I cannot answer your specific question. In theory it is a good idea. However, the solar powered lights I see in gardens always seem to be very dim. My point is that even a small electric pump motor is going to need more juice than what a light bulb needs. I think you would need a decent enough solar panel.
Have you thought about making a small windmill, and rigging it up to the pump in some way? I made a windmill using a part from a flymo for the sail rotation, and a motor cycle wheel axil mounted in 2 small plumber block bearings for the house to rotate on.