Do tidal power plants make the moon get closer or further from the earth ?

Question

Also, any calculations on how big this effect could be. Also - how would you extract the maximum possible energy from tidal movements ?

Answer 1

Most responders seem to have forgoten that for every action, there is an equal and opposite reaction. Tidal drag on the earth as a whole causes the earth's day to increase over time and the moon to recede so as to conserve angular momentum. Tidal power plants operate by delaying the tidal outflow so as to extract energy from the resultant water level differential. This incrementally increases tidal drag. One is, essentially, stealing from the earth's rotational energy to do this.

However, natural tidal drag takes billions of years to have a profound effect; the earth's day won't equal a lunar month (then about 35 present days) until about the time the sun devours the earth anyway. Any feasible acceleration of this process by human activities is likely to remain negligible, unless you're thinking in terms of planet girdling tidal dams in the distant future. I'd worry more about screwing up the ocean's ecosystem with that, though.

Answer 2

Tidal power plants have no measurable effect on the moon. However, the gravitational interplay between the moon and the earth most certainly causes an effect on both bodies, even beyond the water and land tides (yes, the ground does move under your feet depending on whether the moon is overhead or on the other side of the earth). Despite what others may say, the tides do affect the moon and the earth. The moon is much farther away from the earth than it used to be because of tidal drag.

The sun's position also affects the tides and the moon-earth relationship. Standard Newtonian physics can be used to calculate the relationship between any two bodies, but difficult for 3 or more bodies.

What the most energy is that can be extracted from tidal power depends mainly on how great the difference is between high and low tides, assuming the power plant is the same for all locations. It may be possible to maximize the tidal difference in a given area by designing the power plant to do that. After that, it's mainly a question of how efficient the power plant is - that is, how much energy goes off as heat while the plant is working.

Answer 3

This is another one of those media stories which tries to make a big deal out of nothing in particular. The Moon is close to the Earth once a month. There is also a full moon once a month. Once a year, these dates roughly coincide. The minimum distance is not quite the same each year. It varies by a small amount. This year it's all of 15 km less than last year on January 30th. Do you remember all the disasters on that date? Well, there was a magnitude 5.6 earthquake, but there are 3 or 4 of those a day on average. Oh, and there was snow in Germany. This tends to happen every January. This is a non-story and the Moon isn't going to cause anything to happen. The Moon won't even look noticeably different although I'm willing to bet that there will be questions on here saying "Did you see the Moon rise last night? It looked huge!!" despite the fact that you could tell them that any full moon was a 'supermoon' and they would say the same thing.

Answer 4

The Moon is gradually moving away from the Earth and the tides are to blame. Every year, the Moon moves a further 3.82cm from the Earth.

One might expect that the tidal bulge created by the Moon's gravitational attraction would point directly at the Moon. This would be the case if the Earth rotated about its axis at the same rate as the Moon orbits around the Earth. We know that this is not the case since the Earth makes a complete rotation about its axis in only 24 hours while it takes 27.3 days for the Moon to make a complete rotation around the Earth. Because of this difference in rotation speeds, the tidal bulge created by the Moon actually rotates ahead of the Moon in its orbit by about 3 degrees.

Since the bulge leads the Moon in its orbit, its gravitational attraction on the Moon pulls the Moon forward. This effect increases the Moon's energy to resist the gravitational attraction of the Earth. The increase in energy allows the Moon to pull further away from Earth and increase its orbital distance. As its distance increases, the Moon's orbital speed decreases according to the law of conservation of angular momentum.

Answer 5

There is a small flaw in the answer from Thelawye.. in that it is the interplay of the Earth/Moon gravitational effects that is slowing the Moon's rotational speed, hence the Moon is receding from the Earth.

Answer 6

Tidal power plants use tides flowing in to bays to turn turbines generating electricity. They have nothing to do with creating a tide. They do not effect the moon tides, or any other thing.

Answer 7

the gravitational force of the moon causes the tides......the tides do not bring the moon close to us......or far from us for that matter......n for the energy from tides it all depends on how the potential energy of the tides are utilised by the tidal power plants......

Answer 8

The moon affects the tides. Not the other way round.

Answer 9

Don't ask nonsenses.