On a typical industrial street about 30 miles outside of downtown San Diego there sits a unique facility: the largest lithium-ion battery in North America. Its 400,000 self-contained batteries provide the local Escondido and surrounding area in California with reliable power on demand.

“The substation on the other side of the battery bank feeds enough energy to keep 20,000 homes powered for about four hours,” says Ted Reguly, Director of Growth & New Technologies with San Diego Gas & Electric (SDG&E), a provider of natural gas and electricity.

This lithium-ion battery energy storage facility went into operation late February of 2017. The 30-megawatt Escondido plant is capable of storing up to 120 megawatt-hours of energy from any source, such as wind or solar, or natural gas. “We designed the system to support the electric grid when it becomes stressed, and to help avoid potential power outages and blackouts. So if it’s working well, and so far it has been excellent, most customers may not even know it exists,” adds Reguly.

In 2016, the California Public Utility Commission directed Southern California investor-owned electric utilities to fast-track energy storage options to enhance regional energy reliability. In response, SDG&E expedited negotiations and contracted with AES Energy Storage to build two projects for a total of 37.5-MW of lithium-ion battery energy storage. (In addition to this 30-MW facility in Escondido, a smaller 7.5-MW installation was built in El Cajon, about 20 miles from downtown San Diego.)

AES is the maker of Advancion, a complete, battery-based alternative to peaking power plants, which is used at both California sites. Advancion uses AES-certified, high-efficiency sealed lithium-ion batteries, and fast-response IGBT power-conversion technology that meets IEEE 519 and IEEE 1547 standards. When the local electric grid needs more power, the batteries deliver.

“The great thing about these batteries is that they can respond instantly,” says Reguly. “They are similar to those in an electric vehicle, and act like a sponge. They soak and store energy when it’s abundant so we can benefit from excessive power, and release it when demands on the grid are high.”

The batteries were installed in nearly 20,000 modules and placed in 24 metal containers that sit on semi-truck trailers. They provide reliable energy when customers expect it, and maximize the use of renewable resources. That means when the sun is shining or wind blowing and energy use is low in the region, the power gets stored and saved for later.

“The high penetration of renewables is driving energy storage forward in California. In fact, on average 43% of the electricity used at SDG&E is from renewable sources, which leads the nation. And on top of that, our customers have another 800 megawatts or so of rooftop,” he says.

The state is strongly committed to clean energy, even though the California Senate voted down its Bill 100, a proposed adoption of 100% renewables in California by 2045. In fact, a new report from the California Public Utilities Commission says California’s major utilities have already met or will all soon exceed the state’s 2020 renewable energy target of 33%, and will likely meet the 2030 target of 50% by 2020.

“What’s happening with the electric grid now is that there are certain times of the day or days of the year where California actually has more renewables than it can use, and that’s when the price of electricity is falling or negative. Such events make battery storage an ideal option to save excess energy for other times,” explains Reguly.

Indeed, 2016 and 2017 data from CAISO (California Independent System Operator) show clear dips in midday power demands, thanks mainly to the contribution of solar energy. Although that is good news for clean-energy advocates, the midday dips present new challenges for grid operators who must balance power loads, ramping them down and then back up again later in the day or as needed.

The batteries working in Escondido can relieve that strain, and more. “Although the Escondido facility is a 30-megawatt system, it’s technically three 10-megawatt systems. It’s one site with three different units that can work together or independently,” he shares. “So CAISO can set one 10-MW unit to do one thing, such as store power, while the other two 10-MW units contribute power to the electric grid or the reserve market.”

A reliable energy storage system provides utilities with flexibility and an opportunity to be competitive. For example, CAISO may participate in energy arbitrage or the spinning reserve market. Energy arbitrage lets a grid operator buy power at a low cost, and then store or sell it later at a higher market value.

Spinning reserve is the conventional fast response method. It’s extra generating capacity already connected to the electrical grid and available to a grid operator when needed to compensate for insufficient generation or transmission outages. To participate in the spinning-reserve market, an operator must be able to provide a certain load of generated energy within a set short timeframe — an ability made possible with an energy-storage system.

“These are important benefits, however, our main focus with this facility is to support the delivery of more renewables and provide reliable energy to customers,” he says.

Reliability is an achievable goal, thanks to the lithium-ion batteries. They are known for low-maintenance and long-duration features. “There’s not a lot of hands-on care required with these batteries, although we have a 10-year service agreement in place,” says Reguly. “Battery degradation is only about one to two percent per year, and each trailer has room for expansion. That way we can add capacity by adding modules when necessary.”

Operators communicate and control the batteries and inverters through a Distributed Control System (DCS). “This means the operator receives alerts and can check on the system at any time from the comfort of his or her desk. The operator doesn’t have to physically open a battery enclosure to get operations and maintenance updates.”

Reguly says the project addresses the reliability issues that have previously affected natural gas peaking power plants. “California is really leading the way in regards to the future of transmission,” he adds. “And what’s impressive is that this lithium-ion battery energy storage center, the largest in North America, was completed in a matter of months.”

AES and SDG&E built the project in less than six months, a job that typically would have taken two to three years. The expedited process was the answer to a need for reliable, on-demand power after a leak at southern California’s Aliso Canyon natural gas storage facility. By 2030, SDG&E plans to add another 300 MW of energy storage on the system.

“Clean, reliable power is the key,” he says. “We want to ensure our customers have electricity when they need it, and these batteries are proving to be part of the solution.”