2 solar lights, hook em together put a divider between them, then you can read a positive or negative voltage.. from that you could trigger a dc motor to move a panel. sadly the teeny solar cells alone cant do it, atleast not without some sort of charge pump beem bot circuitry.

http://www.instructables.com/id/2-sun-tracker-circuit/

And
A cheap easy joule thief circuit using the charge cotroller ic(from a $1 solar light) and an inductor.
http://www.instructables.com/id/Joule-Thief-Circuits-crude-to-modern/

both of these are easy and could be done in a hacknight.