Etc (vacuum tube collector) system: the vacuum tube collector system is made of glass. It has a vertical tube made of two coaxial glass tubes. Remove the air between the two coaxial pipes to create a vacuum and improve the insulation. In addition, the surface of the inner tube is coated to provide better heat absorption and insulation. These glass tubes are filled with cold water and heated by sunlight. Hot water is lighter than cold water, so it rises and is collected into a usable water storage tank.