The details of material:
The inner tank material: 304 2B stainless
steel—0.7mm
The outer tank material: Galvanized
steel—0.4mm
Insulation:40mm Polyurethane Foam
Remark: 50 pcs vacuum tubes per unit

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.