A direct flow vacuum tube solar collector consists of flat, metal absorbers housed within parallel glass tubes. The metal absorbers, also called fins, are attached to a header pipe. As the fins absorb heat, a heat transfer fluid flows through the tubes to collect that heat. There are three different configurations for a direct flow vacuum tube system. The most common consists of dual piping for an inlet/outlet flow system. Air is removed from the vacuum between the two glass tubes to prevent heat loss. The other types consist of two glass tubes fused together at one end and a concentric inlet and outlet fluid.
A heat pipe vacuum tube solar collector consists of a copper absorber plate placed on a sealed solar tube. The plate is located in a hollow metal heat pipe, where liquid comes to a boil and rises up to the top of the pipe in the form of steam. There, water or a heat transfer fluid, such as glycol, collects the heat, and the condensed water returns to the bottom of the pipe. The absorber strip can also be located in an vacuum glass tube, and the heat transfer fluid flows through the tube. The heat pipe vacuum tube must be placed at an angle to allow for vaporization and condensation.
