Dangermouse: I hadn't realised photovoltaic systems were so very feeble; I really thought this sort of thing would be pretty commonplace these days.
The greatest minds in the world haven't been able to figure it out yet. Solar systems (at least one at a lodge in remote bush I've had experience with) are possibly able to power a few lights at night time but not much more.
This was huge news back in 2006 and my interest was piqued at the time....
http://www.redicecreations.com/specialreports/2006/03mar/sasunpanel.html
But, nothing ever came out of it. Some germans were going to manufacture the panels but it never happened. I guess there were technical issues or the breakthrough was not really one.