How does an evacuated solar water heating tube work in your domestic system or swimming pool?

The evacuated tubes are connected in a bank to form a solar collector.  The solar tubes themselves are a series of old inventions bundled up into one. We have a traditional thermos flask technologies an old fashioned heat pump that are used in solar tubes to computers and a special coating that has maximum absorption properties and minimal thermal losses .  All of these properties combined become very effective in harnessing the suns radiation with a seventy percent efficiency rate compared to a thirty percent efficiency rate for photo voltaic (electric).

The thermos flask

Each solar tube is comprised of an inner and outer tube (both tubes made from a borosilicate glass or pyrex to you or me). The Tubes are sealed top and bottom under extreme temperatures and the air between them is removed so that a vacuum can be created between the tubes, because of the vacuum the inner tube can reach temperatures of two hundred celsius whilst the outer tube is still cold to the touch.  The vacuum allows for good insulation, protecting it against the cold because it minimises heat losses via matter gases or liquids (convection or conduction).  The external tube is clear and allows the solar radiation to pass through the vacuum and onto the surface of the internal tube.  The internal tube is coated with metal-dielectric which is protected by the vacuum.

What is this metal-dielectric coating on the inner solar tube

Some of the most common and effective coatings for the solar tube are metal-dielectric or cermets (these have been used in semi conductors for many years already) which are sandwiched between a copper layer on the surface of the inner tube and a aluminium nitride for absorption of solar radiation at low emissions These cermets can be created from nickel or chromium and both are very reasonable to produce in terms of cost and have thermal absorption rates of about ninety five percent and thermal losses or imitance of five percent.  The energy from the sputtering on the inner tube will be transferred across aluminium sleeves inside the inner tube and onto the out side of the heat pump

The heat pump in the centre of the evacuated solar tube has a vacuum within it.  This vacuum allows the fluid inside to boil at a lower temperature and to turn into vapour.  Once it has turned into vapour it rise up the inside of the heat pump and ends up inside the condenser at the top of the heat pump. Where the energy is conducted across the condenser and heats up your system fluid, that will in turn heat your domestic hot water supply.  The vapour inside the condenser then turns back into fluid as the heat energy is extracted from it and it returns to the bottom of the heat pump ready to repeat the process all over again and gradually heat up your hot water supplies for domestic solar water heating or commercial applications such as swimming pools, hotels, nursing homes etc.

The heat pump at the centre of the evacuated tube

The heat pump comprises of a copper tube that has a condenser at the top.  The heat pump has a strong vacuum so that the fluid contained within can boil and turn to vapour at lower temperatures.  The vapour rises to the top of the heat pump where it meets the inside of the condenser and transfers the solar heat energy, then the vapour turns back into fluid and flows back to the bottom of the heat pump ready to be re heated by the evacuated glass tube with its metal dielectric coating.  The condenser rises in temperature through this repeated process and it is the condenser that acts like a flame and increases the system fluid temperature in the header of the solar heating chassis, which in turn flows to the secondary coil in your hot water cylinder.