This long duration compressed air energy storage project just got a $1.76B DOE loan

Hydrostor’s GEM A-CAES has received a conditional loan guarantee of up to $1.76 billion from the US Department of Energy (DOE) to build the Willow Rock Energy Storage Center, a cutting-edge compressed air energy storage (CAES) system, in Eastern Kern County, California.

If everything goes as planned, Willow Rock will bring 500 megawatts (MW) and 4,000 megawatt-hours (MWh) of long-duration energy storage (LDES) to the southern California power grid.

This system will lower energy costs, improve grid reliability during peak demand, and expand the rollout of renewable energy into the grid. Here’s how it works and why it’s unique.

How compressed air energy storage works

CAES technology is all about storing energy for later use, especially when the sun isn’t shining or the wind isn’t blowing. Here’s how it works:

1. Storing energy: The system takes surplus energy (often from renewable sources like solar or wind) and uses it to compress air, which is stored in underground caverns.
2. Releasing energy: When the grid needs power, the compressed air is released, passing through a turbine to generate electricity. Willow Rock will be able to dispatch stored energy at full power for over eight-hour periods.

Unlike conventional batteries, CAES can scale up based on the size of the storage cavern and doesn’t rely on scarce critical materials. It’s durable, too –systems like Willow Rock are designed to last over 50 years.

Why advanced CAES is different

Traditional CAES systems face two big challenges: wasted heat and inconsistent power output. Willow Rock’s advanced compressed air energy storage system (A-CAES) technology solves these problems:

• Thermal energy capture: Conventional CAES loses around 50% of energy during the air compression process. Willow Rock pairs a proprietary thermal storage system with this process, so it captures, stores, and reuses heat from the compression cycle.
• Constant Pressure: Traditional systems lose efficiency as underground air pressure drops. Willow Rock maintains consistent pressure by using water from an above-ground reservoir. As a bonus, the facility will be a net producer of fresh water, as water condensed during the compression process will be captured and reused.

This innovative design means A-CAES systems can be installed in a greater variety of underground conditions – an estimated 80% of US geology could support similar systems, opening the door for wide deployment.

Willow Rock will create up to 700 construction jobs at its peak, and 40 full-time operations roles will follow. These positions require skills similar to those used in the oil and gas industry, making it a natural fit for Kern County, a region with roots in fossil fuel production.

GEM A-CAES is a subsidiary of Hydrostor USA Holdings, a subsidiary of Hydrostor of Canada.

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