Baseload, Bioenergy, Solar, Storage, Utility Scale

A Look at Liquid Air Energy Storage Technology

Issue 4 and Volume 19.

Large-scale grid storage is seen by some as the holy grail for large-scale renewable energy grid integration. A new technology has the potential to meet that need.

With traditional coal-fired power stations coming to the end of their working lives, the challenge to engineers to develop clean, reliable energy technologies has never been so pressing.

Renewable energy technologies such as wind and solar power both offer potential solutions but the unresolved issue has always been consistency of supply and how to store energy generated for use at a later date.

One energy storage solution that has come to the forefront in recent months is Liquid Air Energy Storage (LAES), which uses liquid air to create an energy reserve that can deliver large-scale, long duration energy storage.

Unlike other large-scale energy storage solutions, LAES does not have geographical restrictions such as the need to be located in mountainous areas or where there are reservoirs, which could render it more viable for a range of operations. However, many great ideas in the energy industry abound so how does new technology such as LAES make the leap from the drawing board into reality and is it effective when it does?

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Image: Transporting LAES tanks is just one of the many challenges facing this new technology. Credit: Stainless Metalcraft.

Highview Power Storage with project partners, Viridor, recently received more than £8m [US $11.4m] in funding from the UK Department of Energy and Climate Change for the design, build and testing of a 5-MW LAES technology plant that would be suitable for long duration energy storage. The site will soon be operational in the north west of England.

“Our liquid air energy storage technology stores liquid air in insulated tanks at low pressure before discharging it as electricity when required,” explained Matthew Barnett, Head of Business Development, at Highview Power. “Like all energy storage systems, the LAES system comprises three primary processes: a charging system; an energy store; and power recovery. However, unlike many other storage systems, these can be scaled independently to optimize the system for different applications.”

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Barnett said that the technology turns air liquid through refrigeration (down to -196°C) and storing the very cold liquid in insulated vessels. When power is required, liquid air is drawn from the tanks and pumped to high pressure, he said. “Stored heat from the air liquefier is applied to the liquid air via heat exchangers and an intermediate heat transfer fluid. This produces a high-pressure gas that is then used to drive the turbine and create electricity. With 700 liters of ambient air being reduced to just one liter of liquid air, the storage capacity this offers is significant, representing GWh of energy potential.”

The technology is also able to use waste heat and cold from its own and other processes to enhance its efficiency. Matthew continued: “During the discharge stage, very cold air is exhausted and captured by a high-grade cold store that can be used at a later date to enhance the efficiency of the liquefaction process. In a similar way, we can integrate waste cold from industrial processes such as LNG terminals.

“Similarly, the low boiling point of liquefied air means the efficiency of the system can be improved with the introduction of ambient heat. The standard LAES system is designed to capture and store the heat produced during the liquefaction process (stage 1), integrating it into the power recovery process (stage 3). This makes it a great option for applications that have their own waste heat source, such as thermal power generation or steel mills.”

Image: Storage vessels in the demonstration project are nearly 12 and a half meters tall, three meters in diameter, 13 mm thick and have an empty weight of 16,230 kg. Credit: Highview Power.

Highview tested and demonstrated a fully operational 350-kW/2.5-MWh LAES pilot plant at SSE’s 80-MW biomass plant at Slough Heat and Power in Greater London from 2011 to 2014 – successfully connecting to the UK grid and complying with the necessary regulations and inspections.

Image: Diagram of the LAES 3-Step Process. Credit: Highview Power.

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Now showcasing the 5-MW pre-commercial demonstration plant at Viridor’s landfill gas generation site at Pilsworth Landfill facility in Greater Manchester, the project will operate for at least one year, providing energy storage as well as converting low-grade waste heat from the landfill gas engines from heat to power.

Building the Supply Chain

While the 5-MW/15-MWh pre-commercial demonstration plant is appropriately sized to demonstrate grid scale storage, the supply chain is equipped to provide components that are scalable to hundreds of MWs in power for multiple hours.

Avintrans’ Stainless Metalcraft business supplied the most important part of the system: the energy storage vessels.

According to Kelvin Boyce, Technical Manager at Metalcraft, the company has a track record of “working with companies to bring new concepts to life.”

Boyce said the vessels in the demonstration project are nearly 12 and a half meters high, three meters in diameter and 13mm thick.

“With an empty weight of 16,230 kg, working on vessels this size and bigger throws up a range of manufacturing challenges, not least of which is finding production facilities large enough to house the vessels and their protective scaffolding as they’re produced,” he said.

A special welding skill set was required to build the vessels correctly since they were manufactured from carbon steel which offers impact energy absorption greater than 27J at -20°C, according to Boyce.

“The high integral welds were non-destructive tested using radiograph techniques at our own, on-site facility, and the completed vessel was also hydrostatic tested to 12.6 bar g, including allowance for static head as the vessel is around 12 meters tall. The actual test weight of the vessel was 94,000 kg.”

Boyce added that his company will be able to provide in-house training to scale up production “as the technology is proven and orders come in.”

Proof of Concept

After co-ordinating the delivery and installation of components from a number of suppliers — including GE, Heatric, Siemens and Nikkiso — the pre-commercial demonstrator is now going through the commissioning phase and is due to be operational in the first half of 2016.

As well as generating power, the project hopes to demonstrate how LAES can be used to help balance supply and demand on the grid during its time in operation, including Short Term Operating Reserve (STOR), Triad avoidance (supporting the grid during the winter peaks), and testing for the PJM regulation market in the U.S.

Image: Rendering of the potential gigaplant that Highview Power hopes to develop should the demonstration project be successful. Credit: Highview Power.

Should all go according to plan, Highview Power hopes to build an even larger 200-MW / 1.2-GWh that it is calling “The Gigaplant.” Barnett said that Highview is selecting components for this larger system. “There’s nothing in the world today available at this scale without geographical constraints and at such a competitive cost. We believe that Highview’s LAES systems will be the cheapest, cleanest and lowest environmental impact GWh scale, locatable storage systems available,” he said.

Austen Adams is managing director of Metalcraft’s Energy & Medical division.