Tidal: http://www.bbc.co.uk/news/uk-scotland-gl...t-12767211
Solar: http://news.bbc.co.uk/1/hi/world/africa/8337735.stm
Wind: http://en.wikipedia.org/wiki/Offshore_wind_power
Nuclear fusion: http://en.wikipedia.org/wiki/Nuclear_fusion
Electrodynamic tether: http://en.wikipedia.org/wiki/Electrodynamic_tether

With the first three we should be capable of producing all the additional energy requirements. The last two are still some way off but that does not mean they cannot be achieved.

And new energy sources come along all the time:
http://www.cbsnews.com/stories/2007/09/1...6430.shtml
http://www.bbc.co.uk/news/uk-england-her...r-12388011