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Gonzalo Roberto Mayoral Fernández's picture
Mining Engineer KEROGEN ENERGY, S.L.

Mining Engineer with 20 years of experience in mining, construction, biogas and geothermy, managing in different role (project manager to executive manager). In Biogás 1,5 years experience in...

  • Member since 2021
  • 2 items added with 594 views
  • Jan 21, 2021


Since the beginning of the Industrial Revolution, coal has been one of the main sources of energy, first directly for steam generation and later for electricity generation, being still today a basic source of energy for many European countries, such as Poland. For this reason Europe has numerous regions in which coal mining has been carried out for decades, being the main economic activity. However, the closure of the coal mines due to the depletion of the resource, excessive operating costs or due to policies to reduce COemissions has been a severe shock to these regions and a threat to their future.

But abandoned coal mines can be a new clean, efficient and environmentally friendly energy resource thanks to the use of flood water for geothermal generation.

The case of Asturias and HUNOSA.

An example of this new life in the old coal mines occurs in Asturias, a region in the North of Spain. Traditionally, coal has been exploited continuously from the 19th century to the present day, but in the 90s of the 20th century a progressive closure began and finished in 2018 with the closure of the last operations. In parallel these last two years, with very aggressive emission reduction legislation, two of four existing thermal power plants in the region (Lada and Narcea) were closed in 2020, losing 888 MW of power capacity, with serious social and economic consequences.

A large part of the coal mines in Asturias were operated by a single state company, HUNOSA, founded in 1967 with the union of more than 20 companies that had operated since the 19th century, reaching 45 underground mines (5,000 Km of galleries) and 10 open pit with 28,000 employees, with a maximum production of 5,000,000 tons per year. The continued closure of operations in the 90s forced the company to diversify, creating several subsidiaries in the fields of engineering, data processing, environment, etc.

On the other hand, in 2006 began to be an interest in geothermal energy in Spain, which until that moment only had a testimonial presence. This interest came in part derived from the great development of residential construction and building and from the need to provide heating and cooling in an efficient way. In this context, in 2006 HUNOSA together with the University of Oviedo proposed the geothermal use of mine waters. The investigation begins with the Central Carboniferous Basin of Asturias, due to the large number of shafts requiring pumping for their maintenance as well as the proximity to urban centers (some of them inside the villages or so near them), which represents a unique opportunity for the development of Geothermal District Heating systems by heat pump or even direct use. In fact, in 2010 a thermal potential of 30.54 MWt was calculated for 5ºC of thermal jump and a pumping of 1,167 m3/s (COP 5).

First project: Barredo Shaft.

In 2010 the European Union sets the definitive end of subsidies to coal mining for 2018, which will mean the end of HUNOSA. It was precisely in that year that the first District Heating project was launched, using the Barredo Shaft, closed since 1995, as a source of water for geothermal energy and which is located in the city of Mieres (46,000 inhabitants).

The calculated capacity for the Barredo Shaft was a stock of 6.4 Hm3 of water and a nominal drainage capacity of 4.25 Hm3 / h at an average temperature of 21ºC. The pH of the water was 7, but its calcium content was high, so to reduce future maintenance costs, a heat exchanger was used instead of direct water circulation.

The first two facilities supplied were the new Vital Álvarez Buylla Hospital with 120 rooms and an area of 28,000 m2, and the Research Building of the University of Oviedo on the Barredo Campus. The annual geothermal energy demand of the hospital is about 7 million kWh and 208,000 kWh of the research building about. Both entered service in 2014.

The success of the installation means that in 2016 a third installation was added for the air conditioning of the Asturian Energy Foundation (Fundación Asturiana de la Energía - FAEN), an entity for the promotion of R&D activities and training in the field of energy. The location of this Foundation is precisely the old compressor room of the shaft which was reformed for this purpose. The energy demand is approximately 72,000 kWh per year.

The investment of the three facilities has been about 1.5 million euros for a total power of 4 MWt.

But the project is still alive and at the end of 2018 the works of a second phase of the project began in order to supply thermal energy to the Polytechnic School of Mieres of the University of Oviedo, the Bernaldo de Quirós Secondary School and two new buildings of 248 homes in the Mayacina district of Mieres. The investment involves 1.4 million euros of which 500,000 subsidized by the European Union through the European Regional Development Fund – ERDF, avoiding the emission of 636 t of CO2 per year.

This extension of the project will add 2 MWt more to the previous 4 MWt until a total of 6 MWt.

Pozo Barredo District Heating Scheme.

Figure: Barredo Shaft District Heating Scheme. 1: 248 viviendas 2: Instituto  3: Edificio de Investigación 4: FAEN 5: Escuela Politécnica 6: Hospital Vital Álvarez Buylla.

Source: Red de Calor- Mieres – Aula Hunosa de la Geoetermia y la Biomasa

Second project: Fondón Shaft.

The success of the Barredo Shaft project led to the development of a second project in the Fondón Shaft, located in the nearby city of Langreo to supply energy to the public health center, a residential building, the Juan Carlos Beiro sports center, the Nuestra Señora del Fresno elderly residence and the Langrehotel building.

The project will avoid the emission of 407 tons of CO2 per year and has a budget of 3.2 million euros with a subsidy of 1.1 from ERDF funds with an execution period of 10 months.

Next projects.

HUNOSA is already studying the possibilities of a third project in El Entrego using the Sorriego Shaft as a geothermal source.

In Laviana there have also been contacts between the city council and HUNOSA about the possibilities of using the Carrio Shaft, currently in the closure phase (its exploitation finished on December 31, 2018), to develop a similar project.

The Riosa city council has shown interest in implementing this technology from its mining shafts.

Future of geothermal energy in abandoned mines.

The technology for using of mine water is being developed and implemented in various places in Europe and in particular in Asturias. The extensive grid of old mines in Asturias, close to urban areas, make them a source of geothermal energy available, clean and economical. If Asturias has been based on the economy of coal for more than a century, now it can use the old mines to have a double future. On the one hand, replace the coal electricity generation by geothermal heating and cooling and, on the other, develop technology and companies that export the know-how of this technology, replacing the economy based on coal with an economy based on renewable energy.


Jardón, S. et al. Uso geotérmico para calefacción del desagüe del pozo Barredo. I Congreso GEOENER (2008).

Jardón, S. et al. Aguas de mina en la Cuenca Central Asturiana: un recurso geotérmico. I Congreso GEOENER (2008).

Cordero, C. et al. Aprovechamiento geotérmico de las aguas de mina. Universidad de Oviedo: Campus geotérmico. II Congreso GEOENER (2010).

Various press news in La Nueva España, local newspaper (2008 - 2020).

Various press news in El Comercio, loal newspaper (2008 - 2020).

Gonzalo Roberto Mayoral Fernández's picture
Thank Gonzalo Roberto for the Post!
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Matt Chester's picture
Matt Chester on Jan 21, 2021

These seems like a great, common sense solution. Is there ability to re-train coal workers to be able to work in these geothermal applications? 

The company's objective is to diversify in order to continue being an economic engine in the old mining areas and to be able to relocate the personnel of the mines, also taking advantage of their professionalism and know-how for the new business lines.

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