Weekend read: Cut to the CAES

From pv magazine print edition 3/24

In a disused mine-site cavern in the Australian outback, a 200 MW/1,600 MWh compressed air energy storage project is being developed by Canadian company Hydrostor. The facility came about after a deal struck with local electricity network operator Transgrid, which had gone to market looking for storage solutions to improve reliability in the famed frontier town of Broken Hill.

Dubbed the Silver City Energy Storage Centre, it will be Hydrostor’s first large-scale compressed air plant and will be one of the first “adiabatic” systems in the Western world, if successfully brought online by its expected 2027 date. Adiabatic CAES systems involve a thermal energy, or heat, storage component, in effect meaning they do not require the fossil fuels which have historically been used in such systems.

Silver City’s compressed air will be stored 600 metres below ground, with a project area of less than 40 hectares and a life expectancy of 50 years, as Hydrostor Australia vice president of origination and development, Martin Becker, told pv magazine.

Since compressed air batteries use turbines, the plant will also provide system strength and inertia to the electricity grid. Its grid services will be far more consistent than the synthetic inertia offered by big batteries, Becker added, since lithium batteries degrade with cycling and therefore can only act as virtual synchronous machines for a few hours per day. Hydrostor expects to reach a final investment decision on Silver City this year.

Proven technology

CAES today sits at a curious nexus. On the one hand, the technological components and individual systems that go into these large infrastructure projects are proven and have been used in industry for decades, sometimes centuries.

Only a handful of compressed air plants have ever made it into commercial operation, however. A 321 MW plant has been running in Huntorf, Germany, since 1978 and, since 1991, a 110 MW plant has operated in McIntosh, Alabama, in the United States. Both of those projects are diabatic – meaning they do not store heat and so use fossil fuels in their processes. Adiabatic compressed air systems are a far more recent phenomenon. Hydrostor opened the first commercial adiabatic plant in 2019, in Goderich, Ontario, in Canada, but the project has a peak power output of just 1.75 MW.

In the years since, China has gone big on CAES, bringing multiple systems online, including a 100 MW plant in Hebei province in 2022. Work began in the same year on a 350 MW/1.4 GWh plant in Shandong and many more projects are in the works.

For Australian agency the Commonwealth Scientific and Industrial Research Organisation (CSIRO), compressed air is one of the most promising deep storage technologies, largely because of its comparatively low cost, long asset life, and relative flexibility. While costs are highly project dependent, a 2021 paper by David Evans et al., published in Applied Sciences noted CAES costs could be as low as $3/kWh to $6/kWh.

“The per-unit cost goes down the bigger it gets, which isn’t true for batteries,” said Ben Clennell, a senior principal research scientist at CSIRO. CAES, said Clennell, “is cost competitive and if it’s also competitive in terms of being able to get projects up and running, and the geological locations are suitable … it could play a large role [in energy storage]. We’re one gigaproject away from having a project that is actually demonstrating this technology in the Western world.”

Compressed air

Compressed air batteries pressurize atmospheric air, storing energy in the form of potential energy, like a spring. To discharge, the air is released via an expander, to spin a turbine. Systems have two core components: the above-ground plant, with its turbomachinery, and the below ground storage void – which can take numerous forms.

There are three different types of compressed air storage systems: diabatic, adiabatic, and isothermal. An isothermal process is a thermodynamic process in which the temperature of a system remains constant, typically when a system is in contact with an outside thermal reservoir. A change in the system occurs slowly enough to enable the system to be continuously adjusted to the temperature of the reservoir, through heat exchange. Such designs reduce energy loss but there is a dearth of operational projects. Adiabatic systems are becoming the industry focus, although Corre Energy and others are now pursuing hydrogen-ready diabatic systems.

Efficiencies between the types differ, with diabatic systems generally offering 50% to 55%, and potentially 60%. CSIRO’s Clennell says round-trip efficiency for adiabatic CAES systems with top-tier technology is somewhere around 70%. “It’s pretty well established what those numbers are,” he said. “There are no bits we don’t understand, it’s just an engineering problem to get the best efficiency possible, really, without having an enormous amount of overbuild on the expense of the components. It’s unrealistic to go above around 75%, I think.”

