Renewable Energy in Power Systems
Description
An up to date account of renewable sources of electricity generation and their integration into power systems
With the growth in installed capacity of renewable energy (RE) generation, many countries such as the UK are relying on higher levels of RE generation to meet targets for reduced greenhouse gas emissions. In the face of this, the integration issue is now of increasing concern, in particular to system operators.
This updated text describes the individual renewable technologies and their power generation characteristics alongside an expanded introduction to power systems and the challenges posed by high levels of penetrations from such technologies, together with an account of technologies and changes to system operation that can ease RE integration.
Features of this edition:
- Covers power conditioning, the characteristics of RE generators, with emphasis on their time varying nature, and the use of power electronics in interfacing RE sources to grids
- Outlines up to date RE integration issues such as power flow in networks supplied from a combination of conventional and renewable energy sources
- Updated coverage of the economics of power generation and the role of markets in delivering investment in sustainable solutions
- Considers the challenge of maintaining power balance in a system with increasing RE input, including recent moves toward power system frequency support from RE sources
- Offers an insightful perspective on the shape of future power systems including offshore networks and demand side management
- Includes worked examples that enhance this edition's suitability as a textbook for introductory courses in RE systems technology
Firmly established as an essential reference, the Second Edition of Renewable Energy in Power Systems will prove a real asset to engineers and others involved in both the traditional power and fast growing renewables sector. This text should also be of particular benefit to students of electrical power engineering and will additionally appeal to non-specialists through the inclusion of background material covering the basics of electricity generation.
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Persons
DAVID INFIELD, Department of Electronic and Electrical Engineering, University of Strathclyde, Glasgow, UK
LEON FRERIS, Centre for Renewable Energy Systems Technology (CREST), Loughborough University, Leicestershire, UK
Content
Foreword xv
Preface to the First Edition xix
Preface to the Second Edition xxi
Acknowledgements xxiii
About the Companion Website xxv
1 Energy and Electricity 1
1.1 The World Energy Scene 1
1.1.1 History 1
1.1.2 World Energy Consumption 1
1.1.3 Finite Resources 2
1.1.4 Energy Security and Disparity of Use 3
1.2 The Environmental Impact of Energy Use 4
1.2.1 The Problem 4
1.2.2 The Science 5
1.2.3 The Kyoto Protocol 7
1.2.4 Economics of Mitigation 10
1.2.5 Efficient Energy Use 11
1.2.6 The Electricity Sector 14
1.2.7 Possible Solutions and Sustainability 15
1.3 Generating Electricity 16
1.3.1 Conversion from Other Energy Forms - The Importance of Efficiency 16
1.3.2 The Nuclear Path 17
1.3.3 Carbon Capture and Storage (CCS) 17
1.3.4 Renewables 18
1.4 The Electrical Power System 20
1.4.1 Structure of the Electrical Power System 20
1.4.2 Integrating Renewables into Power Systems 23
1.4.3 Distributed Generation 23
1.4.4 Renewable Energy Penetration 24
1.4.5 Network Stability 25
References 25
2 Features of Conventional and Renewable Generation 27
2.1 Introduction 27
2.2 Conventional Sources: Coal, Gas and Nuclear 28
2.3 Hydroelectric Power 29
2.3.1 Large-Scale Hydro 30
2.3.2 Small Hydro 31
2.3.2.1 Turbine Designs 32
2.4 Wind Power 33
2.4.1 The Resource 33
2.4.2 Wind Variability 34
2.4.3 Wind Turbines 37
2.4.4 Power Variability 40
2.4.4.1 Variability from Second to Second 40
2.4.4.2 Variability from Minute to Minute 41
2.4.4.3 Variability from Hour to Hour and from Day-to-Day 41
