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
xxiii
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.
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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.
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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.
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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
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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
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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.
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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).
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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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