Yes, Stefan. They are to be used like walls and ceilling. Cristina did a first test at the "hypergrided world":
ucigrid04.nacs.uci.edu 9003 using transparence and not a ceilling to mantain the effect of day/night.
One problem that I see is the FOV (distance that the avatar can see anything) that needs to be changed or sometimes we will see the panel, sometimes not.