When a major public utility like Salt River Project asks its board to approve a 1.7-GW mixed-resource project, the industry should pay close attention. The Marigold Energy Center, proposed for a site about 45 miles south of Phoenix, represents a deliberate and pragmatic blueprint for how large-scale renewables and firm dispatchable power can coexist in a rapidly growing desert market. The project, which SRP will present to its board in September, combines 600 MW of solar generation, 400 MW of battery storage, up to 675 MW of natural gas generation, and a new substation. This is not a binary choice between clean energy and reliability; it is an integrated hedge against both the intermittency of renewables and the volatility of gas prices.
The scale of the Marigold proposal is striking even by southwestern standards. Arizona is one of the fastest-growing electricity markets in the nation, and SRP has been under sustained pressure to add capacity while meeting its own decarbonization goals. The inclusion of 400 MW of battery storage alongside 600 MW of solar is a clear signal that SRP views storage not as a niche addition but as a core component of its resource stack. However, the decision to also include up to 675 MW of gas-fired generation underscores the practical reality that, even with record-low battery costs, multi-day firming capacity remains essential for a utility serving a summer-peaking load that regularly exceeds 7 GW.
This hybrid approach is emblematic of a broader trend among investor-owned and public utilities across the West. Rather than pursuing single-technology solutions, planners are increasingly assembling portfolios that pair solar and storage with gas peakers or combined-cycle units, often co-located at a single site to share interconnection and land costs. The Marigold Energy Center, if approved, would become one of the largest examples of this strategy in the United States. It also raises important questions about asset utilization: how often will the gas units run, and what will their capacity factor look like in a system with 1 GW of renewable-plus-storage? The answer will depend on how SRP dispatches the plant and how quickly the grid can absorb more solar without curtailment.
The implications extend beyond Arizona. As more utilities file integrated resource plans that look like Marigold, regulators and investors will need to recalibrate their expectations for the pace of the energy transition. Gas plants are no longer being built as baseload workhorses; they are being designed as flexible backups. The economics of these hybrid projects depend heavily on the Inflation Reduction Act’s tax credits for solar and storage, as well as on natural gas price forecasts that remain highly uncertain. If gas prices spike, the Marigold Center’s gas component could become a financial drag; if they stay low, the plant may run more often than planners expect, potentially slowing emissions reductions.
For energy professionals, the Marigold proposal is a case study in the art of the possible. It does not pretend that the grid can be decarbonized overnight, nor does it ignore the imperative to cut emissions. Instead, it offers a realistic, near-term pathway that balances resource adequacy with environmental goals. The September board vote will be watched closely, not just for the outcome, but for the signal it sends about how one of the largest public power utilities in the country intends to navigate the next decade of load growth, technology evolution, and regulatory pressure.
Read the full report at Utility Dive.