Evacuated-tube collectors are used in applications that require temperatures over 150°F. The collector is made up of a series of evacuated glass tubes which are connected to a manifold at the top. When sunlight passes through the clear glass tube, it strikes the absorber plate which is coated with a selective
coating which is very efficient in absorbing and retaining heat. The heat is transferred to a heat pipe which in turn transfers the heat to the water flowing through the collectors. The glass tube is made of a durable borosilicate material. Since the collectors are modular, tubes can easily and inexpensively be added, removed or replaced.

When evacuated tubes are made, air is evacuated from the space between the two tubes, forming a vacuum. Conductive and convective heat losses are eliminated because there is no air to conduct heat or to circulate and cause convective losses. These collectors do re-radiate some of the heat gained but these losses are small compared to the amount collected. Evacuated-tube collectors achieve both high temperatures and high efficiencies at those temperatures. Their cylindrical shape allows them to shed dust and dirt that would otherwise accumulate on a flat surface. Evacuated-tube collectors perform well in both direct and diffuse solar radiation and they are able to heat water to 205°F.