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Comment by arcticbull | Hacker News Reader

It's renewable in the sense that there's a massive geological reservoir which replenishes the uranium dissolved in the seawater. There's 4 billion tons dissolved right now in the ocean (enough to run 1,000 reactors for 100,000 years) but that is replaced as it's extracted. [1]

It's about as renewable as solar, which is to say, we will eventually run out - but at that point the heat death of the universe is a more pressing concern.

[1] https://cna.ca/2016/07/27/theres-uranium-seawater-renewable/

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> It's about as renewable as solar, which is to say, we will eventually run out - but at that point the heat death of the universe is a more pressing concern.

Nitpicking:

The sun is expected to stop fusing helium in about 8x10^9 years [1]. The heat death will occur in around 1.7x10^106 years [2]. (if at all, there are some uncertainties around that)

Which means that while they are both far, the heat death as predicted is much much further than the other. In short, the heat death of the universe won't be a pressing concern at all when we run out of solar.

1: https://en.wikipedia.org/wiki/Black_dwarf#Future_of_the_Sun 2: https://en.wikipedia.org/wiki/Graphical_timeline_from_Big_Ba...

It’s oddly reassuring to know that we’ll actually have some time to stay a spacefaring civilization after the sun runs out.

I wonder, does the sun /have/ to run out? Could we find a bunch more hydrogen from outside the solar system and dump it into the sun to recharge it?

Assuming we possesed that capability it seems like it would be simplet to build a dyson sphere around another star and setup shop on a nearby planet.

Stars fail when the elements in their cores stop releasing net energy when fused. This crossover occurs at iron. Adding more mass will just make it's death more violent.

Also the sun contains 99% of the mass of the solar system. The remaining 1% includes Jupiter. I'm not sure how much effect we can have when only leveraging 1% of 1% of the solar systems mass.

I also wonder how one removes mass from the sun. Its the biggest gravity well in the solar system and our biggest power source is the sun itself.

Transform the mass into energy, and radiate it.

Star lifting seems plausible.

https://www.youtube.com/watch?v=pzuHxL5FD5U

Proper management of star lifetime actually requires the opposite approach: subtract mass from the star, so that the star "core" where actual fusion happens can steadily mix with a larger fraction of the remaining mass. The harvested mass can then be stored away as gas-giant planets, and used for miscellaneous purposes.

This is fascinating. Do you have any recommendations for sources so I can learn more about megascale engineering projects to maximize the life of a star?

warning: Isaac Arthur is like crack to sci-fi/intellectuals.

binge at your own risk:

https://www.youtube.com/watch?v=pzuHxL5FD5U

I remember reading some time ago that after the Sun runs out there's only enough energy in a state fit for fusion for like one or two more generations of stars in the universe, and after that the universe will go dark forever.

That may be true, but it's worth noting that the length of a "generation" of stars varies wildly depending on the type of star. Stars like our Sun might only live 10 billion years or so, but red dwarfs live 100 billion years or more so we could presumably live around them long after all the Sun-like stars have burned out.

Can't we dump matter into black holes to draw things out for a while even after that?

From where are you getting the energy to do that?

If you have a bunch of matter (dead stars, planets, interstellar dust) is there some fundamental reason this can't be dumped into accretion disks, etc. in an energy-positive way?

I suspect human will have LONG since destroyed themselves by the time the sun dies, probably before we're spacefaring and out of the solar system.

The distinction is that wind/solar arrive for free without any effort. That just isn't true of nuclear fuel. I don't think that is a problem particularly. More that "renewable" is the wrong word.

I don’t understand what you mean by “arrive for free”. We have to capture it. It is not free of any externalities.

You don’t have to produce/extract/manufacture anything to make the wind blow or the sun shine. We capture them as they are.

Edit: let’s see how many people will continue to ignore other comments to get the same point in I guess.

You don't have to produce/extract/manufacture anything to make the ocean hold uranium for us.

You don't have to build anything to make uranium radiate.

That's a pointless argument and unrelated to "renewable", which means it won't get used up.

the solar panels and wires and plastic that hook these systems up to the grid/end-user require a lot of producing/extracting/manufacturing

Why is that an important difference? To capture wind and solar you have to build turbines and solar panels which aren't free. You also have to have batteries to store them because of seasonal nature of these sources. You also need to transmit the energy thousands of miles through electrical grid because these sources of energy are limited to certain areas. Building the electrical grid itself just needs cutting out millions of more trees. So overall, the environmental impact of going full solar/wind would be worse than a combination of solar, wind, nuclear, and even maybe natural gas.

No one is denying you need those things. We’re talking about a specific step that doesn’t exist for solar/wind akin to being able to drink water you find vs. having to make it clean.

