A compelling solution

Austen Adams explains how Liquid Air Energy Storage (LAES) is offering hope to the energy generation market

As nations the world over move towards renewable energy technologies such as wind and solar power, the requirement for a large-scale, long duration energy storage solution, capable of delivering a consistent supply to help balance the grid, has never been greater.

Like all energy storage systems, Liquid Air Energy Storage (LAES) technology comprises three primary elements; a charging system, an energy store and a power recovery unit. The real selling point however, is that each can be scaled independently to optimise the system for different applications – making it an incredibly versatile solution.

The differences continue further with LAES being free from geographical restrictions thanks to its use of liquid air stored at low pressure in tanks to power turbines. Other benefits of the system: it doesn’t require scarce materials and doesn’t give off harmful emissions, resulting in no damage to ecosystems.

The design has been brought to life by Highview Power Storage, which 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, backed by £8m in funding from the Department of Energy and Climate Change, the Highview team and its project partner, Viridor, have completed the construction of a 5MW, pre-commercial demonstration LAES technology plant at Viridor’s landfill gas generation site at Pilsworth Landfill facility in Greater Manchester.

Having been designed to demonstrate LAES technology at scale, the facility will operate for at least one year, providing energy storage as well as converting low-grade waste heat to power from the landfill gas engines.

How does LAES store and discharge energy?
Matthew Barnett, Head of Business Development, for Highview Power explained: “Our LAES technology stores liquid air in insulated tanks at low pressure before discharging it as electricity when required.

“The process involves taking off peak or excess electricity and using it to turn air into liquid by refrigerating it to -196 degrees and storing it in insulated vessels on a 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 offered is significant, representing impressive GWh of energy potential.” Where the technology really turns heads is in its ability to use waste heat and cold from its own and other processes to enhance its efficiency.

Matthew continues: “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 one), integrating it into the power recovery process (stage three). This makes it a great option for applications that have their own waste heat source, such as thermal power generation or steel mills.”

Manufacturing the technology
A key element of LAES technology is the insulated vessels which store the liquid air. Avingtrans PLC’s Stainless Metalcraft business, in Cambridgeshire, has a long track record of working with companies to bring new concepts to life and specialises in manufacturing pressure vessels in a range of sizes and materials so the project was a great fit for the business.

While the 5MW/15MWh 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.

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 gives rise to a range of manufacturing challenges, not least in finding production facilities large enough to house the vessels and their protective scaffolding as they are produced.

Making use of the specialist welding skills available at Metalcraft, the vessels were manufactured from carbon steel EN 10028-1 P 265 GH (1.0425). With an elongation factor of more than 14 per cent, this material is sufficiently ductile for such an application and offers impact energy absorption greater than 27J at -20°C.

Using the company’s on-site testing facility, the vessels were exposed to radiograph techniques, to in order to certify the high integral welds as non-destructive. Testing for the completed vessels also included hydrostatic testing to 12.6 bar, including an allowance for the static head as the vessel is around 12 metres tall. The actual test weight of the vessel was 94,000kg.

It is manufactured to PD5500:2012+A2:2013 Cat. 2 PED Cat IV Mod G – a code of practice that provides rules for the design, fabrication and inspection of pressure vessels.

Project goals
As well as generating power, the pre-commercial project also aims 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 US regulation market.

Everyone involved in the project is excited by the potential LAES offers the energy industry and, considering the scalability of the technology using readily available equipment, liquid air looks set to become a compelling solution for this huge potential market.

Highview Power Storage/Metalcraft/Avingtrans
Austen Adams is divisional managing director of Avingtrans plc’s Energy & Medical division. Metalcraft forms part of Avingtrans PLC’s Energy & Medical division, which offers a one-stop shop for the design, manufacture, installation and maintenance of systems for the oil and gas, nuclear, power, renewables, environmental and medical markets.

Highview Power Storage is a designer and developer of largescale energy storage solutions for utility and distributed power systems. Using liquid air as the storage medium, Highview can design bespoke Liquid Air Energy Storage (LAES) plants, that can deliver around 5MW/15MWh – to significantly more than 50MW/200MWh to service a growing multi billion dollar energy storage market.

For further information please visit: metalcraft.co.uk     avingtrans.plc.uk     highview-power.com