Disused coal mines could help decarbonise our heating. Here’s how

A disused coal mine in Herten, western Germany, in 2013. Image: Getty.

Fossil fuels currently dominate the production of electricity and heat. Although renewable energy accounts for around a quarter of electricity produced in the UK, the production of central heating is dominated by natural gas, which supplies around 70 per cent of UK heat demand (the UK has been a net importer of gas since 2004).

There are fewer low carbon alternatives for heat production than there are for electricity. Solar hot water and biomass are the two main touted alternatives. Solar hot water is usually produced at a domestic level and requires access to a south facing roof. Biomass can be used as a heat source but may be constrained by availability and the transportation of fuel. And so it is unclear how future heat demands could be met from low carbon sources.

Geothermal heat is one solution that offers a low carbon, secure and continuous energy source. Classic geothermal regions such as Iceland and New Zealand capitalise on their volcanic landscapes by capturing the steam and hot fluids produced as a result of tectonic activity. Geothermal fluids in the UK are over 100°C and hot enough to drive turbines, produce electricity and also supply heat. Also, geothermal fluids may issue naturally at the surface as hot springs and geysers, avoiding the need to drill to access them.

Of course, the UK is not characterised by such tectonic activity. But we believe that abandoned deep mines contain good geothermal potential.

Geothermal potential

The deeper you drill into the Earth, the warmer it gets. Geologists call this the Earth’s “geothermal gradient”, driven by heat produced at the Earth’s core that radiates towards the crust. In non-tectonic areas, temperatures increase on average by around 25°C per kilometre. This means we can predict what temperature may be encountered at any specific depth.

But extracting geothermal energy from these warm depths is only possible if water is present and is able to flow from the rock. Heat and water flow are essential for extracting geothermal energy.

Abandoned coal mines, therefore, seem incredibly promising due to their networks of flooded galleries and shafts lying at depths of up to several hundred metres below the surface. One can be almost certain that the water flow necessary for deep geothermal wells will be found in these flooded underground voids. The risk of not finding flowing water underground can inhibit deep geothermal developments elsewhere.

Vast volumes (over 15bn tonnes) of coal have been extracted from deep mines in the UK over the last century. To put this into context, if this extracted coal were spread over the UK land surface, this would result in a five cm deep layer of coal across the country. Today, UK coal production from deep mining has declined to almost zero and the nation celebrated its first coal free day of power generation in April 2017.

Eco-friendly coal mines

Think about this. The volume of coal extracted compares to an equivalent void volume underground. On this basis (once allowing for subsidence), we estimate that the abandoned mines of the UK contain around 2bn cubic metres of water at temperatures which are constantly around 12-16°C, and in some instances higher still. If heat corresponding to a 4°C temperature drop was removed from this volume, around 38,500TJ of heat could be liberated. This conservative estimate could provide enough heat for around 650,000 homes nationally.

Clearly, you wouldn’t want to take a bath or heat your home with water at these low temperatures, but using a heat pump, the water temperature could be upgraded to more useful temperatures of 40-50°C.

A heat pump takes energy from a source such as water within an abandoned mine and “lifts” it to a more useful temperature. You can think of it working like a fridge: if you put food at room temperature in a fridge, after a while it will be cooled to the temperature of the fridge. The heat removed from the food is lost from the back of the fridge, which is why this area feels warm. The radiators in a home are effectively the same as the back of the fridge. A heat pump uses electricity to boost the temperature but for every kW of electrical power used, the heat pump will produce three to four kW of heat. This is why heat pumps are a low carbon alternative to gas boilers.

Next steps

So we know that the UK has sufficient potential for geothermal heat production in its extensive mines. The next consideration, then, is proximity to the heat demand. Given the low temperatures involved, the heat source needs to be close to the end user to minimise losses. Many UK towns and cities grew due to their coal reserves, meaning that centres of heat demand and areas of abandoned mines often coincide, making them ideal targets. The UK government’s fifth carbon budget sets out plans to decarbonise heat by stating that one in 20 homes should be connected to a heat network by 2030. This is an ambitious challenge but abandoned mines could make a significant contribution here.

Minewater district heating schemes have already been successfully developed at several locations. One early example was developed at the Ropak packaging plant in Springhill, Nova Scotia, in 1998. A minewater and heat pump system that uses minewater at 18°C provides heating and cooling for the 13,500-square-metre site leading to huge savings in avoided fuel-oil costs. And at Heerlen in the Netherlands, a larger scheme has been operating since 2008, supplying heat to 500,000 square metres of commercial and residential buildings. Areas planned for new development in former mining areas make ideal targets as they provide an opportunity to incorporate the necessary above ground infrastructure.

But if coal mines are to decarbonise heat, we need to deploy these systems in more places. Is this possible? We think so. The fact that many coalfields are overlain by urban centres means that there is certainly good potential for many former mining areas. Although abandoned mines provide a lower temperature resource than deeper geothermal sources, they are systems known to flow copious quantities of relatively warm water and provide a readymade subsurface store of heat.

