The other day, I came across this video about the mining of lignite coal in huge strip mines in Germany. While the information about lignite mining and the destruction of nearby towns (sound familiar?) was interesting, the most intriguing part of the video was the section about the experimental development of a mined out deep coal mine as a pumped storage facility.
Pumped storage is a long proven and relatively common way to store electricity using the stored potential of an elevated body of water. This does not produce energy, it simply stores it, like a battery. In times when electricity is abundant (and cheap) on the grid, electricity is used to pump water into a high reservoir. When electricity is scarcer, and also brings a higher price, the water is released through a hydro-electric generator into a lower reservoir, which extracts the electricity back out of the water’s stored energy. This process is almost always done in surface reservoirs, and depends on the natural elevations present in the surface terrain.
Now, engineers in Germany are researching the feasibility of using the large storage capacity of mined out coal and metal ore mines to serve as the lower storage reservoir in this kind of pumped storage process. In some cases, the upper reservoir could be underground in a section of the mine closer to the surface.
Here is what this system would look like (sorry for the blurry print, I had to expand the image a little):
Germany has transformed its system of electricity generation so that it has massive amounts of wind and solar generated power. While the extensive distribution of these resources smooths out the intermittent nature of the power generated, there are still gaps in generation between supply and demand. Natural gas generation is a good way to fill those gaps, but in Europe, natural gas is expensive. Coal-fired and nuclear plants, which have to run all the time, are getting hammered by the cheap and abundant electricity coming from wind and solar power. Germany is ending its nuclear experiment, in any case.
So significant increases in storage are critical to the German energiewende. The research is just getting started in Germany, but it appears that it has started to kick into high gear. Here is a link to a German feasibility study that includes a lot of details about technical problems and the practical potential of repurposing mines. Here is a link to an excellent summary of the current status of German work on the subject. This article provides an excellent diagram of what a mine pumped storage system would look like, as well as a map of potential sites in Germany.
One of the great aspects of this kind of project is that repurposed coal mines require a lot of retrofitting and construction work, as well as ongoing maintenance and operation. Underground coal miners possess almost all the skills that would be needed to operate one of these facilities. Why aren’t federal and state governments looking at what German researchers are doing? Why aren’t US researchers assessing the feasibility of these kinds of projects in the US?
Yes, low US natural gas prices are keeping electricity prices temporarily depressed, so mass storage is not as cost competitive as it might be right now, that won’t last forever. And the US coal and electricity industry is more concerned about their own shareholders than whether WV coal miners have good jobs. And Germany has made a national commitment to renewable power that is still a distant dream in the US, although US renewable power is growing even without Germany’s sensible public policy.
Electricity storage is now a major focus of research worldwide. Why not at least study whether pumped storage technology can keep underground coal miners working in the US?