Aperature and Absorber Area

In the interpretation of collector test certificates, manufacturer's datasheets or the outputs from system sizing, it is important to understand the area that is being discussed. The most common area discussed is the collector aperture area. For a flat-plate, this is the area of the absorber plate that is open to the sunlight and is therefore capable of generating heat. The absorber are is the physical area of the collector plate part of which may be obscured by the edges of the collector. Often overlooked, but on a tight roof space, the gross collector area is oboviously the most important! i.e. will the panel fit!! In vacuum tube collectors, the aperature area is slightly bigger than the absorber area. The absorber is the flat plate inside the tube (in the high efficiency collectors) or the coated surface in the Sydney type vacuum collectors. The absorber area is the outside diameter of the glass tube.
The gross surface area is another measure used. This is the roof area that a collector will require. Vacuum tube panels have gaps between their tubes so for a given aperature area, they will require more roof space than a flat plate collector.