I've got my wizards, who operate by vanilla human biological laws and metabolism. They've got an organ in the pelvis which has its own mechanism - not breaking the laws of physics - which stores energy in some form, and allows rapid dispension to use for their spells.

What this means is that they have a biological battery, storing energy for the long term (weeks), which they can convert at will into some dynamic form. That can be combustion heat, electrical energy, or something else - which my organ (this is the only handwavy part) will turn into magical energy, and magic.

Here's the numbers, and many of these have some wiggle room if necessary to make physical sense:

  • The organ weighs no more than four or five kilograms. Not big enough to displace too many existing organs, and not so dense to upset mobility. A wizard should not constantly feel pregnant.
  • The organ can store up to 200 megajoules of energy.
  • The energy can be released in as little as five seconds.
  • Ideally, the elements composing this energy battery should be able to be produced in the body - or at least composed of materials found in human nutrition. So organic fuels like petroleum are fine, but plutonium is out, because a human living in a pre-industrial era could never acquire any.
  • Ideally, the energy should be possible to be released in doses, but it is not required.
  • It's fine if the organ's energy medium takes weeks to produce, since that's how long it takes to metabolise fat and nutrition to charge it up anyway. Only the discharge needs to be fast.

Now, what options are there for high-density energy storage that allows rapid discharge? Electrical energy was my first bet, but the densest real world batteries allow maybe a single megajoule per kilogram, which is two orders of magnitude below what I want to accomplish.

Gasoline has this kind of energy density, but I do not know if you could combust it rapidly enough. Are there any other options?

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    $\begingroup$ We're talking about 1-2 gallons of gas for that quantity of energy. An M2 flamethrower could easily burn through that amount of fuel in 5 seconds or less. Burning gasoline that fast isn't a problem - controlling that huge release of energy safely is the tricky part. $\endgroup$ Mar 9, 2020 at 14:51
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    $\begingroup$ @NuclearWang A flamethrower throws the flame; the flammable matter is dispersed over a great volume of air, richly oxygenating it. You cannot do that within an organ. $\endgroup$
    – KeizerHarm
    Mar 9, 2020 at 14:53
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    $\begingroup$ Hm, you also can't really do combustion within an organ in the first place, so maybe gasoline isn't the way to go. I wasn't sure if the mage would use the energy-rich medium internally, or spray it externally using his "pelvic organ" to deliver a golden shower of death. $\endgroup$ Mar 9, 2020 at 14:57
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    $\begingroup$ @NuclearWang I'll clarify, thanks. And thank you for the term "golden shower of death". :) I would also not discount all forms of combustion: we can do it within a car, after all. $\endgroup$
    – KeizerHarm
    Mar 9, 2020 at 14:59
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    $\begingroup$ gasoline and body fat are not that far apart in energy density, 46 and 38 MJ/Kg respectively, some organic oils are even higher. Or you could go binary compounds like bombardier beetles, hydroquinone and hydrogen peroxide $\endgroup$
    – John
    Mar 11, 2020 at 20:25

4 Answers 4


Fusion time, baby

Oh boy, here comes the handwavium. For starters, the absolute easiest fuel present in the human body... is hydrogen! Because of what you've said in response to Trish, I'm going to go in the opposite direction and go as far from human biology as I feel I can manage. So we're going to make a magnetically suspended toroid (donut) of hydrogen plasma, and get it hot enough to undergo fusion. Hard to start, surprisingly easy to maintain.


A few things we're going to need right off the bat: hydrogen, carbon, iron, and copper. Hydrogen is actually produced constantly in the body by the krebs cycle in the form of free-floating protons that pass through a corkscrew like protein in the mitochondria to produce ATP. We're gonna borrow some, as we only need a few milligrams of the stuff. Considering that the human body uses 100-150mols per day (if we stole that it would be 100-150g of hydrogen, orders of magnitude more than we need), we're going to have plenty.

Next, we'll need some carbon. This will take some finagling, because what we really need is graphite which as I'm sure you can guess, is not produced naturally in any biological process I know of. However, Hydroxyapatite, otherwise known as bone mineral, is precipitated naturally. So, this is not really so much of a stretch in all honesty.

Iron. Our plasma toroid needs to be magnetically suspended so it can be nice and stable. Believe it or not, the biological precipitation of magnets actually has solid precedent in Magnetotactic bacteria.

Copper, also found in the body although to a much lesser extent (your wizards better eat a lot of mushrooms), can be created in a similar fasion, even easier as it doesn't need to be magnetic.

Design and Operation

Our toroid of plasma will be magnetically suspended (using ferrous and electromagnets) in two layered toroids of graphite. The space between the two layers will be filled with liquid helium which will catch neutron radiation to produce heavier hydrogen atoms (deuterium and tritium) to fuel our fusion even more efficiently, and most importantly, help our graphite stay relatively cool. Assuming the fusion has already started up, we'll be using Neutral beam injection, which uses ionized hydrogen (H+) that the body so kindly provides through the krebs cycle, and shoots it into the plasma to stoke the flames of fusion.

