Big Rock Energy Storage Project goes online in Imperial County, adding 200 MW/400 MWh to California’s grid
The 200 MW Big Rock Energy Storage Project in Imperial County began commercial operations in September 2025, adding 400 MWh of battery capacity to CAISO to enhance resource adequacy, peak reliability and California’s decarbonization efforts.
Key takeaways
- Capacity: 200 MW / 400 MWh nameplate, delivered via 137 modular LS-ES AiON-ESS containers.
- Commercial operation: Began serving CAISO in September 2025 under a 12-year resource adequacy agreement.
- Contract & revenue: 12-year RA contract with CAISO; fixed-price revenue exceeding $165 million.
- Technology & design: Tier‑1 lithium-ion batteries, >1,300 modular 140 kVA AiON-SIS string inverters, modular scaling and serviceability.
Project overview and technology
Big Rock is built from 137 modular LS-ES AiON-ESS containers, each rated at 1.5 MW and holding ~3.5 MWh, totaling 200 MW / 400 MWh nameplate. The facility is configured to meet CAISO’s four-hour RA needs by operating at a 100 MW deliverability level while making the full 400 MWh available across that duration to satisfy the 12‑year RA contract.
The system pairs DC battery strings with AC hardware for direct grid connection. It uses tier‑1 lithium‑ion cells and more than 1,300 modular 140 kVA AiON‑SIS string inverters. The modular design enables sectional scaling, targeted servicing and module replacement without taking the entire site offline.
Purpose and grid services
Big Rock’s stated mission is to provide resource adequacy to the CAISO grid — dispatchable power during peak demand, extreme heat and periods of low renewable output. In addition to RA, the facility offers ancillary services such as frequency and voltage support that stabilize the grid in real time.
“The project strengthens CAISO’s storage portfolio, helping reduce reliance on fossil-fired peaker plants during critical hours.”
Ownership, contracts and money matters
Owners/developers: LS Energy Solutions and Gore Street Energy Storage Fund (GSF). GSF acquired the project from Avantus in February 2023; Avantus continues to provide administrative and development support while LS Energy Solutions led construction and now operates the site.
Contract: A 12‑year fixed-price resource adequacy agreement with CAISO that delivers fixed revenue in excess of $165 million, improving predictability and lowering financing risk. Additional revenue streams include energy arbitrage (charge low / discharge high) and payments for ancillary services.
Incentives: The site qualifies for a 30% investment tax credit under the Inflation Reduction Act, estimated by developers to reduce capital costs by roughly $33 million.
Operations, maintenance and optimization
LS Energy Solutions will provide long-term operations and maintenance, including extended warranties, preventive maintenance and remote monitoring. The operator will manage capacity health and battery replacement cycles to sustain performance over the contract term.
GridBeyond supplies an AI-driven optimization platform to balance revenue opportunities with battery life and contract obligations. The software adjusts charging and discharging based on market prices, grid signals and state-of-health metrics to optimize dispatch in real time.
Industry context and why it matters
Big Rock is among the larger battery installations in Imperial County and expands California’s portfolio of grid-scale storage. By 2025 CAISO had more than 5.6 GW of storage resources serving the grid; Big Rock strengthens that capacity and supports the shift away from fossil-fired generation during peak hours.
Four-hour systems like Big Rock are designed to store midday solar generation and discharge during evening peaks, addressing the “duck curve” and helping CAISO maintain reliability without ramping additional thermal plants.
Safety, lifespan and environmental questions
Modern battery systems include fire detection, suppression and thermal management. LS Energy Solutions cites extended warranties and preventive maintenance as part of its safety plan. However, community and regulatory stakeholders continue to press for robust safety plans, decommissioning strategies and clear end-of-life recycling pathways as warranties expire.
Implications for Sonoma, California
Economic effects: Although Big Rock is sited in Imperial County, Sonoma may benefit from reduced statewide peak price spikes, which can lower energy costs for commercial and industrial customers such as wineries and food processors.
Grid reliability: Sonoma is within the CAISO market and can gain from improved system-wide resource adequacy during heat waves or wildfire threats, subject to transmission constraints and CAISO dispatch decisions.
Local jobs & supply chains: Construction and commissioning created jobs in Imperial County; long-term operations are run remotely, so direct ongoing local job growth in Sonoma is likely limited. Indirect benefits could arise if storage growth spurs regional supply chain and recycling businesses.
Sources and further reading
- Power Magazine: LS Energy Solutions brings California energy storage installation online
- Solar Power World: 400 MWh Big Rock Energy Storage Project now online for CAISO
- WIP Magazines: Key energy storage project destined for California, USA
- AInvest: Strategic case for energy storage; focusing on LS Energy Solutions, CAISO Big Rock project
- Power Engineering: Partners announce 200 MW / 400 MWh energy storage project in California
