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.
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.
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.