FST JOURNAL

UK industry accounts for approximately 15% of total UK energy consumption and 14% of UK greenhouse gas emissions. However, it is estimated that over half of the energy consumed by UK industry is wasted rather than put to productive use. Much of this energy is lost as heat due to system inefficiencies. Reducing these losses and developing systems to re-use surplus heat could cut energy costs for industry, lower the UK’s greenhouse gas emissions, and unlock new sources of heat for consumers. 

As the UK transitions to net zero, there is an opportunity to reimagine the role of heat in the UK energy system, thinking of it as a valuable resource rather than an unavoidable loss. 

Reducing heat losses and putting surplus heat to use will depend on the development and deployment of technologies to capture, transport, store and re-use heat. As the UK transitions to net zero, failing to reduce heat losses and improve efficiency risks locking in energy inefficiencies for decades to come. 

Reimagining heat use

The Royal Society has published its report Unlocking thermal energy that presents a vision of a UK thermal energy system based on heat cascades, where waste heat is captured and re-used across a variety of processes. In this vision, heat is captured at high-temperature point sources, such as factories or data centres, and then ‘cascaded’ through other uses (figure 1). The further the heat travels, the cooler it gets, which determines how it can be used. Under this model, the surplus heat could first be re-used on site, then used in adjacent industries, and finally sent further afield to warm homes, hospitals or offices.

Foundation industries such as the steel, glass, cement, and chemical industries, which form the backbone of UK manufacturing, rely heavily on high temperature heat in their production processes. Waste heat in these industries is often at a high temperature, potentially offering a valuable source of thermal energy suitable for capture, storage and re-use. 

There will also be novel opportunities to harness heat from emerging sources in the UK. Deployment of data centres, for instance, will provide new sources of surplus heat. Where data centres are situated in urban environments, the surplus heat they produce could be integrated into heat networks and used by nearby homes and buildings, providing a new low carbon heat source for consumers while simultaneously helping to cool data centres. 

Similarly, technologies associated with the transition to net zero, for instance carbon capture and storage or electrolytic hydrogen production, will provide new sources of heat. Integrating efficient systems that minimise thermal energy losses and capture residual heat during the development and deployment of these technologies will help avoid locking in inefficient processes and potentially later retrofit costs.

Transporting thermal energy

Re-using heat from existing and emerging sources in heat cascades will require the development of effective heat networks. Today, only 2% of UK buildings are heated via heat networks. This compares to approximately 61% in Denmark and 57% in Sweden (with 45% of the latter’s heat network supply being recovered waste heat). The CCC estimated 20% of UK buildings could be heated through heat networks by 2050. As the UK looks towards net zero, re-use of surplus heat from data centres, industry, or other hot point sources could provide an available low-cost, low-carbon heat source. 

The technologies required to enable transport of heat through heat cascades exist today. District heating networks are mature and deployed widely in Europe. These typically use separate flow and return loops which circulate hot water to buildings, which is then transferred for use in the building via a heat exchanger. These usually require heat energy to be at a high temperature. Newer-generation district heating networks can transport heat with increasing efficiency and can do so at lower temperatures suitable for indoor use. 

Thermal energy storage

Not all heat supply and demand aligns temporally. For instance, while some manufacturing processes might produce a steady stream of heat, demand for heat in the built environment is variable over daily and seasonal cycles. Thermal energy storage systems will be required to balance supply and demand. 

Heat can broadly be stored as i) sensible heat (heat that can be felt, e.g. by increasing the temperature of a medium like water), ii) latent heat (heat energy that is released during phase change of a material, e.g. from a solid to a liquid), and thermochemical heat (in which heat can be stored or released by reversible chemical reactions). For example, for inter-seasonal storage, heat can be stored in the subsurface using boreholes or aquifers. The aquifer is heated during times of surplus heat supply and low demand during the summertime and released for use during the winter (figure 3). 

Wider system requirements

Developing systems to re-use heat at scale depends on a variety of enabling factors alongside technological innovation. Principal among these is the need for systems to measure, value and trade heat. This will require suitable information on available heat resources. Certainty will also be central to heat re-use systems; heat users will require supply reliability, and producers will require demand certainty. Finally, underpinning this system is a need for a suitable regulatory environment, a skilled workforce, collaboration between system actors, and technology development and demonstrations. 

Heat loss is not a challenge unique to the UK. The technologies and processes used in energy systems across the world have inherent inefficiencies. Therein lies an opportunity for UK technology development. Should the UK take a leading role in the development of efficient technologies and systems to capture and re-use heat, there may be an opportunity to become an exporter of these technologies. 

To enable the development of a system to effectively harness surplus thermal energy, the Royal Society’s report proposes that industrial thermal energy efficiency and re-use should be integrated into national decarbonisation and industrial strategies. The transition to net zero is a period of opportunity to integrate thermal efficiency and re-use measures into new infrastructure and systems. 

Enabling heat cascades will also, in part, rely on good data. Further assessment of potential waste heat supply and heat demand, including how these vary over space and time, would further understanding of the quality and quantity of waste heat and its potential for re-use. 

Alongside assessment of the UK’s waste heat resource, appropriate governance and financial mechanisms will be necessary to enable the valuation and trade of heat. Finally, supporting technology development and deployment could enable the UK to become an innovation leader on thermal energy efficiency and re-use technologies. 

Reimaging waste heat as a valuable resource, and deploying the solutions to enable its capture, transport, storage and re-use, could support the UK’s journey to net zero, reduce energy demand and associated costs, and provide new local sources of heat for communities.