Although I am in favour of energy sources which do not rely on fossil fuels from states which may not always be friendly, or crops grown on limited arable land I have one question. Where does the power come from at night, on windless days when wave power will be down also. Days like this tend to be at the extremes of temperature range for a region/country and I would guess that power demands will be above average at these times. Even tidal power generation has its problems due to slack water - I think it is known as The rule of Twelfths. Hydro electric will be affected by periods of low rainfall in most countries.

In the worst case, what happens during the night, in summer with a stalled anticyclone, during a drought and at slack water in a neap tide?