How can storing heat help to decarbonise energy systems?

Decarbonising heat is key to achieving net zero. Innovators from the Birmingham Centre for Energy Storage are playing a vital role.

Reducing carbon dioxide emissions is, undoubtedly, the key element in our global drive to tackle climate change. The popular imagination is captured by a vision of polluting petrol and diesel vehicles yielding to a utopian vision of electric vehicles propelling us into a cleaner future. Power-hungry factories, offices and homes will be fed a lean-burn diet of electricity generated from renewable and low-carbon sources, such as solar and wind.

As important as electricity is, it only provides part of the overall energy demand within a country. Other energy vectors such as liquid fuels and natural gas typically provide greater amounts of delivered energy (see Figure 1). There is a significant contribution from transportation fuels and an even bigger demand associated with heat, which accounts for some 51% of global energy use.

Graph showing gas, liquid fuels and electricity daily demand for Great Britain from January 2017 to September 2020.Figure 1 - Gas, liquid fuels and electricity daily demand for Great Britain.
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Decarbonisation in the UK has focussed on electricity rather than heat for a number of reasons, the main one being that decarbonising electricity was seen as being potentially easier to decarbonise first - meaning decarbonisation of other areas such as transport and heat could follow. Electricity has typically been generated by power stations at a scale from hundreds of megawatts to many gigawatts, which were managed to match the electrical demand by increasing and decreasing output to suit. Although Britain’s electrical system has decarbonised, the flexibility and resilience that underpins the system is still mainly based on fossil fuels; natural gas more than coal.

As with electricity supply grids, gas networks face supply and demand challenges – for example managing early morning demand on local gas networks throughout the heating season from October to March. This is a challenge traditionally met by gas network operators as they increase network pressure to store more gas in pipelines overnight, so it is ready to meet the significant pick-up in demand from 5am.

Given the historic paradigm of buildings simply being a demand at the end of networks, the concept of ‘active buildings’ becomes an important step in accommodating greater and greater levels of low-carbon energy onto energy systems. The hope is that buildings are not just energy efficient to reduce the demand on networks, but that they incorporate novel ways of creating, storing, controlling and releasing energy. In this way they can contribute towards balancing energy networks to a greater degree, which has a number of advantages in terms of cost and resilience.

University of Birmingham scientists are contributing to the Active Building Centre – a collaborative project that supports the UK Government’s ambitious targets for the country to reach net zero carbon emissions by 2050. Funded through the Transforming Construction Challenge, the Centre connects commercial and academic partners in a quest to transform the way Britain’s buildings are designed, constructed and operated.

Active Building Centre'The Active Office' - the UK's first energy positive office. Image credit: Active Building Centre.

Dr Grant Wilson, Lecturer in the School of Chemical Engineering at Birmingham is clear about the way forward.

“Any solution to the energy crisis will have to address the issue of energy in buildings. Active buildings have the potential to substantially reduce both the operational costs of buildings themselves and their impact on the UK energy infrastructure. They present an exciting means of balancing the system – supporting wider networks by harvesting and storing thermal and electrical energy, and making a valuable contribution towards the decarbonisation of heat.

“Thermal energy storage is a major focus of our research in the Birmingham Centre for Energy Storage. As part of this the Energy Informatics Group is focussing on the evidence base to support our hypothesis that thermal energy storage will be an increasingly important technology to support the decarbonisation of energy systems. The technology promises to be an excellent way of accommodating more renewable energy sources onto the system.”

Thermochemical testing rigThermochemical storage rig built at the Birmingham Centre for Energy Storage.

The University of Birmingham has taken a strategic lead in the UK’s drive to decarbonise heat – working closely with the Confederation of British Industry (CBI) on a joint heat policy commission. This commission recommended that a National Delivery Body for heat is established; an independent body working with the UK Government on creating, co-ordinating and delivering a national decarbonisation of heat programme - locally formulated and delivered by local authorities.

Making decarbonisation policy work in practice, in Britain and beyond, however, will depend on the deployment of effective novel technologies. Work at the Birmingham Centre for Energy Storage (BCES) focusses on the development of cost-effective and energy-and-resource-efficient thermal energy storage technologies based on both novel phase change materials and thermochemical materials.

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Current thermal energy storage (TES) technologies fall into three broad categories: sensible heat storage, thermochemical energy storage, and phase change material (PCM)-based latent heat storage. Sensible heat storage has a large footprint and is difficult to control temperature.  Thermochemical storage technology has been regarded in the early stages of development, but recent research at BCES has made significant progress through industrial funded programmes. Both PCM-based latent heat storage and thermochemical based storage technology benefit from higher energy density and smaller footprint, with the PCM based technology also enjoying charging/discharging processes at a near-constant temperature. These make PCM thermochemical technologies highly-promising inclusions into future active buildings and networks.

“Most of our work is about taking carbon out of energy systems – enabling decarbonisation policy to be implemented. Active Buildings hold great promise in balancing networks and decarbonising thermal and electrical power, with thermochemical storage - a next generation technology that can deliver significant impact,” explains BCES Director Professor Ding.

“Internationally, we are working with Beijing District Heating Group to build a commercial demonstrator that could eventually see this technology incorporated into neighbourhood heating systems serving tens of millions of people and helping to remove significant amounts of carbon from the city’s thermal energy production.”

The BCES team invented composite phase change materials (cPCMs) - substances that absorb and release thermal energy during the process of melting and freezing. The materials recharge as everyday temperatures fluctuate, making them ideal for a variety of everyday applications that require temperature control. More importantly, the cPCMs developed by BCES can be used directly as the feed material at their end of service life.

BCES’ collaboration with Jinhe Energy has already led to a world-first commercial plant, in Xinjiang, which harnesses wind power for heating. Funded by UK EPSRC and the Natural Science Foundation of China, the project has taken wind power that would otherwise have been wasted and converted it into heat. This thermal energy is then stored in cPCM materials and used for space heating on a commercial scale.

Filmed in 2019: The world's first commercial composite Phase Change Material plant for curtailed wind power.

The cPCM-based TES technology has a long lifespan and is fully recyclable - reducing environmentally damaging emissions, whilst promising future development of clean, cheap and reliable energy systems that can respond to fluctuating supply and demand. The Xinjiang demonstration plant launched in 2016 and replaced coal-fired heating boilers to warm an area approximately 60,000m2. Operating commercially, it has since achieved significant benefits in harnessing over 34,500 MWh of otherwise wasted wind power and reducing carbon dioxide and sulphur dioxide emissions by 12,000 tonnes and 40 tonnes respectively. This is the equivalent of saving 3,600 tonnes of coal.

The strong potential for global application of cPCM-based TES technology has led the UK government to back the research - a BEIS-funded project with AMP Clean Energy is now working on cPCMs for waste heat recovery for heating decarbonisation in the UK.

“Our work on cPCM and thermochemical based TES technology can undoubtedly contribute a great deal to decarbonisation of thermal energy, both in the UK and globally, but as a consequence of the environmental impacts there are also benefits for health and wellbeing with the reduction in fossil fuels being burned to provide heat,” adds Professor Ding.

“Air pollution is a major health issue for over 90% of the world’s population who live in areas exceeding WHO guidelines on healthy air. Using this technology in Xinjiang has clearly contributed to improvement in local air quality by reducing particulate matter from burning coal – offering global promise for a cleaner, brighter future.”

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