What are the options for adding Exterior Roof Insulation?

The process of dissasembling a metal roof and solar panels then re-installing them is no small affair, so just looking at the labour cost alone, unless you have almost no insulation up there (and if it met R2000 then its not bad at all) I doubt you will ever recoup your investment through energy savings.

Are the scissor trusses filled with cellulose or batt insulation? I assume at this point that under your solar panels and metal roof is sheathing, with likely an air space underneath the sheating at the top of the insulation. If that is the case, laying SIPs or ThermalWall panels on the sheathing won't do anything at all since cold air would be flowing underneath your new insulation. I don't think there is any cheap way to add much insulation to your roof unfortunately as you would need to remove everything and build up to accomodate more insulation in the scissor truss cavity. What kind of insulation is up there and how much? And where is the house? (City or climate zone).

Thanks. We are in Canmore, Alberta (I think zone 7A).  Pretty sure it is fibreglass batt in the scissor truss, and it will be well done based on having pulled back a few things here and there for various projects. I guess the other option, if I really wanted to go there would be to add insulation on the inside of the ceiling. But I think you are right, hard to see it pay back. Will focus on the exterior walls.