The heat is normally absorbed by water, or a freeze resistant water mix, which can then be used to supplement hot water heating, space heating and even space cooling via use of an absorption chiller or dessicant cooler technology.

Below are the key features of the Apricus Solar Collector design.

1. Internationally certified product
2. Reliable, efficient, twin-glass evacuated tubes
3. Copper heat pipes for rapid heat transfer
4. Easy plug-in installation
5. Maintenance Free
6. Suitable for mains pressure water (up to 8 bar/116psi)
7. Corrosion resistant silver brazed copper header
8. All stainless steel frame (439 grade SS)
9. Black or Silver aluminium casing
10. Stable solar conversion throughout the day (tubes passively track the sun)
11. The perfect solar collector for domestic solar water heater systems
12. Ideal for commercial solar water heating applications
13. Comprehensive 10 year limited warranty

The operation of the solar collector is very simple.

1. Solar Absorption: Solar radiation is absorbed by the evacuated tubes and converted into heat.
2. Solar Heat Transfer: Heat pipes conduct the heat from within the solar tube up to the header.
3. Solar Energy Storage: Water is ciruclated through the header, via intermittent pump cycling. Each time the water circulates through the header the temperatures is raised by 5-10oC / 9-18oF. Throughout the day, the water in the storage tank is gradually heated.

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.

Apricus 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 15°C, 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.

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.

The Getter is located at the bottom of the evacuated tube. Left Tube = Vacuum Present. Right Tube = Faulty

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.