2.4.4.4 Seasonal Variability 42
2.4.5 Offshore Wind 42
2.5 PV and Solar Thermal Electricity 47
2.5.1 The Resource 47
2.5.2 The Technology 49
2.5.3 Photovoltaic Systems 49
2.5.4 Solar Thermal Electric Systems 52
2.6 Tidal Power 54
2.6.1 The Resource 54
2.6.2 Tidal Enhancement 54
2.6.2.1 Funnelling 54
2.6.2.2 Resonance 55
2.6.2.3 Coriolis Effect 55
2.6.3 Tidal Barrages 55
2.6.4 Operational Strategies 55
2.6.4.1 Power Variability 56
2.6.5 Tidal Current Schemes 57
2.7 Wave Power 59
2.7.1 The Resource 59
2.7.2 The Technology 59
2.7.3 Variability 60
2.8 Biomass 62
2.8.1 The Resource 62
2.8.2 Resource Sustainability 62
2.9 Summary of Power Generation Characteristics 63
2.10 Combining Sources 64
References 65
3 Power Balance/Frequency Control 67
3.1 Introduction 67
3.1.1 The Power Balance Issue 67
3.2 Electricity Demand 68
3.2.1 Demand Curves 68
3.2.2 Load Aggregation 69
3.2.3 Demand-Side Management - Deferrable Loads 70
3.3 Power Governing 71
3.3.1 Power Conversion Chain 71
3.3.2 Governor Steady State Characteristics 72
3.3.3 Parallel Operation of Two Generators 73
3.3.4 A Multi-Generator System 74
3.3.5 The Steady State Power-Frequency Relationship 75
3.4 Dynamic Frequency Control of Large Systems 76
3.4.1 Demand Matching 76
3.4.2 Demand Forecasting 77
3.4.3 Frequency Limits 79
3.4.4 Generation Scheduling and Reserve 79
3.4.5 Frequency Control at Different Timescales 80
3.4.6 Meeting Demand and Ensuring Reliability 82
3.4.7 Capacity Factor and Capacity Credit 83
3.5 Impact of Renewable Generation on Frequency Control and Reliability 84
3.5.1 Introduction 84
3.5.2 Aggregation of Sources 85
3.5.2.1 The Monthly Distribution of Power Availability 85
3.5.2.2 The Daily Distribution of Power Availability 85
3.5.2.3 Short Term Variability 86
3.5.2.4 The Capacity Factor 86
3.5.3 Value of Energy from the Wind 88
3.5.4 Impact on Balancing 88
3.5.5 Impact on Reliability 90
3.5.6 Discarded/Curtailed Energy 91
3.5.7 Overall Penalties Due to Increasing Penetration 92
3.5.8 Combining Different Renewable Sources 92
3.5.9 Differences Between Electricity Systems 93
3.5.10 Limits of Penetration from Non-Dispatchable Sources 94
3.6 Frequency Response Services from Renewables 96
3.6.1.1 Wind Power 96
3.6.1.2 Biofuels 100
3.6.1.3 Waterpower 100
3.6.1.4 Photovoltaics 100
3.7 Frequency Control Modelling 101
3.7.1 Background 101
3.7.1.1 Modelling a Generator 101
3.7.1.2 Modelling Released Demand 102
3.7.1.3 Modelling the Grid's Inertial Energy Store 102
3.7.2 A Modelling Example 103
3.8 Energy Storage 105
3.8.1 Introduction 105
3.8.2 Storage Devices 106
3.8.3 Dynamic Demand Control 108
References 111
Further Reading 113
4 Electrical Power Generation and Conditioning 115
4.1 The Conversion of Renewable Energy into Electrical Form 115
4.2 The Synchronous Generator 116
4.2.1 Construction and Mode of Operation 116
4.2.2 The Rotating Magnetic Field 119
4.2.3 Synchronous Generator Operation When Grid Connected 120
4.2.4 The Synchronous Generator Equivalent Circuit 122
4.2.5 Power Transfer Equations 123
4.2.6 Three-Phase Equations 124
4.2.7 Four-Quadrant Operation 125
4.2.8 Power-Load Angle Characteristic 125
4.3 The Transformer 126
4.3.1 Transformer Basics 126
4.3.2 The Transformer Equivalent Circuit 128
4.3.3 Further Details on Transformers 129
4.4 The Asynchronous Generator 130
4.4.1 Construction and Properties 130
4.4.2 The Induction Machine Equivalent Circuit 132
4.4.3 The Induction Machine Efficiency 134
4.4.4 The Induction Machine Speed-Torque Characteristic 134
4.4.5 Induction Generator Reactive Power 137
4.4.6 Comparison Between Synchronous and Asynchronous Generators 137
4.5 Power Electronics 139
4.5.1 Introduction 139
4.5.2 Power-Semiconductor Devices 139
4.5.2.1 Diodes 139
4.5.2.2 Thyristors 139
4.5.2.3 Transistors 140
4.5.3 Diode Bridge Rectifier 141
4.5.4 Harmonics 142
4.5.5 The Thyristor Bridge Converter 143
4.5.6 The Transistor Bridge 145
4.5.6.1 Basic Square Wave 146
