Years ago I visited the Seneca Pumped Storage Generating Station [0] reservoir in person. It's a massive man-made lake on the top of a small mountain in Pennsylvania, USA.

They pump water up to it at night (when there is excess energy in the power grid), and let the water out in the day when the demand for energy is high (turning some turbines on its way down).

Prior to visiting I had an intellectual understanding of the concept of pumped storage [1], but I have to admit that it's one heck of an experience when you see it up close and personal. My thoughts standing at the edge of this massively perfect-circle deep lake full of water: "somebody built that... and it's one BIG BATTERY".

If you get a chance to visit one of these, I highly recommend it!

[0] https://en.wikipedia.org/wiki/Seneca_Pumped_Storage_Generati...

[1] https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...

The idea of pumped storage is pretty simple, but compared to lithium batteries the energy density is ridiculously small. If you already have an area that can be used for it (abandoned mine or reservoir) then it's pretty simply technology to build, but otherwise it's probably not worth it.

As an example of how low density it is, imagine having a 1000l IBC tank, filled with water, on your roof at a height of 10m. That water (~1000kg) has a potential energy of 98000J or 27Wh - less than a laptop battery :D

True, but pumped storage can be made ridiculously large given favorable terrain. I've been to one that pumps 5 million tonnes of water up 800 meters (half a mile of head!), generating up to 1GW on the way back down. It probably costs less to maintain that thing than to charge and discharge an equivalent amount of lithium batteries every day.

Density isn’t everything. It’s likely a lot cheaper and less environmentally destructive to dig a big hole in the ground than to manufacture a lithium battery.

That is not entirely a given. Large eathworks have important knock effects on the environment and wildlife. We tend to think that dams and such are harmless but they change their surroundings radically. I had experience living next to one which modified the local climate and made a large contribution to the desertification of the place.

Stripmining was not exactly "environmentally beneficial" ... and that is literally digging a big hole.

> one BIG BATTERY

> The power plant, rated at 451 MW

That's a damn big battery. I love pumped storage, too bad it's not used more.

> I love pumped storage, too bad it's not used more

Pumped storage is awesome and the most cost-efficient way to store energy. It's used as much as possible, but...

I attended a USGS [1] talk about dams (in California) a few years ago.

The key takeaway is: all places worth damming have been dammed. There are no more dammable places, hydrologically and geologically speaking.

When I drive through the central valley, I see a lot of roadside signs about "build more dams!" It's sad to see the miscommunication...

[1] https://www.usgs.gov/science-support/communications-and-publ...

(I cannot immediately find a link to the specific talk. USGS is fun: full of crusty geologists, who even in the heart of the Silicon Valley aren't particularly technologically sophisticated (a nice reminder of how niche we all are) )

With pumped storage you don't need anywhere near the amount of water or storage needed for straight Hydro. In a 24 hour cycle, you can empty the top dam into the low dam, running the generators flat chat (unlike typical hydro which is limited by water supply), then pump it back up again for reuse. If you do the numbers (E=m.g.h) the amount of water required to store energy for a city of millions is quite tractable, assuming a decent head.

Australia is doing exactly this with "Snowy 2.0" (by connecting existing dams).

https://www.snowyhydro.com.au/snowy-20/about/

350,000 megawatt hours of energy storage, which is enough to power 3 million homes for a week, or (if there was enough generation/transmission capacity to get the energy in/out fast enough) the entire nation for 12 hours.

Another recent example in 2021. Kauai is supposed to be up to 80% powered by renewables with their pumped storage install. Small scale, but great example.

https://www.powerengineeringint.com/renewables/kauai-island-...

They are only adding 2GW of generation capacity, so I guess the 350GWh stored would take a week (175 hours) to be consumed by Snowy 2.0 that way.

I think you are describing pump-back hydro dams which are only a subset of pumped storage. Strictly speaking pumped storage only requires an elevation change and a water supply

If not near a water supply or lack of intent to use some of the pumped water for irrigation anyway, as the parent post said, (nearly) everywhere it was worthwhile to do is already doing it.

The alternative is another form of gravity battery, often involving railway on a hillside and cars loaded with stone.

Bah - Bath County can eat Seneca for breakfast and again for lunch and for dinner and then some. Max storage is 24000 MWh and can generate up to 3 GW

As Swiss friend once told me that Switzerland have super cheap electrical power by buying surplus power from the french nuclear power plants in summer and pumping into reservoirs high in the mountains.

