Tidal energy is not renewable • Hacker News Board

Re: Tidal energy is not renewable

#41

Post by sgu999 » Mon, Sep 04, 2023, 6:54 PM UTC

NBJack wrote: post #13

uoaei wrote: post #3

Then technically neither is wind, since it slows down surface air currents and widens the effective boundary layer of the atmosphere. Technically-technically, no forms of energy "generation" (technically just conversion) are 100% efficient so something is always lost to heat. I guess the important question is, what is the net effect in changing that kind of energy into purely thermal energy?

Air currents have a purpose, and I actually believe large scale wind farming will have negative impacts on climate. Not to mention the impact on birds killed by the things. I would even go as far to say nuclear energy has less of an impact (as long as all goes well). The question few seem to ask is should we be this (literally) power hungry in the first place?

Your first paragraph really made the second one a pleasant surprise!

No we shouldn't be this power hungry, we've effectively never replaced an energy source by another... we keep on stacking the new ones on top of more of the old ones [1].

[1] https://ourworldindata.org/grapher/global-energy-substitutio...

Re: Tidal energy is not renewable

#42

Post by wizofaus » Mon, Sep 04, 2023, 6:55 PM UTC

PaulKeeble wrote: post #19

throwaway87543 wrote: post #11

Earlier quoted context omitted.

But is it possible to extract that much energy from the tides with current techniques? That starting point in their math may be invalid. But it is good to know that not very much energy is available from the tides.

If its not possible then we really shouldn't be very interested in it because it can't get us very far, 1% is a rounding error towards solving the CO2 PPM causing climate change.

The difference any individual (or even a single small to medium sized business) can make is never more than a rounding error either - I'm not convinced that means we shouldn't be interested in such changes.

Re: Tidal energy is not renewable

#43

Post by jaggederest » Mon, Sep 04, 2023, 6:55 PM UTC

FriedPickles wrote: post #23

Hmm so if we pump water to amplify the tides we can speed up the Earth's spin and get rid of the leap second.

This has already happened, actually. Some leap seconds have been skipped iirc due to faster rotation from all the impounded water in reservoirs in northern regions.

Re: Tidal energy is not renewable

#44

Post by hkt » Mon, Sep 04, 2023, 6:56 PM UTC

NBJack wrote: post #13

uoaei wrote: post #3

Then technically neither is wind, since it slows down surface air currents and widens the effective boundary layer of the atmosphere. Technically-technically, no forms of energy "generation" (technically just conversion) are 100% efficient so something is always lost to heat. I guess the important question is, what is the net effect in changing that kind of energy into purely thermal energy?

Air currents have a purpose, and I actually believe large scale wind farming will have negative impacts on climate. Not to mention the impact on birds killed by the things. I would even go as far to say nuclear energy has less of an impact (as long as all goes well). The question few seem to ask is should we be this (literally) power hungry in the first place?

> The question few seem to ask is should we be this (literally) power hungry in the first place?

Nobody asks because the answer is "no" - huge parts of our lives are absurdly inefficient, wasteful, or just gratuitous when it comes to energy usage. Heating, transport, all of it. Computing, too.

Re: Tidal energy is not renewable

#45

Post by bobthepanda » Mon, Sep 04, 2023, 6:57 PM UTC

blake1 wrote: post #32

The single most important assumption in this paper is that energy consumption will increase by 2% per year. This kind of exponential growth leads to outlandish estimates for the amount of tidal energy that society will demand. Energy consumption has decoupled from population growth rates and economic growth. How much energy will we consume in 1,000 years? Most projections of the population have it stabilizing at arou…

The UN has revised peak projections down several times; the peak is now expected at 10 billion.

Re: Tidal energy is not renewable

#46

Post by [deleted] » Mon, Sep 04, 2023, 6:57 PM UTC

exitheone wrote: post #37

idlewords wrote: post #4

Every energy source becomes renewable on the right time scale.

That's not actually true. The conditions for the formation of coal and oil may likely never happen again because the bacteria to break decompose trees did not exist then but exist now, making oil formation impossible because trees decompose now. Unless they all die out, we won't get any new oil ever.

[deleted]

Re: Tidal energy is not renewable

#47

Post by thewakalix » Mon, Sep 04, 2023, 6:57 PM UTC

wcoenen wrote: post #27

I'm not sure the author realized this, but they're actually making a statement about how crazy exponential growth is. Not about the sustainability of tidal power. This becomes obvious once you look closer at what that 2% growth rate (as assumed in the post) implies. Our global energy consumption in 2008 was estimated to be 474 exajoules. The total energy received by the earth from the sun during a year is about 5 mil…

If we're still around in 500 years and producing that much energy, I don't expect we'd be limited to Earth anymore!

Re: Tidal energy is not renewable

#48

Post by Rantenki » Mon, Sep 04, 2023, 6:58 PM UTC

It's a neat thought experiment, but the underlying assumption:

  The world's energy consumption was about 5.67x1020 Joules in 2013.[18] This number has increased by more than 2% per year on average in the last 50 years. The average world economic growth rate in the last 50 years is about 3%, which requires a corresponding increase in the energy supply. So, the 2% growth rate for world energy consumption should be a conservative assumption.

... is a bit naive. If we're consuming (does some math) `1.02^1000 = 398264651` ...

Four billion times as much energy as we do today. I don't think there's much risk of us growing our population to that degree, nor of us being that power hungry if our population stabilizes. We'll be either extinct or back to a sustainable agrarian population far before we reach that upper limit. Honestly, if we produced that much power, I suspect we'd have long since boiled the oceans, making the whole argument moot.

TL;DR: Don't extrapolate FAR into the future based on a small (relatively) set of data points.

Re: Tidal energy is not renewable

#49

Post by joelthelion » Mon, Sep 04, 2023, 6:58 PM UTC

Issues with exponential growth set aside, does wind power suffer from the same problem? If I understand correctly, wind mostly caused by the coriolis force, which is a consequence of the earth's rotation. Would building too many wind turbines slow down earth's rotation?

Re: Tidal energy is not renewable

#50

Post by Aachen » Mon, Sep 04, 2023, 6:58 PM UTC

almenon wrote: post #28

Relevant: https://physics.stackexchange.com/questions/6400/are-tidal-p... This theory is very interesting, although the author presents it with too much confidence for such big claims.

In that link:

> The Earth's rotational kinetic energy is about 10²9 J, and the world uses something like 10²² J/year, so you could power the entire world for millions of years before you'd run out of rotational energy.

(my phone somehow has a ² but not a ^9; the first number is supposed to be 1e29)