New Clean Energy Storage Project to Save Water Authority $100,000 Yearly

March 14, 2018

The San Diego County Water Authority will save approximately $100,000 per year with commercial-scale batteries installed at the agency’s Twin Oaks Valley Water Treatment Plant near San Marcos. The energy storage system is designed to reduce operational costs at the facility by storing low-cost energy for use during high-demand periods when energy prices increase.

The batteries were installed at no charge to the Water Authority as part of an agreement with Santa Clara-based ENGIE Storage, a division of ENGIE North America, formerly known as Green Charge. The system charges from either the grid or onsite solar energy production to store low-cost energy. ENGIE Storage’s GridSynergy software allows the Water Authority to use that low-cost energy for plant operations during high-demand periods when market prices typically peak. Onsite energy is generated by more than 4,800 existing solar panels at the Twin Oaks facility that produce an estimated 1.75 million kilowatt-hours of electricity each year.

“Energy storage is a strategic addition to the Water Authority’s solar energy installations, which have already reduced power costs and made the agency more environmentally friendly,” said Mark Muir, chair of the Water Authority’s Board of Directors. “This project is a good example of how we continually look for ways to maximize investments in the regional water treatment and delivery system to the benefit of our ratepayers. This includes advances in our growing list of energy initiatives.”

The Water Authority has 7,500 solar panels at three major facilities, producing an estimated total of more than 2.6 million kilowatt-hours of renewable energy annually. That’s enough to decrease the Water Authority’s energy expenses by nearly $5.6 million over 20 years, and its carbon dioxide-equivalent emissions by approximately 41,000 metric tons – roughly the emissions created by burning 4.6 million gallons of gasoline.

The Water Authority’s energy program includes an energy storage facility at Lake Hodges and a 2016 agreement that allowed the agency to begin purchasing low-cost power produced at Hoover Dam. In addition, the Water Authority and its partner, the City of San Diego, are exploring the development of a major energy storage facility at San Vicente Reservoir. If built, it would be a 500-megawatt facility capable of producing 4,000 megawatt-hours of energy per day.

ENGIE Storage installed the batteries at Twin Oaks through a Power Efficiency Agreement with the Water Authority to install, at no cost to the Water Authority, a 1 megawatt/2 megawatt-hour energy storage system. ENGIE will own, operate and maintain the $2 million system on Water Authority land for 10 years, after which the Water Authority can choose to extend the agreement, purchase the batteries, or have them removed and the site returned to its original condition.

A $1 million incentive from the California Public Utilities Commission helped to fund the project. The incentive, awarded in 2017 under the CPUC’s Self Generation Incentive Program, encourages the adoption of energy storage technologies that reduce both electricity demand and greenhouse gases.

For more information about the Water Authority’s renewable energy initiatives, go to

  • The San Diego County Water Authority sustains a $268 billion regional economy and the quality of life for 3.3 million residents through a multi-decade water supply diversification plan, major infrastructure investments and forward-thinking policies that promote fiscal and environmental responsibility. A public agency created in 1944, the Water Authority delivers wholesale water supplies to 23 retail water providers, including cities, special districts and a military base.

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