment.vol. 1, nº 1, (In Press). DOI: 10.7770/ejee-V1N1-art479

2. Ani, V.A. (2013a). “Optimal operational strategy for hybrid power generation at GSM base station site.”International Journal of Energy Optimization and Engineering.(In Press).

3. Ani, V.A. (2013b). “Simulation and optimization of stand-alone photovoltaic/diesel hybrid system for banking industry”. Int. Journal of Energy Optimization and Engineering.(In Press).

4. Ani, V.A.; Nzeako, A.N. and Obianuko, J.C. (2012). “Energy optimization at datacenters in two different locations of Nigeria.” International Journal of Energy Engineering. vol. 2, nº 4, Pg. 151-164. doi:10.5923/j.ijee.20120204.07.

5. Ani, V.A. and Nzeako, A.N. (2012). “Energy optimization at GSM base station sites located in Rural areas.” International Journal of Energy Optimization and Engineering.vol.1, nº 3, Pg. 1-31. DOI:10.4018/ijeoe.2012070101.

6. Ashari, M. and Nayar, C.V. (1999). “An optimum dispatch strategy using set points for a photovoltaic(PV)–diesel–battery hybrid power system.” Solar Energy. vol. 66, nº 1, Pg. 1–9.19.

7. Bala, E.J.; Ojosu, J.O. and Umar, I.H. (2000). “Government policies and programmes on the development of solar PV sub-sector in Nigeria.” Nigeria Journal of Renewable Energy. vol. 8, Pg. 1-6.

8. Barley, C.D. and Winn, C.B. (1996). “Optimal dispatch strategy in remote hybrid power systems.” SolarEnergy.vol. 58, Pg. 165–79.

lxvi

9. Barley, C.D.; Winn, C.B.; Flowers, L. and Green, H.J.(1995). “Optimal control of remote hybrid power systems.” Part I Simplifed model. In: Proceedings of WindPower’95.

10. Bernal-Agustín, J.L. and Dufo-López, R. (2009). “Simulation and optimization of stand-alone hybrid renewable energy systems.” Renewable and Sustainable Energy Reviews.vol. 13, Pg. 2111–2118.

11. Borowy, B.S. and Salameh, Z.M. (1994). “Optimum photovoltaic array size for a hybrid wind/PV system.” IEEE Transaction on Energy Conversion.vol. 9, nº 3, Pg. 482-488

12. Ministry of Energy, Ghana (2014) “ Renewable Energy Resource Potentials in Ghana” [www] Available from: http://www.energymin.gov.gh/?page_id=205 [Accessed April 25, 2014].

13. International Energy Agency(IEA), 2011. “SOLAR ENERGY PERSPECTIVES,” Paris: OECD/IEA.

14. Ghana Investment Promotion Centre (GIPC) (2014) ICT Infrastructure [www]. Available from: http://www.gipcghana.com/invest-in-ghana/why-ghana/infra structure/ ict infrastructure.html# [Accessed May 2014]

15. National Renewable Energy Laboratory (NREL) (2014) “Photovoltaic System Pricing Trends” [www].Aailable from: http://www.nrel.gov/docs/fy13osti/ 60207.pdf [Accessed May 2014]

16. PolarPower.org (2014) “Photovoltaic Power Systems” [www]. Available from: http://www.polarpower.org/static/docs/PVWhitePaper1_31.pdf [Accessed May 2014]

17. Florida Solar Energy Center (2014) “Solar Electricity Basics” [www]. Available from:http://www.floridaenergycenter.org/en/consumer/solar_electricity/basics/index.htm [Accessed May 2014]

19. SUN ELECTRONICS (2014) “Solar Panels” [www]. Available from: http://sunelec.com/solar panels [Accessed September 4, 2014].

20. SYNERGY ENVIRO ENGINEERS (2014) “Solar Photovoltaic System” [www]. Available from: http://www.synergyenviron.com/resources/solar_photovoltaic_ systems.asp [Accessed May 2014].

