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Comment by strainer | Hacker News Reader

The "near limitless energy" claim of articles like these is very deceptive. The true destination is perpetual heat generation, which is low grade energy and a potential pollutant on this planet.

The only thing we can do with such amounts of heat to produce the kind of energy we need and consume is build thermo-electric power plants to generate electricity. Here is the crunch:

> Thermoelectric power use has a significant impact on water resources and the power sector is highly dependent on these water resources; the United States Geological Survey (USGS) estimated on a national level that 41% of all freshwater withdrawals in the United States in 2005 were for thermoelectric power operations, primarily for cooling needs.[1]

[1] Operational water consumption and withdrawal factors for electricity generating technologies - https://iopscience.iop.org/article/10.1088/1748-9326/7/4/045...

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Heat pollution is a very minor concern. From "Sustainable Energy – without the hot air" by David MacKay, pages 170 to 171:

"let’s assume that in 100 years or so, the world population is 10 billion, and everyone is living at a European standard of living, using 125 kWh per day derived from fossil sources, from nuclear power, or from mined geothermal power. The area of the earth per person would be 51 000 m^2. Dividing the power per person by the area per person, we find that the extra power contributed by human energy use would be 0.1 W/m^2. That’s one fortieth of the 4 W/m^2 that we’re currently fretting about, and a little smaller than the 0.25 W/m^2 effect of solar variations. So yes, under these assumptions, human power production would /just/ show up as a contributor to global climate change."

http://www.withouthotair.com/c24/page_170.shtml

That's assuming that we use the same order of magnitude of energy.

If the promise of a technology is that we can use several orders of magnitude more energy per person, then that .1W/m2 could become 10W/m2.

If we don't increase energy usage, sure, no big deal, but the entire point of pursuing fusion is to enable fantastically more energy usage, at least as I see it.

So we also need a second revolutionary technology, direct conversion of energy rather than thermal energy conversion.

Fusion will never be a cost winner if it's using thermal energy conversion, anyway. Solar and wind will soon undercut the steam turbine lifetime costs, so even if the fusion part were free, there's no way for heat engines to compete on cost.

I have the feeling when we do hit the first milestone on the Kardashev scale that we'll have a lot more options available to mitigate terrestrial concerns, so let's just concentrate on getting there without killing the planet first

I've never understood why people get excited about the Kardashev scale. It's a proposal for classifying civilizations which has no place for the one and only civilization we actually know of. Doesn't that make it kind of silly?

It works great for conversation like this. It lets a person summarise 1 wiki page worth of assumptions and definitions into a single line and quickly establishes an order-of-magnitude scale to frame the discussion.

Fiction, science fiction and storytelling generally are ideal for that sort of usage. They let people pre-consider a lot of the arguments and assumptions of the people they are talking to.

I agree that I would like more energy. If it was limitless you could do all sorts of things that are not really worth it today. Imagine being able to have a hot water tank at the back of your property just because it is nice to wash your hands with warm water. Or to keep your bathroom floor always heated. May as well get a hot tub can finally afford to power that year around. I could go on forever if I had cheap energy. So as you say energy consumption may go up if made possible.

> If the promise of a technology is that we can use several orders of magnitude more energy per person, then that .1W/m2 could become 10W/m2.

Depending on what type of energy you exactly have in mind.

It is totally possible to increase consumption of iee. electric energy and reduce overall energy needs. We burn most of the fuels and use them very inefficiently:

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

In short: you need to burn coal with 3x as much energy to generate 1x of electricity. So when you switch from coal to nuclear (or renewable) and increase 2x your energy usage you still come up ahead in total primary energy consumption.

This comparison isn't valid for nuclear; nuclear power plants use steam turbines to convert heat to electricity, just like coal plants do, and the thermal efficiency (fraction of energy from burning the fuel that actually becomes electrical energy) is about the same.

