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Comment by maxbond | Hacker News Reader

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> Tidal Energy Is Not Renewable

> It is incorrect to consider tidal power as renewable energy. Harnessing tidal energy will pose more severe problems than using fossil fuels. ... Tides are induced by the rotation of the Earth with respect to the gravity of the Moon and Sun. The rotational energy of the Earth is naturally dissipated by tides slowly. Consuming tidal energy further reduces the rotational energy, accelerates the energy loss rate, and decelerates the rotation of the Earth.

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

(I've not evaluated these claims in detail, I just thought you may be interested.)

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It's completely wrong. He assumes energy will increase exponentially into the future to get to his wild claim that we could tidally lock to the moon in 1000 years. Even solar power out nuclear could not power humanity in that scenario

Certainly if we grow exponentially for a further 1000 years we'll exceed the carrying capacity of this planet, however we derive our energy. I don't think that's a very interesting result.

By "completely wrong" do you contend that using tidal energy doesn't decelerate the Earth's rotation?

Can we even change viscosity meaningfully?

(Coastlines already form natural "dams". All we would do is move the coastline inward a bit, so as the tide flows through it it spins turbines. The water gets moved the same. The energy is already dissipated at the coasts, it would happen at the dams. Total dissipated energy is the same this way. Okay, if we start putting 4 km tall dams in the middle of the ocean we might somehow meaningfully change the viscosity.)

The thesis in the PDF seems to be that somehow we can push the brakes more. Maybe. (So if we let the Sun/Moon grab some water then use the Earth to get it moving again, then it necessarily slows down the rotation. But there's already a lot of energy in moving and compressing water itself, sure it's "uncompressible" compared to gases, but there's plenty of molecular stuff to move around where energy can go. There's some tidal heating too.)

It's verbose, but in a bad way, and it's structured in a way that makes it hard to comprehend. (And the whole pro-fossil-fuel framing is just .. huh.)

Imagine what a Dyson sphere is going to do to the lunar orbit around Earth.

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