Introduction 1
 
1 Background 3
1.1 How does the grid work? 3
1.2 What is energy storage? 9
1.3 Why energy storage? 10
1.4 History of energy storage technologies 12
1.5 Factors affecting economic viability 13
1.6 Legal and regulatory considerations 15
 
2 Utility-Scale Energy Storage Technologies 18
2.1 Multiple storage technologies are available 18
2.2 Different energy storage durations have different uses on the grid 35
 
3 Several Challenges May Hinder Energy Storage Technology Development and Use 39
3.1 Planning for storage technologies 39
3.2 Challenging regulatory environment 42
3.3 Existing codes and standards do not fully address energy storage technologies 43
3.4 Crosscutting challenges 44
3.5 Valuing energy storage 46
 
4 Policy Options to Address Energy Storage Technology Challenges 48
4.1 Status quo 48
4.2 Integrating storage technologies 50
4.3 Revising and enacting rules and requirements 52
4.4 Updating or creating codes and standards 54
4.5 Addressing crosscutting challenges 56
4.6 Incentivizing energy storage 58
 
5 Agency and Expert Comments 61
 
Appendix I: Objectives, Scope, and Methodology 63
Appendix II: Expert Participation 68
Appendix III: GAO Contacts and Staff Acknowledgments 69