Flood an abandoned mine with water, let the surrounding rock heat it up, and there you have it: instant geothermal energy.
Researchers at McGill University in Canada have been looking into the idea, and they estimate that geothermal energy from abandoned mines could serve about a million Canadians. That’s not so much on a national scale, but on a local scale this kind of geothermal energy could account for a big chunk of a community’s power supply.
Geothermal energy and the coal mine twofer
If anything, tapping old coal mines for geothermal energy would relieve part of the economic burden of tending to the abandoned sites. According to the McGill study’s lead author, Seyed Ali Ghoreishi Madiseh, “Abandoned mines demand costly perpetual monitoring and remediating. Geothermal use of the mine will offset these costs and help the mining industry to become more sustainable.”
Abandoned coal mines and mine fires
When not properly attended, abandoned coal mines can catch fire and wreak havoc for generations. One classic example is here in the U.S., where an out-of-control coal mine fire in Centralia, Pennsylvania has been burning for decades, forcing local residents to abandon their homes.
Coal mine fires can be caused by lightning strikes and other natural causes, though in the case of Centralia the cause appears to have been a human-engineered accident.
Geothermal from surface mines, too
The McGill study looked at underground or “shaft” mines, but there seems to be potential for harvesting geothermal from strip mines as well. A couple of years ago, Purdue University in Indiana began mapping the geothermal potential of both types in the southwest part of the state, where coal mines account for about 186,000 acres underground and 284,000 acres on the surface. The idea is to identify sites where underground water could be easily exchanged with surface water.
Parts of Ohio, Pennsylvania and West Virginia are also emerging as potential geothermal coal mine hotspots.
Pitfalls of mining for geothermal energy at coal sites
Some local communities in Europe and Canada have already begun tapping into nearby abandoned coal mines for geothermal energy, but as far as their widespread use, the Purdue team sounded a note of caution. New geothermal activity could risk
worsening surface problems that are caused when underground mines start to collapse. In addition, while water is stored in underground mines it could dissolve metals and chemicals, contributing to leachate.