Extrapolation is always a bad thing :-). That said, this guy has some interesting thoughts. Of course he misses out that if you pump the tides you can speed up the rotation of the earth and thus "renew" the lag (think moving your legs while swinging).

Similarly solar isn't renewable because at some point the Sun is going to run out of hydrogen, and if you made a dyson sphere to capture all of the Sun's energy you would wipe out life on earth.