Key Takeaways 1
Introduction 2
The Challenge of Variable Renewable Energy 4
Scale and Duration: The Size of the Variability Challenge  9
Mitigating the Variability Problem 12
Gas and Phase II of the Energy Transition 14
Beyond Phase II: Long-Duration Storage Technologies 18
Pumped Hydro Storage19
Hydrogen Storage  22
Compressed Air Energy Storage 24
Markets and Revenues 26
Who Pays and How? 27
DOE and Electricity Storage 29
Research Conclusions 30
Policy Recommendations 34
Endnotes 38