OK, I double checked and you're right. Nuclear is counted properly difference is only for renewables:

https://energypost.eu/iea-underreports-contribution-solar-wi...

> the entire point of pursuing fusion is to enable fantastically more energy usage

No, it's to enable enough energy usage for, as MacKay says, a first world standard of living for the entire world's population, instead of just a small fraction of it. That's more than today, but not fantastically more.

Also, as technology advances, the energy usage required for a first world standard of living goes down. Our entire house now has LED bulbs; that cuts our energy usage for lighting to about 10% of what used to be the standard (incandescent bulbs), or about a third of the previous "low energy" standard (fluorescent bulbs--which also have hazmat issues since they contain mercury). Computers today use only a small fraction of the energy of older computers while still delivering more computing power. HVAC systems and refrigerators are more and more efficient. Cars are more efficient--I have a small SUV with a four cylinder engine (up until a few years ago I would never have even considered a four cylinder engine for an SUV, but this one has good enough performance) that gets better gas mileage than the 4-door sedan with a V6 engine that I had before it. The list goes on.

> Heat pollution is a very minor concern.

WOHA was a cursory and self acknowledged "back of the envelope" style reference, it is also now outdated.

Heat pollution is often not a minor concern locally, see introductions such as "Thermal pollution: an overview"[1]. Even globally heat pollution may have a significant contribution to climate, see studies such as "Global anthropogenic heat emissions from energy consumption" [2]

>Although the mean Antropogenic Heat Flux is small compared to the forcing of GHGs, it may exert quite distinctive effects on the climate and the environment because of the surface-based emissions and uneven geographical distribution.[2]

[1] https://www.sciencedirect.com/topics/earth-and-planetary-sci...

[2] https://link.springer.com/article/10.1007/s10584-017-2092-z

Aneutronic fusion [1] produces only fast moving charged particles. You can call fast moving particles 'heat', but if they are charged you don't need thermo-electric to generate power. It already is useful power. A fusion plant capable of fusing boron + hydrogen basically produces a 2 million volt battery.

[1] - https://en.wikipedia.org/wiki/Aneutronic_fusion

That sounds cool (sorry couldn't resist) but very much a long shot as the wikipedia article itself notes :

"None of these efforts has yet tested its device with hydrogen–boron fuel, so the anticipated performance is based on extrapolating from theory, experimental results with other fuels and from simulations."

Also, even with good proportion of energy contained in such particles to somehow tap efficiently in practice, the reactor itself is still going to need a great deal of cooling, just to stop it melting.

Also the article we are commenting on, does not seem to concern such a reactor.

The problem here is not direct thermal pollution, it's that thermal power plants in general -- nuclear, fossil, solar, geothermal -- are becoming obsolete.

https://www.forbes.com/sites/amorylovins/2014/09/07/fusion-p...

Apart from warming up the water, I take it there's nothing inherently pollutant about using it for cooling.

Edit: On second read, your point is that heat is a pollutant itself. My next sci-fi daydream will be about cooling down the planet by converting atmospheric heat.

Heat, unlike CO2, is relatively easy to deal with - install cheap giant mirrors in deserts, reflect a ton of heat back into space. Space blanket type of mirrors are VERY cheap, especially at large scales.

I think we may find such schemes happen as we miss our CO2 targets and may need to urgently limit global temperature rise. A controllable sun shade in space would be my preference over consigning regions of earth to heat dumping grounds. But such geohacks will not be able to target the ecological disruption of local heat pollution or make water resources abundant where they are scarce, they will just perhaps be able to ameliorate a global emergency.

With this (absurd) line of thinking, we should probably just not generate any power at all.

The point is that even if unlimited cheap heat becomes possible, turning that heat into useful forms (e.g. electricity) has limits that we are already close to.

I don't see how that observation is in any way absurd. It's actually quite helpful to counter the "fusion as a panacea" narrative with a dose of reality of how power plants actually work.

