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OK, question for and those into

What's a good small scale way to store energy that's not a battery?

@solarbear
big old capacitors are what some cheapo hand crank flashlights that I have use. Other options I've seen include fly wheels, ceramic pelettes to store energy as heat, springs, weighted pullies, but this is all in principle. I imagine you might want practical applications and battle tested solutions.

@solarbear @zens I often wondered whether springs could be used for this, but I have no idea how much energy they can "store" without getting too large.

@tofuwabohu @solarbear depends on what you’re doing with it; pocket watch or big ben

@tofuwabohu @solarbear one thing inkeep foming back to is all our energy originates with the sun- it sounds obvious; but thinking about it forces me to trace back batteries, the storage methods i me tioned and so on. so we could get abstract snd store energy in a lump of coal; just need to wait a few billion years.

or a photosensitive chemical process that can then release heat, pressure (steam) or electricity. sugar is pretty darned energy dense, if you can figure out what to do with it.

@grumpysmiffy @solarbear yeoh ! if we were gona time travel, we could have an archimedes screw or other mechanism pump waree up high to store energy. open a valve on a water wheel to release it. sand could also work.

@grumpysmiffy @solarbear oh hey, technology connections did a video on non-battery solutions for storing energy

youtu.be/0f9GpMWdvWI

@solarbear depends heavily on the usecase, i imagine

@banjo ice seen an article on these in lowtech magazine. It's a really cool idea

@solarbear a couple I can think of:

ice storage air conditioning. essentially, take advantage of a surplus of electricity to make ice, and then use that ice when there's a deficit of electricity to cool a space. there was a startup making residential-scale systems that went out of business (and I'm not entirely sure why), but this is an established thing for commercial building AC systems

heat storage strategies with water heaters. in the US, water heaters are typically kept at 140 F (or 60 C), with some recommendations to reduce the setpoint to 120 F (49 C) to save energy and avoid scalding. (this is probably a bad idea - 120 F is at the upper end of where legionella can multiply. a better strategy for avoiding scalding is to use a mixing valve to mix cold water in and reduce output temperature to that.) once you have a mixing valve, though, your water heater temperature isn't your output temperature, and you can play games like push the heater up to 170-180 F (77-82 C) when there's a surplus of electricity, and then reduce the setpoint to 130 F (54 C) when there's a deficit - you do use more energy overall, but you're time-shifting *when* you use the energy.
What is your reason to avoid a (chemical) battery?

@citc energy usage, lifetime restrictions, lack of recycleability ect

@The Cuddlepunk Cub
It could be argued that legacy lead-acid cells meet those criteria; of course for stationary applications.

@solarbear You've got some options here! If you've got a motor and a sufficiently strong cable, you can do the old clockwork trick and lift a weight, then use its slow descent to run mechanics or the motor as a generator. No spinning parts, no chemicals, no fire/explosive hazard. Problem is power density. LiPo batteries store ~.46 MJ/kg at the low end. An iPhone 8 battery stores (I think?) ~25 kJ. If you've got 2 meters of vertical distance to work with, your working mass needs to be 1275 kg?

@solarbear like the problem with clockpunk is that torsion spring energy density is like 1,500 times lower than the batteries you can get at the corner store

@solarbear so you gotta be specific about what "small" means here, and what you mean by "battery". If you're willing to consider combustion, synthesizing hydrocarbons actually gives pretty good energy density, and you can run either an internal combustion, Stirling engine, or thermocouple off of the heat from burning refined (or raw) biofuels. Another option (if you're working for NASA) is an RTG, but uhhhhh obviously don't deploy radionuclides in your neighborhood; that's a huge safety hazard.

@solarbear Another option is hydrogen fuel cells, but if you're trying to get away from advanced manufacturing that's not a good call. If you've got the land/space for it, you can pump water uphill and run a microhydro turbine on as little as a few meters of head.

@solarbear Another option is to heat a large, insulated mass and then tap energy off of it using a stirling engine or thermocouple. A hot water heater tank holds a surprising amount of energy!

@aphyr but wouldn't the require T least a constant trickle of energy in to maintain heat?
Even with the best insulation it will reduce over time.

Oh! Unless you use something like the ambient heat of a compost heap.

@solarbear All batteries run down over time, yeah. For hot water heaters, you've got the direct losses in running the stirling engine and passive heat losses through the floor, air, and pipes.

And yeah, if you can actually keep the carbon-nitrogen balance right, a compost pile can be viewed as (real inefficient) combustion engine, and yes you *can* harvest waste heat. I'd suggest some kind of heat exchange loop that gets inserted into the heart of the pile.

@solarbear There's also flywheels, but reasonable energy density and low-friction bearings both require advanced manufacturing techniques, and I'm guessing you're trying to avoid that. Compressed air is also an option--compressors and tanks are available on the commercial market, but there's an explosion hazard. I wouldn't want to make one myself.

@aphyr @solarbear you’d also want to be careful not to tap too much of the heat, esp in winter, or your pile will stop composting

@Satsuma @solarbear I don't know if this is feasible for small piles, but some research projects have done compost heat recovery at industrial scale. Your pile is in thermal equilibrium already--just capturing what would ordinarily be lost to radiative/convective processes. biocycle.net/heat-recovery-fro

@solarbear oil barrel water tanks

Slightly uphill Water storage means you can tap electricity while watering a garden, but you need a sufficient volume of water and a very efficient generator

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