4.5.6.2 Quasi-Sine Wave (Modified Square Wave) 146
4.5.6.3 Pulse-Width Modulation 146
4.5.6.4 Comparison of Switching Methods 148
4.5.6.5 Output Control in a Grid-Connected Inverter 148
4.5.6.6 The Three-Phase Bridge 149
4.5.7 Converter Internal Control Systems 149
4.5.8 DC-DC Converters 150
4.5.8.1 Step-Down DC-DC Converter 150
4.5.8.2 Step-Up DC-DC Converter 150
4.5.9 Multi-Level Converters 151
4.5.10 Matrix Converters 151
4.5.11 Z-Source Converters 151
4.6 Applications to Renewable Energy Generators 152
4.6.1 Applications to PV Systems 152
4.6.1.1 PV System Characteristics 152
4.6.1.2 Basic Grid-Connected PV Inverter 153
4.6.1.3 Transformerless Grid-Connected PV Inverter 153
4.6.1.4 PV Inverter Using a High-Frequency Transformer 154
4.6.1.5 PV Inverter Using a Steering Bridge 154
4.6.1.6 PV Inverters for Stand-Alone Operation 155
4.6.2 Applications to Wind Power 155
4.6.2.1 Fixed Versus Variable Speed - Energy Capture [4] 155
4.6.2.2 Fixed Versus Variable Speed - Dynamics 156
4.6.3 Synchronous Generator Supplying an Autonomous Network 157
4.6.3.1 Fixed-Speed Wind Turbines 157
4.6.3.2 Variable Slip Wind Turbines 158
4.6.4 The Principle of Slip Energy Recovery 159
4.6.4.1 DFIG Wind Turbines 160
4.6.4.2 Wind Turbines with Full Converters 162
4.6.5 Synchronous Generators in Wind Turbines 162
4.6.6 Gearless Wind Turbines 163
4.6.7 Hybrid Drive Train Designs 164
4.6.8 DC Transmission for Wind 165
4.7 Applications to Small Scale Hydro 166
4.8 Applications to Tidal Stream Turbines 167
References 168
5 Power-System Analysis 171
5.1 Introduction 171
5.2 The Transmission System 171
5.2.1 Single-Phase Representation 173
5.2.2 Transmission and Distribution Systems 173
5.2.3 Example Networks 174
5.3 Voltage Control 176
5.4 Power Flow in an Individual Section of Line 178
5.4.1 Electrical Characteristics of Lines and Cables 178
5.4.2 Single-Phase Equivalent Circuit 178
5.4.3 Voltage Drop Calculation 179
5.4.4 Simplifications and Conclusions 180
5.5 Reactive Power Management 181
5.5.1 Reactive Power Compensation Equipment 182
5.5.1.1 Tap Changers and Voltage Regulators 182
5.5.1.2 AVRs 183
5.5.1.3 Static Compensators 184
5.5.1.4 FACTS 184
5.5.1.5 RE Generator Interfaces 184
5.6 Load-Flow and Power-System Simulation 184
5.6.1 Uses of Load Flow 184
5.6.2 A Particular Case 185
5.6.3 Network Data 186
5.6.4 Load/Generation Data 186
5.6.4.1 Time Dependence 186
5.6.4.2 Types of Nodes (Buses) 187
5.6.5 The Load-Flow Calculations 188
5.6.6 Results 189
5.6.7 Unbalanced Load-Flow 189
5.7 Faults and Protection 190
5.7.1 Short-Circuit Fault Currents 191
5.7.2 Symmetrical Three-Phase Fault Current 191
5.7.3 Fault Currents in General 191
5.7.4 Fault Level (Short-Circuit Level) -Weak Grids 192
5.7.5 Thévenin Equivalent Circuit 193
5.8 Time Varying and Dynamic Simulations 193
5.9 Power-System Stability 194
5.9.1 Equal Area Stability Criterion 195
5.9.2 Power-System Stabilisers 196
5.10 Dynamic Line Rating 196
5.11 Reliability Analysis 197
References 197
6 Renewable Energy Generation in Power Systems 199
6.1 Distributed Generation 199
6.1.1 Introduction 199
6.1.2 Point of Common Coupling (PCC) 200
6.1.3 Connection Voltage 200
6.2 Voltage Effects 201
6.2.1 Steady State Voltage Rise 201
6.2.2 Automatic Voltage Control - Tap Changers 202
6.2.3 Active and Reactive Power from Renewable Energy Generators 203
6.2.4 Example Load Flow 204
6.3 Thermal Limits 207
6.3.1 Overhead Lines and Cables 207
6.3.2 Transformers 208
6.4 Other Embedded Generation Issues 208
6.4.1 Flicker, Voltage Steps and Dips 208
6.4.1.1 Flicker 208
6.4.1.2 Steps and Dips 209
6.4.2 Harmonics/Distortion 209
6.4.3 Phase Voltage Imbalance 210
6.4.4 Network Reinforcement 211
6.4.5 Network Losses 211
6.4.6 Fault Level Increase 211
6.5 Islanding 212
6.5.1 Introduction 212
6.5.2 Loss-of-Mains Protection for Rotating Machines 213
6.5.3 Loss-of-Mains Protection for Inverters 213
6.6 Fault Ride-Through 214
6.7 Generator and Converter Characteristics 215
