ABSTRACT
The aim
of this study is to design and simulate a hybrid energy system for reliable and
cost - effective power supply to mobile telecommunication sites in developing
cities. The Hybrid optimization model for electric renewable (HOMER) software
was utilized to design the wind-solar hybrid energy system. Long-term wind speed
and solar radiation data were collected for the study location in Nigeria from
the archives of the Nigerian Meteorological agency and the Nations Aeronautics
and Space Admiration respectively. Simulations were carried out for one-year
period, by making energy balance calculations based on HOMER software using
long-term meteorological data and the load profile of a practical mobile
telecommunication site load installed at Agbor, Delta State. Simulation results
showed that the optimized wind-solar-battery hybrid system, which consists of
14 kW PV arrays, 15 kW wind turbine generators, 5 kW power electronic converter
and 110.98 kWh battery bank, gives the lowest cost of US$ 0.165 (N51.23) per kWh of energy consumed but
with 3% annual capacity shortage compared to diesel-alone US$ 0.479 per kWh (N 148.73 per kWh), wind-diesel-battery (N 65.83 per kWh), solar-diesel-battery (N 78.56 per kWh), and
solar-wind-diesel-battery hybrid systems (N
51.85 per kWh). In addition, the application of the designed hybrid energy
system could eliminate the greenhouse gas emissions of mobile telecommunication
sites resulting from the use of diesel generators and thereby making the
environment greener and safer.
CHAPTER ONE
INTRODUCTION
1.1
Background to the Study
The rising costs of energy and carbon footprint of operating mobile
telecommunication sites in the developing countries have increased research
interests in renewable energy technology. The renewable energy system design
usually integrates renewable energy mix, such as biomass, wind and solar
energy. Nevertheless, large area of land, water usage, and social impacts often
characterize the electricity production from biomass, and this requires further
study to verify the techno-economic viability of its power generation
(Okundamiya, 2015). Consequently, it may be required to shift demand to other
energy sources, such as wind and solar. Wind and solar energy are ubiquitous
and freely available. These are used sources for renewable energy generation
because are both technically and environmentally viable options.
Wind energy is one of the most viable and promising sources of renewable
energy globally. Accurate estimate of wind speed distribution, selection of
wind turbines, and the operational strategy and management of the wind turbines
are essential factors that affect the wind energy potential. The first steps a
utility company considers when deploying wind as an energy source is to examine
the available wind speed (Okundamiya and Nzeako, 2013). The next step is to
adjust the wind speed data at anemometer height to wind turbine hub height
using appropriate conversion ratio. The adjustment of the wind profile is
necessary to account for the effects of the wind shear inputs. Moreover,
accurate assessment of wind power potential at a site requires detailed
knowledge of the wind speeds at different heights (AI Abbadi and Rehman, 2009,
Rehman and Ai- Abbadi, 2009). Methods are available in the literature for
improving the estimate of the hub height wind resource (Lackner et al, 2010). The solar photovoltaic
(PV) system is a clean source of power, which does not emit greenhouse gasses.
The performance of the photovoltaic conversion system is highly
dependent on its orientation and period of service (Yang and Lu, 2007). The
orientation of the PV surface is described using its tilt angle and the
azimuth, both relate to the horizontal. This creates the problem of designing
the optimum tilt angle for harvesting solar energy at fixed latitudes, as this
is essential for effective harnessing and utilization of global solar radiation
(Okundamiya et al, 2014a). In
general, there are two steps in determining the available solar energy when
supplying a remote load. The first step involves the determination of the
amount of solar radiation that arrives on the earth at the PV panel’s location.
The next step is modelling of the panel itself, considering its efficiencies,
losses and physical orientation. Each step requires a model that deals with
many variables, and inputs into the second stage of the model utilize the
results of the first step. Using the available solar radiation at the tilted PV
surface, the air temperature, and manufacturers data for a PV module as input
parameters, the power output of the PV module can be deduced (Markvard, 2000).
There has been outstanding interest in the optimal design and management
of stand-alone hybrid energy systems with the aim of achieving energy balance
between the maximum energy captured and consumed energy (Kalantar and Mousavi
2010). The fluctuating renewable energy supplies, load demands, and the
non-linear characteristics of some components complicate the design of hybrid
systems. In addition, the overall assessment of autonomous hybrid energy
systems that incorporate renewable and convectional energy sources depends on
economic and environmental criteria, which are often conflicting objectives.
The technical constraints in hybrid energy systems relate to system
reliability. Several reliability indices have been employed for the evaluation
of generating systems in the literature. The most technical approaches used for
the evaluation of power system reliability are the loss of load probability,
loss of load power supply, and loss of power supply probability.
The various methods for fixing
hybrid energy systems are classified as follows (Zhou et al., 2010): simulation
and optimization software and optimization methods. Hybrid optimization model
for electrical renewable (HOMER), a computer- based model is the most widely
used simulation software for the design options, which makes it easier to
assess the techno-economic benefits of different power system configurations.
Unlike other simulation, HOMER allows for comparison with different design
options based on technical and economic merits, as a result, (Talebhagh and
Kareghar, (2012)), (Teoh et al.2012)
and (Okundamiya et al. (2014b)) have used this tool for the design,
management and sizing of hybrid energy systems.
