Now a form of energy that is less known: generating electricity through tidal waves.
The moon exerts huge energy on the oceans. But we don't really use it on a significant scale to tap this energy. It is a form of hydro power. See this vid:
We should invest more in research into this type of energy. There are plenty of places in the world where this can be done and it can be a welcome source of energy in the 'green mix': a combination of renewable energy sources, like wind, solar, hydro and other sources.