For a country bent on rapidly reducing its carbon footprint, few things are more lamentable than seeing vast amounts of heat, generated by all sorts of installations, go to waste. In 2021, it was estimated that 310 TWh/y was being squandered in the UK – it could be more by now. Waste heat is a resource begging to be exploited far more widely.

That’s something the government intends pursuing as part of its plan to beef up the number of district heating networks in the UK. These are systems of insulated pipes that take heat from a central source and deliver it to a group of buildings. The source can be a combined heat and power (CHP) plant; or heat recovered from industry and urban infrastructure, canals and rivers, mines or waste plants.

Association for Decentralised Energy (ADE) interim CEO Caroline Bragg says heat networks are the ‘only internationally proven route’ for decarbonising heat at scale – ‘established and now entering a new era… building at scale is the next step’.

In 2021, consultant Arup produced a report for the UK government to examine opportunities for bringing more networks onstream. Its focus was on exploiting renewable and recovered heat sources that otherwise cannot be used – now a task for the Department for Energy Security and Net Zero (DESNZ), established in February 2023, to take forward.

The UK Climate Change Committee estimates that 18% of the UK’s heat will need to come from heat networks by 2050 if carbon targets are to be met cost-effectively. Long-term, these are forecast to be cheaper than individual building heat pumps given the economies of scale.

Heat network zones
Following the Arup report, a local pilot programme was launched in January 2022 to develop and refine an approach to creating heat network zones, in which heat networks could be the most cost-effective option for heating buildings. This was also to understand how to identify and designate these zones. It brought together central government, 28 local authorities, zoning technical consultants and model developers.

At 2021 prices, the bill for the pilot programme was estimated at almost £10bn, most of it in the upfront capital costs of providing generation and distribution infrastructure (depending on the type of low-carbon technology deployed). Calculated cost benefits of £10.5bn would come principally from carbon savings – £9.2bn – through a reduction in non-traded emissions.

The report identified some key problems – for instance, the risk of heat loads not connecting to networks, which could create uncertainty and hamper investment. Projects would require high rates of return to attract investors, even if economically viable. Zoning, it claimed, would provide project sponsors and investors with connection assurance.

Crucially, there’s the question of coordination between the heat network developer and multiple local parties – a long-recognised stumbling block that has often caused heat networks to be scaled back or not deployed at all, even if the most cost-effective option.

One financial stimulus from government, the Green Heat Network Fund (GHNF) announced in the 2020 budget, has recently been extended to 2027. Capital grants on offer are targeted towards decarbonising existing systems and developing new low-carbon and zero-carbon ones. GHNF is open to public or private sector organisations in England.

Numerous technologies were listed in the Arup report as suitable for providing heat to district networks – ground, water and air source heat pumps; energy from waste; high and low temperature waste heat; along with back-up boilers. But not, however, geothermal.

The UK Climate Change Committee estimates that 18% of our heat will need to come from heat networks by 2050 if carbon targets are to be met cost-effectively – long-term, these are forecast to be cheaper than individual building heat pumps.

Geothermal for Stoke-on-Trent
While the reality of exploiting geothermal in a big way seems far distant (although it is a feature of Southampton’s long-established heat network), it’s something Stoke-on-Trent City Council is backing to the hilt. There, the grand plan is to create a 32 km system of pipes connecting a geothermal heat source to ‘key heat demand clusters’ focused around public sector buildings across the core city area.

Two shafts are to be sunk below Stoke’s Etruria district. Council partner SSE will deliver the project along with GT Energy. Work on the geothermal well is due to start early 2024. Around 4 km of network infrastructure is already in place.

Building connections – linking key customers to an energy and pumping station – is being worked on this summer. Interim heat sources operating across the current and planned network will be displaced by geothermal as this comes onstream and a connection to the well is built.

Stoke Council hopes the government’s heat zone pilot may point the way towards further expansion. Its investment to date is around £12.5mn. The wider scheme, including the deep geothermal heat source, is currently estimated to cost £84mn and the Council target is for everything to be onstream by the end of 2028. It’s anticipated that the well will be capable of delivering around 20 MW of thermal energy annually.

