Report on “Water Sector Over-Generation Mitigation and Flexible Demand Response” now available for download

California’s next major energy challenge is “over-generation” – a situation in which real-time electric production exceeds real-time electric demand. If not properly managed, real-time imbalances between electric supplies and demand can disrupt electric service.

The challenges of balancing California’s electric grid are presently being addressed through a diverse portfolio of market mechanisms, operating strategies, energy storage, and “smart” grid management technologies. During some hours, however, real-time over-generation exceeds the ability of these remedies to solve the imbalance. When that occurs, some real-time energy production must be curtailed to keep power flowing throughout the State. Presently, most of the energy being curtailed is solar, since over generation occurs predominantly during daylight hours when solar PV generation is highest.

The two graphs below show the large quantities of new grid-level solar PV that have requested transmission interconnection between now and 2023, and the effect they will have on the Duck Curve and over-generation if all of these resources are implemented.

California has invested billions of dollars to put California on a path to 100% carbon-free electricity. Curtailments of renewable energy are antithetical to State policy. More electric storage could substantially reduce and eventually eliminate the need for curtailments. However, the current technology of choice, large scale electric energy batteries, are costly and have long lead-times to permit. Near-term solutions are needed to bridge the gap. Fortunately, remedies exist today that are already distributed throughout the state and ready to deploy. One high potential opportunity is pumped water storage.

This report examines the significant potential to increase grid integration support for carbon-free renewable energy resources by leveraging water storage facilities as “flexible balancing resources.” Candidate opportunities include pumped storage hydropower (open and closed loop), groundwater banks, surface reservoirs, and ponds, tanks, and other types of seasonal and diurnal water, wastewater, and recycled water storage facilities. This report recommends that the State develop a Water Sector Flexible Demand Response Program that leverages the flexibility inherent in water systems to increase the State’s ability to reliably integrate large volumes of carbon-free renewable energy and reduce the frequency and amount of renewable energy curtailments.


Download the full report here



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