World’s First Ocean Hybrid Platform Converts Tidal Waves into Energy | Hacker News Reader

World’s First Ocean Hybrid Platform Converts Tidal Waves into Energy

spectrum.ieee.org

40 pointsheadalgorithm27 comments

This seems to be a combination of tide, wave, wind and solar power on a floating platform.

It's not really clear what the benefits of combining all of them are - you end up compromising in every direction. The wind turbines in the illustration are comically small - wind power increases with the square of the rotor diameter and the cube of the wind speed - which is why modern wind offshore turbines are absolutely massive. They can extract so much more energy from the wind.

There's enough challenges in just solving wave or tidal power on their own - it seems like a waste of effort to try to do everything in one package.

> The wind turbines in the illustration are comically small - wind power increases with the square of the rotor diameter and the cube of the wind speed - which is why modern wind offshore turbines are absolutely massive.

Wow! I just looked this up... these are absolutely nuts. The diameter is over a fifth of a kilometer (220m)!!

[1] https://www.ge.com/renewableenergy/wind-energy/offshore-wind...

I wish I knew enough about physics to take a stab at figuring out how much energy we would need to remove from ocean tides to de-orbit the moon.

I don't think you can increase the rate of extraction with a water power plant. Mining may do so, but I don't think you can do anything with the ocean (except for increasing or decreasing its volume) that will make a change, how small that may be.

I think you're wrong.

1. If the water is fully frictionless, it will form a wave moving in phase with the moon, and extract no energy.

2. If the water is a solid, it will not move, and extract no energy.

1.5. If the water has the perfect viscosity/friction/resistance to flow, it will be 90 degrees phase away from the moon, and extract the most energy.

The real moon is more like 1.1. Adding more resistance in the form of water turbines will get us closer to the 1.5 scenario, extract more energy, and cause the tides to stop sooner. Anything humans can build I suspect would be insignificant though...

The main issue is that the water is interrupted. That means that friction or not, any movement will die off. So it already extracts nearly the most it can (the small difference being energy transmitted through land, the impact here is non-zero).

That power plant is just making it die on it, instead of on land.

(Anyway, the final configuration is not the Moon colliding with Earth, is it getting tidally locked.)

Isn't the moon already tidally locked?

Its rotation is locked to its translation.

Its translation isn't locked to Earth's rotation (that's why we have tides). It will eventually become, but I think the Sun will burn everything up earlier.

Oh, I didn't even realize that was possible. So the moon would only ever be visible from the same half of Earth?

Sure they tend to get in sync, they are interacting, aren't they?

Due to conservation of momentum, tides can't just change the Moon's orbit without affecting something else. That something else is Earth's rotation. And the only way to take energy out of the system while still conserving momentum is for the Moon to move into a higher orbit while the Earth rotation slows (because the Earth rotation is faster).

That can lead to either the Moon being ejected from orbit or to its rotation being locked with the Earth day (that gets very long). Our current configuration leads to the later.

But none of those will actually happen. The Earth tides from the Moon rotation are just not relevant enough for them locking on a Sun-like star lifetime.

If we had immense pumps that could keep the tidal menisci whereever we want, say N degrees ahead/behind of the moon, my gut feeling is that keeping the closer meniscus 60 degrees behind would create the most 'drag'

Along the same lines, I've always wondered how much wind we need to capture before we start to change the weather.

Weather is chaotic, so the answer is simple: epsilon (any number, arbitrarily small, different from zero).

He probably meant to say “climate”.

It's surprising to me that the moon is speeding up and getting further away from Earth. You might think the energy extracted to make tides would have the opposite effect.

The moon is getting further away, but slowing down.

https://en.wikipedia.org/wiki/Tidal_acceleration#Quantitativ...

To get to a higher orbit ("further away"), you need to go faster than what you're going right now.

Once you're in the higher orbit, you're going slower than what you were going at in the lower orbit.

The Earth is pulling the Moon along its orbit faster than the default speed of the orbit, by dragging the tides ahead of where they would normally be. So the Earth's rotational energy is translating into a higher orbital energy for the Moon.

The UK has been thinking about tidal power in a "Severn Barrage" on the Severn river near Bristol since 1849:

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

No progress in recent years though due to environmental concerns, although there is always Salter's Ducks (which is just harnessing plain wave action, not tidal):

https://en.wikipedia.org/wiki/Salter%27s_duck

Sadly, seems like it also suffers from a similar lack of progress.

Out of curiosity, is this a good idea? I'm no oceanologist, but I'd figure using tidal waves for energy would deplete the tidal waves of energy, no? And then that may have unintended consequences on ecosystems and climate? For example, would this have effects on El Nino (ENSO) cycles? I'm just grasping at straws here due to ignorance, but this smells fishy.

The bigger unintended consequence is that this shades the area underneath the platform. That may not be so bad if it's in deep water, but in a shallower area it will have negative effects on the life underneath it.

Great questions that must be asked, but it sounds like having huge amounts of excess carbon in the oceans might have a much greater impact than stealing a percentage of wave energy. I do wonder if there is a percentage we can take without significant impact. Small numbers can add up and having another option for coastal cities can have a huge positive impact.

The tidal power station in Rance, France, which was the largest in the world for almost 50 years, has wiped out a couple of species from the area and attracted another two over the years *

* https://en.wikipedia.org/wiki/Rance_Tidal_Power_Station

As far as the question about depleting the tidal waves of energy, I cannot imagine that it will ever be more than tiniest slice of that pie.

Oceans are very big. Would this have any greater impact than wind turbines depleting energy from the wind?

Interesting to read all these concerned comments about possible risks. The biggest risk to this planet is our species and everything else is being dwarfed by it. Just saying (I will probably be down voted or so...never mind).

It's not one or the other; this solution is not the missing piece of the clean energy puzzle.

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