Our design is essentially going to be a scaled down version of the ITER Tokomak, which is where I'll be getting all of the following numbers. Making it about the size of a large donut, you'd have a comparable power output of 254 watts, using half a nanogram of hydrogen per second. Using Fusion power from a fraction of the body's atp production. This would produce your 200 megajoules in 218.7 hours, or a little over nine days.

Ignition is going to require a pinch of handwavium, as with an efficiency ratio of 10, you'll need to provide 25.4 watts of input power to start and maintain the reaction. Considering that an elite cyclist can maintain a power output of 1000-1100 watts, this is honestly pretty easily attainable. The application of that power can likely come in the form of an upscaled mitochondria, which already use electrical potential to produce ATP. This is biologically improbable, but it's nowhere near impossible.

The Problem

I always hate to say something's improbable, but to produce 200MJ of power instantaneously out of something that small, would not be containable using hard physics. The waste heat alone of just about anything using that amount of energy (like a fission reaction) would likely incinerate your wizard. This is where I'm hoping your magic comes in. The fusion power can easily provide tons of energy from biological sources, but I think the storage itself would have to be made almost entirely of handwavium. But hey, that's why you have magic! Perhaps the energy generated could be stored directly as 'magical potential'.


Regardless, here's an overview of your wizard's energy requirements and performance with this organ:

  • A little over nine days to produce the energy
  • 10% of that energy must be consumed as calories to maintain fusion, that equates to an extra 531 Kcals per day (How efficient!)
  • The storage method must be magical
  • Bonus points if someone hits the organ as it could cause a teensy tiny magnetic explosion followed by a plasma flash. Ouch!
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    $\begingroup$ Oooh, I love this. Biological fusion reactor, yes!! Just a question; where are the wizards going to get the helium? $\endgroup$
    – KeizerHarm
    Mar 9, 2020 at 19:21
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    $\begingroup$ It'll use hydrogen, actually. They reactor will be creating helium. I assume they'll need to expel this helium through some natural method. Comedically timed high pitched burps perhaps? $\endgroup$
    – Skyler
    Mar 9, 2020 at 19:23
  • $\begingroup$ Accepted due to the sheer creativity; all the other answers were great too :) $\endgroup$
    – KeizerHarm
    Mar 31, 2020 at 8:59

The human body already knows three main variants of energy storage: sugars, protein and fat.


Fat is long term, slow availability power that can be metabolized into sugar: 1 gramm of fat is 39 KJ, so for long term available 200 MJ, you'd have about 5.2 kg of fat stored under the skin. That would make you not that much more chubby by the way. It does not satisfy the 5-second demand though.

Glucose & Protein

Glucose and other sugars are the high energy storage form of the body anyway. It is available from the liver by pouring out stress hormones and as a base level. Having a typical physiological availability of 17 kJ/g means that 200 MJ of glucose is equivalent to 11.8 kg of sugars - which is not feasible to be stored in one big organ.

Proteins are the emergency energy, they contain about the same energy as glucose for the body. Burning that means that the body starts to cannibalize itself.

Muscle-energy: ATP

The body, however, does not simply use these substances, it uses the energy of the metabolized nutrients to turn adenosine-mono-phosphate into adenosine-di-phosphate and then into adenosine-tri-phosphate (ATP), which is the energy storage for muscles. ATP has a usable energy density of about somewhere between 0.08 MJ/kgp7 to ADP and 0.128 MJ/kg to AMP. Which means to store all the 200 MJ in instant ATP would demand about 1.5 metric tons of ATP - totally not feasible.

Energy Storage organ

The best energy storage would be in the shape of fat under the skin, followed by a blood sugar that surely would make you diabetic. Best it would be a mix of about 80% in fat shape, 20% as added sugars in the bloodstream or stored in several different organs. This would allow an estimation of the mage's reserves by looking at them: if they are chubby and well-fed, you know that the mage has a lot of reserves remaining, but if they are worn down and sleepy, they are not a threat. Ponder Stibbons is not the dangerous one, but fat Henry Porter is!

If the mages would need a special organ, it should be some kind of glucose-sack, right on top of the liver. Upon casting, an about liver-sized organ could release up to about 33 MJ (~2 kg) of energy almost instantly before it needs to refill itself. Estimating a higher metabolism rate or directed metabolism, such a refill could take the shape of some hours of meditation or a good night's sleep from the fat reserves.

