Energy storage is an essential technology for balancing the differences in supply and demand in a sustainable power network reliant on intermittent renewable generation. Energy can be stored as electricity, as heat and chemically in a sustainable fuel and at different temporal and size scales. Short time variations in the power grid can be effectively managed using batteries but the battery technologies are too expensive for servicing the bulk long term storage requirements to balance variations in demand between seasons and extended periods of low renewable generation. Technologies with a slower response, lower round trip efficiency but lower capital base are preferred for these applications. Liquid Air Energy Storage (LAES) is a long duration storage technology being developed by Highview Power. Energy is stored thermally in three ways; as cold in liquid air and in a backed bed regenerator cold store and as heat in a molten salt hot store. An air liquefier is used to charge the LARS device. LAES has a sweet spot at large (>50MW) scale as plant efficiency increases and relative cost reduces with scale for this technology. But what would happen if a LAES plant could be efficiently deployed at smaller (<50MW) scale? The technology could then 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. In this project, we will investigate the integration of a small to mid scale LAES plant with the liquefaction of locally produced bio methane from waste, such as agriculture, managed grass land (such as parks and sports fields) and sewerage. Similarly, hydrogen produced by small to mid size electrolysers connected to local renewable generators requires a storage solution. We propose cold, pressurised storage of hydrogen at 80-90K which lowers the pressure required to store the gas (for an equivalent energy density) by a factor of 2 to 3 and avoids the high energy cost of cryogenic storage at 20K. Integration of LAES with methane and hydrogen storage opens up new revenue steams and shifts the economics to favour smaller plant serving local communities such as large farms, local authorities and water companies managing sewage waste. We propose a local rather than central solution as (a) the feedstocks for bio-methane production have a low energy density to local production and storage avoids transportation inefficiencies (b) Similarly local production and consumption of hydrogen avoids the need to move cold pressurised gas to bulk storage facilities and then to consumers and (c) imbedding the core electrical energy storage of the LAES plant closer to the end user has benefits in reducing the load on the transmission network.

Compressed Air Energy Storage (CAES) uses compressors to produce pressurised air while excessive power is available; the pressurised air is then stored in air reservoirs and will be released via a turbine to generate electricity when needed. Compared with other energy storage technologies, CAES has some highly attractive features including large scale, long duration, and low cost. However, its low round trip energy efficiency (the best CAES plant currently in operation has a 60.2% round trip efficiency) and low energy density cause major concerns for commercial deployment. The conversion of electricity to heat and storing the heat via thermal storage is a relatively mature and a highly efficient technology; but the conversion of the stored thermal energy back to electricity has a low energy efficiency (less than 40%) through (conventional and organic) Rankine cycles, thermoelectric generators, and recently proposed thermophotovoltaics. The project aims to develop a Hi-CAES technology, which integrates the CAES with high-temperature thermal energy storage (HTES) to achieve high energy conversion efficiency, high energy and power density, and operation flexibility. The technology uses HTES to elevate CAES power rate and also convert high-temperature thermal energy to electricity using compressed air - a natural working fluid. The proposed technology is expected to increase CAES's electricity-to-electricity efficiency to over 70% and overall energy efficiency to over 90% with additional energy supply for heating and cooling. The proposed Hi-CAES will also increase the storage energy density and system power rate significantly. Meanwhile, the technology can convert the stored thermal energy into electrical power with a much higher energy conversion efficiency and lower system cost than current thermoelectrical energy storage technologies. With the integration of HTES with CAES, the system dynamic characteristics and operation flexibility can be much improved in terms of charging and discharging processes. This will place Hi-CAES in a better financial position as it can generate revenue through certain high market value fast response grid balance service. The goal of the project is to improve both the CAES efficiency and energy density considerably through the integration with a HTES system. The research will address the technical and scientifically challenges for realisation of the Hi-CAES system and societal challenges of deep power system decarbonisation.

The energy systems in both the UK and China face challenges of unprecedented proportions. In the UK, it is expected that the amount of electricity demand met by renewable generation in 2020 will be increased by an order of magnitude from the present levels. In the context of the targets proposed by the UK Climate Change Committee it is expected that the electricity sector would be almost entirely decarbonised by 2030 with significantly increased levels of electricity production and demand driven by electrification of heat and transport. In China, the government has promised to cut greenhouse gas emission per unit of gross domestic product by 40-45% by 2020 based on the 2005 level. This represents a significant challenge given that over 70% of its electricity is currently generated by coal-fired power plants. Energy storage has the potential to provide a solution towards these challenges. Numerous energy storage technologies exist currently, including electrochemical (batteries, flow batteries and sodium sulphate batteries etc), mechanical (compressed air and pumped hydro etc), thermal (heat and cold), and electrical (supercapacitors). Among these storage technologies, thermal energy storage (TES) provides a unique approach for efficient and effective peak-shaving of electricity and heat demand, efficient use of low grade waste heat and renewable energy, low-cost high efficiency carbon capture, and distributed energy and backup energy systems. Despite the importance and huge potential, little has been done in the UK and China on TES for grid scale applications. This forms the main motivation for the proposed research. This proposed research aims to address, in an integrated manner, key scientific and technological challenges associated with TES for grid scale applications, covering TES materials, TES components, TES devices and integration. The specific objectives are: (i) to develop novel TES materials, components and devices; (ii) to understand relationships between TES material properties and TES component behaviour, and TES component behaviour and TES device performance; (iii) to understand relationship between TES component behaviour and manufacturing process parameters, and (iv) to investigate integration of TES devices with large scale CAES system, decentralized microgrid system, and solar thermal power generation system. We bring together a multidisciplinary team of internationally leading thermal, chemical, electrical and mechanical engineers, and chemical and materials scientists with strong track records and complementary expertise needed for comprehensively addressing the TES challenges. This dynamic team comprises 15 leading academics from 4 universities (Beijing University of Technology, University of Leeds, University of Nottingham and University of Warwick, and 2 Chinese Academy of Sciences Research Institutes (Institute of Engineering Thermophysics and Institute of Process Engineering), and 7 industrial partners.

