They were the bedrock of our industrial revolution - powering engines and furnaces which turned Scotland into a goliath of global commerce.
Today, however, the coal mines which bit so deeply into the land lie silent - consigned to the history books by cheap imports from overseas and more advanced forms of energy.
But a new dawn may be beckoning for the nation's once mighty collieries as efforts build to position them at the heart of a manufacturing renaissance - one with the potential to create thousands of jobs and tackle the scourge of fuel poverty.
Scientists in Glasgow are poised to bid for a game-changing £32 million funding pot that could lead to development of geothermal sites capable of transporting affordable heat from disused mines to homes and businesses.
Key to their project is the water which naturally floods pits after they are abandoned and then warms once it has come into contact with rocks. Experts believe that this energy source - currently trapped in 600 km3 of disused workings in the Central Belt - could meet up to eight per cent of Scotland's domestic heating demand.
They want to drill down into the mines and install insulating pipes which would carry the water to homes and businesses via a heat pump apparatus designed to lift the temperature further and make it hot enough for radiators, running a bath or use in an industrial process.
Widespread adoption of the technology could slash household bills by hundreds of pounds annually and generate millions in savings for the NHS as the impact of illnesses caused by chilly properties is reduced.
But if the rewards involved in developing such a system are considerable, so are the obstacles - and the prospect of roads being dug up to lay pipes needed for transporting water is unlikely to be welcomed by residents or motorists.
“In Scotland, you have communities living above mines which were only closed in the early 2000s," said Strathclyde University's Professor Zoe Shipton, leader of the HotScot consortium which wants to develop at least three new mine-water geothermal sites in the Central Belt.
"There are people today who worked down these mines and are keen to see the resources being used," she continued. "At the moment the Coal Authority spend £2.4 billion on ensuring abandoned mines are safe. Our work is about turning that liability into an asset.
"Of course, the challenges are huge. Fifty-two per cent of the energy consumed in Scotland is used to heat homes and businesses – and about three quarters of our domestic heating requirement is sourced from gas.
"The Scottish Government has set a target of getting the economy to net zero by 2045. What that means is my gas boiler and yours being replaced; it means gas boilers cannot be installed in new-build homes in Scotland from 2024. So there’s an enormous need to develop new renewable ways of heating homes and businesses."
To this end, HotScot - whose members include Glasgow, Heriot-Watt and Stirling universities, and British Geological Survey - aims to "de-risk" technologies associated with mine-water heating and support Scottish industry to build sites across the UK and globally.
“The larger bid, which we have to submit by November 25, is for £32m in funding from UK Research and Innovation, matched with £5m from industry," explained Prof Shipton, who is based in Strathclyde's Department of Civil and Environmental Engineering.
"This will enable us to generate capital with which we can actually develop sites. Ideally, we would, by summer 2026, like to have three or more working sites up and running throughout the Central Belt, with research happening alongside which will allow us to learn from how the projects are developed and to build new kit and techniques."
And if Scotland establishes itself at the epicentre of a major new industry, it will be in no small part due to the presence of the nearly-completed UK Geoenergy Observatory in Glasgow.
Featuring 12 boreholes fitted with 319 state-of-the art sensors, the observatory is able to measure the chemical, physical and microbiological properties of the subsurface environment, and aims to observe how warm water moves in abandoned mine workings beneath the east end of the city and Rutherglen.
It recently released data and images from depths of up to 199 metres - including high-resolution scans which reveal, among other things, the presence of 300 million-year-old mollusc fossils.
But, for Dr Alison Monaghan, science lead for UK Geoenergy Observatories in Glasgow, the big prize is what the data will do for efforts to drive forward the development of mine water heat.
"There will be an exceptional level of monitoring of the changes that happen in the subsurface and it means you can estimate how much potential heat resource there is and how long it will last for, and if there are any environmental impacts," she said.
“We haven’t had that level of understanding about what’s underground [and] how it changes through time.The data provided will have an impact on assessments of the economic viability of geothermal projects, such as those harnessing the energy of abandoned coal mines, and also on their social acceptance."
Prof Shipton stressed that such data would be vital to fulfilling the promise of early stage work aimed at establishing the technology.
She said: "At the moment, the HotScot consortium has £50,000 to build a bid for a much larger amount of money which will allow us to start developing coalmine-based geothermal energy while carrying out research into what sites are available in Scotland.
"We’ll also be researching factors such as differences and changes in heat or geology – which is where data from the UK Geoenergy Observatory in Glasgow comes in – as well as challenges around retro-fitting existing buildings and how communities feel about such a system.
"It will provide the information we need to manage effectively the capital and operational costs associated with such projects, to maximise the benefits to local communities, and develop these sites with as low an environmental footprint as possible."
Prof Shipton predicted that the transformative impact of mine water heat would extend across society.
"In Scotland’s NHS, every pound spent on affordable warmth will save 42p for the NHS, because the NHS will have to deal with fewer health issues affecting individuals who cannot afford to heat their homes," she said.
“Our projections show the HotScot project could generate nearly 10,000 jobs throughout the Scottish supply chain. But, more importantly, the work could also form the basis for an entirely new manufacturing industry in Scotland, in which domestic firms will make and sell the kit – sensors, heat interface units – needed to operate the heating system.
“It could lead to significant savings for home-owners too. Shettleston in Glasgow previously had one of these coalmine-based geothermal heating systems installed, which is no longer operational. However, analysis found that an average annual spend of £660 on heating was cut down to £150.”
She added: “In terms of tackling the issue of fuel poverty and cutting the amount consumers pay for fuel, the benefits are potentially huge."
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