Musk doesn't believe in the long-term prospects of fusion energy being able to generate green electricity in the future.

The richest man in the world is put off by the costs.

It would be difficult to obtain and transport source fuel, as well as maintain the reactor, according to Musk. It's better to use the Sun's thermonuclear reactor.

The criticisms aren't completely incorrect. Despite decades of research, scientists have yet to crack the code of fusion, with current reactor still requiring far more energy to start than they are able to produce.

We already have the answer to a more sustainable future.

The primary solution to a sustainable energy future is solar/wind with batteries for when the sun isn't shining or the wind isn't blowing. No new technology is needed.

Musk's comments don't come as a surprise, he's right that a renewable grid is a worthy goal.

The billionaire doesn't completely dismiss fusion, but he thinks there are better options out there.

After a team of MIT researchers announced their compact fusion reactor was very likely to work, he said it was cool and should be done.

The best case will be more expensive than wind and solar.

Amazon founder and noted Musk rival Jeff Bezos believes in a future powered by fusion reactor. Bezos invested in General Fusion last year.

Bill Gates has invested in fusion tech.

The jury doesn't think fusion energy is viable. Scientists say they have come closer to achieving fusion, a dream of a perfectly safe and entirely renewable source of energy.

The reality is not what it should be.

Our efforts would be better spent on battery storage and renewable energy if it were up to Musk.

The startup says it is working on a simple solution for practical fusion power.