I accidently clicked on this link today, to find that the Swansea Bay Tidal Lagoon looks like it will happen.
http://www.bbc.co.uk/news/uk-wales-south-west-wales-32874810
At a projected cost of £850m, generating 500GWh/year – will take 17 years to recoup the build costs, based on selling the energy generated at 10p/kWh; and that assumes that there are no operational costs or interest on the money to build it. Given the likely running costs, interest charges and the use of unproven technology, it is unlikely to ever recoup the capital outlay, based on open market generation costs.
Therefore if it does go ahead, you can bet the government will guarantee that you and I will pay a hefty premium (maybe as much as 20p/kWh) for this green energy, ensuring the bankers a pay day.
Compare this project with the Hoover Dam, which cost £833m to build (at today’s costs), generating 4.2 billion kWh/year – nearly 10 times that of the Swansea Bay scheme. With the added advantage that its power output is constant, not dependent on tidal flows.
Source for Hoover Dam info:- Wikipedia