solar vacuum tube 1. CE ISO CCC certificate 2. 15 years' gurantee ... Solar vacuum tube for solar water heater2, ISO900:2000, CE certificate3, 0.91 transmittance of the outer tube Specifications ... of two layer of glass tubes2, ISO900:2000, CE certificate;3, 0.91 transmittance of outer tube4, ... sand, but it is coated with a special selective coating with strong heat absorption and lowest heat loss.6, The ...