system
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human
ELI5: Why is fusion considered the holy grail of energy?

I have a degree in engineering and read a lot of science material, and my own reading has shown:
"The power output of the core of the Sun is about 276.5 watts per cubic metre — that's almost three of the old 100W light bulbs. On a power/volume basis, it's a lot less than your body emits (about 100 W) and around the same as a compost pile."

Basically the only reason the Sun yields so much energy is that it is so staggeringly large.

So, that being said, what is the use in creating a reactor that - albeit will generate a net positive power - will only output such a piddling small amount?

I feel we are wasting millions (likely billions by now) on this. Is there some basic conceptual scale up that I am not aware of?
gpt
> So, that being said, what is the use in creating a reactor that - albeit will generate a net positive power - will only output such a piddling small amount?

The fusion output of the sun per given volume doesn't really apply to how it would be performed in a reactor as our designs aren't reliant on what will naturally occur. Consider the difference between a fission bomb and a fusion bomb, the fusion bomb has a far greater output. A practical reactor will be generating far more energy per cubic meter than the Sun does.

While fission of uranium releases about 17 times the energy of deuterium and tritium fusion, the key difference is the availability of the fuel. There is enough deuterium in a gallon of sea water to produce an equivalent energy output of about 300 gallons of gasoline. Instead of refining trace isotopes of an already rare mineral into fuel we can just essentially dump water into such a reactor and create huge amounts of energy; that we need 17 times more water than uranium isn't really a problem.

Edit: Consider that U-235 has a natural abundance of 0.72% and there is about 40 trillion tons of uranium on Earth. That means there is conceptually about 288 billion tons of U-235 on Earth.

On the other hand deuterium has a natural abundance of about 0.015% and there is about 1.36 million trillion tons of water on Earth. That means there is conceptually 204 trillion tons of deuterium on Earth.

This means fusion fuel is approximately 708.3 times more commonly available than fission fuel. Oh, and the waste products are far less hazardous.