References 216
7 Power System Economics and the Electricity Market 219
7.1 Introduction 219
7.2 The Costs of Electricity Generation 219
7.2.1 Capital and Running Costs of Renewable and Conventional Generation Plant 219
7.2.2 Total Generation Costs 221
7.3 Economic Optimisation in Power Systems 221
7.3.1 Diversity of Generator Characteristics in a Power System 221
7.3.2 Optimum Economic Dispatch 221
7.3.3 Equal Incremental Cost Dispatch 224
7.3.4 OED with Several Units and Generation Limits 225
7.3.5 Costs on a Level Playing Field 228
7.4 External Costs 229
7.4.1 Introduction 229
7.4.2 Types of External Cost 230
7.4.3 The Kyoto Protocol and Subsequent Agreements 231
7.4.4 Costing Pollution 233
7.5 Effects of Embedded Generation 234
7.5.1 Value of Energy At Various Points of the Network 234
7.5.2 An Example Cash-Flow Analysis 235
7.5.3 Value of Embedded Generation - Regional and Local Issues 237
7.5.4 Capacity Credit 238
7.5.5 Summary 241
7.6 Support Mechanisms for Renewable Energy 241
7.6.1 Introduction 241
7.6.2 Feed-in Law 242
7.6.3 Quota System 242
7.6.3.1 Renewables Obligation (RO) 242
7.6.3.2 Contract for Difference (CFD) 243
7.6.4 Carbon Tax 243
7.6.4.1 Climate Change Levy 243
7.6.4.2 Eco-Tax Reform 243
7.6.4.3 Tax Relief 244
7.7 Electricity Markets 244
7.7.1 Introduction 244
7.7.2 The UK Electricity Supply Industry 244
7.7.2.1 The State-Owned Central Electricity-Generating Board 244
7.7.2.2 The Electricity Pool 244
7.7.2.3 The Operation of the Pool and Pool Rules 245
7.7.2.4 Hedging 246
7.7.2.5 Electricity Market Reform (EMR) 247
7.7.2.6 Ancillary Services 247
7.7.2.7 Marketing Green Electricity 248
References 248
8 The Future - Towards a Sustainable Electricity Supply System 249
8.1 Introduction 249
8.2 The Future of Wind Power 251
8.2.1 Large Wind Turbines 251
8.2.2 Offshore Wind Farm Development 254
8.2.2.1 Electrical Integration 256
8.2.2.2 DC Transmission for Wind 257
8.2.2.3 Innovative Collector Systems 257
8.2.2.4 A Proposed European DC Supergrid 257
8.2.2.5 Smarter Wind Farms 260
8.2.3 Building Integrated Wind Turbines 262
8.3 The Future of Solar Power 264
8.3.1 PV Technology Development 264
8.3.1.1 Different Deployment Options 265
8.3.2 Solar Thermal Electric Systems 267
8.4 The Future of Biofuels 268
8.5 Geothermal Power 271
8.6 The Future of Hydro and Marine Power 271
8.7 The Shape of Future Networks 272
8.7.1 Transmission System Evolution 273
8.7.2 Low Inertia Power Systems 275
8.7.3 Distribution Network Evolution 276
8.7.3.1 Active Networks 277
8.7.4 Problems Associated with Distributed Generation 278
8.7.4.1 Fault Levels 278
8.7.4.2 Voltage Levels 278
8.7.4.3 Network Security 279
8.7.4.4 Network Stability 279
8.7.5 Options to Ameliorate the Technical Difficulties 279
8.7.5.1 Planning Standards 279
8.7.5.2 Using Power Electronics Technology 279
8.7.5.3 Islanding 280
8.7.5.4 Dynamic Loads 280
8.7.5.5 Demand-Side Management of Loads 281
8.7.5.6 Storage 282
8.7.5.7 Microgrids 282
8.7.5.8 Virtual Power Stations 283
8.8 Conclusions 283
References 285
Appendix A Basic Electric Power Engineering Concepts 289
A.1 Introduction 289
A.2 Generators and Consumers of Energy 289
A.3 Why AC? 291
A.4 AC Waveforms 291
A.5 Response of Circuit Components to AC 292
A.5.1 Resistance 292
A.5.2 Inductance 293
A.5.3 Capacitance 295
A.6 Phasors 296
A.7 Phasor Addition 297
A.8 Rectangular Notation 298
A.9 Reactance and Impedance 300
A.9.1 Resistance 300
A.9.2 Inductance 301
A.9.3 Capacitance 301
A.9.4 Impedance 301
A.10 Power in AC Circuits 302
A.11 Reactive Power 304
A.12 Complex Power 305
A.13 Conservation of Active and Reactive Power 306
A.14 Effects of Reactive Power Flow - Power Factor Correction 307
A.15 Three-Phase AC 308
A.16 The Thévenin Equivalent Circuit 310
Reference 311
Index 313
1
Energy and Electricity
1.1 The World Energy Scene
1.1.1 History
