Okay, really it is tidal power, but the tides are driven by the moon. Tides are more reliable than sunshine (which is only available half the time and can be blocked by clouds). Tides are more reliable than wind (which doesn’t always blow, and can blow too hard sometimes.) Tides are not constant, however. Tidal turbines rely on the tidal currents. They can work in both directions, but while the tide shifts from coming in to going out or the opposite, the current goes to zero. Put all three together and there is rarely a slack time.
“World’s Largest Tidal Energy Power Plant To Begin Construction In Scotland” – TreeHugger
Pretending Not To Panic 