Solar water heater shock absorbers are evacuated plugs. They can convert solar energy into heat for heating water. Evacuated plugs have been used for many years in Germany, Canada, China, and the UK. Several types of evacuated plugs are available for the solar industry. Solar collectors use the most common "twin-glass plug." Due to its reliability, good performance, and low production cost, the plugs are made of extremely strong borosilicate glass. The outer plug is transparent, allowing light to pass through and minimizing reflection. The inner tube is coated with a layer of a special selective coating (Al-N/Al) with excellent solar radiation absorption and minimal reflection, significantly improving the efficiency of solar energy absorption. The top of the two tubes is fused together, forcing excess air into the space between the two layers of glass by exposing the tube to high temperatures. This "emptying" of the glass creates a vacuum, which is an important characteristic for good performance of evacuated tubes. Please.
Why a vacuum?
As you can use a glass-lined thermos flask before, a vacuum is a good insulator. This is important because we don't want to lose the heat that the evacuated tube converts to sunlight! A vacuum can help achieve this. Insulation properties are good when the inside of the tube is 150°C/304°F, and the outside is cold to the touch. This means that evacuated tube water heaters can perform well even in cold conditions, while flat plate collectors perform poorly due to heat loss (during high Delta-T conditions).
To maintain good vacuum performance, a barium getter is sandwiched between two glass layers (similar to those found in television tubes). During the production of the evacuated tube, this getter is exposed to high temperatures, forming a pure barium layer at the bottom of the evacuated tube. This barium layer can effectively absorb all CO, CO2, N2, O2, H2O, and H2 gasses released from the evacuated tube during storage and operation, ensuring good vacuum performance. The barium layer also provides a clear visual indicator of vacuum status. The silver-colored barium layer will turn white if the vacuum is broken. This makes it easy to distinguish whether the tube is in good condition or not. You can refer to the images below.
The getter is located at the bottom of the evacuated tube. Left tube = vacuum present. Right tube = vacuum not present.
The evacuated tubes are aligned parallel, with the angle depending on the installation latitude of your location. In a north-south direction, the plugs can passively track the sun's heat all day. In an east-west direction, they can track the sun year-round.
The effectiveness of an evacuated water heater depends on several factors, one important one being the level of evacuated solar radiation (solar irradiance) in your area. To learn more about solar irradiance and average values for your area, click here.
