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.

The UK electricity system faces challenges of unprecedented proportions. It is expected that 35 to 40% of the UK electricity demand will be met by renewable generation by 2020, an order of magnitude increase 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 the incorporation of heat and transport sectors into the electricity system. The key concerns are associated with system integration costs driven by radical changes on both the supply and the demand side of the UK low-carbon system. Our analysis to date suggests that a low-carbon electricity future would lead to a massive reduction in the utilisation of conventional electricity generation, transmission and distribution assets. The large-scale deployment of energy storage could mitigate this reduction in utilisation, producing significant savings. In this context, the proposed research aims at (i) developing novel approaches for evaluating the economic and environmental benefits of a range of energy storage technologies that could enhance efficiency of system operation and increase asset utilization; and (ii) innovation around 4 storage technologies; Na-ion, redox flow batteries (RFB), supercapacitors, and thermal energy storage (TES). These have been selected because of their relevance to grid-scale storage applications, their potential for transformative research, our strong and world-leading research track record on these topics and UK opportunities for exploitation of the innovations arising. At the heart of our proposal is a whole systems approach, recognising the need for electrical network experts to work with experts in control, converters and storage, to develop optimum solutions and options for a range of future energy scenarios. This is essential if we are to properly take into account constraints imposed by the network on the storage technologies, and in return limitations imposed by the storage technologies on the network. Our work places emphasis on future energy scenarios relevant to the UK, but the tools, methods and technologies we develop will have wide application. Our work will provide strategic insights and direction to a wide range of stakeholders regarding the development and integration of energy storage technologies in future low carbon electricity grids, and is inspired by both (i) limitations in current grid regulation, market operation, grid investment and control practices that prevent the role of energy storage being understood and its economic and environmental value quantified, and (ii) existing barriers to the development and deployment of cost effective energy storage solutions for grid application. Key outputs from this programme will be; a roadmap for the development of grid scale storage suited to application in the UK; an analysis of policy options that would appropriately support the deployment of storage in the UK; a blueprint for the control of storage in UK distribution networks; patents and high impact papers relating to breakthrough innovations in energy storage technologies; new tools and techniques to analyse the integration of storage into low carbon electrical networks; and a cohort of researchers and PhD students with the correct skills and experience needed to support the future research, development and deployment in this area.

This project will assess a class of systems that blend electricity generation and storage, to understand the role that they could play in future energy systems. Their ability to deliver low-carbon energy on demand, at low system cost, will be investigated from technical, economic, and policy standpoints. With a growing fraction of electricity consumption being supplied by variable renewable energy sources, the ability to match energy generation and energy consumption is rapidly taking centre stage. Flexible ('dispatchable') coal and gas plants are being displaced to lower carbon emissions. At present, both nuclear and renewable energy technologies are generally configured to generate as much electricity as possible, regardless of the electricity demand at the time. Standalone energy storage, in which surplus electricity is converted to an intermediate energy form and then back again, is emerging as a vital partner to these generation technologies but it is prohibitively expensive for the duties that will be required in the near future. Active management of electricity demand (by shutting down or deferring loads) and electrical interconnections with neighbouring countries will also play important roles but these also have costs and they will not obviate the need for storage. This project will build a deep understanding of a class of system which takes a different and potentially much lower cost approach. These Generation Integrated Energy Storage (GIES) systems, store energy in a convenient form before converting it to electricity on demand. The hypothesis is that the lowest cost and highest performance storage can be achieved by integrating generation and storage within one system. This avoids the expense and inefficiency of transforming primary energy (e.g. wind, solar, nuclear) into electricity, then into an intermediate form, and later back to electricity. For example, the heat produced by a concentrating solar power plant can be stored at far lower cost and with lower losses than producing electricity directly and operating a standalone electricity store. A broad range of opportunities exist for low-carbon GIES systems, in both renewable and nuclear applications. The research team's expertise in wind, nuclear, and liquefied air storage will be applied directly to GIES systems in all three. The project will also establish a framework for the wider significance of GIES to energy systems. Technical and thermodynamic metrics that characterise high performing GIES systems will be developed, and used to compare with standalone generation and storage equivalents. The theoretical groundwork laid by this research will have applications far beyond the current project. Opportunities for current and future technologies will be mapped out and publicised, supporting and accelerating further work in the field. The deployment and operation of such technologies will be modelled by means of a pragmatic real options economic analysis. The unique policy and economic considerations of fusing generation and storage will be reviewed in detail, considering challenges and proposing solutions to regulatory and financial hurdles. Taken in concert, these will determine the value and scope for substantial deployment of GIES systems. In bringing to light the potential of the class of GIES systems, the research team will rectify a gap in energy systems thinking, in time to inform what will be a multi-billion pound expenditure in the coming decade. By providing the tools to analyse and deploy these systems, the research will open up a new avenue for cost-effective flexibility across the energy infrastructure of the UK and other regions worldwide.

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.

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.