How vast grid-scale cells are reshaping the state’s power system—and pointing the way for an energy storage revolution

On hot autumn evenings in California, when office towers hum, air conditioners chug and commuter EVs sip electrons after the drive home, an invisible fleet of mega‑batteries now surges to life. Rows of white containers—from the Central Valley to the desert edges of Los Angeles—dispatch electricity gathered from the sun hours earlier, shaving the peak off the famously steep ‘duck curve’ and keeping the lights steady. In 2025, what once sounded like a futurist experiment has become routine grid practice: batteries are a pillar of reliability, not an optional add‑on.

The scale-up has been astonishing. California’s energy storage capacity has leapt from hundreds of megawatts in 2018 to well over 15 gigawatts by early 2025, according to state data—most of it large, four‑hour lithium‑ion systems wired directly into the California ISO (CAISO) grid. On May 20, CAISO batteries hit a new record, delivering about 10 gigawatts at 7:45 p.m., briefly becoming the single largest source on the system. That is not just a headline; it is a structural shift in how a modern grid balances variable renewables with demand that peaks after sunset.

Why batteries, and why now? The state’s solar buildout has been prolific, but solar’s mismatch with evening demand was pushing conventional gas peakers to cycle harder and prices to swing. Storage changes the economics. By soaking up cheap midday solar—sometimes so abundant it drives wholesale prices below zero—and discharging at the evening peak, batteries provide capacity, frequency response and congestion relief in a single, fast‑acting package. Even at four hours of duration, they are displacing new gas peakers and cutting fossil output during the most carbon‑intensive hours.

You can see this transformation from Monterey Bay to the Mojave. At Moss Landing, a former gas complex has become home to one of the world’s largest battery plants, with hundreds of stacked racks that collectively store multiple gigawatt‑hours. In the Los Angeles basin, the Nova Power Bank—a 680‑megawatt facility built by Calpine on the site of a shuttered thermal unit—has joined a rapidly growing fleet serving the region’s evening peaks. Hybrid solar‑plus‑storage projects in Fresno and Kern counties now routinely shift their generation, smoothing day‑ahead forecasts and giving grid operators more tools to manage ramps.

The megabattery buildout is also the product of policy design. The California Energy Commission and Public Utilities Commission have pushed utilities and community choice aggregators to procure storage as part of long‑term reliability plans, while permitting reforms have accelerated siting for projects that co‑locate on existing industrial land. Developers, in turn, have standardized on modular containerized systems that can be erected in months rather than years, tapping a now‑mature global supply chain for power electronics and battery cells.

Operationally, storage has evolved from a niche ancillary service provider into a cornerstone of the day‑ahead and real‑time markets. In 2024 and 2025, batteries supplied a growing share of energy during the critical hours ending 17 through 21, while they represented a double‑digit share of load during late‑morning charging windows. The pattern is clear: the same assets that absorb solar midday are the ones keeping the grid balanced after dark. Crucially, they can also black‑start and provide fast frequency response during disturbances, offering a resilience function that conventional resources alone could not economically deliver.That resilience argument sharpened in January 2025, when a fire at part of the Moss Landing energy storage complex triggered evacuations and highway closures. No one was injured, but the incident—in a state already familiar with wildfires—was a loud reminder that large lithium‑ion installations demand rigorous safety engineering and emergency planning. Regulators have since tightened codes and reporting, standardizing thermal‑runaway mitigation, spacing, ventilation, and firefighter access. The industry response has been swift: new builds are rolling out with enhanced monitoring, gas detection, fire‑suppression upgrades and better incident command integration with local departments.

Even as safety improves, the economics keep tilting in storage’s favor. Cell chemistries are more energy dense, balance‑of‑plant designs have been streamlined and learning curves in construction are visible in shorter schedules and lower soft costs. Batteries are not just earning from energy arbitrage; they stack revenues from capacity, ancillary services, resource adequacy and, increasingly, transmission congestion relief. A handful of projects are testing longer durations and alternative chemistries to push beyond the four‑hour norm—zinc‑based and iron‑air systems among them—or pairing batteries with demand flexibility from fleets of EVs.

