This is the 2MW turbine I was talking about earlier
http://www.scotrenewables.com/technology-development/sr2000Power in Scotland is little use in South England # due to transmission losses.. and the potential for tidal flow power in England is rather limited.
Other countries transmit power over greater distances, it's all about having the right infrastructure to support it, as I said earlier. Here in the UK, we will soon be building a 1400MW, 400 mile electricity interconnector between Peterhead and Norway. Around the South of the UK, there are many potentially significant tidal power (not wave) sites in the Irish Sea, the South West and on the South coast, and there will be many other sites with improved technology.
We may be some time away from a significant contribution from tidal power, but I still think it will be a big part of the future. They estimate that we have 50% of Europe's tidal energy potential around the UK shores.
The main reason everyone has gone big for solar and wind is because the technology is mature, and it's easy and cheap to install capacity. The drawbacks are the obvious intermittent nature, though storage and grid connections over greater distances can solve some of the problems - there has to be wind somewhere.