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Comment by PaulHoule | Hacker News Reader

will need a bit more than four hours of storage though

Horses for courses, right? They build these entire peaker power plants to sit idle most of the time, just to handle the couple dozen or hundred hours of maximum load in the year.

4 hours at a time hopefully buys you your way through such a peak, even if it doesn’t get you through weeks at a time… and presumably you can top it up from base load after demand peaks for the day, right?

In the equatorial and desert regions they’re talking about, I think both seasonal supply changes and demand profile might be more consistent than, say, dreary cold parts of Europe..

That's a big part of what drives me crazy about the papers I've seen on this work. People like to quote some levelized price of energy and say "this costs less than an AP1000" and you never see modeling of "here's the price in California, here's the price in New York"

I would check out these recent articles. They’ve taken the step to model the entire grid hour by hour.

This is of course not how reality will play out, since the grid is market driven, but it’s quite interesting to see the results.

Denmark 2026:

https://www.sciencedirect.com/science/article/pii/S036054422...

Finland 2025:

https://www.sciencedirect.com/science/article/pii/S036054422...

Australia 2025–26:

https://www.csiro.au/en/research/technology-space/energy/Ele...

Sure.

But no one is claiming that there will only be 4h-storage

I don't see a lot of realistic talk about what the actual storage requirements are. You have to be concerned about:

(1) ordinary diurnal variation (overnight, lets say 12 hours)

(2) extremely unfavorable weather (see https://en.wikipedia.org/wiki/Dunkelflaute)

(3) annual variation (you might get 3x the sunlight in summer than winter? do you build 180 days of storage or do you overbuild solar systems 3x and get Casey Handmer to dream up something useful to do with that excess energy that doesn't have a stupendous capital cost?)

The "have a natural gas backup plan" is worse than people think for a lot of reasons, in terms of the laws of political science and economics you're going to find that that tail winds up wagging the dog, the whole market will get designed around the needs of those turbine owners, it's going to cost the same if they are running turbines for 5 minutes a year or 20 days a year, and ultimately you're never going to get rid of it. If you really plan to run the system 5 minutes a year what are the odds it will really work when you need it? You have to not just support the turbines you hardly ever use, pipelines you hardly ever use, drilling and storage operations for gas, etc.

Yeah I think it really only works well in the central latitudes. The American South, the tropics and equatorial regions, Southern Europe, etc. that get a lot of high-angle sunlight year-round.

Otherwise you need to deal with long distance power transmission across many political jurisdictions, or local generation for night or other low-solar times. To my mind, nuclear base load with solar and batteries used for things like charging cars or demand-shifting probably makes more sense. It's really a shame that we mostly withdrew from building nuclear plants for the past three or four decades; instead we have reached the point where we have to re-learn how or recreate the tooling needed to build them and they are still too damn expensive.

nuclear base load makes sense from a pure grid engineering PoV, which i think is why it appeals to so many HN folk. Sadly, it makes no sense economically anymore, so it will probably never be built at scale.

They quit building coal burning power plants in the US at the same time and for the same reason they quit building nukes…. The cost of the steam turbine and heat exchanges. I mean, the steam generators for a PWR are bigger than the reactor vessel, it is just insane to use hot water at high pressure to boil water at low pressure.

If nuclear is ever going to be competitive it is going to have to be some kind of reactor that runs at higher temperatures with a gas turbine power set. Could be a fast breeder or HTGR or molten salt but not water cooled. Anyway it is not a bird in the hand.

I mean yes but also there’s a lot more engineering and materials in a NPP beyond the heat exchanger part that makes it so expensive.

Ultimately though about 50% of the cost of a PWR is in the heat handling (heat exchangers and steam turbine) and the building costs to accommodate those systems. If the nuclear part was free they'd still struggle to compete -- the BWRX300 seems to get a lot of cost reduction by eliminating the pumps and heat exchangers and stuff and going to steel-concrete sandwich construction but to do better than that you have to really do something about that steam turbine.

For that matter, it's shocking how small the actual core is for FBRs. The capital cost of FBRs was long projected to be higher because traditionally you had to add a third cooling loop and some other systems but it is projected an sCO2 system today could be cheaper overall.

TIL, thanks! I didn’t realize the “routine” heat exchanger part was such a high % of cost.

It's a lot of metal! Also the first PWRs had a lot of problems with corrosion causing steam generators to fail and these had to be replaced early. Small improvements in design and better chemistry control solved this.

People are highly aware that we haven't fixed the problems construction new nuclear power plants, they are less aware that we've gotten much better at operating them on all the metrics from uptime to occupational radiation exposure.

yeah i have no objection to them apart from cost, and time to first watt.

Never said we should not have been developing the technology. But even with the old PWR designs you're not pumping carbon into the atmosphere, which is the main point.

> (3) annual variation (you might get 3x the sunlight in summer than winter? do you build 180 days of storage or do you overbuild solar systems 3x and get Casey Handmer to dream up something useful to do with that excess energy that doesn't have a stupendous capital cost?)

what about the variation regarding winds?

How about overbuild and interconnect? You don't have to overbuild for your personal worst case if you can buy power from somebody else if it comes to it.

Bucky Fuller imagined we might build a superconducting power grid that connects the whole world, but... power lines are expensive too and are politically tough because you have to cross so many boundaries that involve so many stakeholders. Realistically moving energy in space as well as time is part of the solution if not the whole solution.

My crazy idea is that you could put some energy producing or consuming facilities (hydrogen factory!) on floating platforms that can move where energy is available.

Sorry for the tangent but as a German I found it interesting (and somehow amusing) to learn that "Dunkelflaute" is an English "Lehnwort" (I couldn't find a proper English translation for that, either).

“loan-word”?

What political/economical problem? This has already been solved in most regulated markets. Capacity payments are already being made on many grids. Companies are already literally being paid for "doing nothing", being paid for being available for an unusual situation.

Renewables & batteries have high upfront costs but really low operating costs, so that's what you want supplying 90-98% of your power if your goal is lowest cost. (see Ember Energy reports). NatGas has low capital costs but relatively high operating costs, so yes, sitting idle and running a few days a year really is optimal.

Great comments throughout as usual. I’ll add that for the last few percent of generation that might need firm on demand combustion, gas turbines can be fed methanol, ammonia, or hydrogen, all generated from excess low carbon energy. I’d like to think that geothermal will be able to fill this gap, but only time will tell.

> you might get 3x the sunlight in summer than winter

In the darker parts of Europe, at least, this is broadly balanced out by an increase in wind. But there are dark and still days every year.

I don't know how much storage is needed, but it's a hell of a lot more than four hours.

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