Thank you for the pipe info, Nick.

Not to be difficult, but the house is going into a tightly controlled
residential neighborhood. We are removing one tree (out of 70+ on the
lot), and doing maybe 1500 yd^3 of grading, all carefully shaped to
blend with the natural contours of the site. Getting the steeply
angled rooftop solar collectors (flush with roof surface) past the
architectural and site control committee is expected to be a challenge.
Talk of above-ground trenches with self-inflating solar covers is just
not relevant to this problem.