Making soda with yeast
I agree with @SAJ14SAJ. What I would add is that


yeast does not require sunlight in any way ... but as UV light can be harmful to microorganisms and might inhibit yeast growth I wouldn't brew it in direct sun.
for bottling beer it is normally suggested to leave the correct amount (1 - 1 ½ inch) of headspace (air) at the top of the bottle for carbonation and proper pressure. But I am not sure if the same conditions apply for soda - I would think it is not too different.
shaking gently occasionally might help to evenly distribute the yeast in the sugar solution, and expose it to more food resources (sugar).