Converting Coal Mines into Pumped Storage

Is it practicable to convert old coal mines into pumped storage facilities? We may find out.
Is it practicable to convert old coal mines into pumped storage facilities? We may find out.

Perhaps the most intriguing idea in the renewable-energy package promoted by General Assembly Republicans (see previous post) is the idea of converting abandoned coal mines into pumped storage generating units.

Dominion Virginia Power operates a pumped storage facility in Bath County. The facility has two reservoirs. During periods of high demand when the price of electricity is high, Dominion releases water from the upper reservoir into the lower; during periods of low demand when the price is low, the company pumps water back into the upper reservoir.

The idea is to replicate this process on a smaller scale inside old coal mines. Frankly, I’m having a hard time visualizing how this would work — the underground coal mines I’ve visited follow are as level as the coal seams they follow — but I’ll assume that proponents of the idea know much more about the subject than I do.

One advantage of using coal mines for pumped storage is that they use water already in the mines, and there is no need to dam a river or creek. Further, Terry Kilgore, R-Gate City, who sponsored the bill, envisions using wind or solar power to pump the water. You can’t get any greener than that.

Here’s the topper: Use the abundance of green power to sell big corporations on locating their data centers in Southwest Virginia. One of the Commonwealth of Virginia’s two data centers is located in Lebanon, Va., on the edge of the coalfields, and the Virginia Tobacco Region Revitalization Commission has invested heavily in equipping the region with the broadband access that any data center requires. High bandwidth and clean energy make a winning combination, the thinking goes.

Dominion, which already has a coal plant in Wise County, doesn’t have a specific project in mind, but says it is keenly interested in what Kilgore’s bill would allow, reports the Roanoke Times.

“This is a BIG deal longer-term in the coalfields,” Jack Kennedy, Wise County’s clerk of circuit court and regional technology advocate, told the Times. “It could lead to hundreds of millions in investment, maybe over $1 billion.”

Hope always springs eternal in Virginia’s suffering coalfield region. The idea of converting underground coal mines into pumped storage facilities sounds extremely conceptual, and the economics are far from proven. But you never know. If the idea does work, and if the region could attract a handful of data centers — stranger things have happened, Microsoft located a data center in Mecklenburg County —  it could be a game-changer.

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11 responses to “Converting Coal Mines into Pumped Storage”

  1. LarrytheG Avatar

    I don’t want to be ugly here but there is some fundamental physics being ignored.

    In essence what is being said is that we’ll use solar to pump water out of these mines and then we’ll refill them with pumps powered by electricity also?

    Back Creek works off of gravity flow. you pump the water in the lower reservoir back up to the higher elevation and then gravity flows that water downstream through turbines to generate electricity.

    when you pump water into mines – it takes electricity to do that – and then they’re saying you’ll use electricity again to pump the water out.

    you could do the same thing with quarries … but how do you get any advantage from doing that if there is no gravity flow through turbines ?

    at least with a river – you’d be pumping water back upstream to flow back down and in theory capture the “head” energy but just like with the Back creek – it “costs” more to pump it upstream that you net out from the downstream flow.. it only works if your goal is to use cheap/unused base load coal plants to power the pumps at night .. then recapture that power as a supplement to peak load during the day.

    with solar – you can only pump during the day- the very time you’ll need the peak power… why would you use solar to pump water instead of add power to the grid when it is needed during the day.

    Trying to be charitable here but I think this concept is loony tunes and if it coming from someone who is in some kind of a leadership position, I fear for the country.

    1. I agree. The idea does not make intuitive sense at all. The idea of pump storage is to move water back and forth between an upper and lower level. Underground coal mines don’t have upper and lower levels.

      That’s why I assumed there was something to the idea that I was missing and the media had not thought to explain. However, say what you will about Dominion, their engineers are not stupid. They would not express interest in the idea if it was ludicrous on the face of it.

