Kaiser Permanente Ontario Commissions Largest U.S. Hospital
- Healthcare Facilities Microgrids News
Marin Holt
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- 6 minutes read
- Kaiser Permanente Ontario Medical Center commissioned the largest hospital-based renewable microgrid in the U.S. in April 2025
- System: 2 MW solar (Ameresco PPA) + 1 MW fuel cell + 9 MWh zinc bromide flow battery + 6 MW existing diesel backup
- California HCAI certified it as a primary emergency backup source, the first hospital to receive this designation
- California Energy Commission EPIC grant of $8.35M to Faraday Microgrids funded battery storage and controls
- System projected to generate 4.1 GWh/year and save $9.84 million in lifetime energy costs
Kaiser Permanente commissioned the largest hospital-based renewable energy microgrid in the United States at its Ontario Medical Center in Southern California in April 2025. The system combines 2 MW of rooftop solar, a 1 MW fuel cell, and 9 MWh of zinc bromide flow battery storage into a single coordinated microgrid that provides 10 continuous hours of emergency power without diesel fuel for daily operations.
What Is Installed
Ameresco installed 2 MW of solar canopies across the medical center parking structure under a power purchase agreement with Kaiser Permanente. Faraday Microgrids (operating as Charge Bliss, Inc.) designed and built the storage and controls layer under an $8.35 million California Energy Commission EPIC grant. The 9 MWh zinc bromide flow battery stores energy during low-price grid hours and discharges during peak pricing or outages. A 1 MW fuel cell supplements the battery during extended grid-off periods. When the battery reaches its 10-hour runtime limit, the facility’s existing 6 MW of diesel generators serve as tertiary backup. California’s Department of Health Care Access and Information certified the system as a primary backup power source in April 2025, a designation that previously applied only to diesel generators under state hospital code.
Critical Analysis
During grid-off transitions, the zinc bromide flow battery inverters must form voltage and frequency reference for the hospital’s critical loads within 20 milliseconds to. Hospital microgrids reduce grid dependence for critical healthcare loads but maintain grid connection as primary power source during normal operations.
5-Year Projection
By 2031, operational data from facilities like this will become the standard requirement for securing interconnection agreements, as ISOs prioritize proven Solar profiles.
Critical Perspective
The article highlights a 9 MWh zinc bromide flow battery installed at Kaiser Permanente’s Ontario Medical Center. Unlike the extensive operational data available for lithium-ion systems, the long-term performance and degradation characteristics of this specific zinc bromide chemistry in a large-scale hospital microgrid remain largely unproven. Neoen’s Hornsdale Power Reserve in South Australia, a large lithium-ion battery project, demonstrated significant grid services capabilities and economic benefits, but its technology differs from the zinc bromide used here. Given the reliance on this system for critical healthcare operations, what are the projected maintenance costs and replacement schedules for this novel battery technology over a 20-year lifespan?
Why It Matters
California hospitals must maintain backup power for critical systems under state code. Until the HCAI certification, microgrids could supplement diesel but not replace it as the primary backup source. The Ontario Medical Center is the first California hospital to receive that certification under the CMS waiver pathway established in 2023. The zinc bromide chemistry avoids lithium-ion thermal runaway risk, which is a significant safety consideration for occupied medical facilities. The system generates 4.1 GWh per year, avoids 650 metric tons of CO2 annually, and projects $9.84 million in lifetime energy cost savings from avoided peak demand charges and lower energy procurement costs.
Funding and Context
The CEC EPIC program awarded $8.35 million to Charge Bliss Inc. under agreement EPC-20-002, with $7.55 million co-funded by the project partners. Kaiser Permanente achieved carbon-neutral operations in 2020 and holds a 2050 net-zero commitment. The organization built its first renewable microgrid at its Richmond Medical Center in 2017 with 250 kW solar and 1 MWh battery storage. The Ontario facility is approximately 9x the capacity of that first system and establishes a replicable template for non-lithium hospital microgrids across Southern California Edison’s service territory.
