Hydrostor Inc.

Overview

Hydrostor is a Toronto company, founded in 2010, that develops advanced compressed air energy storage, or A-CAES. Grid electricity compresses air into a purpose-built underground cavern, the heat of compression is stored separately, and the two are recombined to drive a generator when the grid wants power back. The company has offices in Toronto, Melbourne, Adelaide and Denver, the last of which it named its U.S. headquarters. It has never published a global headcount; the only staffing figure it has given is a plan to grow the Denver office past 30 full-time employees. Curtis VanWalleghem, a co-founder, is chief executive. Jon Norman is president and Beth Summers is chief financial officer.

The built record is one plant. The Goderich Energy Storage Centre in Ontario is rated 1.75 MW and has operated commercially for Ontario's Independent Electricity System Operator since August 2020. Everything else in Hydrostor's materials is pre-construction. Willow Rock in California, at 500 MW, holds a state licence, a conditional federal loan commitment, three offtake contracts and an early grading package. Silver City in New South Wales, at 200 MW, holds planning consent and a land lease. Quinte in Ontario, at 500 MW, was announced in May 2026 and is entering permitting. Hydrostor's operating fleet is roughly 1/285th of a single Willow Rock.

The 7 GW figure Hydrostor uses in press releases describes projects in development in Canada, the United States, Australia and the United Kingdom. It has no independent verification and no published project-by-project breakdown, and the company's current website drops the number in favour of "an extensive pipeline of A-CAES projects" across three continents. An earlier release, from January 2022, put the projects then well underway at 1.1 GW and 8.7 GWh. Investors named across its announcements include Goldman Sachs Alternatives, Canada Growth Fund, CPP Investments, Baker Hughes, Hatch and Realize Capital Partners.

How A-CAES works

Charging runs grid electricity through a compressor. The heat of compression is captured in heat exchangers and stored in pressurised water rather than vented, and the compressed air goes into a purpose-built underground cavern. Discharging returns that stored heat to the air, which then drives an expander and a generator. No fuel is burned. That is the difference from the two legacy compressed air plants at Huntorf in Germany and McIntosh in Alabama, both of which burn natural gas to reheat the air on the way out.

Hydrostatic compensation is the distinguishing element. The cavern is connected to a surface water reservoir by a shaft and sits flooded, pressurised by the weight of the water column above it. Charging pushes water up the shaft into the surface reservoir; discharging lets the water fall back in and displace the air. The cavern therefore stays at close to constant pressure across the cycle instead of falling as air is withdrawn. Hydrostor described the mechanism in a technical submission to Nova Scotia Power's integrated resource planning process and holds a U.S. patent on the arrangement, number 11,835,023.

The claimed commercial consequence is siting. Because the cavern is excavated rather than found, Hydrostor says the technology is not restricted to salt domes or depleted reservoirs the way legacy CAES is, and it claims a surface footprint up to 1/20th that of an equivalent pumped hydro facility. Both are company claims, and neither has been independently verified.

The largest fuel-free compressed air plants now operating are in China. Nengchu-1 at Yingcheng in Hubei is rated 300 MW / 1,500 MWh and entered commercial operation in January 2025, storing air in an abandoned salt mine about 600 metres deep. Its builder, China Energy Engineering Corporation, calls it the world's first "full green, non-supplementary combustion" 300 MW compressed air project. A 600 MW / 2.4 GWh plant at Huai'an in Jiangsu, two 300 MW non-combustion units, was reported switched on in January 2026. Both sit in existing salt caverns and neither uses hydrostatic compensation, which leaves Goderich as the only operating plant of Hydrostor's design. Chinese state media put Nengchu-1's system conversion efficiency at about 70%, a number that comes from the operator and is no better audited than Hydrostor's own.

Goderich: the operating record

Goderich discharges at 1.75 MW peak and charges at 2.2 MW. Hydrostor's project page gives storage of more than 10 MWh, of which 7 MWh is contracted. The plant sells less than it can hold. At the rated discharge, 10 MWh implies roughly 5.7 hours and the contracted 7 MWh about 4 hours, which is arithmetic on the published ratings rather than a measured duration. A figure of "up to 15 MWh" circulates in secondary write-ups and appears in no Hydrostor document located for this profile.

