Shippy
A month or two back, I was at a lecture given by an eminent scientist on this very subject. His answer to this question was that the area required to be covered was actually surprisingly small in the grand scheme of things.

In fact covering an area the equivalent of a fraction of 1% of Britain's surface would provide enough energy for the whole planet's needs.

That's still a hell of a lot of solar panels though.

As far as changing the albedo is concerned, yes, it will make a small difference, but because of the area fraction concerned, it's effectively a negligible one.
( K2k6 has a proper job these days, Tue 8 Jul 2008, 14:32, Reply)