The U.S. electricity system is critical infrastructure that supports the economy, public safety, and national
security. Although the U.S. power grid is very reliable according to standard metrics, there is an increased
interest in resilience—the grid’s ability to respond to and recover from high-impact, low-probability
events. These range from natural events, such as hurricanes, to human-related events, such as cyber and
physical attacks. The impacts on system operations, and hence the responses needed by the system, can
vary in magnitude, intensity, duration, and geography depending on characteristics of the extreme event.
Hydropower facilities are often crucial in responding to these extreme grid events due to their agility and
flexibility. They can quickly change both their real and reactive power outputs, and they are well-suited to
provide voltage support, inertial response, primary frequency response, spinning, and operating reserves.
Readily available conversion of stored energy—water stored behind dams—and low station power
requirements make them ideal for black start restoration of the grid. Additionally, hydropower presently
constitutes the power system’s largest portion of long-duration energy storage, which can act as a buffer
during extended-duration system outages. However, no standard practices presently exist to quantify the
contributions of hydropower resources and their attributes and response characteristics, especially for
non-market and non-monetized grid services such as voltage support and inertial and frequency
responses.
