The energy consumption of the entire human race was about 146,000 TWh per year in 2015 [1]. That's 26 times more than before the industrial revolution. Since energy usage will still rise for a while, let's generously assume for now that the hypothetical future civilization will consume 10 times more than the 2015 value, or 1,460,000 TWh per year.

(I'm assuming that population does not grow more than currently anticipated. I think this is fair because I later compare the number to our current Helium production which probably would scale up as well if the population were to significantly increase.)

The proton-proton chain reaction, the process that creates Helium-4 by fusing hydrogen plasma, releases 26.73 MeV of energy when creating a single helium atom out of 4 hydrogen atoms. [2] The molar mass of helium-4 is 4.002602 g/mol [3]. With this, we can do a quick trip to our favorite unit-aware calculator, units(1), to find how much Helium would be produced if our hypothetical future civilization used hydrogen fusion for all its energy needs:

  (1460000 TWh / year) / 26.73 MeV / avogadro * 4.002602 g/mol
  = 8157132.36 kg / year

Since Helium is a gas, it is more commonly measured in volume, so let's multiply that with its density at STP of 0.1786 g/L [4]:

  (1460000 TWh / year) / 26.73 MeV / avogadro * 4.002602 g/mol / (0.1786 g / liter)
  = 45672633.63 m^3/year

Most Helium is produced by the United States (78% market share as of 2008 [4]), so let's just use their current production numbers as a comparison.

> Helium production in the United States totaled 73 million cubic meters in 2014. [5]

That's 60% more than what would be produced by the future fusion reactors in my scenario. While it's true that I made a generous assumption by inflating the energy usage 10-fold, it appears that covering our Helium needs with fusion reactors is way more attainable than I imagined. We just need to cut back on wasting Helium a bit. The biggest "if" is, of course, if and when fusion reactors become economically viable.

[1] https://ourworldindata.org/energy-production-and-changing-en... [2] https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_re... [3] https://en.wikipedia.org/wiki/Helium_atom [4] https://en.wikipedia.org/wiki/Helium [5] https://en.wikipedia.org/wiki/Helium_production_in_the_Unite...

A few things: I believe your energy per year numbers are electric grid consumption. Steam cycle power plants make roughly 3x more thermal energy than their electrical output. Typically a "1 GW power plant" can produce up to 3 GW thermal power.

Also current target fusion reactions are not based on the p-p chain. That is a much more difficult reaction to achieve. We're currently targeting D+T for first generation reactors. D+D is also very attractive because it is aneutronic and perhaps clever reactor design would allow for direct conversion of electricity. Energy in aneutronic fusion reactions is released as an acceleration of charged particles: a current. This current can be harvested through magnetic fields and thermal to electric efficiency can go up to 50% (maybe higher?). The actual details of this seem rather tricky since magnetic confinement devices are already tightly controlling the magnetic fields inside the reactor. It will be fun science and engineering for sure.

There are a few other commonly examined reactions, such as p+B11, but they're likely not going to be made viable reactions for energy production before D+T. These other reactions are all easier to achieve (in terms of Lawson criterion) than the stellar proton fusion chain.

I'll reuse your math with D+T=He-4+n and 3x energy production.

  (4380000 TWh / year) / 17.59 MeV / avogadro * 4.002602 g/mol
  = 41425784.21 kg / year

  (4380000 TWh / year) / 17.59 MeV / avogadro * 4.002602 g/mol / (0.1786 g / liter)
  = 231947280 m^3/year

Hopefully there aren't any glaring errors here. More views would be appreciated.

I think the largest issues here are:

1. as you acknowledged, the assumption that energy production would increase by tenfold

2. that all electrical energy produced would be made by fusion reactors

By the time we get to a state where a serious percentage of energy production was from fusion power we would likely be looking into more aggressively into other reactions and designs.

Even if we just said 30% of all energy used today was made from D+T fusion that would still be generating 10% of our current helium usage. That's a significant amount and a lot more than the 4 orders of magnitude that is oft cited online (https://www.reddit.com/r/askscience/comments/12r2s7/helium_i...). At a glance, it appears that the posts in this thread miscalculate how much fuel is necessary for a certain amount of energy. They glaze over that part of their calculations. I much prefer your dimensional analysis approach.

For any readers looking for the same warm fuzzy I have, you can paste this into wolframalpha and actually get a rate of helium production over time.

https://www.wolframalpha.com/input/?i=(.3++438000+TWh+%2F+year)+%2F+(17.59+MeV)+%2F+(avogadro%27s+number+1%2Fmol)++(4.002602+g%2Fmol)

  (.3 * 438000 TWh / year) / (17.59 MeV) / (avogadro's number 1/mol) * (4.002602 g/mol)

> I believe your energy per year numbers are electric grid consumption.

No, according to my source, it includes combustion.

Oh I see. My reference for energy consumption is wikipedia. When I was trying to dig for the primary source yesterday I found the link was dead and the equivalent live location of it (IEA key world energy statistics) was behind a paywall. I didn't expect such a large discrepancy between the wikipedia reference and other sources.

https://en.wikipedia.org/wiki/World_energy_consumption