D2Grids and Nottingham City Council at forefront of exciting future for mine energy in UK

As an active D2Grids partner, Nottingham City Council will be commissioning The Coal Authority to undertake a mine energy study for a proposed pilot district heat network at the Crabtree Farm Estate, Bullwell, Nottingham, UK. Around 60 homes managed by a social housing provider could benefit from this scheme, and it will be a vital test bed for further expansion of the technology in the area. This project aligns well with City Council aspirations to become the UK’s first Carbon Neutral City by 2028.

Nottingham has a rich history of mining and coal production that created economic wealth and fuelled innovation. Many of our towns and cities across the UK were developed as a direct result of their coal reserves. Around one quarter of UK homes and businesses are located in coalfield areas. This means that there is good overlap between coalfield areas and heat demand. Following the abandonment of the UK’s deep mines, many former mining communities still experience high levels of social deprivation. Using mine heat offers one solution for low carbon heat delivery during a climate emergency that can also deliver economic and environmental improvements for places that powered the UK’s historic, industrial and economic growth.

Potential in the UK

Over the past century, 15 billion tonnes of coal were extracted from the UK subsurface. Although the coal has long since been extracted, traded and burned, the voids left behind contain warm water that could be used many times over as a source of low carbon heat. The water within the mines is tepid, at temperatures of 12-20°C. Clearly this is not hot enough for taking a bath but by using a heat pump, temperatures can be increased to a more comfortable 40-50°C. The heat pump requires an electrical input but it is an energy efficient device because you can expect to get 3-5 kW of heat output (or more) from the heat pump for every 1 kW of electrical input.  As the carbon content of electricity decreases with the greening of the grid, carbon emission reduce and the UK’s abandoned mines could make a significant contribution to decarbonising the UK’s heat demand for many years to come.

The UK Coal Authority own the abandoned coal mining infrastructure and manage more than 75 mine water treatment schemes across the UK. The water that naturally flows from, or is pumped from, the abandoned mines is estimated to contain in excess of 80MW of heat. Already in the UK, there are several sites where heat energy is extracted and usefully used at mine water treatment facilities – there is significantly scope to scale this up.

Excitingly, extracting heat from mine water treatment is just the tip of the iceberg for mine energy’s potential in the UK. There is a very large resource of heat in mines where no current water treatment is required. The Coal Authority estimates that all the UK’s abandoned flooded mines have the potential to sustainably meet all of the heating requirements of coalfield areas. Former mine workings also offer the potential for heat storage.  

Mine energy is accessed by drilling boreholes into the workings in order to abstract the mine water from which around 5°C is removed by passing it through a heat exchanger that interfaces with a heat pump before the cooled water is reinjected to the workings. It is normal practice to abstract from a deeper seam and re-inject to a shallower one. To develop these schemes, it is necessary to seek permission from The Coal Authority who own the subsurface infrastructure and have experience of drilling through mined terrain. It is also important to have a good understanding of how the mines are configured to increase the chance of finding a good flow of water, this is necessary to bring the heat to the surface.

To explore and maximise the potential of mine energy in the UK, the Coal Authority is currently broadening its traditional role and establishing an expanded Mine Energy team.

Where has this already been done?

Around 30 mine energy projects exist globally, these operate at a range of scales and supply a variety of end users from both operational and abandoned mines. This makes mine energy a very versatile heat source but makes it difficult to generalise capital, development and operating costs as its configuration is strongly linked to the nature and extent of the underlying mine workings.

One very successful large scale mine energy heat network has been operating at Heerlen in the Netherlands for over a decade (the operators of the Heerlen network are also a D2Grids partner). This scheme delivers heating and cooling to 200,000m2 of mixed use new and retrofit buildings through a 7km heat network. This project has enabled economic regeneration through revenue generated from heat sales being retained within the region rather than going to a national energy supplier. In Poland, water pumped from an operational coal mine is used with heat pumps to heat the pithead baths where the miners wash at the end of their shifts and in Spain minewater from the Barredo mine in Mieres is used to heat a hospital.

In the UK, a commercial mine energy system provides around 4MW of heating for two wine warehouses and is understood to be the largest geothermal heat system in the UK. This highlights the potential to provide not only domestic heat from mine energy but also a range of industries that require low temperature heat, such as horticulture.

What will the Nottingham study involve?

The feasibility study at Crabtree Farm will involve looking at the mine abandonment plans for the area and gathering water quality and flow data from any historic records, nearby mine water treatment systems and Coal Authority monitoring points. The mine plans and maps will be used to identify the number of seams worked in the area and assess the extent of and depth to workings. For a mine heat scheme ideally several seams should be present so that water can be abstracted from a deeper seam and re-injected to a shallower seam following heat extraction, this reduces the risk of cooling the source. It is also necessary to target seams that are flooded therefore it is important to know the depth to mine water below surface. Once this is complete, target areas can be selected and if the scheme is taken forward this information will be used as the basis for well drilling.

Looking to the future

Mine energy is of rapidly increasing interest in the UK to national government and local authorities, as they develop decarbonisation strategies, and to those promoting and developing heat networks. As well as Nottingham’s work through D2Grids, there are numerous other projects in the pipeline to scale up the use of mine energy in the UK.

At Seaham, in County Durham in the north-east of England, a new development of 1,500 homes plus a school and shops will be provided heat from the adjacent Dawdon mine water treatment scheme, which has a potential heat supply of up to 6MW. Meanwhile, Bridgend County Borough Council, in south Wales, is also developing a project to extract heat from the former Caerau Colliery mine workings to heat around 200 nearby homes and other buildings.

To put mine energy potential within the context of the UK energy landscape, over half of UK energy demand is currently used to produce heat, much of which is consumed by the domestic sector. Most of this is provided by burning gas. The UK has been a net importer of gas for over a decade which has created dependencies on other nations to maintain supplies. In addition to improving our energy security, we also need to decarbonise our energy supplies to meet carbon reduction targets and combat climate change. Mine energy offers a promising solution for the decarbonisation of heat at scale in former mining areas. The potential to develop this legacy and reuse the infrastructure created by our forefathers for future heat supply provides a really exciting opportunity.

Charlotte Adams (The Coal authority)and Philip James (Nottingham City Council)

 


[1] Farr, G and Busby, J (2020). The Thermal Resource of Mine Waters in Abandoned Coalfields; Opportunities and Challenges for the United Kingdom. Proceedings World Geothermal Congress 2020.

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