A New Use for Old Mines

coal mine

Abandoned coal mines may prove useful in geothermal energy projects. (Photo credit: Photodisc/Getty Images)

As conventional heating and cooling costs rise around the world, many people are looking toward alternative sources of energy to maintain a comfortable temperature in their homes and businesses. A promising source of energy, it turns out, may be lying right under our noses—and our feet, and our floors, and the ground, to be more precise. The use of geothermal heat, or heat from the interior of the earth, is becoming increasingly popular as oil and natural gas prices climb. In many regions of the world, abandoned, flooded coal mines offer an almost ready-made way to access this geothermal heat.

The concept of using geothermal heat is not new. Since Paleolithic times, people have been using geothermal heat as they bathed in water warmed by natural hot springs. In 1911, the first geothermal power plant was built, converting geothermal heat into electricity. In the 1940s, Robert Webber developed a simple method of using geothermal energy in the form of the geothermal heat pump. A geothermal heat pump takes advantage of the fact that in most areas of the world, the temperature just below Earth’s surface remains constant, around 50 to 60°F. The geothermal heat pump works like this: in the winter when the temperature is lower than the ground temperature, warm water is pumped from the ground source to the building. In the summer, when the temperature is higher than the ground temperature, warm water is pumped from the building to the ground.

Today, the geothermal heat pump is one of the fastest growing types of renewable energy systems, and it is used in residential heating and cooling applications throughout the United States, Canada, and Europe. However, the initial drilling costs can be expensive and the process is complex. A clever idea currently gaining popularity is to use abandoned, flooded coal mines as the geothermal ground source, thereby minimizing the amount of new drilling necessary.

Several geothermal installations using water from abandoned mines around the world have already met with success. The first case study came from Canada in Springhill, Nova Scotia, where geothermal heat from abandoned coal mines has been heating and cooling a plastic manufacturing building since 1989. The company estimates the system saves $160,000 annually in energy costs.

In Pennsylvania, Marywood University uses geothermal heat from mine water to heat its Center for Architectural Studies. In Pittsburgh, heat from an abandoned 1800s mine is being used to heat and cool the church that sits above it. The estimated savings from the project are 75 to 80 percent for heating and 50 percent for cooling. In Missouri, a municipal building in Park Hills uses mine water to heat and cool a two-story building. The calculated savings for one year (1996) was $4,800—about 30 percent savings over conventional heating and cooling systems. Sixteen houses in Shettleston, Scotland and 18 houses in Lumphinnans, Scotland were outfitted with geothermal systems using water from abandoned coal mines. Heating costs were reduced by 80 percent annually. Finally, the town of Heerlen in the Netherlands is heating and cooling 350 homes and businesses using an abandoned, flooded coal mine. Only five new wells were drilled around the town to access the existing underground mine shafts. The area served by the geothermal energy includes a supermarket, cultural center, and library.

Many more plans are currently in the works around the world. A study sponsored by the U.S. Department of Energy found that geothermal heat from mines could be a promising source of abundant cheap energy throughout the U.S. There are as many as 500,000 abandoned mines on private and federal lands in the U.S., and most of them are already flooded. Coal mines are the most likely candidates for geothermal energy because they are the most accessible.

Several groups are working now to develop ways to analyze and predict the potential of specific mines. Researchers at McGill University in Canada have come up with a general model to be used by engineers to predict a mine’s geothermal energy potential. The model estimates the ability of a system to supply heat at a sustainable rate, which is dependent on how fast the surrounding rock can replenish heat to the water. Another group at the Oveido Higher Technical School of Mining Engineering in Spain has developed another way to estimate the amount of heat a mine tunnel can provide. Their method relies on gathering data from tunnels while a mine is still active and therefore easily accessible. With this type of advanced planning, modifications could even be made to tunnels while they are still in use to prepare them for use in future geothermal projects.

The advantages of using geothermal energy from abandoned mines are plenty. The energy is efficient, renewable, not dependent on climatic conditions (as are solar and wind resources), inexpensive and environmentally benign to access, and pollution-free. The maintenance costs of geothermal heat pump systems depend on the type of system, but, currently for all types of systems, are less expensive than the costs of maintaining conventional heating and cooling systems. As noted in a Canadian study, utilizing geothermal heat from abandoned mines may be especially advantageous for former coal towns, which may be located in remote areas to which transporting energy is expensive.

All these advantages make one wonder what is preventing more towns and establishments from exploiting heat from mine water. One reason may be due to the relatively low cost of conventional energy in the past. Another reason may be the lack of organized data on the access locations and conditions of modern and historical mines. As newer technologies such as regional geographic information system (GIS) databases are being applied to this problem, we will most likely start to see a lot of growth in this area.

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