Future Energy: Liquid Air Energy Storage (LAES) research

University of Brighton graduate and engineering PhD student Tim Gardhouse, who delivered research for the collaborative research programme that led to the opening of the Highview Liquid Air Energy Storage facility.

What is Liquid Air Energy Storage (LAES)?

Liquid air energy storage (LAES) is a class of thermo-mechanical energy storage that uses the thermal potential stored in a tank of cryogenic fluid.

The device is charged using an air liquefier and energy is recovered through a Rankine cycle using the stored liquid air as the working fluid. The cycle efficiency is greatly improved through the storage and recycling of thermal energy released during discharge and used to reduce the work required to liquefy air during charging. [See Morgan, R., Nelmes, S., Gibson, E., & Brett, G. (2014). Liquid air energy storage – Analysis and first results from a pilot scale demonstration plant. Applied Energy, 137, 845-853.]

The research and development of the LAES cycle began in 1977 with theoretical work at Newcastle University, was further developed by Hitachi in the 1990s and culminated in the building of the first pilot demonstration plant by Highview Power Storage in 2010.

The need for storing heat within LAES may appear counter intuitive, but as a thermal process it can recycle heat to improve efficiency and can also integrate well with other thermal processes. As such, a 'mid temperature range' storage concept that is efficient, low cost and scalable is required. 

Engineering PhD student Tim Gardhouse (right), delivered essential research in the development of the Liquid Air Energy Storage facility at Highview Power Storage, here he is at work with colleague Stuart Nelmes.

Highview, the world’s first grid-scale liquid air energy storage (LAES) plant 

The ‘5MW/15MWh’ LAES plant works by storing air as a liquid in above-ground tanks and, when electricity is required, the liquid air is brought to ambient temperature where it regasifies and turns a turbine, generating electricity at times of need – but without burning the gas and releasing emissions.

In January 2017, the University of Brighton completed a two year Knowledge Transfer project with Highview Power Storage, to develop understanding of the material used in high grade power storage, and influence design guidelines for future plants. 

The project was delivered by university graduate and engineering PhD student Tim Gardhouse, supervised by a team of university academics including Professor Robert Morgan and Dr Angad Panasar. It enabled a new understanding of the company’s High Grade Cold Store (HGCS), a key component of the Liquid Air Energy Storage plant.

The university used lab-scale test rigs to develop knowledge and understanding of the cryogenic performance of materials within the cold store, and was able to develop models of the High Grade Cold Store, simulating temperature changes across the thermal store. The models will be fed into the design guidelines for future cold stores, ensuring cost-effective engineering and procurement practices.

Research on liquid air energy storage

Energy can be stored thermally in three ways:

• as cold in liquid air 
• in a backed bed regenerator cold store 
• as heat in a molten salt. 

Professor Robert Morgan's co-authored 2014 paper, 'Liquid air energy storage – Analysis and first results from a pilot scale demonstration plant', presented analysis and results from the design and testing of the novel LAES concept at pilot scale. This also gave fundamental analysis of the LAES cycle to determine the theoretical cycle performance and in particular the value of cold recycle. The pilot plant was then described together with the results of a series of comprehensive technical and commercial trials. 

Morgan was co-author on the subsequent 2015 report 'Liquid Air in the energy and transport systems: opportunities for industry and innovation in the UK' (Akhurst et al.) and the 2016 'Liquid air energy storage – from theory to demonstration.' (Morgan, R, 2016, International Journal of Environmental Studies, 72(3), 469-480.) The article described optimising the thermodynamic principles of the cycle to deliver improve round trip efficiency, reduce cost and harness waste heat, the use of cold recycle being essential to deliver an efficient LAES cycle. The article looked ahead to large scale deployment and integration with other power generation and industrial processes.

In 2018-19, Morgan then worked with Dr Anghad Panesar and Dr Marco Bernagozzi on the Highview-led, Innovate UK-funded project 'Development of a High Grade Heat Store for integration with Liquid Air Energy Storage'. This resulted in the publication Bernagozzi, M., Panesar, A., & Morgan, R. (2019) 'Low Temperature Molten Salts in Sustainable Energy Production' in Proceedings of the 7th European Conference on Renewable Energy Systems (pp. 260-265). 

In the publication, the University of Brighton authors note that a potential means to overcome the obstacles placed by the intermittent nature of the most common sustainable energy sources was represented by the Liquid Air Energy Storage (LAES) systems. In order to improve its round trip efficiency, which was at that time at 50 per cent, the use of a common thermal medium for thermal storage and heat transfer fluid was considered as an effective solution. Molten salts were selected as the common thermal medium in this work, where a novel methodology for identifying and evaluating alternative mixtures was introduced. Their presented methodology was proven to be an effective and versatile tool in identifying alternative salt mixtures, and can be adapted for comparable applications.

Work is ongoing, with the project Stored Up-valued Concentrated Cold Energy System (SUCCES) extending the future possibilities for improved energy storage. Recognising that the air liquefier used to charge the LAES device has a sweet spot at large (>50MW) scale as plant efficiency increases and relative cost reduces with scale for this technology, the project asks what would happen if a LAES plant could be efficiently deployed at smaller (<50MW) scale?

At smaller scales, the LAES technology could  be integrated with other aspects of the energy network that require cooling at cryogenic temperatures such as the long term storage of bio methane and green hydrogen. Pursuing this interest, researchers investigated the integration of a small to mid scale LAES plant with, for example, the liquefaction of locally produced bio methane from waste. 

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Of the work with Highview on Liquid Air Energy Storage, Professor Rob Morgan, said: “Working with such an innovative company helping to enhance technology in this rapidly developing and important sector has been and continues to be immensely rewarding. The collaboration enables us to exploit our expertise in thermal fluid and energy systems, transferring our research from the laboratory to the real world.”

Further examples of research excellence at the University of Brighton