1.2
Statement of the Problem
The rapid growth of mobile telecommunications in Nigeria creates a
number of problems such as network congestion and poor quality of service
delivery. These problems are fast eroding the gains of the Nigeria mobile
telecommunication sector (Okundamiya et
al. 2014). Lack of a reliable electric power grid and the cost implication
of a supplementary energy source are major problems besetting this sector in
most developing countries, particularly as network operators strive to expand
their communications network to provide global coverage with increased quality
of service. Most mobile telecommunication sites in the developing regions rely
heavily on the use of fossil-fuel led generations either as supplements to the
electric power grid or exclusively in remote locations.
The use of fossil-powered solution at mobile telecommunication sites
presents a number of economic, logistical, and environment problems (Okundamiya
et al., 2014b). The operation and
maintenance of fossil-fueled generators account for about 78% of the total cost
of operations (equivalent to about 35% of the cost of ownership) of the mobile
telecommunication sites (Adegoke and Babalola, 2011). In addition, studies by (
Kovates et al.
(2005)), VandeWeghe and Kennedy (2007) and Rahmstorf (2008) indicate
that the earth’s climatic change is the result of increasing concentrations of
greenhouse gases resulting primarily from fossil fuel combustion into the
atmosphere, yet Nigeria’s grid electricity supply is characterized by high
unreliability index (Ogujor, 2007). Besides, the current and future demand
patterns of energy are not sustainable (Oyedepo, 2012). Sustainable energy
provides accessible, affordable, and reliable energy service that improve the
socio-economic and environmental standards within the overall developmental
context of the society while recognizing equitable distribution (Davidson,
2002).
1.3
Objectives of the Study
The overall aim of this study is to design and simulate a wind-solar
hybrid energy system for reliable and cost-effective power supply to mobile
telecommunication sites in developing cities. The objectives of this study are
to:
(a)
design a wind-solar hybrid energy
system for mobile telecommunication sites in developing cites;
(b)
simulate and determine the
optimum capacity of the wind-solar hybrid energy system for reliable and
cost-effective power supply;
(c)
determine the viability of the
proposed wind-solar hybrid energy system.
1.4
Scope of the Study
The hybrid energy systems discussed in this study are designed to supply
power to outdoor mobile telecommunication sites consuming up to 3KW of power
continuously. The outdoor mobile telecommunication sites consume lesser energy
compared to traditional sites. It is worthy of note that the use of energy
efficient is essential to attaining renewable energy solution.
The
methods proposed to achieve the set objectives for this study are:
(a)
theoretical approach was applied
in the design of the wind-solar hybrid energy system. Load data of a typical
outdoor mobile telecommunication sites was collected from MTN, Nigeria.
Long-term meteorological (wind speed and solar radiation) data were collected
for the study location in Nigeria from the archives of the Nigerian
Meteorological (NIMET) agency, Oshodi, Lagos State and the Nations Aeronautics
and space Admiration (NASA) respectively. The data set was analyzed and
evaluated using stochastic methods.
(b)
Hybrid optimization model for
electric renewable (HOMER) softer will be utilized to simulate the wind-solar
hybrid energy system. The optimum capacity of the hybrid energy system for
reliable and lost-effective power supply is determined by making energy-balance
calculations based on HOMER.
(c)
The viability of the proposed
hybrid energy system will be determined based on sensitivity analysis.
Sensitivity analysis isperformed on the system by varying system design
parameters. Three key performance indices (power supply reliability, cost of
energy, and emission reduction) was applied to evaluate the overall performance
of the proposed hybrid energy system over existing diesel energy generation
system
1.6
Significance of the study
Renewable technologies are essential components of sustainable
development mainly because of the following reason (Okundamiya et al., 2014c). Firstly, these are
eco-friendlier than other sources as such extensive utilization of the
renewable option will help in making the environment friendlier and safe.
Secondly, these are non-exhaustible and if properly utilized in appropriate
application, willcan provide a reliable and sustainable supply of energy
almost indefinitely. Thirdly, these favour system decentralization and
local solution that are somewhat independent of the electric power grid. This
enhances the flexibility of providing enormous benefits to small isolated
populations.
The hybrid renewable energy systems are capable of providing the needed
energy for sustainable economic development in the mobile telecommunication
sectors but critical issues on the enabling technologies are yet to be resolved
(Zhou et al., 2010). The intermittent
nature of most renewable energy sources creates the problem of designing the
optimum configuration for a given location, the use of renewable energy system
as an alternative to fossil –powered source can reduce the unit cost of power,
but the range of financial benefits depends on the geographical coordinates
(Okundamiya and Omorogiuwa, 2015). The reason is that the renewable energy
depends highly on weather conditions. Moreover, the viability of a hybrid
energy system is a function of the configuration, which depends on the size or
allocated capacity, mix of power source and the dispatch strategy. It is worthy
of note that the operational specifications of renewable energy systems are
location dependent (Okundamiya et al., 2014). Potential investors are at a
cross road on the choice of system design configuration, optimum
specifications, capacity projections and the techno-economic implications. In
addition, renewable energy solutions are not commonly used for powering mobile
telecommunication sites in Nigeria presently. Consequently, more research work
on hybrid energy systems and the enabling technology for a sustainable economic
development is needed
1.7
Thesis Arrangement
Chapter 1 discusses the introduction, aims and objectives of the study.
Chapter 2 reviews related literature relevant to this study. The chapter 3
describes the meteorology of the study area, data collection, design and
analysis as well as a case study simulation. The results are presented and
discussed in chapter 4 while chapter 5 gives the conclusion and recommendations
of the study.
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