[hunterpayne]

Nice work but no offense, but it comes off as you describe. I think you are overall right about needing to switch W sources. You are wrong that it will be used for fusion reactors. That won't happen in the lifetime of anyone alive today. It will get used for armor for weapons and possibly some fission reactors. We are nowhere near an actual breakeven fusion reactor. We are only close to theoretical break-evens which are themselves more than an order of magnitude from actual working powerplants. Ask yourself this, how do you efficiently harness 1,000,000C heat? Even at 900C we can only get about 55% and we have materials which can withstand that temperature for decades. We have nothing physical that can take anywhere near 1,000,000C.

[dotancohen]

  > how do you efficiently harness 1,000,000C heat?

The traditional answer to that question is vacuum and magnetic confinement (usual toroidal). Whether that will turn out to be the practical answer is yet to be seen.

[hunterpayne]

I said efficiently, you would be lucky to get 1% efficiency there. Vacuums don't conduct heat very well do they.

[bmacho]

Literally 100% of that heat travels from the 1000000C stuff to the environment throught that vacuum. Vacuum doesn't just remove energy.

If you use a steam engines it doesn't matter if your source of heat is 900C or 1000000C, all heat will be captured, and 40-60% will be turned into electricity.

[Dylan16807]

What you said there is all true, but largely because you didn't mention efficiency. If your heat source is a lot hotter than the steam you make, you do lose a lot of efficiency. If you had a million degree heat source, you could have many steps extracting huge amounts of power before your "waste" heat gets down to 1000C and is used to boil water.

The part about bad conduction being a problem is nonsense. The "lucky to get 1% efficiency" is not nonsense.

[mnw21cam]

Carnot efficiency is 1 - Tc/Th, where Th is the hot side temperature and Tc is the cold side temperature. Tc is set by the surrounding environment, probably in the vicinity of 300K. If you have a hot side temperature around 1,000,000K then the theoretical maximum efficiency is very good. If that heat has to be stepped down by separating it from materials that would melt and you can only sustain a hot side temperature of 1200K, then your theoretical maximum efficiency drops to 75%. Obviously the real life efficiency will be a bit less than that, but the principle shows that the "lucky to get 1% efficiency" bit is nonsense - you're not actually losing that much after all.

[bmacho]

This is all about getting energy out of a very hot heat source. Theoretical efficiency is ~1, and a ~40% practical efficiency also doesn't seem to be hard: let something heat up to 1000C, and don't let much of the energy escape to the environment.

Also deuterium-tritium reactors get energy out of the plasma via capturing high energy neutrons, very similarly to nuclear power plants.

[Dylan16807]

You're right, I was mixing up how the boiling process would work numerically.

[ben_w]

While true in isolation, that is the wrong reason to care.

We get power from the sun very effectively over 150 billion meters of vacuum.

Biggest problem with fusion is doing the fusion for a low enough input power (or for pulsed, energy) cost.

[refulgentis]

Okay, now I'm thinking you're trolling :) (if not: how warm is it where you are, i.e. how much above 0 kelvin? How?)

[noleary]

I'm not smart enough to stake an opinion on the viability of fusion. I pretty much only have high school mechanics and Wikipedia in my toolkit.

I can only ever make material conditional claims about things like this :)

[BigTTYGothGF]

> how do you efficiently harness 1,000,000C heat

Very carefully.

[refulgentis]

> We are nowhere near an actual breakeven fusion reactor.

This isn't true.

I understand why you said it. Always 5 years away from being 5 years away. Years and years and years of nothing and hopecasting. Post-COVID market and startup antics. Data center power antics. Well-educated people pointing out BS and that even the best shots we had were example systems that were designed to be briefly net-positive in the 2030s.

But it's just not true.

Commonwealth Fusion Systems. Book it. 2027. They've hit every milestone, on time, since I started tracking in...2018?

[montyanne]

Commonwealth fusion is theoretically pretty close with their high temp superconductors.

Far from a slam dunk, but I don’t think we’re as far from net gain as we were 10 years ago.