Solar Mike wrote:

Thanks for that Nick I will google somewhere to download it from.
Was going to use 3 reflective air spaced layers behind a trickle
solar panel array system.

Under what kind of glazing? Warm water vapor quickly degrades polycarbonate.

Multiple relfective airspaces require iteration to determine intermediate
surface temps, as described in ASTM STP 1116. Adding individual airspace
resistances does not work.

Nick