California Poised to Establish World’s Largest Solar-Battery Storage Facility

California Set to Become World’s Largest Solar-Battery Storage Hub
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California is poised to establish itself as the world’s largest solar-battery storage hub, further solidifying its leadership in utility-scale battery storage. As of now, the state already boasts the most utility-scale battery systems in the United States, but according to developer Intersect Power, it is about to set a new record.

The Darden project, located in western Fresno County, will feature a battery energy storage system with a capacity of up to 4.6 GW-hours, accompanied by a 1.15 GW solar facility consisting of approximately 3.1 million panels. Additionally, the project will include a 34.5-500 kV grid step-up substation, a 15-mile 500-kV generation intertie line, and a 500-kV utility switchyard. This facility is expected to interconnect with the existing Pacific Gas and Electric Co. Los Banos-Midway #2 500 kV transmission line and will generate enough energy to power 850,000 homes for four hours.

“This is a huge project and a significant advancement for battery energy storage,” commented Zack Perconti, vice president of government affairs at the National Utility Contractors Association. He noted that while the Darden project will be the largest in the world upon completion, it is unlikely to hold that title for long due to the increasing need for energy storage across the U.S., particularly at solar and wind project sites. “Solar-plus-storage energy systems, like Darden, harness abundant clean energy resources to reliably power the grid through the day and well into the night, helping California create a more reliable, affordable, and resilient grid,” added Brian Turner, regulatory director at the advocacy group Advanced Energy United.

Intersect has informed Engineering News-Record (ENR) that it plans to follow a continuous construction schedule starting in late 2025, with full operation expected by late 2027 or early 2028. While the company did not disclose the total project cost or contractor selection, it has indicated that the project will generate over 2,000 prevailing-wage construction jobs.

In relation to its similarly sized Perkins renewable energy project, which will include a 1.1-GW solar and battery storage facility located on both private and federal land east of El Centro, California, local media reported that this project is valued at $2.5 billion and is currently under an Opt-In review.

The Darden project is among the first in California to be permitted under the state’s new Opt-In Certification program, part of Governor Gavin Newsom’s Build More, Faster initiative, which aims to expedite the permitting process for critical infrastructure. The California Energy Commission, which approved the project for this program, noted that this initiative focuses exclusively on energy permitting and aligns with California’s goal of achieving 100% zero-carbon retail electric sales by 2045. The commission has also approved two additional projects for Opt-In: Fountain Wind, a 205-MW wind project in Shasta County, and Compass Energy Storage, a 250-MW energy storage project in San Juan Capistrano, Orange County.

Under the Opt-In program, the commission has a 270-day timeline to complete an environmental review of a project unless significant changes arise that require additional time. The Darden project received clearance in just 265 days. In contrast, a U.S. government environmental review under the federal NEPA law is intended to be completed within two years, but can often extend for much longer. “Permitting delays significantly increase costs and hinder project timelines,” Perconti noted.

Intersect’s extensive storage project is being developed amidst an ongoing investigation into a major fire that occurred in January near San Jose, which destroyed most of a 300-MW lithium-ion battery array at Vistra Energy’s 750-MW Moss Landing storage facility. The cause of the fire is still under investigation, as per the report on Vistra’s website.

In response to concerns about fire prevention, Intersect assured that the chemistry, design, and safety requirements for its battery complex are significantly different from those of the Vistra facility. Darden will exclusively utilize the Tesla Megapack 2 XL, which has undergone rigorous testing and is designed for safety. The company emphasized that “there has never been a thermal event associated with the Tesla MP2 XL, despite its widespread commercial deployment.” Intersect also stated that the project will implement a comprehensive construction health and safety program along with an emergency response plan to safeguard workers and nearby communities during construction and long-term operation.

As part of the Opt-In process, the Darden project underwent a thorough technical and environmental review, which included an extensive fire safety analysis. The project will feature a containerized design, meaning that batteries will be housed in separate, enclosed units, similar to shipping containers. This approach is recognized as safer and more manageable in case of a fire, contrasting with facilities like Vistra’s Moss Landing, where batteries were located in a large building that allowed thermal events to spread. “This design helps isolate potential incidents, minimizing the risk of escalation,” a spokesperson explained.

To further enhance fire prevention, Darden will incorporate several safety features, including deflagration panels for gas accumulation, thermal infrared cameras around the site, a dedicated fire protection program for construction, operations, and maintenance, as well as a command and control center situated outside the storage facility.

Intersect noted that the project will be financed through a combination of equity, debt, and federal tax credits for solar and storage assets, which align with industry standards for such projects. California currently leads the U.S. in battery storage capacity, trailing only China globally. The state has over 200 utility-scale systems and more than 250,000 commercial and residential installations, collectively totaling approximately 15.7 GW statewide.