The tides have a crucial role to play in powering Britain

e live in uncertain times, but some things remain entirely predictable and one of them is the sea. The moon orbits the earth every four weeks and the level of the ocean will rise and fall with it.

Long before we started thinking about harnessing the tides, people were making energy out of water. The Victorians used water wheels to power early textile mills, sometimes with great effect. So long as it keeps raining upstream, water from the hills will continue to rush down towards the sea and if you position turbines in the right place, you can seize some of the energy for yourself.

This kind of thing works much better when you build a dam and establish a large reservoir of water on the upstream side of your turbines. Not only does it achieve consistency of flow but the sheer height of the water behind the dam guarantees a high water pressure and a high speed of flow through the turbines.