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.
@zens springs seem an interesting direction to go
@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.
@solarbear air compressors! https://en.wikipedia.org/wiki/Compressed-air_energy_storage
@banjo ice seen an article on these in lowtech magazine. It's a really cool idea
@citc energy usage, lifetime restrictions, lack of recycleability ect
@singingwolfboy facinating concept.
@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.
@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. https://www.biocycle.net/heat-recovery-from-compost/
@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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