You're likely running into the limitation of Insight Solar that it can't correctly analyze insolation on faces that are within a Family or Group.
Since porting the Solar engine from Vasari, a mass modeling tool, we haven't implemented the geometry transforms for faces inside Families and Groups, so the location of the face in Project Coordinates is relative to it's location in the Family Coordinates. Also we neglected to filter the selection process to only allow selection of supported faces, and we just added a pop-up window describing this limitation when the 'Select Faces' button is checked (if all else fails, read the directions 😉 ).
So what you'll need to do is model your panels using standard Revit Elements like Wall, Ceiling, Roof, Floor or Mass.
I prefer to use a Roof, as that makes it easy to experiment with tilt angle by manipulating pitch. You can do a similar thing by modeling a Roof with a eave outline extrusion, or model with a mass built in a vertical reference plane so it can be tilted easily and maintain it's overall surface area.
There are a few other posts in the Forum about this issue that have some additional tips and examples.
David
