Frequently asked Questions

Understand more about the Silver City project.

"A-CAES is one the few technologies available to provide long duration storage today on the electricity grid, and is the most cost-effective and implementable for the majority of large-scale global applications."
Curtis VanWalleghem
CEO of Hydrostor
  • Grid operators have shown that 8-10hr+ storage is minimum needed to help reliably replace the capacity of fossil-fueled power plants, much of which is end-of-life or inefficient
  • Decarbonization cannot happen without LDES, which is necessary to integrate renewables and ensure a stable grid that can match supply and demand
  • Many electricity markets are recognizing the need for LDES in the near-term and therefore are beginning to form a commercial pathway today, including Australia, California, Ontario, New Yorkand the UK, as a critical component of an affordable, reliable, and increasingly clean grid
  • A-CAES is a simple integration of proven technology and equipment, with mature supply chains and available performance guarantees, and significant operational precedent
  • Based on the traditional CAES platform with enhancements to increase flexibility through siting in hard-rock (vs. salt) and re-using waste heat to eliminate the need for an external fossil-based fuel source for heating, which has had utility-scale plants operating for more than 40 years
  • A-CAES is Goldman Sach’s global play on LDES, and is also backed by the Canadian Pension Plan
  • Selected as reliability solution for the largest utility in Australia as a non-wires’ alternative, and signed one of world’s largest energy storage contracts with utility in California
  • Operating grid-connected asset in Ontario, Canada with two advanced projects in the late stages of development in California and NSW
  • Most cost-effective form of intraday storage for 8hr+ ready to deploy today
  • Analogous to locatable pumped hydro storage, with easier development and permitting pathway due to smaller footprint, water use (footprint & water need 1/20 of what pumped hydro needs)
  • More cost effective than Li-ion batteries to provide LDES, with no performance degradation, a 50+ year lifespan, and ability to support the grid as traditional fossil generation retires by providing grid inertia as a synchronous resource – A-CAES is an infrastructure solution, not commodity solution
  • More proven and bankable at grid-scale than other emerging LDES technology
  • Hydrostor is both a technology provider and a developer of LDES projects using its proprietary technology
  • As a result, Hydrostor has advanced IPP delivery capabilities to develop projects in markets at an early stage (including government, regulatory affairs, strategy and market analysis, project development and power marketing capabilities)
  • Transitioning to cleaner energy resources can’t happen without LDES – it’s a crucial tool for stable baseload generation and integrating variable wind and solar power.
  • As renewable penetration grows past roughly 40-50% and outstrips traditional fossil baseload generation, that’s where we need 8+ hours of storage to maintain reliability.
    • In the U.S., renewables are expected to represent more than 50% of power generation by 2035.
    • Globally, renewables are projected to grow 18x by 2050, representing more than 70% of global power generation
    • By 2020, renewables already made up 29 percent of global electricity generation, and are expected to make up 96% of new capacity added between 2024 and 2028.
  • As more intermittent generation resources, like wind and solar, come online the ability of utilities to mitigate capacity issues during peak times diminishes, requiring longer intra-day storage durations to cover peak load requirements in a cost-effective manner.
    • At COP29 in 2024, all the countries will be asked to back a G7 proposal to increase energy storage capacity by more than six-fold before 2030 – an acknowledgement of how important energy storage will be to the grid of the future. The Global Green Energy Storage Pledge aims to bring global capacity of energy storage to 1500 GW by the end of the decade, from 230 GW in 2022.
  • The company was founded in 2010 by Curt VanWalleghem, our current CEO, and Cameron Lewis, in Toronto. Their initial ideas for energy storage involved storage water in large balloons underwater, creating pressure that could be released to power turbines, but the technology evolved to the current cavern-storage model soon after the company was founded.
  • The Toronto Island project was successfully launched in 2015, a 660 kW facility built as a proof-of-concept pilot to demonstrate the technology, and was decommissioned in 2020.
  • In 2017, the Goderich facility began development, and the 2.2 MW commercial demonstration facility was commissioned and started providing power to the Ontario electricity system operator in 2019.
    • Goderich received the Energy Storage North America Innovation Award in 2019, and a POWER Top Plant Award in 2020.
  • After Goderich went live, things started taking off – Silver City and Willow Rock both began development in 2020, and Hydrostor received a $300 million capital commitment from Goldman Sachs Asset Management and the Canadian Pension Plan Investment Bank in 2021.
    • This financing was in addition to ~$55 million in financing from ArcTern, Lorem, Canoe, Baker Hughes, BDC, and others, that had been raised before 2021.
  • Hydrostor is anticipated to reach FID for the Silver City and Willow Rock energy storage centers in 2025, with Silver City expected to come online in 2028, and Willow Rock to follow soon after, in 2030.
  • As the A-CAES system is charged, off-peak or surplus electricity is used to power an air compressor. The heat generated during compression is captured by a set of heat exchangers and stored separately for later use. The air is compressed to match the pressure needed to inject it into a constructed underground storage cavern, where it can be stored until electricity is required.
  • Hydrostatic compensation is provided by a surface reservoir of water, connected to the cavern typically through a shaft. As air is charged into the storage cavern, water is displaced up the access shaft and into the surface reservoir, storing substantial potential energy in the large elevation difference. With hydrostatic compensation, the air pressure within the cavern is maintained at a near constant level. This is essential for the efficient performance of the air handling equipment (whereas in traditional CAES the storage pressure varies significantly, which limits system efficiency and performance).
