<<Not many people know that mine water heat pump schemes are helping to reduce our carbon footprint. Even fewer are aware that Gateshead has developed the UK's largest project based on a former pit - and some of its best-known buildings are already benefiting. Climate Action Newcastle's site visit report is here - and CAN supporter Mima Cattan, who organised it, explains how such schemes work.>>
Heating homes and businesses accounts for around half of the UK’s energy demand. Most is derived from fossil fuels, so ensuring continuity and security of heat supply from low-carbon alternatives is a significant challenge. Disused mines are now being used to create mine water heat pump schemes, and Gateshead Energy Company (GEC), a subsidiary of Gateshead Council, is a pioneering project. It is demonstrating how a disused mine filled with water can provide 6MW of low-carbon heat for a newly extended heat network.
This is the largest mine water geothermal heat network in Britain, showing that many of Britain's 23,000 disused deep coal mines could help provide low-carbon heat for local networks. Nearby buildings - housing, offices, civic centres and even Gateshead Stadium, Baltic and The Glasshouse - are now linked to the heating network.
Background
The earliest schemes were developed in the US in 1963, and the largest in Europe is in the Netherlands, which started in 2003. Two schemes in Scotland providing heating for social housing for over 20 years were recently decommissioned.
In 2019, Gateshead Energy Company established a 5.5 km network, which supplied heat by 4 MW gas engines to a mix of municipal, commercial and domestic buildings. The council wanted to double the size of the scheme without doubling carbon emissions and approached the Coal Authority's heat and by-product innovation team to explore if the additional heat load could be supplied from the disused coal mines beneath the town.
The feasibility study proved successful, and the council sought funding from the Government's Heat Network Investment Project, securing almost £6m towards the £15.2m project cost.
Viability of former mines to provide heat
When mines were closed, they slowly refilled with water, often over several decades, which then was heated by natural geothermal processes. Closed mines still require management, including pumping and treating water. There are about 70 sites across Britain where mine water is at the surface, offering potential as heat sources.
For a heating project to be viable, there must be water-filled mines worked at different depths beneath the site, so water can be abstracted from the deeper, warmer seam and returned to a separate, shallower seam following heat recovery. In addition, it helps if the mine water is within 100m of the surface to avoid excessive electricity costs associated with pumping, although Gateshead is showing that deeper mines also look likely to be net zero with suitable planning.
How it works
At Gateshead, mine water levels are around 20m below surface. Test boreholes were drilled to a depth of 150 m to intercept the two main coal seams. This ensured good connectivity and mine water flow while keeping points of abstracted – warmer – and reinjected – cooler – mine water separate.
Mine water at around 16°C is pumped from boreholes that intersect the mine workings. Some of the heat is extracted from the water by a heat exchanger at the surface, which is then returned to a shallower depth in the mine where it is reheated by the geothermal gradient. Heat is transferred from the heat exchanger to the heat pump, which uses a vapour compression cycle to increase temperatures. This boosts the temperature of the separate flow of clean water around the network to between 60°C and 80°C. For every kilowatt of electricity used to drive the heat pump, around 3kW of heat are produced – making this a low-carbon heating option. It should be noted that mine water does not flow through any of the buildings connected to the network.
The heat pump works in conjunction with a gas-powered combined heat and power (CHP) plant, which raises the temperature of the water further so that it leaves the site, via thermal stores, which are like huge hot water cylinders, at up to 80o Celsius to be pumped to local buildings. Domestic heat pumps will typically produce water at a temperature of between 35o and 45o Celsius, and a domestic combi boiler will usually be set at between 60o and 65o Celsius. Electricity created by the CHP is exported locally on dedicated cables along with electricity provided by the adjacent solar farm. This site is consequently now self-sufficient for electricity.
A heat interface unit (HIU) basically fulfils the same function as a gas boiler in a property when used as part of a communal heating network. Instead of burning gas to introduce heat into the property, it transfers heat from the heat network to the dwelling's heating system.
Project development at Gateshead - and implications for UK
The Gateshead scheme began operating in March 2023 and its performance is being monitored to investigate the longevity and sustainability of this type of heat resource. This project has demonstrated that UK’s disused mining infrastructure can provide a secure source of heat that may be scaled up while reducing carbon emissions by around 1,800 tonnes per annum.
Offering lower-than-market prices for heat, the scheme enables customers to access low-carbon heat and removes the need for domestic boilers. Mine water heat networks use existing technology such as heat pumps, heat exchangers and boreholes that can contribute to net-zero targets now, helping to decarbonise heat supply in former mining areas. There are now several projects in the planning stages in the North East of England.
***Government paper outlining huge potential for UK heating systems: https://www.gov.uk/government/publications/uk-heat-networks-market-overview/uk-heat-networks-market-overview-html
***This blog draws on a paper by Dr Charlotte Adams, principal R&D manager, mine water heat, at the Coal Authority, 2023