You might want to give a little more thought to offshore wind energy,
which is becoming cost competitve and has virtually no environmental
drawbacks. Many of the worlds largest citites are not that far from
suitable sites. The UK government is aiming to have several GW of
capacity by 2010.

However, in the bigger scheme of things, it's not enough. Currently,
the US, with 4% of theb population, consumes over 25% of the energy.
If all people tend towards US consumption levels over the next 100
years, that would imply a six fold increase in energy consumption. For
those levels, I think SSP is the only long term option.