Could wind and wave energy generation hurt the planet?

The problem with all technologies that harness wind, waves, currents is that they disrupt the normal flow of air or water. You are transferring energy from the air or water into electrical generators. What effect will that have on the weather, if there are wind farms all over slowing down the winds (for that is what wind farms do)? What effect will tidal generators have on ocean currents? Will these river current generators slow down the river so much that it increases salt intrusion into the oh-so-vital wetlands at the mouth of the river, thus causing environmental damage? I don't think people have thought this through enough, or even understand one of the fundamental laws of physics involved, the Law of Conservation of Energy (which applies to all non-nuclear energy transactions). Sure, the current small-scale experiments haven't done much bad other than kill a bunch of birds (eep!), but they're *small*...

One of the things I like about direct photovoltaics is that the only side effect they have during operation, assuming they're placed on rooftops and such rather than in giant farms out in the middle of usable land, is to reduce solar heating of the Earth's surface. This is is a Good Thing(tm) given that so many of man's modifications to the Earth increase solar heating of the Earth, such as all that black pavement in cities and all the CO2 we've belched into the atmosphere. The energy density is low, but the current energy usage of the average American is unsustainable anyhow so we're just going to have to learn to live with a lower energy usage. But some of these other technologies, my suspicion is that we'd have fewer effects on the environment from building nuclear power plants (eep!). Things that are "green" on the micro level aren't necessarily "green" on the macro level, and vice-versa...

-- Badtux the Energy Penguin