Managing the ebb and flow of the seas has long been spoken about as a method of developing power. The earliest form of tidal power was believed to be with tidal mills which used the tides' movements to power mills in areas where there was a strong current and a limited supply of coal.
However, to use tides to generate electricity could only come about with the creation of the turbine, once that was done, it was just a matter of connecting these in a row and creating barrages across the sea. And therein lies the problem, the areas with the best tidal flow are often harbors, after all in the days of sail, it could be useful to have a good tide to get your boat out and back again. But today, this issue with tidal barrages is that they will disrupt the flow of traffic into the harbor as well as the wealth of marine life that maybe affected.
To combat this problem, one solution has been proposed in Swansea, Wales: a tidal lagoon. Tidal lagoons are manmade areas designed to have an electricity barrage at the entrance to an enclosed lagoon where the tide will ebb and flow into. Inside the lagoon the tide will flow normally and natural sea life will still be able to exist.
Swansea Bay Lagoon is, according to their website, going to be the first of this specific style of tidal energy generator in the world and will generate enough electricity to power 120,000 homes (400,000MWh/year) for 120 years.
There are two main points to the lagoon: the first and the largest is the 9.7km wall. In order to minimize the environmental impact, costs, carbon, and materials of this breakwater, they are going to use geotextile casings (Geotube) and sand, dredged from the sea floor, rocks, and a concrete crest. The second part is the turbines, which will be a modification of existing low-head bulb turbines which generates electricity when the water moves past the turbine's blades. The modification of the turbines is to produce better electricity generation during the ebb and flow of the tide.
This project has yet to be installed but other tidal projects are already enjoying success, according to Wikipedia, as of 2010, there are seven tidal power stations in operation in: Canada, China, Russia, France, South Korea, and the United Kingdom; and another nine (including Swansea) in the planning stages
However we do it, it's clear that when fossil fuels do eventually run out, we need to be able to generate electricity in the most efficient way and whether that's using the sun, wind, or tidal power or combinations of all three, only time will tell.