In case of solar or wind the source of energy is fusion reaction in the Sun. Photons bring this energy to Earth. Here they are consumed directly in solar panels or cause an atmospheric motion that moves wind turbines.
But in case of tidal power, what is the source? Is Moon going to fly a tiny bit slower because we consumed part of its energy? Is Earth going to rotate a bit slower?
In: Physics
It comes from the earth’s rotation relative to the moon. The moon itself is actually getting more energy, as the earth is spinning faster than the moon is orbiting. The Earth’s rotation is slowing, which is where the energy for the tides comes from.
They move something physically and it generates power. Like a wind turbine. Think of a hand crank device, the. Imagine scaled up and letting the waves do the work.
The gravity of the moon pulls on the water molecules in our ocean, moving them around. This motion is already a form of kinetic energy: the moving water molecules will impart some of that energy into whatever they happen to collide with, be that other water molecules, stones, fish, boats, etc.
The tidal power plant just converts some of that kinetic energy into electricity. Instead of that kinetic energy being “wasted” by just becoming part of a wave that pushes sand around, it instead pushes against a turbine that spins to produce electricity. The water that spins the turbine gives up some of its kinetic energy and will be moving slower than it was before, but again, this would have happened no matter what the water was interacting with.
The power plant itself has zero affect on the moon. The amount of energy the moon lost in adding to the kinetic energy of our ocean water is the same, whether or not we use that energy to produce electricity.
**Ed to add:** The thing that defines what we call “renewable” energy sources like this is that using them to produce electricity will not affect how much of it is available in the future. A solar panel will not reduce the amount of light the sun produces tomorrow, a wind turbine will not reduce the amount of wind, and a tidal turbine won’t reduce future tides. On the grandest, most abstract timeline, these energy sources will all naturally deplete on their own — the universe is almost certainly destined for a heat death after all. But the rate of that depletion is unaffected by whether the energy produces electricity, or just dissipates naturally as unharvested heat.
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