Table of Contents
The Future of Electrical Energy Storage
Executive summary 10
Introduction 10
Pumped storage hydropower 10
Compressed air energy storage 11
Batteries 11
Flywheels 12
Hydrogen storage 12
Capacitors 13
Superconducting magnetic energy storage 13
The economics of electrical energy storage 14
The potential for electrical energy storage 14
Chapter 1 Introduction 16
Introduction 16
Storage technologies 18
The report 19
Chapter 2 Pumped-storage hydropower 22
Introduction 22
The pumped storage principle 25
Pumped storage technology 26
Variable speed technology 28
Plant siting 29
Operational performance 30
Renewable-pumped storage projects 31
Costs 32
Chapter 3 Compressed air energy storage 36
Introduction 36
The CAES principle 37
Compressed air storage sites 39
Site availability 42
CAES technologies and cycles 42
Integrated wind energy and CAES 44
CAES performance 45
Proposed projects 46
Costs 47
Chapter 4 Batteries 52
Introduction 52
The principle of operation 53
Principle battery types 54
Lead acid batteries 55
Nickel-cadmium batteries 58
Sodium-sulfur batteries 60
Zinc bromide flow batteries 63
Vanadium redox batteries 65
Polysulfide bromide flow batteries 67
Other battery types 68
Battery properties 69
Chapter 5 Flywheels 74
Introduction 74
The flywheel principle 75
Flywheel technology 76
Performance characteristics 78
Applications 80
Costs 81
Chapter 6 Hydrogen storage 84
Introduction 84
Fundamentals of a hydrogen storage system 85
Electrolyzers 86
Hydrogen storage 87
Electricity generation 88
Performance characteristics 89
Costs 91
Chapter 7 Capacitors 94
Introduction 94
Electrochemical capacitor fundamentals 95
Types of electrochemical capacitor 96
Performance characteristics 97
Applications 99
Costs 100
Chapter 8 Superconducting magnetic energy storage 104
Introduction 104
Superconducting fundamentals 105
SMES applications 107
Performance characteristics 108
Costs 109
Chapter 9 The economics of electrical energy storage 112
Introduction 112
The capital cost of energy storage systems 114
Operation and maintenance costs 118
Energy storage efficiency 121
Is energy storage economical? 123
Chapter 10 The potential for electricalenergy storage 128
Introduction 128
Storage applications 130
Renewable energy 131
Regulatory barriers 133
Future outlook 134
Index 137
List of Figures
Figure 2.1: Pumped storage plants with capacities in excess of 1,000MW by country 24
Figure 3.2: Estimated costs for storage caverns ($/kWh) 40
Figure 3.3: CAES plant costs ($/kW) 48
Figure 4.4: Efficiency vs cost by battery type 71
Figure 9.5: Unit cost of energy storage systems ($/kW) 115
Figure 9.6: Annual operational and maintenance costs for energy storage technologies ($/kW year) 119
Figure 9.7: Round trip efficiency of energy storage technologies (Efficiency %) 122
List of Tables
Table 2.1: Pumped storage plants with capacities in excess of 1,000MW 23
Table 2.2: Typical operational and economic parameters and costs of pumped storage hydropower 34
Table 3.3: Commercial CAES plants 36
Table 3.4: Estimated costs for storage caverns ($/kWh) 40
Table 3.5: CAES plant costs ($/kW) 48
Table 3.6: Typical operational and economic parameters and costs for CAES plants 49
Table 4.7: Utility scale lead-acid energy storage facilities 57
Table 4.8: Utility-scale sodium sulfur facilities 62
Table 4.9: Comparison of battery properties for utility applications 70
Table 5.10: Typical operational and economic parameters and costs of flywheels 82
Table 6.11: Typical operational and economic parameters and costs of hydrogen storage 91
Table 7.12: Typical operational and economic parameters and costs of capacitors 101
Table 8.13: Typical operational and economic parameters and costs of superconducting magnetic energy storage 109
Table 9.14: Capital cost of energy storage systems 114
Table 9.15: Annual operational and maintenance costs for energy storage technologies ($/kW year) 119
Table 9.16: Round trip efficiency of energy storage technologies (Efficiency %) 121

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