SRP advances Marigold Energy Center with solar, storage, and gas

Solmar Insights

Salt River Project (SRP) will seek board approval in September 2026 for the Marigold Energy Center, a new large-scale hybrid power project set to deliver 600 MW of solar, 400 MW of battery storage, and up to 675 MW of gas-fired generation. The site, located roughly 45 miles south of Phoenix, is being planned to address rapid load growth in Arizona’s Maricopa and Pinal counties.

Project scope and location

The Marigold Energy Center represents one of the largest integrated renewables-plus-storage-and-gas projects planned by a U.S. public power utility in recent years. Site selection places the project about 45 miles south of Phoenix, enabling the facility to directly support electric demand in the fast-growing regions of Maricopa and Pinal counties. The project will feature a new substation and the development of four miles of 230-kV transmission lines, connecting the new capacity to the regional grid.

Since its initial announcement last year, SRP has prioritized outreach in the local Stanfield, Arizona community, conducting informational sessions at the Stanfield Elementary School and planning further public meetings both in-person and online in July. These actions indicate SRP’s intent to engage early with stakeholders and address any permitting or interconnection processes that may arise from such a large-scale initiative.

Besides the generation mix, the Marigold site reinforces SRP’s commitment to enhancing grid infrastructure. Expanding transmission in a region with persistent peak load growth and integrating a diverse mix of energy resources are key grid reliability measures. By locating the facility south of Phoenix, SRP can help alleviate transmission constraints and support resilience for urban and industrial customers.

Resource mix and grid functions

The project’s resource composition is designed to provide operational flexibility while addressing the state’s dual pressures of growth and decarbonization. The planned 600 MW of solar generation aims to leverage Arizona’s high-irradiance conditions, providing ample energy during daytime peaks. The 400 MW battery component, likely lithium-ion or similar technology, will enable arbitrage of excess solar production and support grid reliability through contingency services or ramping support.

Adding up to 675 MW of gas-fired generation, SRP balances its need for firm dispatchable power. This approach reduces reliance on imports and mitigates intermittent supply risk from renewables. With economic development accelerating in the region, particularly data centers and manufacturing, hybrid facilities like Marigold become critical for serving both base and peak loads. The battery storage will also help flatten peaks and provide reserves, further supporting grid balancing efforts.

The facility’s control over multiple dispatchable and non-dispatchable resources allows SRP to respond efficiently to intraday load swings and volatile solar output. This operational flexibility is increasingly valuable as Arizona utilities contend with grid integration of renewables, while maintaining capacity sufficiency for summer demand spikes.

Stakeholder engagement and partnerships

SRP has engaged local stakeholders throughout the project planning phase, highlighting transparency and responsiveness as cornerstones for the initiative. Public informational sessions have focused on sharing technical details, outlining the project timeline, and addressing citizen and landowner questions. Further, SRP has maintained open lines through both live and virtual venues, showcasing a methodical approach to community relations, an increasingly important component for siting and permitting energy infrastructure.

The utility also cited the potential for a partnership with Electrical District No. 3 (ED3), another regional public power entity. ED3 is evaluating whether to procure part of Marigold’s output, which could broaden the project’s impact across central Arizona and provide scale benefits for both utilities. Such collaboration is emblematic of evolving resource sharing and bilateral procurement strategies among western public power agencies, particularly as resource adequacy and cost competitiveness grow more challenging.

By bringing additional stakeholders into the fold, SRP is poised to build a more robust business case for the project, potentially diversifying offtake agreements, and enabling greater cost-sharing for new transmission and interconnection infrastructure. The result could be a template for future mixed-resource hubs in other high-growth power markets.

Context of SRP’s broader resource strategy

This announcement fits within a larger context of SRP’s ongoing investments in storage and cleaner energy. In June, SRP signed an agreement with Energy Dome, backed by Google, to add a 19 MW, 10-hour carbon dioxide-based battery system to its grid. Separately, last October, ESS Tech was selected for a pilot 5 MW/50 MWh iron flow battery, further diversifying the utility’s storage portfolio. Both projects were selected via competitive RFPs and represent pilot-scale deployment of emerging storage technologies.

Consistent with these efforts, the Marigold Energy Center demonstrates SRP’s evolution from reliance on legacy fossil generation toward a balanced resource portfolio. While the presence of new gas-fired capacity indicates a pragmatic recognition of reliability requirements, the simultaneous expansion of renewable and storage resources positions SRP to flexibly manage carbon and cost objectives as the state’s regulatory and economic landscape changes.

For the wider utility sector, SRP’s approach illustrates an emerging trend toward hybrid resource installations, deliberately combining established and advanced technologies to hedge against both near-term shortages and long-term climate mandates. This is especially pressing in Arizona, where grid constraints and uncertain hydrological conditions heighten the value of firm, flexible supply.

Market implications for Arizona and beyond

The Marigold project comes amid surging electricity demand in Arizona, driven by population growth, economic development, and new construction of energy-intensive infrastructure. As large industrial loads, including data centers and manufacturing, enter the region, utilities are challenged to build out both primary and backup supply.

By integrating solar, batteries, and gas generation at a single site, SRP aims to avoid power shortages as more intermittent resources come online. This resource diversity increases operational resilience and may mitigate wholesale price volatility during extreme demand or generation shortfalls. Moreover, the project’s reliance on in-state resources could reduce transmission losses and improve local system efficiency compared to distant imports.

The operational model could influence resource planning decisions by other utilities in the Western Interconnection. As the mix of renewables and distributed resources grows, hybrid projects like Marigold highlight best practices for physical grid integration, community engagement, and multi-party procurement strategies. Ultimately, the Marigold Energy Center could serve as a reference case for scaling reliable, grid-supportive clean energy infrastructure, both in Arizona and across similarly situated Southwest power markets.