21. ENGINEERING.com (2014) “Sustainable Engineering” [www]. Available from: http://www.engineering.com/SustainableEngineering/RenewableEnergyEnginee ring/SolarEnergyEngineering/Photovoltaics/tabid/3890/Default.aspx [Accessed May 2014].

22. Wikipedia (2014) Battery (electricity) [www]. Available from:

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http://en.wikipedia.org/wiki/Battery_ (electricity) [Accessed May 2014].

23. The Parliament of the Republic of Ghana, Renewable Energy Act 832, Date assent: 31st

December, 2011.

24. Hon. Emmanuel Armah Kofi Buah, Minister for Energy and Petroleum, Ghana; Renewable Energy in Ghana: Policy and potential, UNEF Spanish Solar Forum, Madrid 18-19 November 2014.

25. http://www.ghanatrade.gov.gh/Latest-News/bank-of-ghana-rates-commercial-banks-interest-charges.html, Bank of Ghana rates commercial banks’ interest charges. Sourced: 21/04/19.

26. http://www.tradingeconomics.com/ghana/inflation-cpi, Ghana statistical Service - Ghana inflation rate. Sourced 21/04/18.

27. http://www.bog.gh.com, Bank of Ghana, Daily interbank FX Rates, Wednesday 20th January, 2016. Source: 21/01/16.

28. http://www.ecodirect.com, Solar panels. Sourced: 14/05/18

29. http://support.homerenergy.com/index.php?/Knowledgebase/Article/View/292/91/10303---total-net-present-cost-in-homer, Total net present cost. Sourced: 22/05/18.

30. Kangyi Mao, Engineering Economics; Overview and Application in Process Engineering Industry, 2006.

31. Paul Samuelson and William Nordhaus, Economics, 12th Ed, McGrawHill, New York, 1985.

lxviii

APPENDIX 1

System Architecture for possible simulationStandalone PV – Outdoor terminal site

Standalone PV – indoor hub site

Hybrid system – Outdoor Terminal site

Hybrid system – indoor hub site

Diesel Generator only – Hub site

PV Array 40 kW 50 kW 25kW 30kW NA

Battery 60 Surrette 4KS25P

72 Surrette 4KS25P

36 Surrette 4KS25P

48 Surrette 4KS25P

36 Surrette 4KS25P

Inverter 3 kW 4 kW 12kW 12 kW 16 kW

Rectifier 3 kW 4 kW 12kW 12 kW 14 kW

Generator size NA NA 20 kW 25 kW 25 kW

APPENDIX 2

Net Present Cost of Components for Standalone Solar PV alone

ComponentCapital Replacement O&M Fuel Salvage Total

PV Array 183,696 155,057 2,243 0 -111,468 229,528

Surrette 4KS25P 126,000 216,627 94,222 0 -93,448 343,401

Converter 792 697 1,122 0 -214 2,398

System 310,488 372,382 97,587 0 -205,129 575,328

APPENDIX 3

Electricity Usage in various TechnologiesStandalone PV Hybrid system Diesel Generator only

Excess electricity (kWh/yr)

26,455 15,121 0

Unmet load (kWh/yr.)

24.0 0 0

Capacity shortage (kWh/yr.)

28.0 0 0

Renewable fraction 1.000 1 0

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APPENDIX 4

Battery details of projectsStandalone PV – Outdoor terminal site

Standalone PV – indoor hub site

Hybrid system – Outdoor Terminal site

Hybrid system – indoor hub site

Diesel Generator only – Hub

String size 1 1 1 1

Strings in parallel 60 84 36 36

Batteries 60 84 36 36

Bus voltage (V) 4 4 4 4

Autonomy (hr) 73 81 44 35 35

Energy in (kWh/yr) 23,336 29,862 23,592 29,177 33,842

Energy out (kWh/yr)

18,723 23,962 18,942 23,454 27,197

Storage depletion (kWh/yr)

64 86.0 79 128 140

Losses (kWh/yr) 4,549 5,814 4,570 5,595 6,505

Annual throughput (kWh/yr)

20,933 26,790 21,178 26,222 30,407

Expected life (yr) 12.0 12.0 12.0 12.0 12.0

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