ECO-POWER


T


he use of renewable energy to power the UK’s electricity grid has never


been higher. But, while wind and solar are sustainable, their output varies with environmental conditions, presenting a significant challenge when trying to balance the grid. If the UK is to move away from a baseload of electricity generated by fossil fuels, the variable nature of renewable energy must be addressed. Energy storage is widely viewed as a potential solution. Last year, the European Patent Office and


the International Energy Agency published a detailed report on innovation in batteries and electricity storage, based on patent data. The report suggests that battery storage is the main area of innovation – in particular, lithium-ion batteries. However, while these are very useful for portable storage – such as in electric vehicles – they can be difficult and costly to scale up. Another energy storage option is pumped storage hydropower, which in 2019 accounted for 90% of the world’s energy storage for stationary applications. Pumped storage offers large-scale energy storage, but is geographically constrained, capital intensive and impactful on the environment.


LIQUID AIR ENERGY STORAGE (LAES) The main benefit of LAES is that it can provide medium to long duration energy storage, which could be crucial in complementing the short duration storage provided by batteries. Like other energy storage solutions, the idea of liquid air energy storage is to balance out electricity supply and demand. During periods of high electricity production, rather than curtailing production, the excess energy is stored, to be used later during periods of high demand.


HOW LAES WORKS LAES systems require three main stages, the first of which is charging. When excess energy is produced during periods of high production or low demand, the energy is used to form liquid air. This is achieved by compressing the air to form


LIQUID AIR: Energy storage for the future?


Last year, construction started on a 250MWh liquid-air energy-storage system in Greater Manchester. Supported by a £10 million UK Government grant, when completed it will be the largest liquid-air energy-storage system in the world. Katie Smith, technical assistant of Reddie & Grose LLP - a firm of patent, trade mark and design attorneys, looks into the benefits of liquid air energy storage (LAES)


a high-pressure gas, and the air is then cooled by heat exchange with a cold fluid. The cold compressed air is then expanded, which further decreases the temperature of the air, condensing it to liquid form at around -196°C. The second stage is storage. 700L of


gaseous air can be stored as 1L of liquid air in insulated tanks at near ambient pressures. Finally, when the demand for electricity


increases, the energy is discharged. The liquid air is pumped to a high pressure and heated, to produce a high pressure gas. The gas is then expanded across a turbine, driving the turbine to generate electricity. Unfortunately, simply running the three-


step process would be too inefficient to be economically viable. To increase efficiency, LAES plants recycle the waste cold that results from the discharge stage, to help cool incoming air when charging. Additionally, the heat produced by initial compression of the gas during charging can be recycled and used for expansion of the air during discharge. The key to the efficiency of LAES is heat integration of the entire process in the plant.


INNOVATION IN LAES A significant benefit of LAES is that


much of the technology is old and well established. For years, components of LAES systems have been used in other processes across the industrial gases industry. While the fundamental technology is decades old, innovation is required to improve efficiencies and make LAES commercially viable. A search of patent databases indicates


that the patents in this field are directed towards the improvement of LAES system


Katie Smith, technical assistant of Reddie & Grose LLP


“Like other energy storage solutions, the idea of liquid air energy storage is to balance out electricity supply and demand.


During periods of high electricity production, rather than curtailing production, the excess energy is stored to be used later during periods of high demand”


efficiency and heat recovery. For example, EP2895810 is a patent application directed towards an improved version of the Claude cycle (a common process used for liquefying air). Using cold recovery, the process provides more cooling to the gas prior to liquefaction. The improved cooling increases liquid production. Other patents such as US9638068 propose liquid-air energy storage based on modifications to the Linde-Hampson cycle (another process for liquefying air) and heat integration. So far most research into LAES has been


limited to theory. To test the theoretical efficiencies, large-scale plants needing high initial investments are required. If the new Greater Manchester plant proves successful, it could be the turning point for industrial scale developments of LAES systems in the future and position the UK at the forefront of this renewable energy storage technology.


Reddie & Grose LLP www.reddie.co.uk


10 ENERGY MANAGEMENT - Winter 2021 www.energymanagementmag.co.uk


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