ABSTRACT

 

This study work, Evaluation of Levelised Cost of Electricity Generated From Hot Spring Geothermal Resources in Nigeria aims to investigate the economical and technical prerequisites for electricity generation from Rafin Reewa hot spring located at Lere local government of Kaduna state; a potential development sites.
Geothermal energy is thought to have great potential in Nigeria due to the high abundance of sedimentary rocks and numerous hot springs. However, it is still a relatively new technology that has not yet been proved to be economically viable at commercial scale in Nigeria.
The study investigated both the technical and economical aspects of geothermal energy as a resource for electricity production. The technical investigation is based mainly on identifying the resource temperature at Rafin Reewa hot spring and subsequently which technology is suitable for use in the study area. In the economical section of the study, the impact of resource flow rate and resource depth (variables) on factors that determine the geothermal power plant construction costs are analyzed. Within each variable, geothermal power plant cost factors are calculated, and subsequently the levelised cost of electricity (LCOE) at power sales of 50MW was evaluated.
The result of the study shows that the temperature of the geofluid at the study sites (Rafin Reewa) is 122.14oC, and hence this shows that Rafin Reewa hot spring is a hydrothermal geothermal resource suitable for air-cooled binary power plant. Consequently, the results of the study show electricity generation from geofluid of Rafin Reewa hot spring is viable.
On the economic aspect of the study, the result shows that the total plant cost, exclusive of wells, for an air-cooled binary is $663,609,961 (N132, 721,992,200) for 50MW plant capacity at study site. The Levelised Cost of Electricity (LCOE) in cent/kWh is calculated using Geothermal Electricity Technology Model (GETEM). To evaluate the LCOE of the geothermal power plant, the impact of production flow rate and resource depth on the cost factors that influence LCOE were evaluated. The result of the study shows that the LCOE at a flow rate of 100kg/s and a resource depth of 1000m is 43.010cent/kWh (N86.02/kWh). Although both variable parameters influence the LCOE, the study shows that the LCOE is more sensitive to the production flow rate than the depth of the resources.

 

TABLE OF CONTENTS

Title page i
Declaration ii
Certificatification iii
Acknowledgement iv
Abstract v
Table of Contents vii
List of Tables xi
List of Figures xii
List of Appendices xiii
List of abbreviation xiv
List of Symbols xvi
List of Units xviii
CHAPTER ONE: INTRODUCTION 1
1.0 Background 1
1.1 Statement of the Problem 5
1.2 Present Research work 5
1.3 Aim and Objectives 6
1.4. Scope of the Study 6
CHAPTER TWO: LITERATURE REVIEW 8
2.0 Introduction 8
2.1 Geothermal energy 8
2.2 Heat Flow and Heat generation 11
2.3 Geothermal Resources Potential 13
2.4 Geothermal Reservoirs 14
2.4.1 Resource Variable 16
2.4.2 Types of Geothermal Resources 17
2.5 Applications of Geothermal Resources 22
2.6 Environmental Effects of Geothermal Energy 24
2.7 Geothermal Energy Conversion Technologies 25
2.7.1 Direct Steam Power Plant 25
2.7.2 Flash Steam Power Plant 26
2.7.3 Binary Power Plant 27
2.8 Low-Temperature Geothermal Technology and
Binary Cycle Power Plants 28
2.9 Geothermometry 32
2.9.1 Water Geothermometers 34
2.10 Hot Spring 37
2.10.1 Hot Spring Characteristics 38
2.10.2 Hot Springs Flow Rates 41
2.10.3 Classification of Hot Springs 41
2.11 Geological Setting of Nigeria 45
2.11.1 Geological Investigation of Nigerian Crystalline Province 48
2.11.2 Geological Investigation of Nigerian Sedimentary Province 49
2.12 Geological Setting of the Study Area 52
2.13 Geochemical Analysis of the Water in Rafin Reewa Hot Spring 53
2.14 Levelized Cost of Geothermal Electricity 55
2.14.1 Levelized Cost Factors 57
2.15 Economies of Scale 59
2.16 Financing Mechanisms and Macro Economic Environment 60
2.17 Operation and Maintenance Cost 61
2.18 Calculation of Levelized Cost of Electricity (LCOE) 64
2.18.1 Net Present Value 65
2.18.2 Generated Electricity 66
2.19 GETEM Software Description 69
CHAPTER THREE: MATERIALS AND METHOD 73
3.0 Introduction 73
3.1 Methodology 75
3.2 Evaluation of Resource Temperature 76
3.3 Evaluation of Levelized Cost of Electricity the Study Area 76
3.3.1 General Assumption 76
3.3.2 Evaluation of LCOE with Flow Rate as the Variable 77
3.3.2 Evaluation of LCOE with Resource Depth as the Variable 78
CHAPTER FOUR: RESULTS AND DISCUSSION 79
4.0 Introduction 79
4.1 Results 79
4.2 Discussion 79
CHAPTER FIVE: SUMMARY, CONCLUSION AND RECOMMENDATION 88
5.1 Summary 88
5.2 Conclusion 89
5.3 Recommendation 90
5.4 Contribution to Knowledge 92
5.5 Limitation 93
References 94
Appendix 99

