What is IAM?

Incidence Angle Modifier (IAM): refers to the change in performance as the sun's angle in relation to the collector surface changes. Perpendicular to the collector (usually midday) is expressed as 0', with negative and positive angles in the morning and afternoon respectively. Collectors with a flat absorber surface, only have 100% efficiency at midday (0'), whereas solar tubes provide peak efficiency mid morning and mid afternoon, at around 40' from perpendicular. This results in good stable heat output for most of the day. What is the Aperture? The part of the collector through which light enters. For evacuated tubes this refers to the cross-sectional surface area of the outer clear glass tube measured using the internal diameter, not the outside diameter. (Eg. 0.0548m x 1.72m = 0.094m2). 1.72m is the exposed length of the evacuated tube.