Energy storage plays a crucial role in building a sustainable energy system. New technology tackling challenges in the area of domestic space heating and water heating will make significant contributions to the energy consumption,CO2 emission, and to improve the quality of life, because among all energy consumed by end users, ~45-47% is for domestic space heating and water heating accounts for another 40%. Among different storage technologies, thermal energy storage provides a unique approach for efficient and effective peak-shaving of both electricity and heat demand, efficient use of renewable energy from wind, tide and sun, and low grade waste heat, as well as distributed energy and backup energy systems. In Europe, it has been estimated that around 1.4 million GWh per year could be saved-and 400 million tonnes of CO2 emissions avoided by thermal energy storage. Despite the importance and huge potential, very limited research has been done in the area. Phase Change Material (PCM) based technology has a great potential to provide a cost effective solution to the problem, if we can tackle the density and efficiency challenges and overcome the cost barrier. PCMs have an energy density 3-6 times higher than the use of water as a storage medium, and have the potential to compete with sensible heat storage materials such as MgO in terms of cost per unit kWh and is far more compact, and is cheaper than the electrochemical thermal storage. Thus, this bears significant national importance to the UK energy system, peak-shaving and quality of life, but composite PCMs for domestic heating is severely understudied. This project, building on individual achievements in nanocomposites and in thermal storage research and adopting a multi-institutional and experimental-modelling approach, aims to develop new PCM-based nanomaterials, that are suitable for high energy density (6 times higher than existing technology), affordable and sustainable PCM-based composite thermal storage device applications. It primarily addresses the Materials and Materials Design aspect of this Energy Storage Challenge Call to provide high energy and power density. The project will also develop experimental and modelling Diagnostic Tools, in order to monitor and maximise the efficiency of the PCM composite deveice. The well-organised investigators from five different research groups of three universities, will first tackle the fundamental PCM composite challenges to solve the low conductivity, thermal expanson and supercooling issues, then move on to investigate at module and system levels to assist validate and optimise the new PCM composites, to achieve optimal device thermal effiency over 92-95%, with >at lease 25% electricity bill saving, 40% weight reduction and 6000 cycle duration. Finally we will construct example domestic space heater to demonstrate the practical improvement of our materials, and we will deliver 10 kW high effiency, compact and low cost device prototypes for demonstration at the Nottingham Creative Homes.

Project aim This project proposes a solution for integrated supply of zero carbon heating and cooling using near ground temperature networks that enable buildings to use heat pumps and cooling machines to exchange thermal energy with the network and meet their heating and cooling demand. When a building demands cooling, it rejects its excess heat to the network that can balance the heating demand of another buildings. Therefore, in this project we refer to such networks as 'balanced heating and cooling network' (BHCN). Key contributions of this research are: (i) To investigate the optimal design and operation of BHCN using a multi-objective optimisation approach to balance costs of the system and the value it can provide to the whole power grid via providing flexibility services. In particular, we will examine inter-seasonal heat storage, and also the feasibility of using NH3 and CO2 (as alternatives to water) for heat transport mediums in BHCNs. (ii) To design a local heat market that enables peer-to-peer (P2P) heat sharing to maximise the use of zero carbon sources of thermal energy on-site, and (iii) To identify technical, regulatory and policy barriers against implementing BHCNs (i.e. managing the transition from status quo to BHCN). This research will also build significant UK research capacity in zero carbon and ambient temperature heat networks. Background The need for decarbonising heat supply: According to the 2017 Clean Growth Strategy, the UK Government believes 'decarbonising heat is our most difficult policy and technology challenge to meet our carbon targets'. Progress on energy efficiency and low carbon heat provision remains below expected levels and natural gas infrastructure continues to be expanded which poses risk to achieving the recently set net zero goal for 2050. The role of heat networks: The Clean Growth Strategy suggests 17% of domestic heat and between 17% and 24% of service sector heat could be provided through heat networks in 2050. The Committee on Climate Change suggests around 5 million homes could use district heat by 2050 based on techno-economic modelling. However, heat network growth is slow despite requiring around a tenfold increase from the current level by 2050. The growing demand for cooling: Coinciding with the crucial need for supplying