One of the more widespread "renewable" ways of generating power is by harnessing hydropower, i.e. by exploiting the movement of falling or flowing water. Some of the most commonly seen implementations are river dams and tidal power stations.
All hydroelectric power stations obviously remove some kinetic energy from the water, usually by requiring it to turn a turbine. What I'm curious about is whether the removal of this energy is actually sustainable, i.e. whether energy is introduced back into these bodies of water at such a rate that we don't need to worry about depleting our bodies of water of kinetic energy.
Some might say that removing kinetic energy from the oceans on that scale is an obvious impossibility, but this strikes me as a foolish assumption in light of the dilution hypothesis, which clearly turned out false. Two-hundred years ago, people assumed that the oceans were so incredibly vast that man could never have an environmental impact on them. Today, here we stand, with oceanic acidification, warming, and overfishing being prime environmental concerns.
The exact same question and argument can be repeated for wind energy.
Do we have any idea exactly what the patterns and rates of energy transfer into our planet's water (and wind) systems are?
What are the potential environmental impacts of the large-scale removal of kinetic energy from our bodies of water?
(Note: among these environmental impacts, please don't focus on well-known impacts like damage to local ecosystems, loss of land, noise pollution, etc. I am chiefly interested in how this way of generating power affects our natural systems of energy storage and circulation, like oceanic and wind currents.)
The following question is off-topic, but it's a good follow-up: how is energy even introduced into our oceanic and wind current-systems? For example, I assume the moon's push-pull is responsible for the tidal movement of the oceans. What impact does the sun play? How fast is this entire system of energy transfer?
Comment: I strongly endorse the use of wind and hydropower as sources of energy over the further use of fossil fuels. However, I still think it is important to do research into the actual renewability of presumed-renewable energy sources, as we don't want to end up with another fossil fuel-type situation, in which we become aware of dependency on these energy sources and their malignant environmental side-effects long after widespread enthusiastic adoption.