 

 

CHAPTER ONE

INTRODUCTION
1.0 BACKGROUND
Energy is fundamental to development in all facets of life: economical, technological, industrial, ecological, educational and standard of living (Alozie et al., 2011). Energy is a multifarious entity, which may transform into highly diverse aspects. Despite the abundance of energy resources in Nigeria, the country is in short supply of electrical power. Only about 40% of the nation‘s over 170 million has access to grid electricity and at the rural level, where about 70% of the population live, the availability of electricity drops to 15% of the domestic and industrial demands (http://odinakadotnet.wordpress.com/). Nigeria requires per capital power capacity of 1000 Watts per person or power generating/handling capacity of 170,000 MW as against the current capacity of 3,920 MW. This will put Nigeria slightly below South Africa with per capita power capacity of 1047 Watts, UK with per capita power capacity of 1266 Watts and above Brazil with per capita power capacity of 480 Watts, China with per capita power capacity of 260 Watts (http://odinakadotnet.wordpress.com/). Currently Nigeria has per capita power capacity of 28.57 Watts and this is grossly inadequate even for domestic consumption (http://odinakadotnet.wordpress.com/).
To achieve the goals of development, a strong energy sector is essential. However, in Nigeria energy supply has been epileptic in nature causing the socio-economic status of the country to be low. In a quest to realize a sustainable energy supply, Nigeria has turned to different sources of energy some of which are renewable. Currently a high proportion of the Nigeria‘s total energy output is generated from fossil fuels such as oil and coal.
Nigeria as a nation has started feeling the impact of climate change, especially those climate conditions caused by greenhouse gases produced by thermal power plants, manufacturing industries, oil spillages following the activities of oil prospecting firms as a result of the country‘s dependence on crude oil and gas.
Renewable energy (RE) has been identified as the only alternative of addressing these problems. RE is energy derived from an energy source that can regenerate itself through natural processes within a relatively short period; unlike fossil type resource that takes millions of years to form and which is non-regenerative. Such energy sources generally include solar, wind, biomass, hydropower, tidal wave, ocean thermal and geothermal (Chinyere, 2011). Amongst these renewable energy sources, geothermal offers a clean base load source of power; it also provides a consistent electricity production nearly 24 hours a day with little to or emissions.
Geothermal energy is present everywhere in Earth because temperature increases with depth. Existing technologies can extract heat from deep layers and utilize it to produce electricity. Geothermal energy is one of the few renewable energy resources that can provide continuous power with minimal visual and other environmental impacts. Geothermal systems have a small footprint of carbon dioxide emissions (Eyal et al., 2008).
Geothermal power development consists of successive development phases that aim to locate the resources (exploration), confirm the power generating capacity of the reservoir (confirmation) and build the power plant and associated structures (site development). Various kinds of parameters will influence the length, difficulty and materials required for these phases thereby affecting their cost (Hance, 2005).
Geothermal energy provides a robust, long-lasting option with attributes that would complement other important contributions from clean coal, nuclear, solar, wind, hydropower, and biomass (Jefferson et al, 2006). When compared to other energy sources (both renewable and non-renewable), geothermal energy has many benefits, including: extremely low emissions, low environmental impact, high capacity factor, base-load, low surface footprint, and low levelized energy cost (Kimball, 2010).
The geothermal energy is one of the sources of renewable energy available for exploitation in Nigeria. Some African countries like Kenya have already started harnessing this clean source of energy (Uyigue et al., 2009). Nigeria also has the potential to harness energy from this source of renewable energy. There are geothermal resource areas in Nigeria with the potential for power generation: Ikogosi warm spring in Ondo state, Rafin Reewa in Kaduna state and the Wikki warm spring in Bauchi state etc. Within sedimentary areas, high geothermal gradient trends are indentified in the Lagos sub-basin, the Okitiputa ridge and the Abakaliki Anticlinoruim. The deeper cretaceous and tertiary sequences of the Niger delta are pressured geothermal horizons (Babalola, 1984). Bauchi state, Plateau state, and the Adamawa areas, have experienced Cenozoic volcanism and magmatism. Geothermal gradients (rate of increasing temperature with respect to increasing depth in the earth‘s interior) indicate that hot steam would be encountered at a depth of about 4,250 ft (1,300 m) in the Abakaliki area and of about 6,000 ft (1,800 m) in the Lagos and Auchi-Agbede areas (Babalola, 1984).