The plant was developed jointly with NRStor Inc. and inaugurated in November 2019, about two years after construction began, with commercial operation for the IESO starting in August 2020. Hydrostor's project page lists an in-service date of 2019, which refers to completion of the plant rather than the start of commercial operation. The IESO arrangement covers peaking capacity, ancillary services and full participation in the merchant energy market; secondary sources describe a 10-year term, which could not be confirmed in an IESO document. The ownership split between Hydrostor and NRStor has never been disclosed. Public and quasi-public support named at completion includes Export Development Canada, Sustainable Development Technology Canada and the Government of Ontario through Ontario Centres of Excellence, alongside a US$37 million growth financing, and Natural Resources Canada added roughly C$500,000 in April 2021 under the Energy Innovation Program.

Efficiency is where the record thins out. Hydrostor publicly uses a round-trip efficiency of around 60% to 65% for A-CAES, which is a claim about the technology as a class rather than a measurement at Goderich. The peer-reviewed literature repeats a figure of roughly 60% for the plant: Sarmast, Rouindej, Fraser and Dusseault, writing in Applied Energyin March 2024, say the 1.75 MW Goderich plant "has reported efficiencies around 60%," and then qualify it. Those reported efficiencies are not identified as averages, medians or maximums, nor is it stated whether they come from short-term or long-term operation. The paper repeats a reported number; it does not measure one.

Six years into commercial operation, the plant has no published, independently audited round-trip efficiency. Hydrostor's own Goderich page carries no efficiency figure at all. Nor is there any availability figure, capacity factor, cycle count or dispatch record, from Hydrostor, from NRStor or from the IESO. The nearest company statement is that the plant conforms to all interconnection, uptime, performance and dispatch standards set out by the IESO, which is a compliance assertion rather than a performance number.

Projects

Funding & partnerships

Hydrostor's disclosed capital comes in preferred equity, convertible notes and a development loan facility, each at a different level of the capital structure. In January 2022 Goldman Sachs Asset Management committed US$250 million of preferred equity, and the release states that Goldman would fund in tranches tied to project milestones to match Hydrostor's capital needs, which makes the headline an upper bound drawn over time rather than cash received. Three Goldman representatives joined the board: Charlie Gailliot, Sebastien Gagnon and Gunduz Shirin. In February 2025 the company announced US$200 million in two further instruments, neither of them common equity: a US$150 million convertible note commitment from Canada Growth Fund Inc., Goldman Sachs Alternatives and CPP Investments at the corporate level, and a separate US$50 million convertible development expenditure loan facility from Canada Growth Fund alone, drawn against development spending on Canadian projects including Quinte.

Hydrostor announced a US$230 million equity investment on August 12, 2026. It includes the previously announced convertible note commitments from Canada Growth Fund Inc., Goldman Sachs Alternatives and CPP Investments, so it does not sit on top of the February 2025 US$200 million. The new element is a strategic equity round with Baker Hughes, Hatch, Realize Capital Partners, a Social Finance Fund wholesaler and undisclosed others. Hydrostor says the money funds development of the 7 GW pipeline and will take Willow Rock to financial close later this year.

Hydrostor publishes no cumulative total raised, and adding these commitments together would produce a figure the company has not stated.

Baker Hugheshas been an investor since 2019 and expanded that on January 28, 2026 with a strategic technology and equity agreement, announced at its annual meeting in Florence, covering up to 1.4 GW of Baker Hughes compression, expander, motor and generator equipment for Hydrostor's flagship projects. Hatch, the Canadian engineering firm, announced a project execution partnership and equity agreement on February 25, 2026 and will lead the design and execution of Willow Rock. Neither company disclosed the size of its investment, the stake acquired or the valuation.

