[pfdietz]

I don't believe cost projections for fusion. If you look at them, they're filled with assumptions that aren't supported by much of anything(*), but magically make the technology just competitive. As the competition has improved, the assumptions have gotten more desperate. They're less "this is what the technology will cost" and more "this is the least ridiculous set of assumptions we could find that would let our technology not be dead."

If you apply the same level of assumptions to, say, light water fission reactors, I'm sure you'd get cost estimates vastly lower than what they actually cost in practice.

(*) For example, one paper assuming the efficiency of converting thermal energy to power in the fusion reactor is 60%, a level that combined cycle power plants achieve by expanding combustion gas that starts at a temperature that would soften or even melt the turbine blades.

[ZeroGravitas]

I've seen some claims that even a magically costless heat producing device connected to a steam turbine won't be competitive with solar PV so I'd guess Fusion would also fail that test if it is basically being used to generate heat (note, they're claiming they have some new tech that avoids this problem, but we don't know if actually does or not)

[DennisP]

The real question is whether it'd be competitive with solar PV on cloudy winter days with enough battery to get through windless nights. If so, there's probably a place on the grid for it.

(In any case, Helion is planning direct energy conversion, without a heat cycle.)

[ZeroGravitas]

At that point you're competing against energy storage, not renewables. No way you can afford to run any such power system just a few days a year.

It could all pencil out if you had some massive incentive for production on those specific days and some legally mandated quota for other times, but at that point you'd probably be beaten by a few factories saying they'll shut down for a few days if you gave them the same cash and/or renewables producers using the money to add storage.

Practically, it needs to run full out constantly and compete with an average of other power producer prices to be viable.

[DennisP]

Energy storage is not all that cheap.

There's a reason I mentioned "cloudy winter days." The cheapest way to address those is probably to overbuild PV. That overcapacity probably won't be used on bright summer days, raising the capital cost of PV across the board.

I don't think you're going to find many factories that can be economically shut down for entire seasons. None of this is an issue right now because we use natural gas for backup, but we need to stop doing that.

[ZeroGravitas]

The cheapest way to generate power on cloudy winter days is wind power, not overbuilt solar. Though, yes, overbuilding wind and solar is generally more cost effective than most other alternatives and the overbuilt wind and solar will both contribute power even when not working at their seasonal peak and provide abundant cheap power for storage when overproducing near their peaks.

I had assumed we were both taking that as the baseline alternative, since every country in the world is basically building that out right now, hence my suggestion that demand response would be a better choice than any plausible nuclear option to cover any gaps in that provision due to unseasonal weather which is both less windy and more cloudy than predicted.

But we appear to be starting from radically different assumptions about what power grids will look like (and already look like today)

[DennisP]

Yes, we have a lot of wind power, but that also is backed by fossil.

[pfdietz]

Hydrogen burned in combustion turbines would likely be cheaper. For this use case minimizing capital cost is all important; the cost of the hydrogen itself much less so.