In spite of its immense potential, geothermal remains an underutilized resource and represents zero fraction of the Nigerian renewable energy portfolio. Exploiting the geothermal energy potential in Nigeria has been limited by several factors which include
poor policy and regulations, financial, technological barriers, minimal public awareness and low investment (Federal ministry of Power and Steel, 2006). Improved access to resource data, more efficient drilling processes, increased understanding about the industry‘s potential, and improving access to finance are driving expanding interest in the sector.
There is basically one primary prerequisite for any energy resource to be commercially exploitable, and that is for it to be economically competitive with other energy resources. Hence, the unit cost of producing and utilizing the energy resource is the most sought after for a viable energy project.
The levelised cost of power is a very useful tool for alternative power options. It is on the levelized cost that geothermal projects are evaluated for investment, approval and financing by prospective investors, governments, consumers or regulators and bankers or credit providers. The levelized cost is premised on the net present value of cash flows arising from a power project. Investors engage in power projects to increase their wealth. The application that considers tax and depreciation provides better basis for investment decision. The levelised cost of power is project specific and must therefore be established for each individual project.
1.1 STATEMENT OF THE PROBLEM
Geothermal technology is heat mining from sedimentary rock which has been successfully used around the world but is ignored in Nigeria despite our energy needs.
Consequently, this has led to undervaluing the long-term potential of geothermal energy available from large volumes of accessible sedimentary rock in Nigeria.
Geothermal power is sometimes misconstrued to be an expensive source of electricity. While it is true geothermal power plants require a significant amount of start-up capital and some government assistance in the earliest phases of exploration, the overall capital costs and operating costs of geothermal power are significantly lower than many other technologies. To ascertain its competitiveness and viability among other renewable energy sources, it levelised cost of power must be evaluated.
1.2 PRESENT RESEARCH WORK.
Considering the need for additional energy sources due to the growing Nigeria energy demand couple with the environmental effects of fossil fuels and the opportunity for utilisation of geothermal energy; it is clear this resource should be further studied and developed.
The present study examines the competitiveness of geothermal energy in contributing to Nigeria energy-mix by establishing the levelised cost of generating power using this abundant resource.
1.3 OBJECTIVE OF THE STUDY
The main aim of this research work is to establish the levelised cost of electricity generation by using ―low temperature‖ geothermal resource from Rafin Reewa hot springs.
The cost of geothermal power is, obviously, dependent upon the technology employed in bringing geothermal energy to the surface and converting it to electricity. Consequently, the specific objectives of this research work are as follows:
i. To determine the reservoir temperature.
ii. To select energy conversion (EC) systems appropriate for Rafin Reewa hot spring needed to demonstrate feasibility of geothermal power plant at a commercial-scale.
iii. To determine the effects of mass flow rate as well as resource depth on the levelised cost of power generated using geofluid from Rafin Reewa hot spring.
iv. To estimate the Levelised Cost of power generation from Rafin Reewa geothermal resource.
1.4 SCOPE OF THE STUDY
It is recognized that the cost of geothermal power will depend upon the choice of variables associated with the subsurface and surface design of the production system, construction and operation of the power plant, and the economic model used in the cost analysis. In this study, primary attention will be focused on the levelised cost of power generated from low geothermal resources. Hence, it is beyond the scope of this study to
project the cost of geothermal power using high grade geothermal resources. Also, the detailed design of the power plant is not considered in the course of this work.

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