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Comment by codeismath | Hacker News Reader

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...

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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

https://en.wikipedia.org/wiki/Castaic_Power_Plant

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

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

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.

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.

Not extra, excess. Demand is lower at night.

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.

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