In 2017, the Water Authority received a $1 million incentive from the California Public Utilities Commission to build an energy storage project that is expected to save the Water Authority nearly $100,000 per year in energy costs by using commercial-sized batteries at the Water Authority’s Twin Oaks Valley Water Treatment Plant.
The batteries store low-cost energy – either excess solar energy or retail energy purchased during off-peak hours – for later use during high-demand periods, maximizing the value of energy generated at the treatment plant. The energy storage project was developed through a no-cost Power Efficiency Agreement with ENGIE Storage to install a 1 megawatt/2 megawatt-hour energy storage system at the Twin Oaks Valley Water Treatment Plant.
ENGIE Storage owns, operates and maintains the system for 10 years or until 2029, after which the Water Authority can choose to extend the agreement, purchase the batteries, or have ENGIE Storage remove the batteries and return the site to its original condition.
San Vicente Energy Storage Facility
One of the most promising pumped energy storage solutions in California is the San Vicente Energy Storage Facility under consideration in San Diego County. This project could store 4,000 megawatt-hours per day of energy (500 megawatts of capacity for eight hours). This potential project would have a small footprint by taking advantage of the existing San Vicente Reservoir owned and operated by the City of San Diego. The Water Authority, which owns approximately two-thirds of the reservoir’s water storage capacity, is partnering with the City on this potential project.
The project would involve creating a small upper reservoir above the existing San Vicente Reservoir, along with a tunnel system and an underground powerhouse to connect the two waterbodies. The powerhouse would contain up to four reversible pump turbines. The upper reservoir would be in an area with no natural lake or stream. During off-peak periods – when power is inexpensive and renewable supplies from wind and solar facilities exceed demand – turbines would pump water to the upper reservoir where it would act as a battery of stored potential energy. During peak energy use, the system would discharge energy as water from the upper reservoir flows downhill through the turbines. The exchange between the two reservoirs would not consume water.
Planning and investing for large-scale energy projects like the San Vicente Energy Storage Facility takes time. It is important to take steps now to ensure this potential project can help California realize a clean energy future.