The ConversationThere is a delightful irony that the legacy of the dirtiest of fuels, coal, now has the potential to deliver a low carbon energy future.

Charlotte Adams and Jon Gluyas, Durham University.

This article was originally published on The Conversation. Read the original article.


Mayor Marvin Rees' hope for Bristol: A more equitable city that can 'live with difference'

“I call on everyone to challenge racism and inequality in every corner of our city," Bristol Mayor Marvin Rees says. (Matt Cardy/Getty Images)

When the statue of 18th century slave trader Edward Colston was torn from its plinth and dumped in Bristol’s harbour during the city’s Black Lives Matter protests on 7 June, mayor Marvin Rees was thrust into the spotlight. 

Refraining from direct support of the statue’s removal, the city’s first black mayor shared a different perspective on what UK home secretary Priti Patel called “sheer vandalism”:

“It is important to listen to those who found the statue to represent an affront to humanity,” he said in a statement at the time. “I call on everyone to challenge racism and inequality in every corner of our city and wherever we see it.”

48 year-old Rees, who grew up in the city, has since expanded on his approach to the issue in an interview with CityMetric, saying “wherever you stand on that spectrum, the city needs to be a home for all of those people with all of those perspectives, even if you disagree with them.”

“We need to have the ability to live with difference, and that is the ethnic difference, racial difference, gender difference, but also different political perspectives,” he added. “I have been making that point repeatedly – and I hope that by making it, it becomes real.” 

What making that point means, in practice, for Rees is perhaps best illustrated by his approach to city governance.

Weeks after the toppling of Colston’s statue, a new installation was erected at the same spot featuring Jen Reid, a protester of Black Lives Matter. However, the installation was removed, as “it was the work and decision of a London-based artist, and it was not requested and permission was not given for it to be installed”, Rees said in a statement.

Bristol may appear a prosperous city, logging the highest employment rate among the UK’s “core cities” in the second quarter of 2019. But it is still home to many areas that suffer from social and economic problems: over 70,000 people, about 15 percent of Bristol’s population, live in what are considered the top 10 percent most disadvantaged areas in England. 

In an attempt to combat this inequality, Rees has been involved in a number of projects. He has established Bristol Works, where more than 3,000 young people from economically disadvantaged backgrounds are given work experience opportunities. And is now setting up a commission on social mobility. “Launching a Bristol commission on social mobility is not only about social justice; it [should not be] possible for a modern city to leave millions of pounds worth of talent on the shelf, just because the talent was born into poverty,” he says.

The mayor is also a strong supporter of the UN’s Sustainable Development Goals (SDGs), explaining that SDGs offer a way to talk about sustainability within a framework of many issues, ranging from climate change and biodiversity to women’s issues, domestic violence, poverty and hunger.

“What we want to achieve as a city cannot be done as a city working alone,” he insists. “We don’t want to benefit only people inside Bristol, we want to benefit the planet, and the SDGs offer a framework for a global conversation,” suggesting that a vehicle should be launched that allows cities to work together, ideally with organisations such as the UN, the World Bank and the International Monetary Fund involved. 

Greater collaboration between cities would be “beneficial in terms of economies of scale,” he argues, “as cities could get more competitive prices when buying materials for building houses or ordering buses, rather than each city acquiring a few of them at a higher price.”

In an attempt to focus on the long term, Rees launched One City Plan in January 2019, setting out a number of goals for Bristol to achieve by 2050.

Investing in green infrastructure to meet 2030 carbon emission targets spelled out in the SDGs is a key area here, with the mayor noting that transport, mass transit and energy are important sectors looking for further investment and government funding: “The sooner we meet our targets, the sooner we will benefit from them, and invest in sectors that will provide people with jobs.”

Jobs, especially following the outbreak of Covid-19, are of paramount importance to Rees. Bristol’s council wants to ensure that any government money given to the city will be quickly passed on to businesses to help prevent redundancies, he says, though given that mass job losses seem inevitable, reskilling options are also being looked into, such as through a zero-carbon smart energy project called City Leap.

Another important area for investment in Bristol is affordable housing, with 9,000 homes already built under Rees’s term of office. “People could build a base for life with affordable housing, [and this would mean] their mental health would be better because they have a safe place,” he explains. “Children in families that have a home that is affordable are more likely to able to eat and to heat, [and they are more likely to enjoy a] better education.”

Taken in the round, Rees’s agenda for Bristol is its own blueprint for shaping history. The Colston statue now lies in safe storage, with a local museum likely to play host to the controversial monument. But the Black Lives Matters protestors were fighting for a fairer, more equal future, and it is here where Rees is determined to deliver.

Sofia Karadima is a senior editor at NS Media Group.