Critics point out that four hours of storage cannot cover a multi‑day lull in wind or a stormy week of low solar. California’s planners agree, which is why the state’s mix includes flexible hydro, geothermal, imports and the extended life of the Diablo Canyon nuclear plant. But as a tool for the daily cycle that dominates system stress and emissions, storage is already delivering. During summer heat waves, batteries have supplied a quarter or more of evening demand for brief intervals, blunting the need for emergency conservation pleas and reducing the risk of rotating outages.

The buildout is also changing where and how we site power infrastructure. Projects targeting urban load pockets reduce transmission losses and defer expensive substation upgrades. Repowering former fossil sites shortens interconnection timelines and reuses grid infrastructure, cutting costs and community impacts. On the supply side, developers are co‑optimizing storage size with solar nameplate capacity to absorb curtailment and firm deliveries into the evening market, improving project financeability.

In the control rooms, software is the unsung hero. Machine‑learning dispatch models forecast net load, prices and congestion patterns, deciding within seconds whether to charge or discharge and how to bid into day‑ahead and real‑time markets. CAISO has refined rules to better align battery incentives with system needs during the net‑peak, and market monitors have recommended further tweaks so assets are reliably available at the most stressed hours. The effect is a steadier ramp and fewer price spikes—an operational upgrade that customers feel only as quiet reliability.

Looking ahead, California envisions roughly 20 gigawatts of batteries online by the mid‑2030s and on the order of 50 gigawatts by 2045 to meet its clean‑electricity law. That will require more diversification in duration, chemistry and use cases: eight‑hour systems for evening peaks that stretch longer in winter, community‑scale batteries for distribution deferral, and vehicle‑to‑grid fleets capable of responding in aggregate. It will also require sustained attention to safety, recycling and equitable siting so that the benefits of clean, flexible power are shared broadly.

For the rest of the country—and increasingly for grids abroad—the California experiment has become a template. Build solar and wind fast; layer on storage even faster; reform markets so batteries earn when they make the system cleaner and more reliable; and pair it all with pragmatic operational safeguards. In 2025, the mega‑battery has left the pilot stage. It is a workhorse, storing sunshine for supper and making the promise of a high‑renewables grid less a dream than a daily practice.

Sources

[1] California Energy Commission, California Energy Storage System Survey (accessed Oct. 2025): https://www.energy.ca.gov/data-reports/energy-almanac/california-electricity-data/california-energy-storage-system-survey

[2] CAISO, 2024 Special Report on Battery Storage (May 29, 2025): https://www.caiso.com/documents/2024-special-report-on-battery-storage-may-29-2025.pdf

[3] PV Magazine USA, “Solar and battery output records set…” (May 27, 2025): https://pv-magazine-usa.com/2025/05/27/solar-and-battery-output-records-set-as-california-continues-aggressive-ramp/

[4] Reuters, “California’s solar and battery combo…” (Oct. 3, 2025): https://www.reuters.com/markets/commodities/californias-solar-battery-combo-packs-transformational-punch-2025-10-03/

[5] Reuters, “US power sector battery storage momentum…” (June 24, 2025): https://www.reuters.com/markets/commodities/us-power-sector-battery-storage-momentum-keeps-charging-2025-06-24/

[6] Vistra, Moss Landing backgrounder: https://investor.vistracorp.com/2023-08-01-Vistra-Completes-Milestone-Expansion-of-Flagship-California-Energy-Storage-System

[7] The Verge, Moss Landing fire coverage (Jan. 17, 2025): https://www.theverge.com/2025/1/17/24345859/battery-plant-fire-california-moss-landing-vistra

[8] CPUC/SED, 2025 BESS Facility Survey: https://www.cpuc.ca.gov/-/media/cpuc-website/divisions/safety-and-enforcement-division/esrb/generation/bess/2025-battery-energy-storage-system-facility-survey.pdf