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Sat Dec 28, 2013, 09:49 PM

Hydraulic Energy Storage - Another Way to Use Gravity

Hydraulic Energy Storage - Another Way to Use Gravity
Davis Swan | Dec 23, 2013

I recently joined a discussion about how gravity might be used to generate and store energy. One of the comments provided a link to Gravity Power, a company that has proposed a modified take on "pumped storage" whereby a vertical water reservoir is used with a heavy piston. During the discussions a few variations on this technology were proposed. I suggested that abandoned open pit mines might represent a good starting point for very large facilities.

As in my earlier posting on Funicular Power the principle behind Hydraulic Energy Storage is to use excess electricity generated mainly from wind farms when demand is low (for example at night) to raise the potential energy of a mass by moving it to a higher elevation. In this case the means to do that is a relatively standard hydro turbine in a very non-standard configuration.

In energy storage mode a massive solid piston is raised by increasing the water pressure below it by running the turbine in reverse, acting as a pump to force water down the penstock.

In generation mode the piston is allowed to sink forcing water back up the penstock and through the turbine.

The piston would be a large concrete "cup" filled with as heavy a material as could be justified by the economics of the project. This could be rock debris, dense concrete, or even iron ore. The denser the material the better.

The containing cylinder would also have to be reinforced concrete. ..


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Reply Hydraulic Energy Storage - Another Way to Use Gravity (Original post)
kristopher Dec 2013 OP
longship Dec 2013 #1
NickB79 Dec 2013 #3
AZCat Dec 2013 #4
cprise Dec 2013 #2

Response to kristopher (Original post)

Sat Dec 28, 2013, 10:24 PM

1. Well, I don't think that's going to work so well.

That piston had better seal well against the sides of the tank because any water slipping by the sides is energy lost. At the scale this would require to be theoretically practical, the loss may be significant enough to make it impractical. Of course, these are engineering problems, not theoretical ones.

Myself, I like the pumping water uphill into a lake and opening the dam for clean hydroelectric power during off peak. It's the same principle, but one does not have to buy a million Acme anvils to make it work. The energy difference is nil, because potential energy is simple.


This plan has a complex system with engineering issues. It increases the energy by increasing mass (m) at the cost of height (h). But one could just increase the height and not have to worry about the piston full of Acme anvils. It's a null sum game. It's simpler by just pumping the water up hill. You want more energy, pump it up higher. In CA, or other mountainous areas, this would work pretty damned well, no Acme anvils necessary. (Please inform Wlie E. Coyote.)

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Response to longship (Reply #1)

Sun Dec 29, 2013, 01:35 AM

3. Dam-stored pumped hydro is difficult on the Great Plains, though

The open, flat nature of the central US that allows the wind to blow so hard and steady and earn the title "the Saudi Arabia of wind" also makes pumped hydro via artificial lakes impractical.

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Response to NickB79 (Reply #3)

Mon Dec 30, 2013, 01:48 PM

4. Really? I seem to remember lots of artificial lakes in the midwest.

Tuttle Creek Reservoir, outside of Manhattan, Kansas, comes to mind as an example.

I don't think the differential head would need to be that great if the mass of water were sufficiently large enough to compensate. There might be a minimum drop for the hydroturbine to function, but that's probably dependent on turbine selection. Evaporation could also be a problem. It would be higher with large, flat bodies of water than with deeper ones.

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Response to kristopher (Original post)

Sun Dec 29, 2013, 01:25 AM

2. Interesting!

I love seeing 'new' ideas like this.

There is also a long list of electric-powered processes that can be used at supply peaks. A few I can recall at the moment:

Desalinating water

Running IceBear air conditioners (cold storage)

Storing heat

Computer batch processing

Charging cars (storage)


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