Nuclear fusion
Possible energy source - not viable yet.
Energy inputs
Takes more energy than it produces. EROI is still below 1.
Every once and awhile, there are "major breakthroughs" in nuclear fusion (a recent one being in December 2022), and misleading news articles are quick to make it look as though scientists have finally achieved a "net energy gain". However, it's only a net gain relative to some of the energy inputs, not the whole system in total. In other words, fusion is not a viable power source yet. We don't know how long it will take to be. Since climate change is already near a tipping point, we need to explore other solutions besides fusion only.
Scarcity of fuels
- page 47: World energy balance, 2018
- - Total Energy Supply (TES), first 4 columns combined
There are no viable reactors yet, but of the prototypes so far, some rely on tritium, an extremely rare form of hydrogen. Supply would be an issue.
Other possible fuels include deuterium, lithium or boron, which are comparatively less rare. In any case, only small amounts of the fuel would be needed to produce large amounts of energy. [QUANTIFICATION needed]
Ideally, fusion reactors could rely on ordinary hydrogen, which would be abundant enough to last for billions of years. [show maths] If we assume... ~ that losing 0.1% of the world's oceans would be enough to be a problem, and ~ that hydrogen fusion energy consumption would be 10 times today's fossil fuel energy consumption (because cheap energy), Then at that rate, it would take more than ten billion years to have even a minor effect on the ecosystems: (calculation loading) Side note: For the same amount of energy, the hydrogen losses are even less than the would-be atmospheric losses in a non-nuclear scenario where hydrogen gas replaces natural gas.
For now, all of this is hypothetical - regardless of fuel, no prototype so far has been able to produce more energy than it takes to run it.
See also
- Nuclear fission (not fusion)