Never verified the story, but geography checks out.

Interesting. The first thought that comes to mind when I see that circle is Apple HQ.

I just measured on Google Maps:

Apple HQ - around 1,600ft diameter

Seneca Pumped Storage Lake: around 2,400ft diameter

Extra power at night? Where's it coming from?

Demand is low at night, but many types of power plants are not easily/efficiently throttled down for lower supply (e.g.: nuclear, wind). So it makes sense to use the extra supply to pump water up.

They generate the energy probably all of the time. At night, however, fewer customers are using and so they can store the excess. That stored energy can then smooth out large changes in the daytime operating hours, or it can just supplement the supply as necessary.

At least in the case of https://www.electricmountain.co.uk/Dinorwig-Power-Station it provides near-instantaneous peak power (especially at the top of the hour when everyone turns on their kettle for tea), and is recharged through the early am via nuclear and other power plants that can't be shut down that quickly.

I believe the main power generation is hydroelectric, so there is some flow through the turbines at all times.

Not extra, excess. Demand is lower at night.

Apparently there is already the concept of rail train batteries: https://www.vox.com/2016/4/28/11524958/energy-storage-rail

You run the trains up the hill when energy is cheap or, for example, when the sun is out and solar works. Then when you need it, you run the trains down hill to generate electricity. Similar to pumped hydro where they do the same by pumping water up hill and then draining it downhill later. Super cool!

It's interesting as a thought, but I don't think it's likely to be large-scale practical.

Suppose you wanted to run a normal electric train up a mountain. It would certainly take a decent amount of power but not so much that it would be a big challenge for a city-scale power grid. So far you're not yet talking the scale of power where storing it would really be interesting to a grid.

One option to store more power would be to make the train much, much heavier. Sounds simple enough -- fill all of the cars with concrete and now hauling it up the mountain will store a lot more power. However now the rails and the trains themselves will need to be far sturdier than a normal railway, and will wear out quickly.

The other option will be to simply scale up -- start the day with a hundred trains in a rail yard at the bottom of the mountain and over the course of a day move them all to a rail yard at the top. Now you have successfully stored a decent amount of juice.

But hold on a minute... you've now built two large rail yards, meaning you'll need a lot of relatively flat real estate at both altitudes. How about instead you just dig a hole on each side, called it a reservoir, and put a pipe between the two? Certainly it must be a lot easier to store and move mass in the form of water than it is in the form of trains!

That is why I don't see much potential in rail-based storage: if you have the geography to build one at-scale, probably you could build pumped hydro there cheaper. Even if you were in a water-scarce area where you would need to enclose both reservoirs to avoid evaporation loss it still sounds simpler to me than building and maintaining a hundred heavy trains would be. Also, routing a pipe between two reservoirs is a lot more flexible than building a railway.

Yeah the idea is the trains are filled with tons of weight.

In my head it still seems like it would be cheaper than digging out massive reservoirs for pumped hydro. Rail seems relatively cheap even if you do have to replace it regularly because of the wear. It also seems like you could put the rail in all sorts of geographies, big and small. Maybe it isn't worth it unless you go big though... and at that point why not hydro.

It's good questions though. No idea how the economics of it will work out vs pumped hydro.

Perhaps the trains could partly be passenger trains, costing amusemant park rates.

Then collected money could eventually pay off the cost of construction, and eventually maybe even offset the maintenance cost.

If nothing else, it would certainly boast the advantage of being more fun than water storage.

Ideally have the transportees walk up the hill by themselves, summer sledding style. That way you are by some strange definition guaranteed to be net positive ;-)

I think you are on to something here. Make all elevators in hi-rises down-only and all stairwells up-only. Convert falling excess desk-jockey blubber into usable electricity while lowering rate of CV disease and generally improving fitness. Downside is probably a lot of BO that didn't exist before.

Clean power and mountaintop removal are mutually exclusive. That is neither clean nor renewable. Among other things, the water that flows through mineshafts, collects in quarries, or over strip-mines is often toxic as hell. When you dig into the rock like that, you expose a lot of water soluble toxic shit to the elements which poisons everything downstream.

> Maybe in the future clean power can be generated from pulling down mountains.

it takes a lot of power to dismantle mountains and load them onto trains. and folks get real grumpy about mining operations leveling off mountains.

