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19 April 2019

Time may have come for old Chestnut – water hydro down a mine

The fate of the coal industry is, with the possible exception of two or five major countries (Australia, China, India, Indonesia and USA) clearly in a rapid downward spiral. Those five mentioned are sticking more to coal than others, but for the most part at least paying lip-service to dropping it from electricity generation, while the remaining recalcitrant coal lovers are smaller nations.

So owners of not just coal mines but any type of mine, are always looking for some future use for the land, which would not require completely healing its of 500 meter deep holes in the ground and mountains of slag. In Germany we have seen how when coal mines and coal plants are side by side, the mining site is filled to overflowing with solar panels, and the plant’s existing boilers are turned into molten salt energy storage, which can make electricity using the sites existing steam turbines.

This week in the US, Michigan Technological University has come up with a very old plan, that has been tried time and time again, but perhaps, due to the broader implementation of intermittent renewables, it is an idea that may have finally come of age – using abandoned mines for hydro storage. However this is not purely for use with coal mines, more with mineral ore mining as the 2-year pilot project will focus on an old iron mine.

Our first brush with this technology goes back to 2016 when a gold mining group in Australia planned to abandon its mines, and looked at turning its 50,000 gold mines into pumped energy storage, at a time when pumped storage made up 99% of the market, and when renewables were not so widely installed.

In 2017 it comes up multiple times in Germany, and again in the USA in the Appalachians, where Dominion Energy looked at precisely the same idea to fill its mines with water and use electricity from wind and solar farms to pump it up to a reservoir on the surface. History does not tell us if either of these attempts were successful, but the idea still has not caught on, so we suspect not.

To a certain extent this is really about countries which have the problem of “mines” and what to do with them, but that’s a pretty widespread problem. Michigan Tech in the past has asked the question can mine-water be used to create geothermal energy? This was attempted a few years ago by pumping out water from the mines and running it through a heat exchanger to transfer to other water pipes running through buildings – although that turned out to be little more effective than heat pumps are today, so why not simply use them.

Now the idea has become pumping groundwater which tends to flood unused mines, uphill to some holding area, like a reservoir, using surplus renewable energy. When energy demands are higher, the water would drop down the mine shafts through turbines which then give out electricity. It could be used to support a local minigrid as part of a tiered-storage strategy.

The University hopes to prove the idea working with the Marquette County city of Negaunee, with a population of just 4,550. Obviously there is an awful long way to go and we suggest that they first find out what happened to those 3 years old experiments which tried the same thing. Then it has to prove the idea is feasible, and can work with just about any mine, and then log effects on the environment and then finally design a generic solution which makes money. Most battery or energy storage ideas stumble over that last hurdle, economic feasibility. The University says it will design such a facility and will translate their findings for policymakers and developers.

The end point would be to build a US wide map of disused mines suitable for storing energy, and if they can prove that last point, economic viability, then these sites could easily be harnessed with money borrowed against future revenues, as soon as any energy company agrees terms for storing energy and builds the process into the grid workflow. That idea has come of age, but it would really need a high level of computerized automation to get that far.

Socially it is a clever use of a mine, because if it is underground pumped hydro totally underground, who can complain that it is an eyesore.

The American West has thousands of abandoned mines mostly from mineral mining as frontier moved westward. In the mid-1990s, a Michigan University team cataloged 2,000 shafts from 800 mines across 8 counties. There are literally 100,000s across the entire USA.

Preliminary research suggests that just one of the mines can indeed store enough electricity to power the surrounding town for several hours – which would mean that a handful of shafts is all that is needed to support local renewables efforts. The nice thing is that pumped hydro is a well established technology and there is mature equipment available, which is well designed and relatively efficient.

If this idea cannot come of age now, then it is in danger of being bypassed forever, in an era where there are many battery technologies, not least of which is the traditional Lithium Ion technology, not to mention Vanadium Flow, Molten Salt and liquid air. Hydro projects of any type tend to be put on the back burner these days and Irena (International Renewable Energy Agency) said that in 2018 just 21 GW of hydro was built, but of that, just 45 MW was pumped storage – an indicator that there are roadblocks in the way of such an approach, despite scale advantages.