      Using solar may not be the problem you suggest it is. Solar generation peaks in mid-afternoon three or four hours before electricity consumption peaks. It still could make sense to use solar power and pumped-storage to shift production to when demand is greatest.

  2. Steve Haner Avatar
    Steve Haner

    A lot of curiosity lingers about how that acidic water in an old coal mine is going to work with those pristine steel turbine blades….Seriously, as Larry notes, a lot of energy gets used pumping water back and forth and not powering houses, which makes sense when you pair this with a nuclear plant running all night – but might not make as much sense with an intermittent renewable power source. Then there is this little issue called line loss, the amount of electricity that bleeds off the transmission lines as they travel a few hundred miles back to Dominion’s service territory. If this ever happens at all, beyond a small demonstration project, it seems more likely APCO or Kentucky Utilities might do it so it fits better with an existing service territory. Unlike some other bills I’ve seen, this one didn’t futz with the SCC’s “reasonable and prudent” review authority. Unless some big backer other than Dominion is lurking out there in the shadows, this may be a long way from reality. Not least because, as former Delegate Kennedy said, if a utility does it by itself this may require more than $1 billion in capital from somebody’s ratepayers. Through the entire legislative process, a number was never mentioned.

  3. LarrytheG Avatar

    I did not even mention the acid issue with mines .. you put water in mines and it gets acified … this is how rivers and creeks in West Virginia get ruined forever except that over there the source of the water is natural springs and seepage that fills the mines then they overflow into streams.

    but geeze.. if you are going to pump water OUT of a mine – where would you put that water and how would pumping it out – generate energy?

    I too suspect Dominions engineers are not stupid and that’s why they kept a straight face when responding to the guy that proposed this – then they could hoot their butts off once they got back to their offices…

    I’d LOVE to see their emails.. !!!

    this sounds like the proverbial perpetual motion machine. All you have to do is dig a deep pit .. fill it water and put a solar pump on it and VOILA – you’ve got another energy source for the grid. I can see the farmers lining up in droves!!! Maybe they could use their SILOs.. and towns could use abandoned water towers… heck the possibilities are almost endless!

  4. Pumping water uphill and then letting it fall and run the pump in reverse to generate electricity is not 100% efficient — you get back around 70-80% of the electricity you put in — but the ability to time-shift when you must consume bulk electricity can be hugely valuable and that offsets the huge cost of these projects.

    Bath County’s pumped storage project was built in the 70s, at a time when nuclear power was forecast to exceed the lowest daily levels of demand (late at night). Since nuclear units cannot be shut down in the short run, the excess power would otherwise have been “dumped” — that is, simply wasted — during those hours so the cost of pumping the water uphill would have been essentially zero. It turned out, not that much nuclear power was ever built; but even so, the difference between the price of baseload power on the grid at night (even if not zero) and the price during the workday is great enough to more than offset the losses due to storage/retrieval; also, the flexibility of hydro power is extremely useful to the grid operator for fine tuning generation to match load on the grid as it fluctuates. I don’t know if the Bath County project would have made financial sense without that zero-cost power in the mix, but once it was built, it has been a God-send to DVP to have it.

    Now utility planners must deal with a different time shift — not from the middle of the night but from the middle of the day; not cheap night-time baseload nuclear but cheap day-time solar; but the same rules for pumped storage of water apply: the difference between the cost of the power to pump it up (plus 20-30% for losses), and the price at which you can sell or use the power generated when you let it fall, is the benefit of storing it. The daily consumption of power on the grid will still generally peak in the early evening, so that’s when the wholesale price will be highest. The challenge is predicting when the price will be lowest and how low it will go. As more solar generation is built, older fossil-fueled cycling generation will be retired and the daily cost curve will become flatter; but it will be many years before enough solar generation is out there to drive the daytime wholesale price lower than night-time levels.