We put the plant near a river. It intakes river water, which is heated to steam to make the electricity, and is then cooled and reused or released. I don't see how that is terrifically destructive; I must be missing something. Explain it to me, please? (Serious question.)

Imagine that we decide to increase energy usage by 5x-10x, and increase size of the plant, and the change in river eater temperature goes up by that much. Eventually the plant starts to change the river water temperature to the degree that it changes the ecosystem.

This is already regulated, see for example this discussion of monitoring systems for proving compliance:

https://www.power-eng.com/articles/2007/01/external-temperat...

How do you cool it down? The only way to cool one thing is to heat another. Evaporative cooling is usually the method if you must cool your water, but it has diminishing returns and isn't practical to cool all the way to inlet temperature (because source water is colder than the air wet-bulb temperature). This results in water above ambient being discharged to the environment, which affects fish and plant life in the water body.

We already do that, and those nuclear power plants (and other thermal plants) already have to shut down under certain climate conditions to avoid damaging the local ecosystem by overheating it. [1]

[1] https://www.chicagotribune.com/news/ct-xpm-2012-08-20-ct-met...

Wind and solar do not require cooling or have problematic thermal emissions. It is possible for solar to have a slightly lower (or higher) albedo than ground it is situated, and possible for wind to cause some local heating from air mixing (with corresponding distance cooling) but these effects are much less intense than thermoelectric plants essential need to release Gigawatts of heat in order to produce gigawatts of electricity (in addition to the heat which the produced electricity ultimately results as).

Even if solar albedo is equal to the ground it was on, that will cause a net cooling at the solar collection site, since ~20% of the absorbed solar energy is converted to electrical power, not heat. The power then eventually gets converted to heat by the consumers, but that's true of power from any source.

1) This is an absurd complaint

2) It's not even totally accurate. Aneutronic fusion can create electricity directly from charged particles without going through the heat generation step[1]. It's an active area of research with the highest profile group working on it being TAE[2].

[1]https://en.wikipedia.org/wiki/Aneutronic_fusion

[2]https://en.wikipedia.org/wiki/Tri_Alpha_Energy,_Inc.

The people associated with TAE were told 20 years ago that their scheme would straight up not work.

https://www.researchgate.net/profile/Wallace_Manheimer/publi...

The story reminds me of Transatomic. Venture capital doesn't necessarily evaluate science well.

That study was using assumptions based on a 1987 study which predicted that the fusion chain would result in 1 high energy and 2 low energy alpha particles. More recent results suggest that this is incorrect[1], with the reaction actually generating 2 high energy and 1 low energy alpha particles. This would push the CBFR method well within the realm of possibility.

[1]https://www.sciencedirect.com/science/article/pii/S037026931...

Your argument there does exactly nothing to counter the criticisms in the paper I cited. It's totally irrelevant.

But isn't water a renewable resource?

Thermoelectric plants often change their local ecosystem by raising the temperature of natural water bodies used for cooling.

However, it doesn't have to. And in particular, as water becomes more constrained by growing population and climate change, using water the same way that it has in the past is becoming untenable.

Recent regulations are starting to end "once through" use of water this way, which is leading to the shut down of older plants that are close to the end of their lifespan anyway.

And then there are plants like this nuclear plant in Arizona which cools using treated sewage, which has almost zero impact:

https://en.m.wikipedia.org/wiki/Palo_Verde_Nuclear_Generatin...

Afaik the arizona plant doesnt use sewage but grey water, from drains and canals and such. Large amounts of it, and it gets straight up evaporated. Grey water should ideally be remediated and used for irrigation, not just evaporated - not in desert regions at least.

We will need to use water resources better! There are options for doing that, but no way to make thermoelectric power plant use insignificant.

Sometimes and not everywhere. The problem with water is that there’s usually too much or to little in the spot you want it. For cooling purposes the water should be of particular quality (eg fresh), so building on the beach comes with its own problems.

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