With a few exceptions, sources of renewable energy tend to be inconveniently unreliable. Things like wind and wave energy are subject to the whims of weather, and even if you manage to find something that isn’t weather dependent (like tidal flow), you still can’t rely on a constant output of power.
Strictly speaking, solar power is the worst: it's heavily weather dependent, and half the time, it doesn't work at all. (Even the moon gets in the way sometimes.)
Some think the way to make solar power the backbone of a renewable energy economy is to avoid the problematic Earth entirely and head out into space, where the sun is always shining and weather means something entirely different.