I know it doesn't look like much, but my boys were pretty impressed.
Get some construction paper
Lay it on the ground in the sun
Place various objects on top
Let sit in the sun for a while (ours were out approx. 6 hours)
Take objects off and see how powerful the sun can be!
This was such a simple little project.
My 7 year old (the "future scientist") loved explaining this experiment to his dad that night
and he's ready to do it again tomorrow with different objects.