@GiraffeEars- It is funny that you mention tidal hydroelectricity. I was recently in Strangford Loch in Northern Ireland, where I saw an actual tidal generator in action. It looks like a red light tower sticking out of the water with a wake following behind it. I was told by someone I met on my way to Portaferry that it was actually the top of a underwater tidal mill that produces enough electricity to power 1000 homes. The tidal generator is supposedly very low risk t the local ecosystem because the blades spin slow enough that all sea life in the area can move out of their way. If you are ever in Northern Ireland, you should ask about the tidal generator in Stangford Loch.