Strategy & outlook

Hydrostor's stated case rests on what A-CAES buys with the efficiency it gives up. The company told POWER magazine in 2020 that the technology's synchronous capacity and flexible siting matter to grid operators, a benefit it said outweighs the impact of slightly lower round-trip efficiency, and it points to a design life above 50 years against the shorter replacement cycle of a battery. The comparison it draws is between a cavern that provides inertia and lasts five decades and a lithium-ion system that gets augmented and replaced.

The most detailed public critique comes from Michael Barnard, an individual commentator writing on CleanTechnica, an outlet with a stated advocacy orientation, in a May 2026 piece on Quinte. On efficiency, he sets A-CAES at 60% to 65% against lithium-ion at 85% to 95% DC: a 65% system needs roughly 6.2 GWh of input to deliver 4 GWh, against roughly 4.4 GWh for a 90% battery, so every delivered MWh costs about 40% more input energy. On capital cost he puts Quinte at C$3.0 billion to C$4.0 billion, with C$3.5 billion as his planning case, against C$1.3 billion to C$1.8 billion for an equivalent lithium-ion build. His benchmark is Oneida, Canada's largest battery storage facility at 250 MW / 1 GWh, which came in at roughly C$700 million against a C$800 million estimate at financial close in 2023 and reached commercial operation in May 2025 ahead of schedule. That is a delivered cost rather than a budget, which makes it a firmer benchmark. He argues 2035 to 2038 is a more defensible schedule than the public 2033 to 2034. One risk he names has no battery analogue: geotechnical discovery, where cavern conditions become known during construction, when changes are expensive.

The counterweight comes from the cost literature. Peer-reviewed work published in iScience in 2025 finds an experience rate of roughly 15% for adiabatic compressed air storage, comparable to roughly 12% for lithium-ion, and argues that A-CAES could become economic at durations of 10 to 100 hours where the geology cooperates. That same finding sits awkwardly against Hydrostor's current portfolio, because Willow Rock and Quinte are 8-hour systems, inside the duration band where lithium-ion is strongest rather than the 10 to 100 hour band the cost argument favours. Trade coverage puts the same point from the market side, reporting that lithium-ion still outcompetes long-duration alternatives on cost and supply chain maturity, including in the 4 to 8 hour segment. Form Energy, which targets 100-hour durations with iron-air, and Antora Energy, which stores heat for industrial users, sit in different parts of that same market.

The next 12 months turn on Willow Rock. Hydrostor said on August 12, 2026 that the new equity will take the project to financial close later this year, which is a target rather than a closing. Three things decide whether the company gets its first utility-scale plant: whether the DOE commitment converts into a closed loan, whether equity and debt reach that close while Granite's grading package runs to March 2027, and whether the remaining 190 MW of the rating, the balance left by the announced contracts, finds buyers.

Key considerations

No utility-scale Hydrostor project has been confirmed to have reached financial close. Willow Rock had not closed as of August 2026. Silver City's expected end-2025 close was never confirmed either way. Quinte began permitting in May 2026. Goderich was built with a mix of government and quasi-government support plus a US$37 million growth financing, and no source located states whether it reached a conventional project financial close. Private financings are not always announced, so the absence of a public closing is not proof that none occurred. What is on the record is that the Central Coast Community Energy contract has been amended three times, twice explicitly because financing had not been secured on schedule.

Goderich is the one plant that could settle the efficiency question for Hydrostor's design, and it has not. Any assessment of A-CAES economics rests on company figures, on modelling, or on a peer-reviewed number whose own authors say they cannot identify its basis.

Several headline figures are softer than they look. The 7 GW pipeline is a company claim with no project-by-project breakdown, and the company's own releases have used different numbers over time. No company-confirmed capital cost exists for Willow Rock; the roughly US$1.5 billion in circulation is inferred from the DOE principal and repeated by a commentator, which makes it an order of magnitude rather than a budget. The Baker Hughes and Hatch equity amounts are undisclosed. Global headcount is not published. Even the operations headcount for Willow Rock differs between documents: 40 full-time jobs in the January 2025 materials, 25 to 40 on the current project page.

The DOE loan should be read with a date attached. It was conditional in January 2025 and, on the record available in August 2026, conditional still, across a period in which federal loan and grant policy shifted materially.

Sources