    LG asks the obvious questions. The whole point of pumped storage is to pump the water against gravity, converting electric energy into potential kinetic energy, which you convert back to electricity by letting it fall. Obviously the water must change elevation. if you are using chambers in abandoned mines to hold the water, you must find two that are at different elevations but near enough to connect them somehow, either by drilling a tunnel through the rock or by running a pipe externally down the side of a mountain, and with space and access to build a powerhouse for the pumps/generators at the lower chamber. Also these chambers must be watertight. In fact the Bath County project was plagued initially by leaks from the upper and lower reservoirs, so using a mine that’s already flooded may demonstrate that the leaks don’t exist or have filled naturally over many years. And you will need a water source to fill the chambers initially and to replace leakage. And yes, it doesn’t make any sense to store and retrieve the power unless you can overcome, with cost savings, the 20-30% physical losses for storage plus the small amount lost due to transmission losses between the storage facility and the grid.

    1. LarrytheG Avatar

      I’ve wondered if you could – on a length of river – have a small dam and a pipeline just below the dam that captures the water and pumps it upstream perhaps many miles – with as many needed – solar pumps all along the way so water could be carried far upstream and put back into the river and when it gravity feeds back downstream, hits the dam – it goes through the turbines – then is captured again and sent back upstream with the solar pumps.

      this is what they call “run of the river” power generation … you normally only see this on very large rivers.. like the Columbia or St Lawrence, Niagara etc, because lower flow rivers with seasonal variations are not going to generate reliable daily electricity and during low periods – none.

      Of course the upstream pumping would only occur during the day – and the obvious question is why would you use the solar to pump water to then go through a turbine rather than just feeding the solar directly into the grid? Every time you convert energy – from solar to pump then to turbine – you lose efficiency… the highest net energy is directly from the first thing generating the energy… every subsequent conversion loses energy.

      1. It wouldn’t gain you anything to pump the water upstream any further than just behind the dam where the generators are located. But that’s with one dam. There are indeed two dam arrangements on rivers that work exactly like non-river pumped storage. All you need is two dam-made lakes on the river separated significantly in elevation and not too far apart laterally to run a pipe between their lakes — and you use the water pressure (head) at the bottom of the pipe where it discharges into the lower lake (not, below the lower dam) for generation and pumping.

      2. Re using solar power to pump water uphill — you wouldn’t, so long as the solar power could be sold to the grid for a decent price right when it was generated. The ONLY reason to time-shift electricity availability through storage (by battery or pumped water) is if it’s worth so much more to sell the power later that it more than makes up for all your costs and losses from storing it.

  5. Peter Galuszka Avatar
    Peter Galuszka

    I am puzzled about how this would work without polluting groundwater and surface water. Combining pumped storage, old coal mines and renewable energy is an intriguing idea, but I would assume that tremendous lengths of metal piping would have to be installed in coal shafts. If not, the water in the dirty coal areas would become badly polluted. Massey Energy was fined some years ago when polluted coal water broke into another underground shaft and ended up with massive pollution of river water.

    1. Don’t know either. Jim mentioned recycling the water, in which case I’d expect at the least the operator would want to clean the recycling water of suspended particles and harsh chemicals to extend the life of the hydro turbines. Leakage into the surrounding coal and rock seams would depend a lot on local geologic conditions. Connecting two such abandoned mine chambers by pipe would probably take place through a drilled tunnel which could be lined with a casing to prevent water losses laterally. These are problems with solutions that ought to be addressed up front — and there’s the rub. If a utility builds it, the project has to undergo SCC/DEQ review; but if not . . . ..

  6. Smith Mountain Lake is another pumped-storage facility in Virginia that some may be aware of. The Bath County facility sounds amazing: who knew we had something like that? (think I originally learned of it here on Bacon’s Rebellion). Between the two facilities, Virginia is essentially a national leader in pumped storage.

    Not at all sure about the coal mine idea…we’d have to hear a lot more about who came up with the idea and how it is supposed to work.

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