In my previous question, I dealt with the possibility of harvesting the energy of the accretion disk and jets of a quasar Milky Way, by the use of multiple mirrors and panels that are orbiting around the black hole, similar to a Dyson Sphere, but around a Supermassive Black hole. In this question, the problem dealt with how to get the energy. But after the energy is collected, there is another problem- storage.

Harvesting energy is one thing. Storing it is another.

You could get quadrillions of joules of energy from a quasar, and still be able to do absolutely nothing with it, if you can't store this energy. So we need to look for an alternate solution. Fortunately a solution exists, and this thing is known as a battery

However, a problem arises......

Current tech-batteries are terribly inefficient for storing electricity. The conventional lithium-ion battery can store only a few million joules per kg. Millions of joules might sound impressive, but when we are talking of harvesting the energy of a quasar, this sounds terribly inefficient. You would need billions or even trillions of batteries to store the energy of a quasar. And since lithium is really rare in the universe, this would lead to rapid depletion of lithium and probably a complete wastage of material.

What we need to look for is a battery material that has a high energy density, which can store billions or even trillions of joules of energy, be rechargeable and easily available in the Universe. This should perhaps bring the no. of batteries down to a few million at the least

What sort of material should I use in designing really energy-dense and compact batteries to store the energy of a quasar?


  • My battery should be made of a material that is easily available and not rare like lithium.
  • It can be recharged.
  • Lasts for astronomical times, as in millions of years.
  • It is energy dense and compact.
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    $\begingroup$ "The conventional lithium-ion battery can store only a few hundred watts per kg.", "watts of energy": watts are not a unit of energy. $\endgroup$ Commented Oct 23, 2022 at 22:57
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    $\begingroup$ This should not have the hard-science tag. It's virtually a brainstorming question, nothing requires citations and equations in asking for an "impossible" energy storage solution. $\endgroup$
    – Zeiss Ikon
    Commented Oct 25, 2022 at 11:12

6 Answers 6


Antimatter - yes, yes. How droll. Been done, been done. Not that there is anything wrong with that. But how about some form of fictional energy storage that has not been done to tired dusty little bits. Something fictional but plausible. Something new. Dangerous - possibly an existential threat to the universe. Something which takes up absolutely no space and which stores unfathomably large quantities of energy.

High energy false vacuum.


false vacuum decay

Definition of true vs. false vacuum A vacuum is defined as a space with as little energy in it as possible. Despite the name, the vacuum still has quantum fields. A true vacuum is stable because it is at a global minimum of energy, and is commonly assumed to coincide with the physical vacuum state we live in. It is possible that a physical vacuum state is a configuration of quantum fields representing a local minimum but not global minimum of energy. This type of vacuum state is called a "false vacuum".

Your people store energy in artificially generated false vacuum state of their batteries. The consequent high energy false vacuum gives up its energy on collapsing back to the ambient vacuum state of our universe.

Devices which move vacuum from one state to the next could be dangerous if our own universe is not at the least energy state, and could itself go through false vacuum collapse.

Existential threat If our universe is in a false vacuum state rather than a true vacuum state, then the decay from the less stable false vacuum to the more stable true vacuum (called false vacuum decay) could have dramatic consequences.

If I understand right, matter, energy and physical laws are at risk from such a collapse.

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    $\begingroup$ HandWavium meets Hard Science. $\endgroup$ Commented Oct 23, 2022 at 21:22
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    $\begingroup$ How much wood could a woodchuck chuck if a woodchuck could chuck wood - how much energy could a false vacuum release if a false vacuum could release energy? $\endgroup$ Commented Oct 23, 2022 at 21:45
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    $\begingroup$ @FuriousNukefrostArcturus - I am but the architect. For general contractor type questions I refer you to your team that is out harvesting energy from quasars 600 light years away. $\endgroup$
    – Willk
    Commented Oct 24, 2022 at 12:32
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    $\begingroup$ The graph is what I look like when I take my shirt off. $\endgroup$
    – Daron
    Commented Oct 24, 2022 at 13:51
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    $\begingroup$ @Daron - That means you have high energy! I think. $\endgroup$
    – Willk
    Commented Oct 24, 2022 at 21:47

Matter - antimatter pairs is the densest energy storage you can get, even denser than Uranium.

Mandatory XKCD quote

enter image description here

And if you are able to harvest the energy from the accretion disk and not be able to create antimatter, it must be some sort of joke.



The quasar eats up whatever you drop into it and converts 6% or so of the mass-energy into kinetic energy. You will not find a denser way to store the energy than just leaving it as matter.

Store it as matter until you need it. When you need more power just chuck more matter into the quasar. Then reflect the outgoing stuff into a beam and shoot it across the galaxy to whatever planet needs it.

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    $\begingroup$ Beat me to it. If you are at a level you can store energy on a galactic level you can manipulate the orbit of anything around a Quasar. Rack it Pack it and Stack it. Divert and arrange any material that would fall into a quasar into ordered shelled orbits. Ready to be fed into it when it is needed. $\endgroup$
    – Gillgamesh
    Commented Oct 25, 2022 at 12:21

Micro black holes.

Black hole with a mass like an asteroid or less produces detectable Hawking radiation. Once you can manufacture them, they will eventually convert 100% of their mass to radiation - hard to get better than that. However there are drawbacks:

Energy production follows fixed decay curve, so you can't regulate or turn it off.

The black hole is microscopic and does not have very strong gravitational field thus "recharging" it by feeding it material can be difficult.

Moving it around is nontrivial but possible by strong electric fields.

But it can be useful in other ways as a local source of gravity.


Electrostatic Force

Theodore Gray's awesome book Molecules deals with a lot of stuff, but one point it makes that if you were to separate all the electrons from all the protons of a single gram of iron and put them across from each other on a one-centimeter gap,

...you would be able to hold up a cube of iron about eight miles on edge, or a good-sized mountain.

Molecules, p. 137

My calculations show that that iron cube weighs $1.68\cdot10^{16}$ kilograms, which Wolfram|Alpha tells me is 13 times the mass of all life on Earth.

So all you need to do is borrow a planet (you've got plenty of those right? Should be easy to move for a type III civilization. If you want a lower-bid model, go with a moon or an asteroid), and basically completely ionize it. You will need some way to keep the nuclei and the electrons separate. To get your energy back, simply reunite the electrons with the protons. As a bonus, you can fine-tune your energy storage/retrieval more carefully than you could with matter/antimatter. Not very compact, yes, but the at least you won't destroy the universe if it gets out of hand.

Based on my other calculations, using the entire Earth as one of these batteries (and assuming the Earth is pure iron), you could store up to $6.142\times10^{76}$ joules of energy, plenty to justify the size of the battery.



Reverse a star's demise. Fission all of that helium back into hydrogen.

Alternatively, fuse lots of it to get loads of Lithium-6.

You could react Li-6 with H-2 to get 2 He-4 and a load of energy. You could react Li6 with a neutron to get He-4 and H-3, and you can react H-3 and H-2 to get He-4 and a neutron.

It's nowhere near as energy dense as antimatter, but it's easy (with unlimited energy, we could already do it), and the storage form: a star, is pretty convenient.


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