Solar Make Money The typical household uses 10,000 to 15,000 BTUs of hot water per person per day. A 20 vacuum tube solar collector can produce 30,000 BTUs on a summer ... more>>


Mr Simon Chen:

Ms Jessica Zhuang:

Add: Solar Energy Zone, Yuanhua, Haining, Jiaxing, Zhejiang, China

Technical info
Evacuated tubes
Evacuated tubes are the absorber of the solar water heater. They absorb solar energy converting it into heat for use in water heating. Evacuated tubes have already been used for years in Germany, Canada, China and the UK. There are several types of evacuated tubes in use in the solar industry. Shentai collectors use the most common "twin-glass tube". This type of tube is chosen for its reliability, performance and low manufacturing cost.
Each evacuated tube consists of two glass tubes made from extremely strong borosilicate glass. The outer tube is transparent allowing light rays to pass through with minimal reflection. The inner tube is coated with a special selective coating (Al-N/Al) which features excellent solar radiation absorption and minimal reflection properties. The top of the two tubes are fused together and the air contained in the space between the two layers of glass is pumped out while exposing the tube to high temperatures. This "evacuation" of the gasses forms a vacuum, which is an important factor in the performance of the evacuated tubes.
Why a vacuum? As you would know if you have used a glass lined thermos flask, a vacuum is an excellent insulator. This is important because once the evacuated tube absorbs the radiation from the sun and converts it to heat, we don't want to lose it!! The vacuum helps to achieve this. The insulation properties are so good that while the inside of the tube may be 150oC / 304oF , the outer tube is cold to touch. This means that evacuated tube water heaters can perform well even in cold weather when flat plate collectors perform poorly due to heat loss (during high Delta-T conditions).

In order to maintain the vacuum between the two glass layers, a barium getter is used (the same as in television tubes). During manufacture of the evacuated tube this getter is exposed to high temperatures which causes the bottom of the evacuated tube to be coated with a pure layer of barium. This barium layer actively absorbs any CO, CO2, N2, O2, H2O and H2 out-gassed from the evacuated tube during storage and operation, thus helping to maintaining the vacuum. The barium layer also provides a clear visual indicator of the vacuum status. The silver coloured barium layer will turn white if the vacuum is ever lost. This makes it easy to determine whether or not a tube is in good condition. See picture below
Evacuated tubes are aligned in parallel, the angle of mounting depends upon the latitude of your location. In a North South orientation the tubes can passively track heat from the sun all day. In an East West orientation they can track the sun all year round.

The efficiency of a evacuated water heater is dependent upon a number of factors, one important one being the level of evacuated radiation (insolation) in your region.
Evacuated Tube Basic Specifications
Length (nominal)
1500mm /1800mm
Outer tube diameter
Glass thickness
Thermal expansion
3.3x10-6 centi-degree
Borosilicate Glass 3.3
Absorptive Coating
Graded Al-N/Al
>92% (AM1.5)
<8% (80centi-degree)
P<5x10-3 Pa
Stagnation Temperature
Heat Loss
<0.8W/ ( m² centi-degree )
Maximum Strength
Heat Pipes
As a key component of the heat-pipe collector, heat-pipe plays a very important role in this solar collecting system. The heat-pipe is composed of heat-energy absorption unit and condenser unit, and is hollow with the space inside evacuated. Under the vacuum circumstance, the air pressure inside heat-pipe is very low, thus the medium can be evaporated easily when absorbing certain energy. This vapour rapidly rises to the condenser zone and transfers heat, then becomes the liquid and returns to the bottom of the heat pipe since the heat is lost. This process repeats again and again, so the solar energy is transferred continuously.
On HURRAS heat-pipe collector, the condenser zone of the heat-pipe is inserted to the copper sleeves which are distributed on the water pipe averagely. After the solar energy is absorbed by the vacuum tubes, it is transferred to the heat-pipe through the aluminum fin. Heated by the energy, the medium in the heat-pipe is working and transferring the heat energy to the condenser zone. When water or other medium in the water pipe flows across the copper sleeves, they would bring the energy and be heated.

The heated water or other medium makes water in the tank hotter and hotter by walking across the coils in the tank.
Copyright (C)2010:Zhejiang Hurras Solar Energy Technology Co., Ltd.
Technology Supported by:Hangzhou Chuangyi Science & Technic Company(EC-world)