low carbon heat, the demand for cooling is also increasing in the UK (and globally) due to population increase and climate change impacts which are leading to more frequent heatwaves and temperature rises. According to BRE, up to 10% of all UK electricity use is for air conditioning and cooling. Because of this established trend toward increased use of cooling, the proportion of UK electricity used for cooling is expected to rise further. A potential solution for zero carbon supply of heating and cooling: Balanced Heating and Cooling Networks (BHCN), are a form of district heating system which circulates water at near ground temperature to buildings allow them to use their own heat pumps to extract heat for heating, or to export heat to the network when cooling is required. BHCNs address many of the drawbacks of conventional heat networks through operating at reduced temperature and therefore minimising heat losses and reduce the cost of highly insulated pipes. They also open up opportunities for integrating various sources of renewable heat into the networks. The circuit can also be extended to new buildings at limited cost. Work Programme WP1 - Case study definition WP 2 - Assessing renewable heat sources and inter-seasonal storage WP 3 - Techno-economic appraisal of BHCN WP 4 - Development of a methods and tools for Peer-to-Peer (P2P) heat sharing WP 5 - Managing implementation and transition to BHCNs

Heating indoor spaces by burning natural gas accounts for ~30% of the UK's total CO2 emissions. Around 23 million properties are connected to the gas network. Each 1kg of gas burned delivers ~12kWh of heat and releases ~4kg of CO2. That cannot continue in a future net-zero UK and capturing CO2 at individual buildings is completely implausible using any known technology. Many consider that hydrogen should replace natural gas in the gas network. Technically, this is feasible. Hydrogen can be produced from electrolysis or from natural gas. In case of the latter, 'carbon-capture' methods can collect most of the resulting CO2 and pump that underground. However, distributing hydrogen through the gas network might not necessarily be the most sensible course of action in all cases. This project will answer the question about how best to use different parts of existing gas network in a future net-zero UK. Even with carbon-capture, producing hydrogen from natural gas does cause some CO2 emissions. Typically >5% escapes. Using renewable electricity to make 'green' hydrogen via electrolysis and then burning that in boilers delivers less than 7kWh of heat into homes for every 10kWh of electricity used. By contrast, using electrically driven heat pumps can deliver 40kWh of heat for every 10kWh of electricity consumed. Although there are other advantages to producing hydrogen for heating, it remains questionable whether this is optimal in many parts of the UK. It is very likely that a large fraction of the existing infrastructure will be used for distributing hydrogen across the country. However, some specific parts of the network could be better exploited in a different way. This project will explore the different possible uses for those parts of the gas network. All of these potential uses are motivated mainly by solving problems that would arise if heat pumping were deployed very extensively in the UK as the primary heating mechanism. One possible future use for parts of the gas network is to feed non-potable water into properties. This water could serve as the source of low-temperature heat to support heat pumps. A new variety of heat pump turns incoming water into an ice slurry and discards the slurry to melt again later. This 'Latent Heat Pump' (LHP) can extract a lot of heat out of cold water (12L of water provides ~1kWh of heat). That heat emerges from the water at about 0C and as a consequence, the LHP can have a coefficient-of-performance (COP) >4 even when the outside air is very cold. For most air-source heat pumps, the COP falls sharply in very cold weather and, for obvious reasons, the COP matters most in very cold weather. A second possible future use for the gas network is to serve as a return (collection) network rather than as a delivery (distribution) network. Here, the fluid returning through the gas network would be an aqueous solution of a chemical that was hydrated (mixed with water) at the property to release heat. This measure would be taken only in very cold weather. Calcium Chloride and Magnesium Sulphate are two very cheap salts that release heat when dissolved in water. There are other inexpensive substances that release large quantities of heat upon reacting with water. Finally, if water was being conveyed in the low-pressure tiers of the gas network, the high-pressure tiers of the gas network would be free for another use. A very attractive possibility here would be to use those parts as the pressure vessel for a compressed air energy storage system. That system would simultaneously be able to assist the electricity transmission system by doing a parallel transmission from North to South at times of high North-South power traffic. How acceptable each of these propositions is to key social stakeholders (including policy makers, prospective business, and public end-users) will be integral to their real-world viability, and so will be examined here also.

