[Petrochemicals (OP)]

If we harness the power of the tides as is suggested by some as a source of renewable energy what effect will this have on the orbit of the moon?

[Origin]

"Will tidal power cause the moon to crash into us?"
No.

If we harness the power of the tides as is suggested by some as a source of renewable energy what effect will this have on the orbit of the moon?

No.

[Kryptid]

Tidal interactions are the result of the Earth spinning faster than the Moon orbits around it. The ultimate result is for rotational kinetic energy to be extracted from the Earth and transferred to the Moon which slowly increases its orbital distance from us. So tidal power ultimately comes from the Earth's rotation, not the Moon's orbit.

The rotational kinetic energy of the Earth is truly immense and it's already being drained by the Moon. Human use of that energy would be minuscule by comparison. Eventually, you'd expect Earth's rotation to slow down until a day was as long as a lunar orbit. At that point, the two are tidally locked and you can no longer use tidal power.

[Origin]

Eventually, you'd expect Earth's rotation to slow down until a day was as long as a lunar orbit.

I think it is more likely that the earth would become tidally locked with the sun.

[vhfpmr]

The rotational kinetic energy of the Earth is truly immense.....Human use of that energy would be minuscule by comparison.

Kinetic energy: 259000YJ
Global annual energy consumption: 634PJpa

259000YJ/634PJpa = 409 billion years

[Janus]

Eventually, you'd expect Earth's rotation to slow down until a day was as long as a lunar orbit.

I think it is more likely that the earth would become tidally locked with the sun.

The tidal effect of the Moon on the Earth is roughly twice that of the Sun's, Tidal forces fall off by the cube of the distance, so even with its great mass disadvantage, the much closer distance to the Moon more than compensates.

[Kryptid]

I think it is more likely that the earth would become tidally locked with the sun.

You do now have me wondering if it is possible (barring the Sun's future death, as we are talking about very large time scales here) for the Earth-Moon system to evolve in such a way that the Moon ends up at the L₁ Lagrange point. That way, the Sun, Moon and Earth could all be tidally locked to each other.

However, given that L₁ is about 1.5 million kilometers from Earth and the Moon is currently only about 384,000 kilometers from Earth, that would require some substantial retreat from Earth on the Moon's part.

[Origin]

The tidal effect of the Moon on the Earth is roughly twice that of the Sun's, Tidal forces fall off by the cube of the distance, so even with its great mass disadvantage, the much closer distance to the Moon more than compensates.

[slaps forehead] Of course.  Since the tides are due to the moon (primarily) that should have been a hint to me that I was incorrect...

[Halc]

You do now have me wondering if it is possible (barring the Sun's future death, as we are talking about very large time scales here) for the Earth-Moon system to evolve in such a way that the Moon ends up at the L₁ Lagrange point. That way, the Sun, Moon and Earth could all be tidally locked to each other.

Barring the Sun's imminent death indeed, so we'll ignore that.

The future is a tidal lock occurs around a 1440 hour day/month, which is about two current months. At that point the angular momentum of the system is what it is now, but with everything spinning at the same rate, so no more energy to push it further.
At that point the sun becomes the primary drag and the energy/momentum slowly drains away. The days begin to get shorter again and the moon starts dropping in orbit, all while the two stay tide locked. Eventually the day gets back down to around 12 hours (it used to be less than that in the past) and the moon crosses the Roche limit and Earth gets some spectacular rings like Saturn. Most of that will fall to Earth eventually, but in pieces, not one big chunk.

Mars is on the verge of doing this right now with Phobos to cross the Roche limit in perhaps 70 million years, but it's so small the rings resulting won't be that dramatic. It's also different with Mars since it is not tide locked with either moon, which heavily contributes to the rate at which its orbit declines.

[Petrochemicals (OP)]

The rotational kinetic energy of the Earth is truly immense.....Human use of that energy would be minuscule by comparison.

Kinetic energy: 259000YJ
Global annual energy consumption: 634PJpa

259000YJ/634PJpa = 409 billion years

According to this it is world energy usage is the best part (0.58zj) of a zeta joule per year and increasing. So call it 1zj, 1 x 10^21, or 259 million years.


https://www.theworldcounts.com/challenges/climate-change/energy/global-energy-consumption

[Peter11]

The moon is actually moving away from the earth in 1969 when they landed on the moon  they  put a reflective panel there and its been measured at 3.8 cms a year.It will be an extremely long time but it is moving away from the planet.