[dcsan]

Since batteries are always the issue... How inefficient is mechanical storage? For example using electricity to just raise a heavy mass then as that lowers it can produce power. It seems that would be cheap to build at scale with the chance for almost unlimited storage.

I have to assume there would be a more than 50% loss through the process, hope someone on hn can comment. Maybe it's not worth it when you can tap into unlimited sunlight the next day.

[pjc50]

> How inefficient is mechanical storage?

The density is the problem.

If you raise a 25,000kg mass by 100m, that's 24.5MJ, or roughly the energy contained in one kilogram of coal. Or 6.6kWh (standard meter units) of electricity.

(and that's on the input side, not accounting for losses)

[pjc50]

.. or, if you want a fun comparison, a 2000kg Tesla with a 100kWh (360MJ) battery pack would have to be raised over 18km into the air to equal the energy stored in its battery.

[heavenlyblue]

That’s not how water storage works though for example. You are forgetting that for every unit of mass raised 1 unit, you can add another unit of mass where the previous unit was. Thus you are getting a progression of 1+2+3+4…up to the height units of power stored.

[maxerickson]

The water tower in my town is several hundred feet tall (many units) and has a big bulb tank at the top. When you pump a gallon of water up into the tank, it is raised hundreds of feet and contributes a fraction of an inch to the total height of the water stored.

It's an actual implementation of energy storage, the water is pumped up there and then gravity distributes it, so there is a buffer if the pumps can't run for some reason.

[spoonjim]

This system is currently only cost-effective with water, and only where you have a natural place to put it (i.e. a crater on top of a mountain vs. building a tank on a tower). Constructing a greenfield mechanical apparatus is too expensive for the energy stored.

[amalcon]

Pumped hydro is usually considered the best way to do this. Basically, you pump water from the bottom of the dam back up to the top. This is great because you probably already wanted most of the infrastructure for hydroelectric power; the pumps are a relatively inexpensive addition once you have that. There are other techniques, but pumped hydro is generally what you'll see for this reason.

Flywheels are also pretty good short term, but supercapacitors mostly do their job better these days. That said they are competitive, and technological changes could nudge them into more use. Just making your wind turbine really large gives a flywheel effect, e.g., so again if you already have a spinning thing they are often worth it.

[toomuchtodo]

Not worth it, easier to scale up battery manufacturing (which the world also needs for all vehicles to transition to electrification).

https://youtu.be/iGGOjD_OtAM

[wereHamster]

People are actively researching and working on kinetic energy storage systems, for example https://www.energyvault.com/ev1