... Solar vacuum tube for solar energy water heater 2,ISO,CE 3,Available in various size 4.5days delivery 5.OEM available 1, Vacuum tube ... is consists of two layer of glass tubes2, ISO900:2000, CE certificate;3, ... 0.91 transmittance of outer tube4, The outer tube is made ... between the two glass tubes to form a vacuum, so it eliminates heat loss.7, ...