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Bringing thermal energy store vessels to life

Austen Adams

In order to meet emission reduction targets, the challenge to engineers to develop clean, reliable energy technologies has never been so pressing. With the global potential for grid energy storage by 2017 expected to account for 185GWh (52GW) of capacity, 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 power generated for use at a later date.

One energy storage solution that has come to the fore is Liquid Air Energy Storage (LAES), which uses liquid air to create an innovative energy reserve that delivers large scale, long duration energy storage. 

The Government is taking the technology’s potential seriously, committing millions of pounds over the past three years to fund immediate demonstration projects in grid and transport applications and a new multi-million pound research institute, the Birmingham Centre for Cryogenic Energy Storage at the University of Birmingham.

Highview Power Storage with project partners, Viridor, recently received more than £8m in funding from the Department of Energy and Climate Change for the design, build and testing of a 5MW LAES technology plant that would be suitable for long duration energy storage. The site will soon be operational in the north west of England. We caught up with the team and some of their suppliers to explain how the technology works and how it can solve some of the toughest energy challenges.

“Our liquid air energy storage (LAES) 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 optimise the system for different applications, making it an incredibly flexible solution.

“The process works by turning air into liquid by refrigerating it to -196 degrees and storing it in insulated vessels at very large scale. When power is required, liquid air is drawn from the tanks and pumped to high pressure. 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 litres of ambient air being reduced to just one litre of liquid air, the storage capacity this offers is significant, representing GWh of energy potential.”

A large-scale energy storage solution, LAES offers the opportunity to store or ‘bank’ energy and time-shift its delivery to periods of peak demand or hold it in reserve. This is critical to enabling the use of intermittent renewable power (e.g. wind or solar) or facilities that have power generation capabilities (e.g. power stations). 

Unusually for a large-scale energy storage solution, LAES also enjoys a wide range of applications and does not suffer from geographical limitations. This contrasts with competing technologies such as compressed air energy storage (CAES) or pumped hydro that require particular geographical features e.g. mountains or reservoirs in the locations they are situated.

Additionally, it is hoped that LAES will help tackle some of the toughest challenges of the low-carbon transition: balancing an electricity grid increasingly dominated by intermittent renewables; and harvesting low grade waste heat from industrial processes..

In addition, where the technology really scores is in its ability 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. 

“The low boiling point of liquefied air means the efficiency of the system can also 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 industrial plants such as steel mills.”

Highview tested and demonstrated a fully operational LAES pilot plant (350kW/2.5MWh) at SSE’s 80MW 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. 

Now showcasing the 5MW 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 to power. 

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

Kelvin Boyce, Technical Manager at Stainless Metalcraft, part of Avingtrans plc’s Energy & Medical division, takes up the story. “We became involved with the LAES project at an early stage as our Stainless Metalcraft business in Chatteris, Cambridgeshire, has a long track record of working with companies to bring new concepts to life and specialises in manufacturing pressure vessels, which are key to the LAES system’s design.

“The vessels used in the pre-commercial project are nearly 12 and a half metres high and three metres in diameter with a shell thickness of 13mm. With an empty weight of 16,230kg, 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.

“The vessels used in the LAES pre-commercial demonstration plant were manufactured from carbon steel EN 10028-1 P 265 GH (1.0425). This material is sufficiently ductile (greater than 14% elongation) and offers Impact Energy absorption greater than 27J at -20°C but also requires specialist skills to weld effectively.”

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 focus of the pre-commercial project is to demonstrate how LAES can be used to help balance supply and demand on the grid during its time in operation. This will include Short Term Operating Reserve (STOR), Triad avoidance (supporting the grid during the winter peaks), and testing for the US regulation market. The plant will be operated by KiWi Power, the UK’s leading demand response aggregator. 

Matthew continued: “The technology will enable customers to manage intermittent renewable generation, as well as providing local energy security, reactive power and voltage support, among other services. 

“LAES will also be suitable for energy-intensive industries that have low-grade heat or waste cold available to them, providing invaluable energy security while helping them mitigate the environmental impact of their activities. 

“The potential of liquid air is now being realised. We’ve been working with the supply chain on component selection for a larger scale system of 200MW/1.2GWh named ‘The GigaPlant’. 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.”


Austen Adams is Division Managing Director of Avingtrans Energy & Medical Division.


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