The Toronto-headquartered company commercialising an adiabatic compressed air energy storage (A-CAES) technology, is developing a demonstration plant at a legacy mine site in South Australia.


The 5MW plant is expected to be operational in the first half of 2019. The project’s costs will be reduced by making use of an existing underground cavern.

It marks the first project in Australia that Hydrostor’s engineering procurement and construction (EPC) partner, AECOM, will deliver. Once operational, there are plans to add solar PV as well.

Curtis VanWalleghem, chief executive of Hydrostor (Courtesy: Hydrostor)

“Australia is a very exciting market for our technology. The combination of high penetration of renewables, high power prices and big spreads, a liberalized energy market, plus good rule of law, makes it comparatively straightforward market for getting contracts and building energy storage assets,” says Curtis VanWalleghem, Hydrostor’s chief executive.

In a CAES plant, ambient air is compressed and stored under pressure in an underground cavern. When electricity is required, the pressurised air is heated and expanded in an expansion turbine driving a generator for power production.

Hydrostor has engineered surface equipment that flows compressed air into and out of the cavity, steadily building pressure used for storage. This variable pressure system can repurpose existing infrastructure in stabilising the grid.

Heat from compression is captured from the airstream and stored to be used during generation, known as adiabatic CAES, which increases system efficiency and eliminates need for additional heat, avoiding fuel costs and emissions.


Combining solar and CAES

“Initially the facility will buy and sell energy from the grid as well as additional tap into revenue streams, such as frequency regulation, inertia and black-start services. “The plant will allow us to refine the algorithms to maximise revenues whilst playing to the characteristics of A-CAES storage. It will let us optimise the system,” VanWalleghem says.

Once the plant is operational there are plans to build solar PV capacity – in the region of 5-10MW – and connect to the plant so the whole system provides baseload solar-generated electricity and sell into the power market.

To maximise revenues, Hydrostor may hand over the reins of the plant’s operation to a third party, such as an energy retailer.

On the CAES – Hydrostor has developed various versions of its proprietary A-CAES system, for underground, marine and surface locations (Illustration courtesy of Hydrostor)

At the same time, Hydrostor will also identify and develop other sites suitable for bulk energy storage, which its A-CAES technology provides. In the coming months Hydrostor will open a local office in Adelaide.

As a large-scale bulk energy storage technology capable of long-duration storage – from a minimum of six, but ideally 10-12 hours – Hydrostor is looking into utility-scale opportunities, in the region of 100-300MW of capacity is required. “Our competition is pumped hydro, natural gas power plants and transmission lines.”

In smaller capacities, coupled with solar PV, the technology could also appeal to mine owners and operators in remote locations where a grid connection would be costly.


Mining opportunities

The company is talking to a couple of mine site operators in Australia, where its A-CAES system can be built with solar PV, to provide baseload solar generated electricity. One of these projects is sizeable, in the region of 100MW solar-plus-storage capacity, with up to 85MW of charge and 15MW of discharge, with the ability to store 15MW for up to 24 hours.

The mining operator will buy the power produced under a power purchase agreement, which is likely to be with a third party project entity as opposed to Hydrostor.

If legacy mine sites coincide with locations on the grid where bulk storage is needed, then Hydrostor is able to shave the cost of building its plants. In the US and Canada, the company has identified several retiring coal plants that cannot be converted over to gas as they are not on gas lines.

Often these sites have an existing electrical connection, as well as existing relevant permits covering water drawing and land use. Taking into account these balance of plant and soft cost savings can collectively shave 10-20% off of the CapEx if Hydrostor’s A-CAES system is built at a legacy coal mining or rock mining site, with existing underground caverns.