Say that we have many undead zombies/vampires/ghouls/whatever. I want to use them to generate electricity, because they never get tired, never need to take breaks, and can exert great force without needing large amounts of material inputs. What is the best way to do this? Should I have them ride some sort of stationary bikes attached to generators? What should they be doing with their arms to generate extra electricity?
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1$\begingroup$ How much is "great" force? Olympic athlete, or hydraulic press? (This affects how best to harvest energy from your undead power supply.) $\endgroup$– jdunlopCommented Mar 9, 2019 at 1:51
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$\begingroup$ At the moment, this isn't about worldbuilding. You're asking about a "narrative necessity," or a function of your plot. There won't be a "best" way (unless you specify judging criteria) and the help center explains you shouldn't ask questions where "your answer is provided along with the question, and you expect more answers: 'I use ______ for ______, what do you use?'" Can you improve your question by explaining the specific strengths and weaknesses of the undead in your world (there is no "generic" definition), the way you'll judge the answers, and a specific description of the goal? $\endgroup$– JBHCommented Mar 9, 2019 at 2:31
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$\begingroup$ "because they never get tired, never need to take breaks" : traditional zombies rather than the more recently modern brain eating trope would seem to fit your bill, vampires & ghouls need to eat (or drink) so may not as that would seem to suggest their energy is a finite resource that needs "fuel" (or food) ~ I've used zombies & skeletons as the motive force for "magical" engines (that aren't really, accept fort the hidden "battery" sealed away out of site on a treadmill inside them of course) in old D&D games before myself. $\endgroup$– PelinoreCommented Mar 9, 2019 at 2:36
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1$\begingroup$ "What should they be doing with their arms to generate extra electricity?" What arms? you don't need the whole corpse, just the legs head & connecting parts, I just chop off all non-essential non-useful bits to save space & weight on the finished construct :) for smaller engines a skeleton rat is recommended. $\endgroup$– PelinoreCommented Mar 9, 2019 at 2:41
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1$\begingroup$ @Pelinore I'm pretty sure the TV-land zombies are actually ghouls. I wouldn't be a pedant about this, but the OP did mention ghouls, so that name isn't off the table for them. $\endgroup$– Ed GrimmCommented Mar 9, 2019 at 14:14
5 Answers
If your undead are humanoid the best method is to use a treadwheel. It has been used since classical times and is really the best solution. Humans have evolved to walk longer than almost any other animal and treadwheel uses that. Some of that is lost with undead since they do not get tired anyway but it should still be optimal method for humanoid form.
With proper bearings and light weight materials efficiency should be good. Since undead do not breathe or need to take breaks you can optimize the wheel in ways that would kill live humans. Such as replace air with low pressure helium or make the wheel entirely closed without any way to exit.
Just add an electric generator.
EDIT: Forgot to mention.
It is not part of the question but you need to remember that it is still a muscle engine. That means that power density will be inferior to modern power production. That means more volume per watt. Which usually means higher construction cost per watt. Which usually means more expensive electricity.
So you need to either accept that electricity is more expensive and hence used much less or cheap out on construction and accept lower efficiency or build for very long term which only works for more stagnant economy.
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2$\begingroup$ The construction cost per watt would decrease with time. Maintenance of simple treadwheels would be easy and there is much less fuel required to keep generating electricity, basically after the initial setup costs you just need to replace the piece of meat you hang in front to encourage them to go in one direction. In the meantime most other forms of electricity require high maintenance or lots of fuel. $\endgroup$– DemiganCommented Mar 9, 2019 at 20:50
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$\begingroup$ @Yes, that is why I edited in that "build for very long term", If you can afford to wait very long time the low upkeep can make it worth while. $\endgroup$ Commented Mar 9, 2019 at 21:18
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$\begingroup$ The infinite energy it can offer is too appetizing. So you make the treadwheel big enough that the zombies are always climbing the slope, pre-select zombies so you only put zombies of similar speed in one treadwheel. Sporting people can average anywhere between 40 to 400 watts of energy while a 1 m2 solar panel is expected to generate between 150 to 200 watts in direct sunlight. Shambling zombies dont really work that hard so if we assume 15 watts per Shambling meatbag you get a solar panel worth of energy all day and all night for 10 to 14 zombies! and far less conatruction and maintenance! $\endgroup$– DemiganCommented Mar 9, 2019 at 23:07
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$\begingroup$ On a treadmill, on a raised incline, if you have them all carry a heavy weight you will get more power out of them. If your supply is huge, then you do not want to worry about weaker females and children. If females do not get pregnant and children do not grow up, they are useless. $\endgroup$ Commented Mar 10, 2019 at 16:34
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$\begingroup$ And if you put moving handrails, like an escalator, with a heavy enough weight in a pack pack, they would have to 'pull' themselves up as well, thus using the strength in their arms. $\endgroup$ Commented Mar 10, 2019 at 16:46
Raise the corpses of great authors from the past. Then cover their bodies in magnets and bury them again.
