The clean energy transition and the effects of climate change have shifted the way we think about electric power reliability and resilience. These two separate but related concepts have grown in significance as the electric power sector makes a massive shift away from a mostly-dispatchable thermal fleet to one dependent upon the weather (sun, wind, and rain).
A new U.S. Department of Energy report, “Hydropower’s Contributions to Grid Resilience,” finds that hydropower in the western interconnect (WI) is critical to ensuring electric power reliability and resilience.
The Deep Dive: What Is Transmission Grid Resilience?
Although there’s not a widely accepted definition of resilience, in 2018, the Federal Energy Regulatory Commission (FERC) took its best shot at defining resilience as:
The ability to withstand and reduce the magnitude and/or duration of disruptive events, which includes the capability to anticipate, absorb, adapt to, and/or rapidly recover from such an event (FERC Order, AD18-7)
I often think about resilience as managing the tail risks or the risks associated with high-impact and low probability events like severe weather, wildfires, or cyberattacks. The flexible characteristics of conventional hydropower and pumped storage hydropower align perfectly with a grid’s need to respond and recover quickly to extreme disruptive events. The table below from the report outlines those contributions.
But, actually proving this has been more difficult.
Defining Hydro’s Contribution to Resiliency, Reliability
Enter the brilliant folks at the national laboratories – Pacific Northwest National Laboratory (PNNL), Argonne National Laboratory (ANL), Idaho National Laboratory (INL), National Renewable Energy Laboratory (NREL), and Oak Ridge National Laboratory (ORNL) — who used historical data as well as future simulations to better define hydro’s contribution to resilience and reliability.
The study’s two main conclusions are:
- Hydropower is critical to stabilizing the western interconnect after sudden loss of generation
- Hydropower’s storage and dispatch capabilities are critical to ensure system reliability during extreme weather events
One illustrative example of hydropower’s reliability value is its contribution to frequency response and reactive power during a simulated generator trip at a large nuclear facility. The results of the simulation, shown in the graph below, found that even though hydro represents only about 20 to 25 percent of installed capacity in the western interconnect, hydro is providing the bulk of the governor response during the crucial 30 seconds after a large contingency (i.e., the loss of two units at Palo Verde nuclear plant).
In addition, the results found that hydro provided substantial support (more than all other units combined) in all seasonal, loading, and water availability conditions.
Additionally, after the simulated nuclear trip, it’s crucial to maintain voltage levels. One way to do this is through reactive power supplied by online generators. Most thermal generators (excluding natural gas) operate at their rated output and thus have little ability to provide reactive power. Hydropower and natural gas, which typically have units that operate below their rated power output, can provide a significant amount of MVARs during post disturbance events. The graph below demonstrates this in the immediate aftermath of the Palo Verde trip.
Why It Matters
As the mix of electric power generation sources evolves toward predominantly renewable and as climate change increases extreme weather events, the contributions of hydropower and pumped storage to resilience and reliability will be even more vital. Currently, many of these services provided by hydro are either uncompensated for (example: inertia) or undercompensated (example: reactive power).
If we are serious about building a resilient grid, we need a serious examination of these tail risk events and the value of preventing them or reducing their impact.