... 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 ... space between the two glass tubes to form a vacuum, so it eliminates heat loss.7, This ... Solar irradiation under stagnation≤3.5MJ/≤3.5MJ/Hailstone resistancehailstone diameter25mmhailstone diameter25mmPressure-endure ability0.6mPa0.6mPa 2mm thickness solar vacuum tube