  • When energy is required, the compressed air is permitted to flow back to surface, which it does while the compensation water re-floods the cavern. The stored heat is reinjected through the same heat exchangers before the compressed air is used to drive a turbine, generating electricity and supplying it back to the grid.
  • Because of the use of hydrostatic compensation, all the stored air is fully recoverable; this is unlike traditional CAES which requires a substantial portion of the air to maintain a minimum storage pressure for either cavern protection or turbine operation. This drastically reduces storage volume requirements.
  • One of the few LDES technologies proven and deployed at grid-scale in commercial applications
  • Jurisdictions that are advancing on LDES have generally recognized compressed air as the third key pathway for LDES applications that is available today (along with pumped hydro and lithium-ion batteries, but without their limitations described above)
  • CAES plants operating at multi-100MW scale for 40 years (proven asset class)
  • All sub-systems proven in equivalent applications at scale all over the world. 3 major subsystems:
    • Off-the-shelf turbomachinery – core of the system operations
    • A simple form of heat transfer and storage (pressurized water)
    • Well-proven construction techniques for cavern
  • Integration proven via Goderich project in Ontario, a commercially-contracted facility
  • Given proven delivery channels for construction of A-CAES infrastructure, and the integrated performance of A-CAES demonstrated through multi-year operations, A-CAES is able to line up standard project financing and performance guarantees for large-scale project applications
  • Hydrostor’s technology isn’t limited by the same parameters as lithium-ion systems, which can only cycle as stated under their warranties to ensure maximum efficiency and battery life, with specific depth of discharge and state of discharge boundaries.
  • Specifically, A-CAES systems experience zero degradation over their 50+ year asset lifetime, so it doesn’t require any augmentation (with the exception of replacing certain top-side equipment).
    • Battery systems require augmentation every 7-10 years to maintain their contracted capacity threshold, or require more up-front capital to overbuild.
  • Additionally, A-CAES does not have a floor for the depth of discharge, you can fully deplete the stored energy with every cycle if you want to
  • Subsurface construction represents less than 1/3 of total project cost
  • Rigorous stage-gated screening process that includes data analysis, rigorous geology analysis and site visits, and leads to a detailed borehole program once a commercial pathway has been established
    • The borehole program consists of 4-8 verification boreholes fully characterize the limited areal extent of the cavern
  • Half of subsurface cost consists of the vertical shaft construction, which is 100% characterized through boreholes prior to construction starting
  • Cavern construction is flexible since it is not targeting a specific alignment (like a tunnel that must meet planned path or mine that must hit an ore body), so in the unlikely event unexpected conditions arise, construction can easily be adapted to mitigate
  • Additional mitigation measures can also be implemented, but not necessary in most standard applications of A-CAES
  • Fracking and A-CAES are done with very different goals in mind, are sited in different geologic settings, and use entirely different methods.
  • The fracking process requires intentionally fracturing sedimentary rock formations underground, purposely cracking the rock to create a more permeable environment in order to free gas trapped within the rock.  In contrast, A-CAES cavern construction uses traditional mining approaches to develop an underground cavern in impermeable geologies, according to precise specifications.
    • By design, the geologies selected for A-CAES caverns are impermeable in order to contain the compressed air and water within the cavern.
  • Rock caverns for A-CAES facilities are sited in impermeable formations with no hydrocarbons, and operate well below the hydraulic fracturing threshold of the rock. This means that the gas leaks and groundwater contamination that can be concerns with fracking operations aren’t applicable when building an A-CAES cavern. 
    • The impermeable rock where A-CAES caverns are sited are isolated from aquifers. Additionally, unlike fracking, there are no chemical additives used in the water for cavern construction.
    • Increased seismic activity, also a potential issue in areas where fracking occurs, is not a risk when building an A-CAES cavern. 
  • A-CAES facilities use 1/20th of the water compared to similar size pumped hydro for a one-time fill (approximately 160 m3 per MWh)
  • We are a net water producer during operations as there is water generated through the compression process, unlike pumped hydro, which can be used for irrigation or other uses as appropriate
    • To do this, Hydrostor uses a reservoir cover made up of interlocking floating shapes which dramatically reduces evaporation, and we design a water balance, which balances produced water from our process, precipitation, evaporation, as well as consumption for other activities on site.
    • Our goal is to manage seasonal and annual fluctuations with the reservoir volume range.
  • Waste rock is managed through on-site reuse (berms and reservoir) and creation of aggregate for commercial use
  • A-CAES uses land efficiently, requiring only 100 acres for very large-scale 500MW, 8hr facility – a solar farm with the same capacity uses ~25x as much land
  • Hydrostor facilities rely on a one-time water draw of 530 acre-feet for 500MW, 8hr facility – 20x less volume than an equivalent pumped hydro facility – and are actually a net water producer during operations
  • Groundwater management is done during construction using standard cavern construction techniques, and pre-construction siting work ensures our projects are hydraulically isolated from aquifers
  • A-CAES by its nature as infrastructure relying primarily on air, rock, and relatively low amounts of water, has a very low life-cycle impact
  • The cavern is filled with water and capped
  • The top-side facility is fully decommissioned and site brought back to near original condition
  • Generally, A-CAES will continue operating well beyond 50 years, through standard maintenance, as has already been seen with hydropower and pumped hydro. Cavern is an ongoing asset like a pumped hydro reservoir