The last deep coal mine in the UK closed in 2015. The Coal Authority has a record of 177,000 known mine entries. This proposal examines the potential to use abandoned mine shafts for interseasonal storage of curtailed wind energy in the form of thermal energy. In 2020, wind curtailment payments in the UK were £282M: enough to power 1.25 million homes and equivalent to £4 per MWh of energy generated. There is 120GW of 'spare' electricity in East Ayrshire alone. Thermal stores have been studied previously but are limited by size and the need to insulate. Flooded mine shafts are ubiquitous across much of the UK, yet the thermal storage opportunity within shafts has never been explored. The rock mass around the shafts are insulators and pilot work by our consortium has shown that as the rocks heat up the efficiency of the heat extraction rises considerably in as little as three years. We will investigate the feasibility of using the spare electricity on windy days to heat up water in abandoned mine shafts, to be extracted on cold days by heat pumps into homes and businesses. The UK is peppered with mine shafts from the days of coal mining - we want to turn these holes in the ground into thermal stores to help balance the electrical grid and to decarbonise homes and businesses. Mine shafts were lined with concrete or brick (sometimes unlined). To safely and efficiently utilise this legacy subsurface infrastructure we need to understand the effect of heating up the water in the mine shafts on: the water body in the shaft, which may be naturally stratified and will contain minerals that could cause contamination or scaling; on the lining material, which is likely to have degraded in the decades since mine closure; on the surrounding rocks and the water they contain (in pores and fractures). We will develop sophisticated coupled thermal-hydraulic-chemical-mechanical (THCM) modelling informed by case studies we develop from an assay of the UK's shafts, as well as data collected from a test site. We will also take a whole-systems approach to looking at how such an energy store could sit within the wider energy system, taking into account the economics of such a project, and any carbon emissions generated through construction and operation of a site. We are planning a test at a site where we drill into a shaft to retrieve samples of water and capping materials for analysis, and then monitor the injection of heat to validate our models. The example shaft that we are proposing to work on is the Barony colliery, once the deepest in Scotland. Our project partners, East Ayrshire Council have funding for an observation hole close to the site that will provide a baseline of data for the modelling and for observing the progress of our experiment. The outputs of this work will be applicable for assessing the mine shaft thermal store resource at mine shaft sites across UK coalfields, any risks associated with utilising that resource, and the optimal way to use that resource within the local energy system. We will also provide useful new data for the more well-understood concept of extracting natural geothermally recharged heat from mine workings; for consideration of the best way to abandon active mines so that they are thermal storage-ready; produce a fully coupled THCM model of mine shafts and the surrounding rock mass; and develop the first integrated energy system model to include subsurface infrastructure and geology.

Decarbonising both heating and cooling across residential, business and industry sectors is fundamental to delivering the recently announced net-zero greenhouse gas emissions targets. Such a monumental change to this sector can only be delivered through the collective advancement of science, engineering and technology combined with prudent planning, demand management and effective policy. The aim of the proposed H+C Zero Network will be to facilitate this through funded workshops, conferences and secondments which in combination will enable researchers, technology developers, managers, policymakers and funders to come together to share their progress, new knowledge and experiences. It will also directly impact on this through a series of research funding calls which will offer seed funding to address key technical, economic, social, environmental and policy challenges. The proposed Network will focus on the following five themes which are essential for decarbonising heating and cooling effectively: Theme 1 Primary engineering technologies and systems for decarbonisation Theme 2 Underpinning technologies, materials, control, retrofit and infrastructure Theme 3 Future energy systems and economics Theme 4 Social impact and end users' perspectives Theme 5 Policy Support and leadership for the transition to net-zero