As the world increasingly weans itself off coal as a source of energy, the abandoned mines left in its wake could someday be used to help generate renewable power.
The Wall Street Journal reports that companies in the U.S., Germany and other countries are increasingly interested in the possibility of installing pumped hydropower systems at former coal mines.
Pumped hydropower, which dates back about 100 years, involves pumping water into a reservoir at times of cheap, abundant energy, then, when additional power is needed, releasing it into a lower reservoir. The resulting current turns a turbine to produce electricity.
In the projects reportedly under consideration, utilities and companies envision using renewable power to fill the upper reservoir, then releasing water through an empty coal mine to an underground storage system.
The systems could, in effect, be a more practical way to store power from inconsistent sources like the sun or wind.
German coal company RAG hopes a $560 million system at a former mine near the Dutch border could power up to half a million homes, while utility Appalachian Power is investigating the potential for those systems in Virginia mines. The Journal noted earlier this week that a California company hopes to install pumped hydropower at a former iron mine.
Although observers view the projects as promising, investors are currently reluctant to sign on due to cheap energy rates in both countries, the result of public subsidies in Germany and the shale boom in the U.S.
Proponents acknowledged the hefty upfront cost but said those systems would last for decades and are "virtually maintenance-free."
“The advantage of pumped hydro is that it’s high capex, but it’s there for 100 years,” Alexa Capital's Gerard Reid told the Journal.