Next step is making movies out of those authors' works, produced and directed by people who have never read them. The authors will forever be spinning in their graves. Due to the magnets, that will work like a dynamo per coffin and with some wiring you will be able to extract energy.
This is not an original idea. It was proposed by Aaron Diaz from the Dresden Codak.
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One giant 'water wheel', but instead of water, use the zombies. Herd them into a chute at the top, and they step onto the paddle. They ride the paddle to the ground, just like water would, turning the wheel. When they reach the ground, they get dumped out. Jut herd them back up to the top, and keep the cycle going. The wheel drives whatever device you wish - generator, grinding mill, saw mill, whatever.
No real intelligence necessary, just an unlimited supply of zombies who want to do nothing but walk aimlessly in a herd.
EDIT
Just as a reminder, the energy that you obtain out of the zombies is the energy they expend in climbing back to the top of the cliff or structure, and then lose again in their descent down the wheel. You would get even more energy if you had them carry rocks or something up to the top, and take them down the wheel.
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3$\begingroup$ Wouldn't it really make a lot more sense to have them inside the wheel like a bunch of giant hamsters so you don't have to keep wrangling them back to the drop point above the wheel. $\endgroup$– PelinoreCommented Mar 9, 2019 at 3:57
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2$\begingroup$ @Pelinore Depends on how much they weigh and how far the drop is. .And if they are inside the wheel, it limits how many you can use at a time. If you have enough and the 'stream' is continuous, you have power in numbers. $\endgroup$ Commented Mar 9, 2019 at 4:04
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1$\begingroup$ @Mike the ability to shuffle consistently in a single direction isn't really an issue to a subject confined inside a sealed hamster wheel & constrained from turning to either the left or right though is it :) $\endgroup$– PelinoreCommented Mar 13, 2019 at 22:47
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2$\begingroup$ @Mike well my own thinking on this question usually revolves around a D&D perspective so I just come at it from a different angle, my normal construct of this ilk would be an animated skeleton with the arms chopped off nailed to one wall of a sealed treadmill (to keep it in position if the construct is one that might tip) & simply instructed to "run" by the spell-caster ~ a simple cog connect / disconnect to the drive shaft lever is provided on the external casing for the "engines" operators. $\endgroup$– PelinoreCommented Mar 13, 2019 at 23:04
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1$\begingroup$ @Mike ^ it's basically used by the mages I use it with as a means of selling animated undead for cash to artisans without letting the buyer know they're buying an animated corpse :) something like an explosive ruins (spell) is normally used to dissuade the users from trying to open the case & finding what's inside. $\endgroup$– PelinoreCommented Mar 13, 2019 at 23:05
As always, it depends:
Zombies
Zombies most likely are not the smartest, so strapping them to a stationary bicycle wont work. This would mean you couldn't have a zombie spin class.
If you have a lot of zombies, that REALLY are relentless, so not just stop moving cause they can't see someone with brains, then you could have something like a giant pressure plate, generating power with movement the zombies make. A company called Pavegen promotes something like that and states that each footstep produces 2 to 4 Joules of power.
To put that in perspective, a Joule per second is a Watt, so you would need around 20 steps per second to power a 60 Watt LED lamp. Assuming a zombie takes a step every 2 seconds, you would need 40 zombies to power just one lamp constantly.
Vampires
Vampires are problematic, as they still have their own mind and don't just do as they're told. Additionally, they (famously) need food.
If neither of these things are a problem, they could make for a great power cell. In most vampire fiction, they are stronger and faster than a normal human. Wikipedia states in the article about Human Power that a an elite cyclisst can produce close to 400 watts of mechanical power sustained over an hour and in short bursts can sustain power levels of 1000 to 1100 watts.
A vampire should be able to hold twice that intensity, so just one blood sucker could power a small house, with lights, TV, and refrigerator.
Ghouls
Ghouls seem similar to the zombies, but with more control over their actions. In DnD they routinely dig up graves to feed on the body parts. So either they are more active zombies that could power your generators even more effectively (though unlikely to power them directly like a vampire strapped to a bicycle), or they are worse, as they won't move when they see no escape.
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2$\begingroup$ fantasy D&D style zombies don't need any brains to chase & will happily peddle away until their feet fall off, their creator (the spell-caster) just has to tell them to peddle before sealing them inside the contraption. $\endgroup$– PelinoreCommented Mar 9, 2019 at 2:45
Decaying bodies emit methane which could be collected and burned as "unnatural" gas.