In this Energy-Storage.news roundup, Hydrostor receives permitting approval for its California project, Hawaiian Electric is set to begin construction on a Maui battery energy storage system (BESS) and Peregrine and Wärtsilä advance construction of a Texas BESS.
Hydrostor receives permitting approval for 4,000MWh project
Long-duration energy storage (LDES) developer-operator Hydrostor has received final permitting approval from the California Energy Commission (CEC) for the 500MW/4,000MWh Willow Rock Energy Storage Centre.
Willow Rock is an advanced compressed air energy storage (A-CAES) project. A-CAES technology works by pressurising and channelling air into a storage medium to load the system. During discharge, the stored air is released via a heating system to expand, which then drives a turbine generator.
A-CAES functions similarly to traditional CAES but captures heat from the compressor, passing it through heat exchangers to store in pressurised water. This water is stored in a reservoir and released into a cavern to displace air during discharge, a process called hydrostatic compensation.
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Hydrostor first signed a 200MW/1,600MWh power purchase agreement (PPA) for Willow Rock in 2022, with California community choice aggregator (CCA) Central Coast Community Energy(3CE).
At that time, the company said it was discussing multiple offtake deals for the rest of Willow Rock’s available capacity.
Recently, the agreement between the two entities was scheduled to be amended for the third time. According to documents from a 3CE Board of Directors (BOD) meeting, Hydrostor contacted the CCA in April 2025, asking for a change in price along with a 13-month delay to Willow Rock.
3CE previously extended the contractual commercial operations date associated with the agreement by 18 months, in 2023.
Around this period, the CEC temporarily paused Hydrostor’s Application for Certification (AFC) while the developer reevaluated the design of its Willow Rock project, concentrating on cavern and transmission suitability. By June, the CEC had halted progress on the project as Hydrostor carried out additional site viability assessments.
Now, having received final permitting approval from the CEC, Willow Rock is expected to be “shovel-ready” in 2026.
Hawaiian Electric set to begin construction of Maui BESS
Hawaii utility Hawaiian Electric is set to begin construction of Maui’s first large standalone load-shifting BESS, the 40MW/160MWh Waena BESS, in January.
Approved by the public utilities commission (PUC) in December 2023, the Waena BESS will be located at the Hawaiian Electric-owned property along Pulehu Road in Central Maui.
The Waena BESS contributes to the company’s broader goal of lowering its carbon footprint and achieving 100% renewable electricity by 2045. At present, Hawaiian Electric claims that 41% of Maui County’s power is generated from renewable resources.
Expected to come online by 2027, the Waena BESS will connect to the company’s Waena Switchyard and serve as an energy-shifting resource capable of storing and dispatching large-scale renewable sources like solar and wind as required.
Hawaiian Electric states that the Waena Switchyard and Waena BESS are key components in the shutdown process of Kahului Power Plant’s four steam units, which currently supply power and maintain system stability on the island’s transmission network.
The company is also aiming to secure replacement generation resources by developing larger renewable energy and battery projects on Maui. Currently, four contracts for renewable energy and battery projects, both variable and firm,have been approved by the PUC and are at different stages of negotiation with Hawaiian Electric.
Waena is a Hawaiian Electric “self-build” project, developed, constructed, and owned by the company. The company did not disclose the manufacturer of the BESS or cell supplier, but noted that it has completed other projects in Hawaii.
Peregrine and Wärtsilä advance Dallas BESS
Developer Peregrine Energy Solutions and system integrator Wärtsilä are advancing construction of the 250MW/500MWh Mallard Energy Storage project, near Dallas, Texas.
Mallard entered into a tolling agreement with an undisclosed Fortune 500 Company, which the companies claim will “support their reliable, affordable, and sustainable energy solutions in Texas.”
The project will deploy Wärtsilä’s Quantum2 energy storage system, making it Peregrine’s second large-scale project with Wärtsilä technology.
Quantum2 offers a more streamlined design for compact project setups at high energy density locations, complying with ISO standards for 20-ft containers. It includes pre-installed, factory-tested, IP67-rated liquid-cooled lithium-ion (Li-ion) battery modules and meets important safety standards such as NFPA855.
Mallard builds on the 150MW/300MWh Wizard Energy Storage Project, which is currently being built in League City, Texas. In March, Peregrine secured US$168 million for a 150MW BESS. The company did not verify if this was for the Wizard project, but there are multiple similarities.
WHC Energy Services will act as the engineering, procurement, and construction (EPC) contractor to oversee Mallard’s construction.
Once operational, Peregrine and Wärtsilä state that Mallard will provide critical flexibility and resilience to the Electric Reliability Council of Texas (ERCOT) system by responding to rapid grid fluctuations, supporting renewable generation, and participating in key reliability services.
The Energy Storage Summit USA will be held from 24-25 March 2026, in Dallas, TX. It features keynote speeches and panel discussions on topics like FEOC challenges, power demand forecasting, and managing the BESS supply chain. For complete information, visit the Energy Storage Summit USA website.
