Dirty old mines could be a source of clean new energy

In a strange twist of irony, abandoned coal mines that once produced among the dirtiest fossil fuels are starting to be exploited for clean energy.

Water that has seeped into the mines, and has been naturally warmed by heat from the Earth's core, can be used to provide low carbon heat and clean energy storage.

This isn't exactly a new idea, but in our continued search for clean energy, engineers in Canada, the U.K. and several European countries are taking another look at mine water as an underutilized resource. 

This is a version of geothermal energy, which has been seen as having significant potential as an alternative energy source. 

The way geothermal energy typically works is by exploiting the fact that the earth gets warmer the deeper you go. Energy is harnessed by drilling into the earth, where water is circulated deep underground through a bore hole and heated. The heated water is then pumped back up, and used for warmth or for generating electricity.

Using old mines allows you to skip a step or two. The large, deep holes in the ground are already there. After mines are abandoned, water tends to naturally fill in the chambers and tunnels, and it's heated by the Earth. 

Springhill, N.S., once known for its coal mining disasters, has become a green energy pioneer by using geothermal energy from water heated in an abandoned coal mine. The energy is used to heat several of the town's buildings. (Anjuli Patil/CBC)

So all that remains is to pump this water to the surface and use it to heat buildings that are close to the mine. By using heat pumps, it can also be used to cool buildings during hot summer days, maintaining constant temperatures year round.

In the U.K., with its long history of coal mining, it's been estimated that one quarter of British homes lie above coal fields, representing a huge source of geothermal energy.

Canada was actually a pioneer in this technology. The town of Springhill, N.S., has been doing this on a small scale since the late 1980s to heat industrial buildings, using an estimated 4 million cubic metres of water that had flooded an abandoned mine under the town. 

The water has been heated to 18 C in the mine. It's pumped to the surface and run through a heat pump, which extracts the energy from the warm water to heat the buildings.

 

Last December, the province of Nova Scotia invested money for research into the possibility of expanding the concept to provide low-carbon energy to other towns located near mines. 

An earlier study in 2006 looked at thousands of mines across the country that have been abandoned and identified numerous sites that might be able to take advantage of this kind of thermal energy source. These include: Noranda copper mine near Murdochville, Que.; Con gold mine under Yellowknife; Wellington coal mine under Nanaimo, B.C.; two sites in Sudbury, Ont. and several sites in Nova Scotia.

Iceland has many above-ground geothermal energy sources, as seen in this photo at the Hellisheidi Geothermal Plant. The province of Nova Scotia is looking into tapping into the Earth's internal heat in abandoned underground mines, a technology that was first tested in Springhill, N.S. (Saul Loeb/AFP/Getty Images)

The amount of thermal energy available depends on the depth of the mine, volume of water and temperatures. Initial costs of piping and pumps can be higher than conventional heating, but operating costs are lower and it is carbon free. 

Geothermal energy has been somewhat slow to catch on in Canada, partly because much of the country is covered by the Canadian Shield — very hard, dense rock that is difficult and expensive to drill through.

But there are many geothermal hot spots, particularly in B.C. and Alberta. And, of course, in locations where mines have already been dug, abandoned and flooded, access to the heat of the Earth is much easier. 

This won't work everywhere, of course. But it could work in many communities that once depended on mining operations and suffered financially when those operations shut down.

This could be an opportunity for the mines to give back in the form of clean energy for the future.