Evacuated Tube Solar Hot Water
Evacuated tube solar hot water systems capture and convert solar energy into hot water. Each tube is made up of two very strong transparent borosilicate glass tubes, able to resist impact from hail up to 25mm in diameter. The inner tube is coated with layers of select materials which efficiently absorb solar heat and minimise heat reflection. The air between the two tubes is extracted (evacuated) to form a vacuum, which eradicates conductive and convective heat loss. Solar energy is absorbed and retained within the inner tube, then transferred to a body of water. The most common methods for transferring heat from evacuated tubes are the Heat Pipe or Wet Tube method.
Heat Pipe Evacuated Tube Collectors are used with split-systems design, allowing the Solar Collector to be mounted on the roof with the storage tank located elsewhere. With this configuration, each inner tube has a copper heat pipe which transfers the heat into the collector's manifold. A sensor wire at the collector and at the storage tank allow a temperature assessment to be made by a differential controller which in turn activates a reticulation pump. The reticulation pump moves the stored water up to the collector. As the water runs through the manifold, heat is transferred into the moving water, returning to the tank for storage.
Wet Tube Solar Hot Water Collectors are used with close-coupled design. The tank is mounted on the roof with the evacuated tubes installed directly into the storage tank itself. Circulation between the evacuated tubes and the storage tank occur passively through natural thermosiphon. An open vent pipe allows expansion of the stored thermal mass to regulate itself through cycles of expansion and contraction, no valves are needed to maintain circumstances of overpressure build up.