WHAT ABOUT DAYS WHEN THE CENTER OF THE EARTH ISN'T HOT?:

Abandoned coal mines generally fill with water when the mining has ceased. That water contains heat from far below the earth's surface. People can drill bore holes to bring that heat to the surface, then pass it through heat exchanges and heat pumps in buildings and in homes.

The first neighborhood mine-water heating scheme in Great Britain just went into full operation at the end of March and will eventually serve over 1,200 homes.

"Each minable scheme poses its different challenges, and there will be expenses involved with drilling bore holes or laying district heat network pipes in the ground," explained Gareth Farr, head of heat and by-product innovation at the Coal Authority in Mansfield, England. "But hopefully most of these schemes, if not all of them, will be able to operate at a similar or better cost to the traditional fossil-fuel heating schemes we have at the moment."

Geothermal energy is not new, but taking it from abandoned coal mines is not yet common, especially in the United States.

Professor and director of the Environmental Studies Program at Ohio University, Natalie Kruse-Daniels, and her students are studying abandoned mines in Appalachian Ohio to see which ones are close enough to towns to be used for home heating.

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