I understand what you are saying, and I'm saying it's a pointless argument which doesn't add any value to the discussion.

Duly noted.

We need tons of coal and plastics to capture the sun shine.

If we ran the entire world off of nuclear reactors, we could increase the energy we used and still not worry about exhausting the amount of uranium available to us. Proliferation would be a concern though.

That said, why would we run the entire world on nuclear, or go for a nuclear-only strategy when we also have solar and wind and geothermal and hydroelectric? For that matter, why should we exclude nuclear from the energy mix available to us?

Different sources of power have different properties with different tradeoffs, but if you can cover your bases with multiple types, why wouldn’t you?

Hydro is actually not a particularly good choice in most cases. Some hydro installations can actually produce just as much global warming impact as a fossil fuel plant (largely methane produced in the flooded area - which has a far greater impact than CO2; about 80X greater). They also have significant ecological impact that isn't usually accounted for in folks mental models. [1, 2] Hydro isn't really green energy.

Geothermal I think only works in some places without causing earthquakes. [3]

Wind and solar are good, though.

[1] https://www.science.org/content/article/hundreds-new-dams-co...

[2] https://www.utilitydive.com/news/hydropower-emissions-fossil...

[3] https://news.stanford.edu/2019/05/23/lessons-south-korea-sol...

From a Californian perspective, hydro and geothermal are basically tapped as far as I know, in-State anyway. The plants that are operational already is about the extent of what we can probably build.

Actually something of a dream of mine is to see nuclear reactors eventually replace some of our dams, maybe restore some of the lakes and tributaries that have been lost, but presently new reactor construction is prohibited here per a ballot initiative from before I was born.

My larger point is that society is going to continue to demand increased electricity generation, which means new plants and installations. It’s one thing to want to replace existing installations but if you’re going to service future demand, then new sources of multiple types have to remain on the table. I would take nuclear over gas-fired plants, but I would take gas-fired plants over coal-fired plants.

> From a Californian perspective, hydro and geothermal are basically tapped as far as I know

For what I understand, the California State Water Project as visioned in the 1960s, had Stage I and Stage II. Only Stage I was built. Then from the 1980s onward, there was political opposition and Phase II was never started.

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

True, but the Klamath River is in the grand scheme of things a fairly minor watershed in California. Some room for growth, but effectively tapped out as far as the major watersheds in the State go. We have just a lot of dams and we’re still importing more and more of our energy from other States as we make it harder to build plants here.

The massive advantage of hydro is that it also serves as energy storage. Too much wind today? Just use the excess electricity to pump water back up

> Proliferation would be a concern though.

https://whatisnuclear.com/non-proliferation.html

Non-proliferation as a movement is only as strong a movement as nuclear-equipped nations are willing to enforce it. I’m not willing to hold up deploying reactors in the US over it, but proliferation is a legitimate concern.

I'm more concerned about global warming personally...

What happens when every country has nuclear weapons at the ready and dictators in power? Pretty sure global warming (Climate change) won't be as disastrous as a nuclear winter.

Really, this week? With nuclear war looming over us all?

Also lets put things in perspective, Global Warming means future generations will need to adapt to new weather patterns. Some animal and plant species will become extinct, others may thrive.

Nuclear war will end civilization and make many parts of the world completely uninhabitable.

There is nothing we can do if Putin decides to push the button. The world as we know it ends at that point because the USA won't hesitate to answer with our own nukes, and I wouldn't have it any other way. I don't worry about things that I could never have any control over. I am worried about global warming per this conversation about energy sources that won't destroy human civilization via natural disasters.

I thought we were talking about proliferation of nuclear technology, and we _do_ have control over that.

> Really, this week? With nuclear war looming over us all?

Nuclear war has been looming over us all since 1949, this week is no different than last week or 10 years ago.

I don't think the word "renewable" implies anything about effort involved?

You have to build solar panels and wind turbines. Then have connecting service roads able to carry heavy equipment. Wash the panels frequently or watch their performance plummet. Grease moving parts to avoid friction losses. Maintain the rotor blades at the cost of significant downtimes. Replace everything after 20 years as that is their average lifespan. Deal with all poorly recyclable waste you have created. Overbuild all transmission lines by a wide margin, to compensate for the low density and intermittent nature of wind and solar. Accept that what could have been truly space reserved for wild nature is now used for low density energy farming. I really don't see how wind and solar are renewable in the true sense of the word. From an ecological perspective the point should be to use our resources efficiently so as to return large swaths of land to pristine nature. Currently you can do this two ways: one use high density technologies like nuclear, the other is to go extinct voluntarily. My choice was made after becoming a parent.

Wind generators aren't free. Solar cells aren't free. And (even more importantly) backing storage for when the sun isn't shining and the wind isn't blowing is most definitely not free.

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