A similar one would be a hot water cylinder that only heats up when the sun is shining.
And maybe something that fills scuba bottles to store electricity as compressed air. etc.
The best and most reliable method of non-battery storage of energy is the traditional water tower. It used to be standard practice for buildings to maintain water storage tanks on their roofs. Mate a water tank with some solar panels and you can create an energy storage system without heat, high pressures, chemicals, high voltage or even moving parts (the pump has only one moving part).
Mind you, I don't discharge the system past 23.5v ever, and I check my electrolyte levels weekly adding distilled water as needed, but lead acid are cheap, effective, long lasting, and recyclable with minimal effort. The only thing against them is maintenance, and they are big and heavy. My house doesn't seem to care.
See the chart in [0], where 100% discharge nets 200 cycles, 50% gives you ~500, 30% is ~1200. One would expect that if you discharge 50%, thats half a cycle, and therefore get 400 cycles, but in reality you get 500.
That said, this thread has descended from a comment about apocalyptic scenario planning and this general principle of maintaining batteries makes sense. Learning how to build and repair lead acid batteries doesn't seem to be beyond the realms of possibility.
A good MPPT charge controller will handle stepping up and down the voltage as need to provide optimum life.
https://batteryuniversity.com/learn/archive/advancements_in_...
I disagree with the 1000 cycles concept. Modern battery controllers are very good at preserving oldschool batteries. I don't see every off-grid house replacing their batteries every few years, just as I don't see automotive or marine batteries die so quickly.
Assuming off grid prepper mentality is being used.
Are you sure about this? Lead-acid batteries are highly recyclable, but lithium cells are straightforward to recycle, too. I know that Tesla has a recycling center set up at their gigafactory.
Water towers have to be built on site, which can be difficult. Not to mention, to get appreciable storage, you have to build a really tall tower or a really big one. This is difficult too. Especially if you are in a location where the soil shifts or you get high winds. Because now your tower has to survive the elements.
There is definitely a strong case against water towers for distributed energy storage.
Similar system from the age of steam:
However there's something about living off grid that makes one want to simplify, and batteries are one of the big, expensive, and limited life time components of a solar system. If you can reduce the load on, and the required capacity of your battery bank, then you have improved reliability significantly.
As you say, pumped hydro is certainly a great storage system if the situation permits. It just takes a very large storage system to store as much as batteries. If you have a pond or lake and an easy supply of water it would certainly be my choice.
On the other hand, so is a big chest freezer!
So in sunny days I let the water tank heat as much as possible(usually around 70-80C), and can go 3-4 days without even needing to turn it on. We are 4 in the household and it holds nearly 100liters of water. It is a kind of battery :)
I find it ironic that this sort of thing is so overlooked with solar/wind power on the electric grid. Consumer electricity prices should be allowed to rise and fall with the availability of solar and wind. Then, you can heat one hot water tank only when electricity is cheap, and also use that tank to heat your house in winter. In summer, a separate tank can be chilled when power is cheap, and used to cool the house.
Or even simpler, a pile of rocks will work.
With such a scheme, the need for grid batteries would be reduced enormously. Instead grids have the problem of what to do with the extra power when there's too much of it.
For example, the power goes out around here often. I've noticed it can take up to two days for the house to cool down. The water in the hot water tank is hot enough for a comfortable shower for 3 days.
Water/rock batteries are cheap as dirt, no maintenance, no fire risk, etc.
https://en.wikipedia.org/wiki/Solar_water_heating#Energy_pro...
[Silly to ignore equipment costs, sure, but if you have other uses for PV power ... using PV for heating water isn't necessarily nuts.]