To get to the demanded 200 MJ of energy, a mage would need about 6 of these sugar bladders, each containing their 2 kg of glucose juice. Distributing them evenly over the body would be the most feasible method without disturbing the body shape too much. Chest, belly, and sides - where fat is stored anyway, would be the most logical positions. It also allows to partially neuter mages, by removing some of the organs.

  • $\begingroup$ Thank you for your answer, but for clarity; vanilla human processes feed this organ, but the organ itself does not need to abide by human biology, just by the laws of physics. The wizards burn fat slowly, to fill up this organ with that energy, to serve as a capacitator for rapid discharge when necessary. $\endgroup$
    – KeizerHarm
    Mar 9, 2020 at 15:10
  • $\begingroup$ @KeizerHarm I have adressed this - and without seriously disturbing the shape of a body, you can't even have more than 2 kg of organ.you might get away with multiple though... $\endgroup$
    – Trish
    Mar 9, 2020 at 15:19
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    $\begingroup$ @KeizerHarm even better, you could implant the organs one after another or remove them to limit capabilities of students or dangerous mages $\endgroup$
    – Trish
    Mar 9, 2020 at 15:24
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    $\begingroup$ @KeizerHarm That risks a mage exploding if you punch him, or at least strike him in the right (wrong?) place with a blade. $\endgroup$
    – StephenS
    Mar 11, 2020 at 22:13
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    $\begingroup$ @StephenS you would still need ignition... perhaps if the blade had a taser at the tip? $\endgroup$
    – KeizerHarm
    Mar 12, 2020 at 0:47

Not possible on science-based.

The best chance for storage stays with electrical power and frantic handwaving - something like superconductive coils at body temperature and high saturation magnetic cores - just don't ask how such things naturally evolved into those wizards, it's magic

But even so, there's a problem at the moment of using that 200MJ of energy in 5 secs (=4MW of power). At the moment of use, the superconductive coil is interrupted at some point and the current is diverted through some other circuit that causes the "magic". When switching, the voltage - otherwise null in a superconductor - will grow to provide an electromotive force. Looking to max voltages produced by the electric eels, some biological tissues could withstand 860V without breaking down - I'll assume then 860V of operating voltage to the magic-producing aparatus.

Ok, so 4MW of power at 860V mean currents of 4650 amps, give or take. With even a 1e-3 Ohm resistance, the power dissipated by the conductors would be... - if your 800W toaster seem hot, imagine how a 21kW is (ohmic power losses to heat = $I^2\times R$) - over 5s, the amount is enough to boil 4kg+ of water.

Now the problem: even if I'm assuming the diversion of this current to the magic circuit takes place through superconductive tissues (like the one in the storage coil), you know what happens when a single loop is connected to a source of immense currents? Exactly, rail-gun happens!
Or anything that will try as hard as possible to keep the magnetic flux through that loop as it was - namely zero. And if the source of current is compelling enough to dissuade the loop away from keeping a null current, then the area of the loop will desperately be trying to increase as fast as possible - this is how the armature of a rail-gun gets accelerated to hypersonic speeds if and only if those rails are stubborn enough to stand their ground.

Alas, the question doesn't allow the laws of physics to be broken, so I can't see what biological tissue can have the tensile strength to resist the circuit loop expansion forces; the only trick those vanilla-metabolism wizards could perform is to electro-mechanically explode first at hypersonic speeds, followed by a big ball of electrical arching and superheated plasma from the unconsumed portion of those 200MJ.

If you want to see what I mean, look at this backyard railgun - 26kJ and watch carefully to those connecting cables on the sides of it. Then for the superheated plasma ball, have this one

Big-EF Palpatine-thunderbolts-from-fingers, the reality is more exciting

  • $\begingroup$ Evolution is not an issue: (((aliens))) added the organ to the genome; humans just need to be able to conceivably grow it. $\endgroup$
    – KeizerHarm
    Mar 10, 2020 at 16:01
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    $\begingroup$ Other than that, I must say that answers like these are what I visit worldbuilding.SE every day for. "Accidental biological railgun" is even cooler than "biological fusion reactor". Thank you so much man! $\endgroup$
    – KeizerHarm
    Mar 10, 2020 at 16:03

The organ synthesizes and stores explosives, like TNT, in specialized cells. The organ can channel the energy released by exploding cells into mana, and also contain the gasses produced by the explosion.

It vents into the digestive system slowly and safely, but the side effect is that wizards will pass an extraordinary amount of gas while this is going on.

But this solution highlights a problem with your requirements. While protein has the elements needed to make TNT (and the nitrogen is already "fixed"), and while the stuff can quickly release the energy, the amount needed is excessive. To get 200 MJ, you will need about 50 kg of TNT.

Nitro cellulose or nitrostarch might, biologically, be better choices. Possibly nitroglycogen. The body already produces glycogen, and sources of nitrates. All it has to do is to put them together, in large quantities.


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