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I was discussing with a friend about renewable resources in which you can generate and store power for a long time. In this one way which I know is hydropower where when you have huge requirement of energy you run the water over motors which drive a shaft which in turn moves a turbine and which in turn gives you a huge boost in energy for say that 1-2 hrs. The rest of the day when energy usage is not so much, you use the same energy to lift the water. Now other examples of energy which I saw sometime back was a giant hole in which something like a huge wreaking ball or something was lowered and then taken back up, using the same principles. Now can somebody tell me what that should such energy producing machines should be called? For me it is gravity-assist but I'm sure there is much better name for it.

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  • Also, "for a long time" means you need a system that is cheap to build and maintain, because operating costs will make up a big part of the cost per unit of energy stored. It's exactly the same as renting a warehouse - the cost of putting an item into the warehouse and getting it out again is usually most important because most things don't stay in the warehouse very long. But if you're leaving stuff there for years... that daily storage charge adds up. Most energy storage is expensive so the owners want to run it as much as possible. Multiple cycles per day, ideally.
    – Móż
    May 24 at 1:44
  • medium.com/land-buildings-identity-and-values/… this pumped hydro project is designed to store power for 1-5 years and it would be one of the biggest pumped hydro projects ever... for a country with only 5M people.
    – Móż
    May 24 at 1:47
  • Yes, that's called "pumped storage" and it's definitely on the playing field, but not at a small scale. If you're fitting a 50 megawatt plant you'll have factory sales reps lined up out the door to sell you bidirectional generator-pumps. Jun 6 at 21:45
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I think you have exactly the right term already. The Institute of Electrical Engineers use "gravity energy storage" and wikipedia has a Gravity Battery page.

The main issue is that pumping and storing huge amounts of water is a mature technology - people have been doing that for ages. And since gravity isn't very energy dense storing decent amounts of energy that way means at lot of mass or height, so the solid mass storage systems are typically quite small compared to the (pumped) hydro ones.

This question about home pumped hydro shows how hard small systems are. Browsing the "energy-storage" tag might help give you an overview.

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    There are some interesting solutions appearing to gravity energy storage. A couple worth mentioning are lowering heavy weights down disused mineshatfs, and sending railcars filled with ballast up the side of a mountain. Worth bearing in mind that as hydro schemes also require lots of height and huge amounts of water, it's not always easy to find suitable locations.
    – John M
    May 20 at 17:52
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The industry term is "pumped storage" and it's used all over the place at a large scale.

  • Some systems, like Oroville Dam, reverse their turbine-generators to be "motor-pumps", pumping water from the bottom of the dam to the top*.

  • The Niagara Falls installation sits well above the Falls, and has separate pumps: they pump from the high side of the falls, and obviously the generators discharge to the low side.

On a small scale, you just cannot obtain reversible generator-pumps. So you're better off following the Niagara model, with pumps and generators separate.

Micro-hydro turbo-generators are readily available, and there are many installations. They are mainly used in "run of river" applications.

Water pumps are, obviously, also readily available commercially. One of them - the Aermotor - is even a windmill! Aermotor strongly insists their windmill is not made to generate electricity... well, it can now!

It's certainly a boon if you can pump from a higher place than you discharge the turbine. But it all works at the same level too. **The important thing is having locations for sufficiently large reservoirs, and not having a reservoir breach from overfilling it.


* Oroville has a huge reservoir at the bottom, but it's hard to see on a satellite view. Here's the trick: The Thermalito Diversion Pool (former Feather River at the bottom of the dam) is at the same level, and connected to a broad, shallow reservoir several miles west called the Thermalito Forebay.

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