Clean the plastic surface with soap and water. Wash away any tree sap, bird droppings or grime on the surface. Dry thoroughly to remove any soapy residue.
Wet-sand the plastic surface with 600-grit sandpaper. Wet-sanding requires using water to keep the sandpaper free of sanding dust. Pour water over the sandpaper and light every 5 to 10 seconds to keep the sandpaper free of clogs. Sand the surface in a circular motion until the damaged outer layer is removed. The plastic will have a dull sheen as a result of sanding.
Wash and dry the solar light again to remove any sanding dust. Wet-sand the surface with 1,200-grit sandpaper to remove the dull sheen left by the 600-grit sanding process. Wash and dry the surface.
Polish the plastic with a car wax containing UV blockers. Rub the car wax onto the plastic surface then wipe the residue away. Buff with a cloth to a high shine. The UV blockers in the car wax protect the plastic from clouding during exposure to the sun. The car wax does not prevent the operation of the solar cell.