Options

There are many ways for adiabatic systems to store the heat resulting from the compression of air and companies are pursuing a range of techniques.

“We’ve tried different approaches but we’ve actually landed on the simplest approach because it’s so bankable,” said Hydrostor President and Chief Operating Officer Jon Norman.

The company has opted to simply store heat in the form of pressurized water within insulated spherical tanks. That and every other aspect of Hydrostor’s system is designed around existing industrial kit.

“We are more a systems integrator with IP [intellectual property] on how we are integrating the system, rather than a new technology provider,” said Norman.

That approach also holds true for another burgeoning player in the European market, Corre Energy.

“There’s dozens of examples of failures in compressed air but it’s always associated with this issue of letting the perfect be the enemy of the good,” said Norman, noting the failed CAES pilots and projects that have dotted recent decades have tended to involve re-engineered supply chains and project locations that overlooked grid demand and constraints. Funding has also been a factor.

Hydrostatic compensation

Gleaned from the hydrocarbon storage industry, Hydrostor’s systems also involve hydrostatic compensation, a water component to help them overcome air pressure anomalies within caverns – a key stumbling block for CAES.

This water reservoir sits above ground and is connected to the underground

SDGs, Targets, and Indicators

1. SDG 7: Affordable and Clean Energy

   • Target 7.1: By 2030, ensure universal access to affordable, reliable, and modern energy services.
   • Indicator 7.1.2: Proportion of population with access to electricity.
   • Indicator 7.1.3: Proportion of population with primary reliance on clean fuels and technology.

2. SDG 9: Industry, Innovation, and Infrastructure

   • Target 9.1: Develop quality, reliable, sustainable, and resilient infrastructure.
   • Indicator 9.1.1: Proportion of the rural population who live within 2 km of an all-season road.
   • Indicator 9.1.2: Passenger and freight volumes, by mode of transport.

3. SDG 13: Climate Action

   • Target 13.2: Integrate climate change measures into national policies, strategies, and planning.
   • Indicator 13.2.1: Number of countries that have integrated mitigation, adaptation, impact reduction, and early warning measures into their national policies, strategies, and planning.
   • Indicator 13.2.2: Total greenhouse gas emissions per year.

Analysis

The issues highlighted in the article are connected to several Sustainable Development Goals (SDGs) and their respective targets and indicators. The relevant SDGs, targets, and indicators can be identified as follows:

1. SDG 7: Affordable and Clean Energy

The article discusses the development of a compressed air energy storage project that aims to improve reliability in the town of Broken Hill. This aligns with SDG 7, which focuses on ensuring universal access to affordable, reliable, and modern energy services.

• Target 7.1: By 2030, ensure universal access to affordable, reliable, and modern energy services.
• Indicator 7.1.2: Proportion of population with access to electricity.
• Indicator 7.1.3: Proportion of population with primary reliance on clean fuels and technology.

2. SDG 9: Industry, Innovation, and Infrastructure

The article discusses the development of infrastructure for the compressed air energy storage project. This aligns with SDG 9, which focuses on developing quality, reliable, sustainable, and resilient infrastructure.

• Target 9.1: Develop quality, reliable, sustainable, and resilient infrastructure.
• Indicator 9.1.1: Proportion of the rural population who live within 2 km of an all-season road.
• Indicator 9.1.2: Passenger and freight volumes, by mode of transport.

3. SDG 13: Climate Action

The article mentions that compressed air energy storage is considered a promising deep storage technology for renewable energy, which contributes to climate action. This aligns with SDG 13, which focuses on taking urgent action to combat climate change and its impacts.

• Target 13.2: Integrate climate change measures into national policies, strategies, and planning.
• Indicator 13.2.1: Number of countries that have integrated mitigation, adaptation, impact reduction, and early warning measures into their national policies, strategies, and planning.
• Indicator 13.2.2: Total greenhouse gas emissions per year.

Table: SDGs, Targets, and Indicators

Behold! This splendid article springs forth from the wellspring of knowledge, shaped by a wondrous proprietary AI technology that delved into a vast ocean of data, illuminating the path towards the Sustainable Development Goals. Remember that all rights are reserved by SDG Investors LLC, empowering us to champion progress together.

Source: pv-magazine-australia.com

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