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 the “CRYOBattery” will be the largest liquid-air energy-storage system in the world.
Use of renewable energy to power the UK electricity grid has never been higher. Wind and solar are sustainable, but their output varies with environmental conditions. This makes balancing the grid a significant challenge. 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.
In our blog last year we discussed innovation in electricity storage, following a detailed report by the European Patent Office and the International Energy Agency on patenting activity in this field. The report suggested that battery storage is the main area of innovation, and in particular that lithium-ion batteries may be essential in meeting our future energy storage needs. Lithium-ion batteries are very useful for portable storage such as in electric vehicles. For larger-scale storage they can be difficult and costly to scale up, but perhaps not impossible, as shown by Tesla’s Hornsdale Power Reserve. Another option is pumped-storage hydropower, which in 2019 accounted for 90% the world’s energy storage for stationary applications. Pumped storage offers large-scale energy storage, but it is geographically constrained, capital intensive and impactful on the environment.
Liquid Air Energy Storage (LAES)
The main benefit of LAES is to provide medium to long duration energy storage, believed by some to be crucial in complementing the short-duration storage provided by batteries.
Like other energy-storage solutions, the idea of LAES is that during periods of high electricity production (i.e. when there is a lot of wind), rather than curtailing production, the excess energy is stored, to be used later during periods of high demand.
LAES comprises three stages.
The first stage 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 a high-pressure gas, the air is then cooled by heat exchange with a cold fluid. The cold compressed air is then expanded. This expansion further decreases the temperature of the air, condensing it to liquid form at around -196oC.
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 then 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; LAES needs to have efficiencies to rival battery storage.
To achieve this, LAES plants recycle the waste cold that results from the discharge stage, to help cool incoming air when charging. This reduces the amount of power used for cooling and increases overall efficiency. The heat produced by initial compression of the gas during charging can also 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 gas industry. But although the fundamental technology is decades old, innovation is required to increase efficiency 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 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. As a result, the efficiency of the system is increased, and crucially the price per unit of power can be reduced. 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 achieve commercially-viable efficiencies large-scale plants are required and therefore a high initial investment in equipment is needed. If the new “CRYOBattery” plant proves successful, it could be the turning point for industrial-scale developments of LAES systems in the future.
This article is for general information only. Its content is not a statement of the law on any subject and does not constitute advice. Please contact Reddie & Grose LLP for advice before taking any action in reliance on it.