Solar Evacuated Tube Panels.
Evacuated Tube collectors (sometimes referred to as Vacuum tubes), are ideally suited to the UK climate providing useful heat all year round even in overcast weather. In April, on an overcast day without any sunshine a single 20 tube panel is still able to heat a 210 litre hot water cylinder to 40°C. A sunny day in April will warm the cylinder as high as 60°C!
Tube Construction
Evacuated tubes are the absorber of the solar water panel. They absorb solar energy converting it into heat for use in water heating. There are several types of evacuated tubes in use in the solar industry. Our 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 (i.e. Pyrex). 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 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.
How It Works
Within the centre of the glass tube is placed a copper heat pipe. The sun's radiation is absorbed by the selective coating on the inner glass surface, but prevented from re-radiating by the silvered innermost lining. This is in effect like a one-way mirror which has been optimised for infra-red radiation. In fact it is very efficient, of the sun light's energy hitting the tube's surface, 93% is absorbed, whereas only 7% is lost through reflection and re-emission.
The suns radiation boils the liquid in the heat pipe and the vapour rises to the tip of the heat pipe where the heat is transferred to a copper manifold. At this point the vapour condenses and runs back to the bottom of the tube due to the reduction in temperature. The manifold runs across the top of the panel in which water is circulated to heat the hot water tank. If a tube is placed in direct sunlight on a summer day, the tip temperature can reach 250°C - so the system easily heats domestic hot water cylinders to 60°C even in cooler weather! The manifold is heavily insulated with a 2" thickness of pre-formed rockwool to keep the heat in.
Panels
Panels can be produced in a number of sizes (of both the number of tubes and the length/diameter of the tubes themselves) The most common size of tube is 47mm diameter and 1500mm in length and has 15 tubes or 20 per panel. We can source other options as and when required.
Specifications
| Panel Dimensions | 1690 x1170 x 130 mm (L x W x H) |
| Tube Dimensions | 1500 x 47 mm (L x ) |
| Panel Area | 1.98 m2 |
| Absorber Area | 1.37 m2 |
| Nominal Thermal Output | 825 kWh per annum |
| Certificates | EN 12975-1,2 Solar Keymark |
Price £413.58 + VAT.
| Panel Dimensions | 1690 x1495 x 130 mm (L x W x H) |
| Tube Dimensions | 1500 x 47 mm (L x ) |
| Panel Area | 2.53 m2 |
| Absorber Area | 1.84 m2 |
| Nominal Thermal Output | 1100 kWh per annum |
| Certificates | EN 12975-1,2 Solar Keymark |
Price £475.27 + VAT.
Note :- VAT rate will be 5% on installations or 17.5% for supply only.
