The Lemon Fool

Very interesting paper here. Seems (unfortunately) rather plausible. Unintended consequences and all that.

https://cs.stanford.edu/people/zjl/tide.html

Complete rubbish. Have you never considered that tidal energy is dissapated all the time because of friction, both in the water column and the flexing of the land tide. Why promote this stuff?

JohnB wrote:Complete rubbish. Have you never considered that tidal energy is dissapated all the time because of friction, both in the water column and the flexing of the land tide. Why promote this stuff?

I wasn’t “promoting” it, I just stumbled on it and thought it was perhaps a concern. Yes, tidal energy is dissipated naturally, and perhaps I shouldn’t be taken in by this paper from such a disreputable source as Stanford University.

Debunking (very long forum discussion): https://news.ycombinator.com/item?id=37383283

mc2fool wrote:Debunking (very long forum discussion): https://news.ycombinator.com/item?id=37383283

Didn't read the forum discussion but my one-line debunk would be that the author postulates that energy use in the future will be 400m (=1.02^1000) times greater than it is today which is clearly preposterous.

The dude needs to visit TLF and learn about compounding! LOL.


GS

GoSeigen wrote:

mc2fool wrote:Debunking (very long forum discussion): https://news.ycombinator.com/item?id=37383283

Didn't read the forum discussion but my one-line debunk would be that the author postulates that energy use in the future will be 400m (=1.02^1000) times greater than it is today which is clearly preposterous.

The dude needs to visit TLF and learn about compounding! LOL.


GS

That's the very first point raised in the linked-to discussion.

GrahamPlatt wrote:perhaps I shouldn’t be taken in by this paper from such a disreputable source as Stanford University.

I don't think the paper is actually approved in any form by Stanford. The author appears to (have) worked there and is able to host articles on a personal page. There's no evidence of peer-review or anything else to give it any formal status.

chas49 wrote:

GrahamPlatt wrote:perhaps I shouldn’t be taken in by this paper from such a disreputable source as Stanford University.

I don't think the paper is actually approved in any form by Stanford. The author appears to (have) worked there and is able to host articles on a personal page. There's no evidence of peer-review or anything else to give it any formal status.

Yep, see that now. Anyhow, it was worth posting here - for me - to have it pulled apart.

I'd have thought tidal energy originates from the motion of the moon making the sea slosh about and is a such, not 'renewable'.

I think all passive orbits decay, which means the moon's orbit is decaying and the moon will eventually escape or crash. Might take quite a few millennia though.

Am I overthinking this?!

Mike4 wrote:I'd have thought tidal energy originates from the motion of the moon making the sea slosh about and is a such, not 'renewable'.

I think all passive orbits decay, which means the moon's orbit is decaying and the moon will eventually escape or crash. Might take quite a few millennia though.

Maybe so, but according to this article that'll take some 65 billion years, so we don't have to worry about it too much now ... and especially not as the sun will turn into a red giant in about 6 billion years.

https://www.forbes.com/sites/brucedorminey/2017/01/31/earth-and-moon-may-be-on-long-term-collision-course/

Mike4 wrote:I'd have thought tidal energy originates from the motion of the moon making the sea slosh about and is a such, not 'renewable'.

Am I overthinking this?!

Surely tidal energy originates from the rotation of the earth (relative to the moon), hence 2 tides per day. If it was the motion of the moon, it would be 2 tides per month.

--kiloran

kiloran wrote:

Mike4 wrote:I'd have thought tidal energy originates from the motion of the moon making the sea slosh about and is a such, not 'renewable'.

Am I overthinking this?!

Surely tidal energy originates from the rotation of the earth (relative to the moon), hence 2 tides per day. If it was the motion of the moon, it would be 2 tides per month.

--kiloran

Hmmm that's a good point. So is the true origin of tidal energy actually the momentum of the Earth rotating?

In which case will tidal power be slowing down the Earth's spin a little bit each year making our days get slightly longer? (In the short space between now and our sun turning into the red giant that is.)

Mike4 wrote:
Hmmm that's a good point. So is the true origin of tidal energy actually the momentum of the Earth rotating?

In which case will tidal power be slowing down the Earth's spin a little bit each year making our days get slightly longer? (In the short space between now and our sun turning into the red giant that is.)

Yes, that was exactly the point of the article in the OP. It makes a tiny difference though, the article claimed the earth would slow down in a mere 1000 years, but that was based on a forecast of endless growth of energy use to the extent that we'd eventually have tidal generators stretched across entire oceans like gigantic Trumpian walls.

So the idea that tidal energy is not renewable I think is broadly accepted ,but the 1000-year calculation is not, nor is his conclusion that tidal energy could become as big a problem as global warming (the cure worse than the disease).


GS

Maybe the point being made is that attempting to capture tidal power by collecting water at high tide, then releasing it as the tide recedes, does not capture all the power available. That was demonstrated by the Rance Barrage in Brittany. Barrages are the wrong method. Tidal flow turbines are a far better method, because they capture all the movement of the water.