Energy has played a key role in the development of society. In the pre-industrial world, this energy was provided mostly by man and animal power and from the burning of wood for heating, cooking and smelting of metals. Coal, through the then new technology of steam engines, mechanised production, improved transportation and powered the industrial revolution. The inter-war years saw the rise of oil exploration and use. Access to this critical fuel became a key issue during the Second World War. Post-war industrial expansion and prosperity was increasingly driven by oil, as was the massive growth in private car use. More recently, a new phase of economic growth has been underpinned by natural gas; most recently much of this derived by fracking. Nuclear power makes a contribution to electricity generation. However, transport still depends almost entirely on oil.
A substantial proportion of coal and gas production, and all nuclear power, is used to generate electricity, which has been widely available now for over a century. Electricity is a premium form of energy due to its flexibility and ease of distribution and use. Demand worldwide continues to grow driven by increased industrial activity and the widening of access to electricity from consumers in the developing world.
1.1.2 World Energy Consumption
The present global yearly primary energy1 consumption is in round figures about 550 EJ2 This is equivalent to about 1.5 × 1017 Wh or 150 000 TWh. Dividing this figure by the number of hours in the year gives 17 TW or 17 000 GW as the average rate of world primary power consumption. The pie chart in Figure 1.1 shows the percentage contribution to world primary energy from the different energy sources according to data taken from the International Energy Agency (IEA) Key World Energy Statistics, 2016 [1].
Figure 1.1 Percentage contribution to world primary energy in 2014 (2peat and oil shale included with coal,3 other includes the remaining renewable energy sources, wind, solar, geothermal and tidal).
Figure 1.2 Recent growth in world primary energy supply by fuel in Mtoe (2peat and oil shale included with coal,3 other includes the remaining renewable energy sources, wind, solar, geothermal and tidal).
World energy supply continues to increase steadily as can be seen in Figure 1.2 (also taken from the IEA Statistics 2016), with most of this being accounted for by an increase in fossil fuels, particularly coal and gas. The rapid development of the economies of India and China is contributing significantly to this growth, despite currently much lower per capita energy consumption in these countries than in Europe and North America.
1.1.3 Finite Resources
It is extremely difficult to determine precise figures on the ultimate availability of fossil fuels. According to the major oil and gas companies, significant new resources of oil are still being developed or remain to be discovered. A safe assessment is that there is enough oil from traditional sources to cover the present demand for at least 30 years. The latest figures for global gas reserves indicate that these are approximately 50% higher than for oil, at some 60 years of current demand. And gas is far less explored than oil so there is probably more to be found. There are, however, unconventional hydrocarbon resources - such as heavy oil and bitumen, oil shale, shale gas and coal bed methane - whose total global reserves have been assessed very roughly to be three times the size of conventional oil and gas resources. These are more expensive to extract but are now being exploited as the price of fossil fuels increases due to the steady depletion of the more easily accessible reserves. Most notable has been the recent increase in shale gas extraction in the USA derived through the process known as fracking. Fortunately for fossil-fuel dependent economies, coal reserves are considered to be many times those of oil and gas and could last for hundreds of years. The down-side of coal is its high carbon content, a topic to be discussed later.