Post-2030, Stoke plans on building a new energy recovery facility, able to supply heat to a further expanded network. This would ensure increased resilience and allow for completely removing fossil fuel back-up systems.

Some notable networks
District heat networks are already well-established in a few cities – Southampton (a pioneer set up in 1987 and also with a deep geothermal element); Olympic Park, East London, the UK’s biggest; Birmingham; and Coventry. All are council enterprises working in partnership with private sector operator Equans.

Olympic Park is powered by two energy centres. CHP engines and chillers provide heating and cooling to venues, commercial buildings and homes. The engines have been designed to use natural gas, but also gas blended with biogas and other fuels with lower carbon content. A biomass boiler provides heat to the network, mainly using arboriculture waste from within a 100 km radius. The centres have been designed for additional boilers and CHP engines to be added when needed.

Birmingham District Energy Company (BDEC) is a joint venture between the city council and Equans, which owns and operates three networks. The Broad Street scheme is a tri-generation (heat, power and cooling) system. The others, Aston University campus and Birmingham Childrens’ Hospital are both CHP-led systems. An interconnection through New Street Station linking the Broad Street and Aston schemes provides scope for further expansion.

Southampton’s heat network, operating as Southampton Geothermal Heating Company, has more than 40 public and private sectors energy users, including the Civic Centre, West Quay shopping centre and Ikea. It uses heat from an aquifer 1.7 km below ground, supplemented by large-scale CHP and conventional boilers; and it incorporates a district cooling system.

Jason Taylor, the city’s Energy Manager is a firm believer that local systems such as this are the practical and economic way ahead for decarbonising. But, he points out, there’s a potential problem of constraint, where local grid systems might not be able to cope with extra power generated by local sources – something, he says, Southampton is already experiencing.

The Coventry scheme provides heat via a 6.6 km network of buried pipes to consumers in the city centre. It produces more than 44 MW of energy-from-waste and claims to give customers a carbon saving of almost 90% compared with a conventional stand-alone gas-fired system.

Moving forward into zones
Arup’s report was wary of predicting how much waste heat could be exploited over time. Some sources, it pointed out, may become incompatible with decarbonisation pathways. That said, others may emerge through developing industrial sites near areas of demand.

What does the industry make of progress in the two years since the Arup report was published? ‘The whole point of zoning from ADE’s perspective is that the connection rate increases exponentially over the next two years,’ says ADE’s Bragg. ‘There are difficulties with constraints regarding distribution and transmission. It’s stopping new generation connections. We need to understand the problem much more clearly – we’ve told government this. Links between the heat and network sectors are historically weak.’

Meanwhile, the UK District Energy Association (UKDEA) has frustrations over the process. ‘We’ve been closely involved, but we’re concerned that the level of information being shared isn’t consistent or at the level we would have hoped,’ says UKDEA Chairman Simon Woodward. ‘The government has moved to the Advanced Zoning Protocol (AZP) stage, supporting local authorities to reach a point where there are deliverable heat networks in their zones in 2025, but we’d like more transparency.’

There are, he says, key issues to wrestle with – for instance, not only the obligations on sources to provide heat but also the terms on which they’ll do so. There are other concerns too, relating to ‘mandatable connections’, for example. These apply to buildings within a zone which are required or mandated to connect to a heat network.

The process of choosing a Zone Developer (ZD) – the party that creates heat networks in the zone – is a further preoccupation. ‘Some from the private sector want a swift process with little recourse to the local authority in whose area the zone is,’ says Woodward. ‘But the government’s view is that there will be a number of steps the ZD has to go through. Our concern is that this could make things very slow.’  

UKDEA is pushing for a working group to be set up so business can feed in questions and discuss any risks it sees. That said, Woodward supports the government’s thrust – to use as much waste heat as possible in networks, either directly at temperature or in a heat pump with a higher COP (coefficient of performance).

One challenge in getting any scheme off the ground is to secure demand. Others, says Woodward, include the relatively high cost of district heating networks and being able to set fair prices while delivering investor return. ‘This is what heat network zoning, an integral part of the Energy Bill currently going the Parliament, is meant to deliver by 2025. It’s key to know that you’ll have customers to take your heat and that they’re required to connect to your network,’ concludes Woodward.