TJH

Tide height is 2/3 due to moon, 1/3 sun. No energy is treuly renewable, and anyone predicting 2% energy growth for 1000 years and ignoring space based solutions is a fool. In 465 years at that rate we'd be a Kadashev Type I civilisation using all Earth's energy resources

https://en.wikipedia.org/wiki/Kardashev ... _Kardashev

Mike4 wrote:

kiloran wrote:Surely tidal energy originates from the rotation of the earth (relative to the moon), hence 2 tides per day. If it was the motion of the moon, it would be 2 tides per month.

--kiloran

Hmmm that's a good point. So is the true origin of tidal energy actually the momentum of the Earth rotating?

In which case will tidal power be slowing down the Earth's spin a little bit each year making our days get slightly longer? (In the short space between now and our sun turning into the red giant that is.)

I think that's right Mike4. Another side effect applies on the moon, I remember as a teenager reading about the tidal barrage in Rance Brittany. The Guiness book of records claimed it was making the moon's orbit of the Earth take longer which means (I think) that the moon is steadily moving away from the earth but not much at 3.82 cm per year. And a tiny percentage of that is due to the Rance barrage.

Sorcery wrote:

Mike4 wrote:
Hmmm that's a good point. So is the true origin of tidal energy actually the momentum of the Earth rotating?

In which case will tidal power be slowing down the Earth's spin a little bit each year making our days get slightly longer? (In the short space between now and our sun turning into the red giant that is.)

I think that's right Mike4. Another side effect applies on the moon, I remember as a teenager reading about the tidal barrage in Rance Brittany. The Guiness book of records claimed it was making the moon's orbit of the Earth take longer which means (I think) that the moon is steadily moving away from the earth but not much at 3.82 cm per year. And a tiny percentage of that is due to the Rance barrage.

This sort of thing utterly staggers me about astronomy and physics.

From a standing start (i.e. without the benefit of giants upon whose shoulder to stand) I doubt I'd even figure out the moon is a heavenly body orbiting the Earth. Let alone work out how quickly it is moving away from us to a resolution of a tenth of a millimetre per year.

Mike4 wrote:This sort of thing utterly staggers me about astronomy and physics.

From a standing start (i.e. without the benefit of giants upon whose shoulder to stand) I doubt I'd even figure out the moon is a heavenly body orbiting the Earth. Let alone work out how quickly it is moving away from us to a resolution of a tenth of a millimetre per year.

They don't have to work it out, they simply measure it. Well, "simply"....

"Scientists have been using reflectors on the Moon since the Apollo era to learn more about our nearest neighbor. It’s a fairly straightforward experiment: Aim a beam of light at the reflector and clock the amount of time it takes for the light to come back. Decades of making this one measurement has led to major discoveries.

One of the biggest revelations is that the Earth and Moon are slowly drifting apart at the rate that fingernails grow, or 1.5 inches (3.8 centimeters) per year. This widening gap is the result of gravitational interactions between the two bodies."

https://www.nasa.gov/feature/goddard/2020/laser-beams-reflected-between-earth-and-moon-boost-science

mc2fool wrote:

Mike4 wrote:This sort of thing utterly staggers me about astronomy and physics.

From a standing start (i.e. without the benefit of giants upon whose shoulder to stand) I doubt I'd even figure out the moon is a heavenly body orbiting the Earth. Let alone work out how quickly it is moving away from us to a resolution of a tenth of a millimetre per year.

They don't have to work it out, they simply measure it. Well, "simply"....

"Scientists have been using reflectors on the Moon since the Apollo era to learn more about our nearest neighbor. It’s a fairly straightforward experiment: Aim a beam of light at the reflector and clock the amount of time it takes for the light to come back. Decades of making this one measurement has led to major discoveries.

One of the biggest revelations is that the Earth and Moon are slowly drifting apart at the rate that fingernails grow, or 1.5 inches (3.8 centimeters) per year. This widening gap is the result of gravitational interactions between the two bodies."

https://www.nasa.gov/feature/goddard/2020/laser-beams-reflected-between-earth-and-moon-boost-science

Brilliant. I doubt I'd have been able to put myself a reflector on the Moon though, from the standing start I described.

Also given my assertion that orbits decay, I'd be astounded if the moon stayed the same distance away. It MUST be progressing to either breaking loose or crashing into us. Quite pleased to hear it escaping rather than getting closer.

Not sure why I'm pleased, though!

Mike4 wrote:Also given my assertion that orbits decay, I'd be astounded if the moon stayed the same distance away. It MUST be progressing to either breaking loose or crashing into us. Quite pleased to hear it escaping rather than getting closer.

Not sure why I'm pleased, though!

Didn't you read the earlier linked-to article? It'll do both. Not at the same time of course ... it's moving away from us now but will later fall into us. Well, if there's anything left after the sun has turned into a Red Giant at least.