Sun and or heat damage to back of monitor or computer
Heat and direct sunlight can damage plastics, usually increasing the degradation of the materials, resulting in discoloration, brittleness, and eventual structural failure.
Leaving computer equipment in direct sunlight is not generally the best idea over the long run, especially as you have describe.
If you have something, anything really, that can go over the lid of the laptop while it is closed to keep the direct sunlight off, it should be just fine. A book or magazine should be sufficient, though a case or cover may be more convenient over the long run.