In 1989, Sacramento voters did something almost unheard of: they shut down a working nuclear reactor. The Rancho Seco Nuclear Generating Station, a 913-megawatt pressurized water reactor southeast of the city, was closed after a public referendum driven by years of safety concerns and costly outages. The cooling towers came down. The fuel rods were shipped off-site. But the substation, the switchgear, and the high-voltage transmission lines that once carried reactor power into the grid stayed put.
Now, more than three decades later, that leftover infrastructure is the foundation for something new. In early 2025, the California Department of Fish and Wildlife issued a construction permit for a large-scale battery energy storage system on the former Rancho Seco grounds at 14440 Twin Cities Road in Herald, California. The developer, Dry Creek Energy Storage, LLC, plans to install roughly 100 battery storage units on the property, connecting them to the existing substation that once served the reactor. Grading, fencing, stormwater work, and trenching for a collection line have all been authorized.
The project’s target capacity has been reported as 640 megawatt-hours, though that figure does not appear in the state environmental filings reviewed for this article. What the permit record does confirm is a utility-scale footprint: 100 containerized battery units, dedicated collection infrastructure, and a direct tie-in to grid hardware that most new storage projects in California would spend years and tens of millions of dollars trying to build from scratch.
Why the old reactor site matters
California’s grid is desperate for storage. The state’s clean energy mandates, anchored by SB 100’s requirement to reach 100 percent carbon-free electricity by 2045, have driven the California Public Utilities Commission to order utilities to procure thousands of megawatts of new battery capacity. As of late 2024, the California Independent System Operator (CAISO) reported more than 300 gigawatts of generation and storage projects sitting in its interconnection queue, with study timelines stretching five years or longer for many applicants.
The bottleneck is not batteries. Lithium-ion cell costs have fallen sharply, and manufacturers can deliver containerized storage units in months. The bottleneck is plugging those batteries into the grid. New projects need substations, transformers, switchgear, and transmission access, all of which require engineering studies, utility coordination, and construction timelines that routinely push past initial estimates.
Rancho Seco’s substation was built to handle the output of a 913-megawatt nuclear reactor. That kind of grid connection, already wired into the transmission system with high-capacity transformers and switching equipment in place, is exactly what a large battery installation needs. By building on a site where that infrastructure already exists, Dry Creek Energy Storage can potentially skip the most expensive and time-consuming phase of development. The filed Notice of Determination explicitly references the collection line connecting to the existing substation, confirming that reuse of legacy grid hardware is central to the project’s design.
The Rancho Seco property is owned by the Sacramento Municipal Utility District (SMUD), the publicly owned utility that operated the reactor and that has since developed solar generation on portions of the site. SMUD has been one of California’s more aggressive utilities on storage procurement, and the Rancho Seco grounds have long been discussed as a candidate for energy reuse. The permit filings reviewed for this article do not detail the commercial relationship between SMUD and Dry Creek Energy Storage, LLC, or identify the parent company behind the LLC.
What the state permit record shows
The controlling document for construction is Incidental Take Permit No. 2081-2025-043-02, issued by the California Department of Fish and Wildlife. The permit authorizes ground disturbance on a site that harbors species protected under the California Endangered Species Act, and it sets enforceable conditions the developer must meet before and during earthwork. Pre-construction biological surveys, seasonal work windows, and habitat restoration obligations will shape how quickly heavy equipment can move onto the property.
A state clearinghouse entry for the project, listed as record SCH 2017092042, appears in the CEQA database and confirms the project involves construction and operation of a battery energy storage system. The lead agency is CDFW, and the environmental review is tied to the incidental take permit rather than a broader land-use approval, meaning most non-biological entitlements are being handled through other regulatory channels.
The Notice of Determination spells out the physical scope: approximately 100 BESS units, grading, stormwater infrastructure, fencing, and trenching for the collection line to the substation. The document includes parcel numbers and geographic coordinates that place the facility on the former nuclear plant grounds. Additional CDFW materials name Dry Creek Energy Storage, LLC as the permittee and reference the biological mitigation requirements the company must satisfy.
These filings carry legal weight. Misstatements in CEQA documents and incidental take permits expose agencies and developers to legal challenge, which makes the confirmed details, including the project entity, site address, unit count, and substation interconnection plan, reliable anchors for reporting.
What the record does not yet reveal
The 640 megawatt-hour capacity figure that has circulated in coverage of this project does not appear in any of the primary state documents reviewed here. The CEQA filing, the Notice of Determination, and the CDFW permit package describe the physical footprint and unit count but do not specify a nameplate energy capacity or power rating. Different battery containers can house markedly different amounts of energy depending on chemistry, cell configuration, and intended discharge duration. A field of 100 short-duration units designed for fast frequency response would yield a very different MWh total than 100 four-hour units built to shift solar generation into evening peaks.
The 640 MWh figure may originate from CAISO interconnection filings, developer presentations, or utility procurement contracts that have not surfaced through the state environmental review process. Readers should treat it as unconfirmed until it appears in an interconnection agreement, power purchase contract, or formal developer disclosure.
Construction timing is also an open question. The incidental take permit sets biological conditions that must be met before major earthwork begins, but the documents do not specify a target date for commercial operation. There is no public indication yet of when battery units will be delivered, when substation upgrades (if needed) will be completed, or when the project expects to begin providing grid services. Future filings with CAISO, SMUD, or state procurement agencies should clarify both capacity and schedule.
A pattern bigger than one project
Dry Creek is not the only project eyeing retired power plant sites for battery storage. Across the United States, developers have been targeting decommissioned coal, gas, and nuclear facilities for the same reason: the grid connection is already there. Vistra Energy’s Moss Landing facility in Monterey County, currently one of the world’s largest battery installations at 750 MW / 3,000 MWh, was built at a retired gas plant. In the Midwest and Southeast, several coal plant sites are being studied or permitted for storage conversions.
The logic is straightforward. A substation and transmission interconnection can represent 20 to 30 percent of a storage project’s total development cost and an even larger share of its timeline risk. Reusing that infrastructure collapses both. For California, where CAISO’s interconnection backlog has become a structural barrier to meeting the state’s climate targets, every project that sidesteps the queue by plugging into existing grid hardware represents capacity that can come online faster than a greenfield competitor.
Whether Dry Creek ultimately delivers 640 megawatt-hours or some other figure, the project’s significance is already visible in the permit record. A named developer has secured wildlife clearance, defined a construction scope, and locked in a grid connection at a site with reactor-grade transmission access. On a former nuclear plant where Sacramento voters once chose to turn the lights off, the grid is preparing to turn them back on.
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*This article was researched with the help of AI, with human editors creating the final content.
