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Tidal energy is not renewable

cs.stanford.edu

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Re: Tidal energy is not renewable

#111

Post by cornel_io »

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…

I was super skeptical of this article, because I was trying to imagine how we'd have to arrange extractors in the oceans to pull any meaningful amount of energy out of the rotation of the earth based on tides, and only at the end of the article did I see that assumption of 2% compounding multiplied out as far as needed...ugh.

The implausibly is staggering, we'd run out of resources to build extractors way before causing any meaningful shift in the rotation: if the monstrous land barriers of the continents take millions of years to drain a small percentage of the energy, we have zero hope of achieving much more with the solid mass available to us on Earth, short of a Dyson sphere-level breakthrough in "moving mass around", oh, and by the way it has to happen deep underwater as well, and we need to channel all the energy somewhere useful! Way harder than just making a ginormous but thin solar array in space, which is almost certainly what we'd do instead from a "energy cost to arrange matter" optimization POV.

Re: Tidal energy is not renewable

#112

Post by arnaudsm »

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…

Your idea sounds similar to the Kardashev scale [1], and we seem to be at 0.733. The concept of the Dyson sphere emerged from that theory.

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

Re: Tidal energy is not renewable

#113

Post by uxp8u61q »

paulmd wrote: post #82
skywhopper wrote: post #17

This is a CS professor doing some naive math and assuming that the energy usage patterns of the past 50 years (an increase of 2% usage each year on average) could or would keep going for the next 1000 years.

Despite all the scoffing in this thread, they’ve gone on at about that rate for 200+ years now. Expecting a deviation from this is kinda “climate change will slow down in the 2000s and 2010s from green energy ” level magical thinking.

200 years is, what, a thousandth of the duration humans have been on this Earth? 44 billionths of the age of the Earth? It's a blip.

Re: Tidal energy is not renewable

#114

Post by octacat »

nirse wrote: post #96
qayxc wrote: post #73

Earlier quoted context omitted.

That's not what renewable means. Renewable energy means that the source is naturally replenished within a human lifetime. In other words, the source isn't permanently depleted by tapping into it. This is the case with solar energy: the Sun's energy output doesn't change depending on whether we use it or not. Renewable doesn't mean perpetual - that'd be physically impossible for all we know.

But also the sun is burning fuel and eventually that will run out and we don't really have any means of renewing that fuel (I don't know where to order intergalactic hydrogen).

Sadly it is not even means of intergalactic hydrogen. The game is over once the hydrogen in the core is fused :( Tidal energy would probably never go mainstream to cause major issues (too easy to break during the storms, not all places are good to build it, other types of energy sources are more attractive).

The whole article sounds like something that fuel companies would sponsor to make the renewable energy look bad (look, tidal is not renewable too, so buy our gas/oil).

Re: Tidal energy is not renewable

#115

Post by uxp8u61q »

skywhopper wrote: post #17

This is a CS professor doing some naive math and assuming that the energy usage patterns of the past 50 years (an increase of 2% usage each year on average) could or would keep going for the next 1000 years.

I would have expected HN users to have learned their lesson after this superconductor fiasco. Expertise in a field grants you no expertise in another.

Re: Tidal energy is not renewable

#116

Post by paulmd »

uxp8u61q wrote: post #113
paulmd wrote: post #82

Earlier quoted context omitted.

Despite all the scoffing in this thread, they’ve gone on at about that rate for 200+ years now. Expecting a deviation from this is kinda “climate change will slow down in the 2000s and 2010s from green energy ” level magical thinking.

200 years is, what, a thousandth of the duration humans have been on this Earth? 44 billionths of the age of the Earth? It's a blip.

it’s 1/5th of the period under consideration, which is a pretty reasonable basis for extrapolation

not sure how any of those numbers have any relevance to projecting the growth of energy usage under industrialized society lmao. yes, if we extinctify ourselves in the next few decades, or return to an agrarian, pre-industrial existence, the earth will be fine and will eventually return to an equilibrium.

Re: Tidal energy is not renewable

#117

Post by graypegg »

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…

Wouldn't energy available to be consumed become a limiting factor in our rate of using that energy?

Re: Tidal energy is not renewable

#118

Post by Baeocystin »

detourdog wrote: post #91
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…

I think the next step is to figure how many exajoules goes to waste heat.

Minus the tiny fraction embodied in global temperature increases, all of it.

It's the same reason that the Earth radiates exactly as much energy as it receives from the sun, just a larger number of lower energy, higher entropy photons. What the sun really provides is a source of low entropy.

Re: Tidal energy is not renewable

#119

Post by giantg2 »

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…

"Think about that: if energy consumption growth continues at the current pace, then in 500 years we'll either be using ALL solar energy received by the earth (leaving none for the biosphere), or we'll have figured out some magic technology to produce 5 million exajoules of energy per year."

So nuclear?

Re: Tidal energy is not renewable

#120

Post by hollerith »

hn_throwaway_99 wrote: post #64

But don't the tides naturally dissipate a lot of that energy anyway? E.g. whenever you go to the beach and see waves crash upon the shore, that's tidal energy being dissipated as heat. If you stick a turbine in the mix to extract useful work before it turns into heat, isn't it still turned into heat regardless?

Quoting from the OP:

>it will take about 10.468 billion years for Earth to lock to the Moon naturally.

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