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Geothermal Energy - Turning the Old Black into the New Green

Writing in the Scotsman, Heriot-Watt's Chief Scientist Professor John Underhill considers whether it is the legacy of coal, currently deemed the scourge of our energy mix, that could help alleviate the fuel poverty and energy crises gripping the UK today.?

Fuel poverty is one of the leading social challenges in Scotland today and it will be the renewed focus for many as the nights draw in, the clocks change and we ready ourselves for winter. As more than one in four households will struggle to make ends meet over the next few months, it may come as a surprise to learn that a solution to this dual social and energy crisis may lie directly beneath our feet.

Currently defined as a household that needs to spend over 10% of its total income on domestic heating, fuel poverty impacts 650,000 (26.5%) Scottish homes. Over 183,000 are classified as extreme cases because 20% or more of their annual household budget is spent on heating. One in ten are families with children and around 90% are either owner occupiers or people living in social housing.

The largest concentration of households affected lie in densely populated urban areas which grew up around heavy industry and manufacturing centres. Many of these have long since reduced in size or closed, leaving a landscape and community blighted by high unemployment and deprivation. Given the scale of fuel poverty, the time is ripe to reap the benefits of geothermal heat generated by old coalmines.

It’s ironic and perhaps paradoxical to suggest that a solution to the fuel poverty crisis could come from the most polluting, black and dirty fossil fuel which we, as a nation, have worked so hard to remove from our energy mix. This effort has been so effective that the UK power generation had its first coal-free day last April.

To date, the focus on geothermal energy in the UK has concentrated on areas like the granites of the Cairngorms and Cornwall because they have a higher geo-thermal gradient. While it’s evident these areas can provide heat locally, industrial-scale supply to the people that need it most is impractical because of the difficulty of storage and transportation from sitesthat are so distant from the cities in which they live.

But a different kind of geothermal heat source could provide an answer: renewable energy from the most unlikely of sources. Despite the demise of coalfields as a source of domestic heat, a major benefit is that mostare located close to and often directly beneath large conurbations. Although they are not going to be as productive as areas marked by volcanic activity, like Iceland or Hawaii, they could provide enough heat to serve the needs of the stressed communities where fuel poverty hits hardest.

Coalmine geology is also highly favourableand, unlike solid rocks where natural porosity, permeability or fracture patterns dictates flow, water can pass through a pit’s trellised network of adits and shafts more easily since they are akin to fluid ‘super highways’.

The process by which heat can be extracted is similar to that used by a fridge. The warm water from the mine is moved into a store in which a refrigerant can extract the heat and convert it to a gas. The gas passes through a compressor which heats it to around 50˚C to warm the water in a tank. This then supplies warmth to the property. The compressor does use up some electricity but is hugely efficient, giving back around four times more energy than is needed to power it.

The cooled water extracted from the mine, the gas needed to heat the water tank and the hot water used to heat the house can all be recycled and used in the same process once more. Importantly, the system can be reversed and a building may be cooled during summer months.

Small pilot schemes are already working to supply heat from coal mining areas to a housing estate in Rutherglen and a swimming pool in Stanley, County Durham. The Scottish Government’s Geothermal Energy Challenge Fundis supporting studiesat Fortissat, North Lanarkshire, Polkemmet in West Lothian and Grangemouth in Stirlingshire.

In addition, a sedimentary aquifer project is being investigated at the site of an old paper mill at Guardbridge near St Andrews and a large-scale district heating network is serving a low-carbon development in Kilmarnock.

While the Rutherglen housing scheme demonstrates that old mine workings can supply heat locally, the question remains-can heat supply be replicated on a scale with a positive impact on social well-being? A large subsurface research site is being developed in the Clyde Gateway, an area of urban regeneration located in the east end of Glasgow.

Funded through the Department of Business, Energy & Industrial Strategy (BEIS), commissioned by the Natural Environment Research Council (NERC) and delivered by the British Geological Survey (BGS), the UK GeoenergyObservatories project will assess the feasibility of heat sources from abandoned mine workings. The Clyde Gateway lies above former coal mines in whichthe main seams occur at depths of up to 300m below the surface and at an ambient temperature of around 15˚C.

The Observatory for Glasgow could prove that shallow geothermal energy within abandoned mines offers an alternative to gas-fired domestic heating that can be scaled up to provide a cheap, local alternative source of warmth to areas with some of the highest levels of fuel poverty in Scotland.

In so doing, it offers the opportunity for the UK and Scottish Government to move towards meeting low-carbon energy targets. Significantly, it would also see the sites of the most polluting, old, black and dirty fossil fuel translated into a new, reliable, cheap, low-carbon, renewable green-energy source.

Professor Underhill is currently sitting on the Natural Environment Research Council’s UK Geoenergy Observatories Science Advisory Group which is overseeing the delivery of the UK GeoenergyObservatories project.

Intro image: British Geological Survey 2018

This article first appeared at https://www.hw.ac.uk/about/news/2018/turning-the-old-black-into-the-new-green.htm

 

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