Much debate is currently focused on when the so called, peak oil and gas might occur. This is when the oil and gas extraction rate starts to fall, and occurs well before resources run out. It is important because it signals that demand will most likely not be fully met with prices rising significantly as a consequence. Certainly, the UK's North Sea reserves of oil and gas are fast declining with peak extraction having already occurred in 2003. Given the enormous investment in extraction and supply infrastructure, and the profits to be made, it would be surprising if those with vested interests did not work hard to maintain confidence in these sources.
Fuel for nuclear fission is not unlimited and several decades ago this prompted interest in the fast breeder reactor that, in effect, extends the life of the fuel. However, the political dangers inherent in the fast breeder cycle, with its production of weapons grade plutonium, has limited its development to a few prototype reactors that had major operational problems and are now decommissioned. The lifetime of uranium reserves for conventional fission at current usage has been estimated by some as around 50 years but such calculations are very dependent on assumptions. If an extremely high ore price is tolerable, then very low grades of uranium ore can be considered as possible reserves. The DTI cites OECD/NEA 'Red Book' figures to claim that based on 2004 generation levels, known uranium reserves (at $130/kg) will last for around 85 years (see References [2, 3]).
1.1.4 Energy Security and Disparity of Use
Energy security is a major concern worldwide. A large part of the world's oil is located in the Middle East and other politically unstable countries. The conflict between 'Western' and 'Islamic' cultures is at present exacerbating the anxiety over reliability of energy supply. Russia is a major producer of gas but recent events in Ukraine have made European countries aware how dependent they are on this single source. Until 2010, the USA was the world's largest consumer of energy (at which point it was overtaken by China following years of significant economic growth there); it remains dependent on imported oil and gas, although much less now than in the past due to increased levels of domestic production of gas from fracking. With economic growth seen as being intrinsically linked to cheap fuel it is difficult to imagine political parties, in the USA or elsewhere, proposing policies that require voters to drastically curtail their consumption and therefore alter their lifestyle.
Another disturbing aspect is the disparity in consumption between rich and poor countries: the richest billion people on the planet consume over 50% of all energy, while the poorest billion consume around 4%. This is an added source of tension and of accusations that the developed countries are profligate in their use of energy. To excuse this high consumption on grounds of high industrial activity is simply wrong. Japan for example is the world's third largest economy but has a per capita energy consumption roughly half that of the US. Pricing has a lot to do with this; it is not surprising perhaps that the US has the lowest costs by far for diesel and petrol (IEA Key World Energy Statistics, 2016, data for 2016).
1.2 The Environmental Impact of Energy Use
1.2.1 The Problem
Fossil fuels have one thing in common: they all create carbon dioxide when burned. They are a key part of the Earth's long term carbon cycle, having been laid down in geological periods when the climate was tropical across much of the planet and atmospheric CO2 concentrations were very high. This storing of carbon through the growth of plant matter, and its subsequent conversion to coal, oil, peat and gas dramatically reduced atmospheric CO2 levels and played an important role in cooling the planet to temperatures that could support advanced life forms. The concern now is that by unlocking this stored carbon climate change is being driven in the other direction, with global warming the direct result of an excessive greenhouse effect.
Ice core samples indicate that the level of carbon dioxide in the atmosphere was more or less stable at 260 parts per million (ppm) over the last few thousand years up to the onset of the industrial revolution at the beginning of the nineteenth century. Subsequently, atmospheric CO2 levels rose, slowly at first as a result of coal burning, but since the Second World War the release of CO2 has accelerated reflecting the exploitation of a wider range of fossil fuels. Current CO2 levels are near 400 ppm and rising fast as made clear in Figure 1.3, taken from NASA based on ice core samples and other data.
CO2 is not the only pollutant created by fossil-fuelled generation: combustion in air comprising 78% nitrogen by volume inevitably produces nitrogen oxides, NO and NO2 and N2O, collectively known as NOx; and any sulfur content of the fuel results in SOx emissions. NOx and SOx together contribute to acid rain and, as a result, it is now common to reduce any SOx emissions from fossil-fuelled power stations through flue gas desulfurisation. The down side of this is reduced thermodynamic...
