Abstract

Pumped storage hydropower (PSH) technologies have been a form of valuable energy storage for electric power systems around the world. A PSH unit typically pumps water to an upper reservoir when loads and electricity prices are low, and releases the water back to a lower reservoir through a turbine when loads are high and electricity is more expensive. PSH is a flexible resource that contributes to help balance supply and demand in the power grid and integrate variable renewable energy sources like wind and solar. As variable energy resources, such as solar and wind generation, become more prevalent, a corresponding increase in demand will arise for a wide range of ancillary services to balance supply and demand in real time. These services take place over time and scales from fractions of seconds (voltage stability and primary frequency control) to seconds (regulation) to minutes (spinning and non-spinning reserves). Due to their high level of operational flexibility, PSH units provide many of these ancillary services to support grid operations. We conclude that providing further support for the development of new PSH units and ancillary service upgrades to existing PSH units will contribute to grid reliability and will facilitate a larger expansion of variable renewable energy, thereby reducing power system emissions in the United States.

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