Thirty-seven years after Sacramento voters forced the Rancho Seco nuclear power plant into early retirement, the 2,000-acre site south of the city is getting a second act. The Sacramento Municipal Utility District has secured environmental and wildlife permits to install roughly 100 battery energy storage units on land that once sat beneath a working reactor, according to state regulatory filings reviewed in May 2026. If the project reaches its reported 640-megawatt-hour target, it would rank among the larger standalone battery installations in California and mark one of the first times a decommissioned nuclear property in the United States has been converted directly into grid-scale energy storage.
From reactor to power bank
Rancho Seco Unit 1, a 913-megawatt pressurized water reactor, generated electricity from 1975 until 1989, when SMUD’s ratepayers voted to close it after years of operational problems and cost overruns. Decommissioning took two decades. In 2009, the U.S. Nuclear Regulatory Commission released the property for unrestricted civilian use, removing all radiological controls on the land. The twin cooling towers still stand as landmarks visible from Interstate 99, but the site’s industrial chapter appeared to be over.
SMUD had other plans. The utility had already built a 160-megawatt solar farm on the property, branded Rancho Seco Solar, taking advantage of the flat terrain, industrial zoning, and high-voltage transmission lines that still connect the site to the regional grid. The battery project, filed under the name Rancho Seco Solar II, extends that strategy by adding storage capacity designed to absorb excess solar generation during the day and dispatch it during evening demand peaks.
What the permits show
An addendum to the project’s certified environmental impact report, tracked under California’s CEQA database, documents a relocation of the battery array from the southeast side of the decommissioned cooling towers to the north side of the site near Twin Cities Road. The addendum also describes new collector and communication lines connecting the storage units to an existing collector substation. A formal Notice of Determination, endorsed by the Sacramento County Clerk and prepared by SMUD, lists battery energy storage among the project’s installed components.
Separately, the California Department of Fish and Wildlife issued Incidental Take Permit No. 2081-2025-043-02 for the buildout, filed under the name “Dry Creek Energy Storage.” That permit authorizes grading, stormwater infrastructure, installation of approximately 100 BESS units, fencing, and about half a mile of collection lines. It also provides biological coverage for two sensitive species found on the property: the California tiger salamander and the burrowing owl. The permit’s approval of ground-disturbing activity is the strongest available signal that physical construction has been cleared to begin.
Both filings share the same CEQA registry number, confirming that the battery component was reviewed as part of the broader Rancho Seco Solar II environmental process rather than as a standalone project.
Why a former nuclear site matters
Building grid-scale batteries in California is often slowed by two bottlenecks: permitting and interconnection. New projects on undeveloped land can spend years securing environmental clearances, negotiating transmission access, and waiting in the California Independent System Operator’s interconnection queue. Rancho Seco sidesteps much of that. The property already carries industrial land-use designations, completed environmental baselines from the solar farm, and high-capacity transmission corridors built to handle a 913-megawatt reactor. While no agency filing explicitly quantifies the time or cost savings, the infrastructure advantages are difficult to overstate for a site that was wired into the grid half a century ago.
SMUD, a publicly owned utility that serves about 1.5 million people in the Sacramento region, has committed to eliminating carbon from its power supply by 2030. Battery storage is central to that goal. Solar generation in SMUD’s territory peaks in the early afternoon, but customer demand peaks in the evening after the sun drops. Without storage, the utility must either curtail cheap solar power or fire up natural gas plants to cover the gap. Large battery systems like the one planned for Rancho Seco are designed to bridge that mismatch.
California as a whole has moved aggressively on battery storage. The state’s grid operator reported more than 10 gigawatts of battery capacity either operating or under construction by early 2025, driven by reliability mandates and a series of summer heat emergencies that strained the grid. SMUD’s project would add to that total while demonstrating a reuse model that could apply to other decommissioned power plant sites across the country.
What remains unconfirmed
Several details that would normally anchor a project announcement are absent from the public record. No filing reviewed specifies a total capacity of 640 megawatt-hours for the battery system, and no document directly ties that figure to the roughly 100 BESS units described in the wildlife permit. The number has appeared in trade coverage and project summaries, but the permitting record itself does not confirm it. Readers should treat the capacity figure as provisional until SMUD or another official source provides verification.
The precise construction start date is also missing. The CDFW permit authorizes ground-disturbing work, and the CEQA addendum reflects approved design changes, but neither includes a notice to proceed or a date when heavy equipment first arrived on site. Whether construction is actively underway as of mid-2026 or simply authorized is a distinction the available documents do not resolve.
Other gaps include the battery manufacturer, cell chemistry, fire-suppression design, and operational parameters such as cycling limits and expected lifespan. Lithium-ion technology dominates the grid-scale storage market, but the permits do not specify a chemistry. Those details matter for assessing long-term performance, safety, and how the system will integrate with SMUD’s broader generation mix.
A decommissioned site finds new purpose
For decades, Rancho Seco’s cooling towers have served mainly as a backdrop for a recreational lake and a reminder of a reactor that never lived up to its promise. The permitting trail now shows a different trajectory: a publicly owned utility layering solar generation and battery storage onto land that federal regulators cleared of nuclear contamination, using transmission infrastructure that dates to the Ford administration. The regulatory scaffolding is in place. The wildlife permits are signed. What happens next will determine whether a shuttered nuclear plant becomes a working model for how the country repurposes its retired energy infrastructure, or just another project that looked good on paper.
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*This article was researched with the help of AI, with human editors creating the final content.