And it sounds like a rather visible ... race to the bottom, as it were. :-)

>Maybe in the future clean power can be generated from pulling down mountains.

With added bonus efficiencies from combusting the coal that fortuitously falls out!

A thousand (1e3) metric tons (1e3 kg) of anything, up a thousand meters (1e3), has 1e9x(10)=1e10 Joules of potential energy on earth (g=~10 m/s2).

At 80% conversion (8e9 J) and assuming 1/8 of the energy is "payload" after paying for the train to go up, that's still ~1e9 or a GigaJoule.

At a -20% grade, you're looking at a 5km train ride, which reasonably might take a half hour or less (1800s). So, you're generating GJ/1800s = 555 KW by pulling down the mountain, assuming the rocks magically teleport into and out of your hoppers. (Thanks @calvinlh )

That's approximately 100-200 households per train pair, which might generate 10 K$ / month in electrical sales?

A 20% grade is probably unachievably steep for ordinary railways. Even a 5% grade is considered remarkable.

Wikipedia says (https://en.wikipedia.org/wiki/Saluda_Grade):

Saluda Grade is the steepest standard-gauge mainline railway grade in the United States.[1] Owned by the Norfolk Southern Railway as part of its W Line, Saluda Grade in Polk County, North Carolina, gains 606 feet (185 m) in elevation in less than three miles between Melrose and Saluda. Average grade is 4.24 percent for 2.6 miles (4.2 km) and maximum is 4.9% for about 300 feet (91 m).

Unless you're gonna build that mountain style with gear drive and toothed tracks, you're probably looking at 5% grade and a 20km ride, which drops you down to ~140kW for 2 hours.

Ion the other hand, it seems you can get 11 thousand tonnes in a coal train:

https://www.australianmining.com.au/news/%E2%80%8Bnew-coal-t...

So on my 5% grade track I could get 1.5MW and if you can get your 20% grade to work that'd be just over 6MW

per train. Long track: more trains, right?

Great points though!

Then you also need hefty wires and adjacent infrastructure on whole track to collect all this electricity.

Sure, and magical robots that take no energy loading / unloading the trains.

If they are only moving blocks of concrete, loading/unloading is optional.

You're off by a factor of 3600-- 1 watt is a Joule/second, not a Joule/hour. 1 GJ / 1800s ~= 555kW, not 2GW.

I knew it seemed high. The GW description didn't match the wikipedia article.

This would make for a great oatmeal comic material.

Scifi novel idea: A habited planet without a sun (these actually exist) with heavy elements and high gravity. The surface unevenness is the best source of energy. After millions of years of extracting energy from flattening, the planet becomes a perfect ball and all life ceases as there is no energy to be found anywhere.

Geothermal energy is the way to go for this kind of worlds.

If there is a live core.

This idea is sort of being explored already: https://www.youtube.com/watch?v=itbwXMMkBQw

There's other ways of doing this too. Rolling a ball up a hill, inflating a balloon under water, etc.

That looks like a real life battery level indicator.

My take: it's cheating at jenga.

Energy Vault is a startup that stores energy using big concrete blocks. Pretty close to your idea: https://en.wikipedia.org/wiki/Energy_Vault

A similar concept is the Snowy Hydro project in Australia - essentially it is a battery for clean energy generators such as wind and solar when they cannot generate. There are two lakes - one at the top of a mountain and one at the bottom. When the wind is blowing or the sun is shining the wind generators and the solar panels power pumps that pump water from the bottom lake up to the top lake. When the sun is down or the wind is not blowing and electricity cannot be generated from panels or wind, water is run using gravity from the top lake to the bottom lake through a turbine, generating electricity that way and ensuring constant supply.

Melting down glaciers that subsequently pass through turbines on the way down should come close enough I guess? That future is here.

The iron ore was pulled up from the ground, so "some" energy is used there, to lift it into the trains. Now the mine is not quite as deep as ocean level, so there is still a net potential energy gain (you could say).

Literally destroying a mountainous environment is not clean energy.

But endless fields of solar panels and wind turbines is?

That seems like a somewhat arbitrary, fine line to walk.

neither of them strike me as great but taking down the solar farm is probably cheaper and easier than rebuilding a mountain.

Those sources of energy are both renewable and can be deconstructed with no permanent environmental impact, which makes them "clean" in my mind but I agree it's an ambiguous word.