[XorNot]

I cannot stress this enough: anti-matter is not a power source. It never will be, on account of "it doesn't exist in our universe naturally".

You cannot mine anti-matter, you cannot even efficiently make it and you certainly can't store it.

[akvadrako]

You can mine antimatter, in particle accelerators. One can think of energy as made up of matter and antimatter, it just needs to be separated.

And of course they do store it. Charged antimatter can be stored in magnetic fields, for example.

[XorNot]

No, you can't. Particle accelerators make anti-matter. And they do so extremely inefficiently. This is not an energy source: it's at best, a conversion or storage system. Making anti-matter is an inefficient, energy losing process, it is not a fuel source.

And the storage sucks: the longest anti-matter confinement time is 405 days in a Penning trap and we've only done so for amounts measured in total count of atoms, in the thousands. Not even micrograms.[1]

[1] https://en.wikipedia.org/wiki/Antimatter

[akvadrako]

We will probably mine antimatter near the sun, where energy is virtually free.

It's as much an energy source as anything. You would also spend more energy than you got out if you tried to mine coal in your backyard.