What is the clear coating over the solar cells? I am concerned about the durability, scratch resistance, relative CTE of cells to paint.

CTE is the Coefficient of Thermal Expansion of a material. Solar cells typically have very low CTE's. Composites have moderate CTE's based on the the resin and fiber used. As automotive applications go through one of the worst hot to cold temperature cycles in any industry, the adhesive used to glue the cells to the body and the resin going over the top of the cells has to be selected very carefully. Otherwise, the cells can begin to delaminate from the body, or the clear overcoat can begin to craze at the interface between the cell and the body. Soft materials have a high CTE and hard materials have a low CTE. The topcoat seems to have conflicting requirements - soft to provide some give, and hard to provide scratch resistance. I hope there is some PV industry tech they can leverage for this, and that they plan to temp cycle the solar array to verify it will hold up over time. It could get ugly very fast if they don't. These guys have done everything else right so far. I am sure they are on top of it.