Increased energy storage storage is needed on the electrical network to support high levels of variable renewable electricity such as wind and solar to enable us to reach our net-zero goals. The UK network currently has 5.3GW of energy storage of which 1.3GW is battery energy storage and this is expected to grow by at least 8GW by 2030. However, this alone does not meet the estimated required capacity, we therefore need to use the storage that we have optimally, for example, the location of storage and when we use it is critical to avoid congestion on the network. We also need to promote the installation of different types of storage that can operate over different time scales so that for example excess generation in one season can be used in the next. The aim of the project is to determine how different distributed energy storage assets, of different sizes and technologies, can be integrated into the grid as part of a whole-system solution to enable adaptability, flexibility and resilience. The project will investigate where and how assets are connected to the grid, how they are controlled and what policies and market conditions are required to meet our storage requirements. The research will be carried out across 5 collaborating institutions with the work underpinned by experiments using operational grid-scale storage demonstrators operated within the consortium. The outputs will include: - Recommendations for optimal planning and scheduling of distributed storage under different policy and market conditions including incentives/regulation of locational deployment - The impacts of different levels of coordination of distributed storage across location, scale, and markets - Demonstrations of practical, scalable solutions for the coordinated control of storage assets and other sources of flexibility - A roadmap that describes the decision points and options for the energy system as distributed energy storage grows according to different scenarios to 2035.

Decarbonising the energy system in many countries (including both China and the UK) is likely to involve the large-scale deployment of renewable electricity generators with intermittent output and the electrification of energy services such as heat and transport that have very low load factors. These changes in electricity supply and demand will lead to a great need for energy storage. Our work for the Carbon Trust has estimated that the effective deployment of energy storage in the UK could reduce the cost of a low-carbon electricity system by £15 billion in 2030. The deployment and operation of storage is a complex task, since it can provide many different services, including energy arbitrage (buying off-peak and selling at higher peak prices), energy reserves, resolving transmission and distribution constraints and improving system reliability. The weight placed on each of these could affect the pattern of investment, and sophisticated planning tools are required to ensure that optimal decisions can be taken. We will improve these tools so that we can accurately represent a variety of storage systems. Much of the existing work on storage assumes that it might be used simply to postpone the "like for like" replacement of network assets that would otherwise be overloaded, but we will consider more radical options, using storage to actively manage the distribution network as part of the broader smart grid. We can use our models to calculate the economic value of energy storage when it provides a range of services to network companies and system users. We will measure the option value of having a storage system that can be deployed in much less time than it takes to get consent to build a transmission line, adding flexibility in how we respond to uncertainty over the future evolution of the energy system. It is important that such decisions are made on the basis of appropriate models, capable of quantifying the wide range of services that storage can provide, taking account of the way that electricity generation and demand varies over the course of the day and the year, and measuring the impact of transmission and distribution network effects. It is important to recognise that many countries (including the UK) have liberalised their electricity industries, and storage will only be pursued if companies believe that a viable business case exists. Work has started (via the Low Carbon Networks Fund) to test particular business models for demonstration projects, but this needs to be generalised. We will provide a quantified assessment of whether there is a business case for energy storage at present, and of what needs to be done to create one. This will involve a detailed study of the contracts that would be written around electricity storage, drawing lessons from existing arrangements for other kinds of storage, such as for gas or agricultural commodities. We will study how the rules of the electricity market could affect the choices of storage and generation technology. We will ask what policies are needed to ensure that storage can be economically viable when sensibly deployed and operated. We will identify technology policies that can help move energy storage from prototypes to large scale deployment. International transmission may complement energy storage within a country, and we will assess the potentially conflicting incentives if neighbouring countries adopt different strategies for dealing with intermittency. Too many debates around energy policy today are based on assertions without sufficient evidence. The models that we will develop, and the analysis that we will perform, will provide numerical estimates of the effectiveness of a range of policies, allowing regulators and other policy-makers to choose options that will lead to decarbonisation in the most effective way.