Letter to the Editor

Dear Ms. Ingram,

Regarding your November 2014 article, “A (Potentially) Bright Future for Pumped Storage in the U.S.,” the “heyday” of U.S. pumped-storage construction and capacity-building coincides, or correlates strongly, with the “heyday” of U.S. nuclear power plant construction/capacity build-out.

This is not a coincidence. Other regions mentioned in your article that have considerable pumped-storage capacity, Europe and Japan, also have lots of nuclear plants.

Nuclear plants are baseload facilities that cannot be ramped down (due to safety and technical reasons) nor ramped up (because they are typically already running at or near full capacity), and certainly not turned off due to the massive efforts and time required to restart nuclear. Thus, nuclear plants require grid operators to have similar grid-balancing components, systems and operations methods as do intermittent renewables, in order to maintain grid stability.

It is easier to “see” (understand) the grid-balancing issues/challenges from the supply side perspective of intermittent renewables, for example. But it is somewhat more difficult to see/understand that variable, unpredictable changes of load on the demand side (inherent in the “freedom to consume or not” paradigm of North America) create nearly identical grid-balancing issues. Issues that nuclear plants can do nothing to mitigate.

The grid load (demand side) is constantly, unpredictably changing, so both unpredictable supply (intermittent renewable energy) and in-flexible fixed supply (nuclear power) present issues and problems for grid managers and operators to maintain balance. Hence, the build-out of pumped storage that coincides with large nuclear capacity increases.

Do hydro industry members discuss or acknowledge this reality?

— Robert Mathews, Appropriate Energy Systems, British Columbia, Canada

Rick Miller, P.E., senior vice president of renewable energy services with HDR, responds:

Mr. Mathews points to a very real challenge to the reliability of the future grid — how to manage the new net load problem. Net load is simply the difference between load (or consumer and industrial demand for energy, in blue in the figures below) and subtraction of must-take variable energy supply (typically wind and solar, in yellow below). This is a very different challenge than decades ago, when grid planners had a stable or known supply portfolio and only had to manage the well-understood change in load or demand (really driven by weather, time of day, and day of the week).

This is most obviously seen in southern California, where the California ISO (independent system operator) has published the well-known “Duck Curve” that shows the impacts of integrating significant amounts of solar into the grid (see Figure 1).

As the former asset manager at Duke Energy, where I had 2,000 MW of pumped storage in my portfolio, I can attest that grid operators have known for decades about the need for flexible grid supply solutions, such as pumped storage. The newer net load challenge posed by integrating intermittent renewables is creating a reinvigorated market for new pumped storage. This future grid scenario means there will be excess supply of solar energy during the noon hours, and that supply will disappear by about 4 p.m., while at the same late afternoon time frame the air conditioning load will skyrocket. This leads to an afternoon load ramp of about 12,700 MW as compared to the ramp for load only of maybe 3,000 MW.

So, as you propose, this very real future is creating a nightmare for the grid system operators who are looking for new flexible tools in their grid supply toolbox. And this is the primary driver behind this renaissance of new pumped storage around the globe.

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