ESTEC Solar Vacuum Tubes | Clean Energy
Clean Energy Ireland
Clean Energy, solar vacuum tubes
The VRK evacuated tube collector with CPC reflector technology is a high-end, mature product. The VRK demonstrates its performance capabilities especially with low irradiance values and low ambient temperatures. These properties make the VRK highly suitable for the provision of backup heating.
Advantages of Vacuum Tubes
- Minimal heat loss due to best possible insulation with vacuum – the solar energy can be effectively used.
- High collector temperature, even in winter – ideally suited for heating.
- Optimised exploitation of diffuse sunlight and light striking at an angle via the CPC reflector and the round evacuated tube absorbers.
- The high solar yield relieves the boiler, even with low outdoor temperatures.
- Low costs due to simple installation, very manageable and easy to connect.
- Easy to repair damage caused by vandalism, since the tubes can be replaced without draining the solar circuit.
Thermos flasks can keep coffee and tea hot for hours because there is a vacuum insulated intermediate layer between the double vessel walls. With the two concentric glass tubes, VRK evacuated tubes also form a hermetically sealed space that is vacuum insulated. In addition to this, the outer surface of the inner tube is coated with a highly efficient, environmentally friendly absorber coating. This converts incident sunlight almost completely into heat and radiates almost no heat. The inner tube becomes hot while the outer enclosing tube remains cold.
To also irradiate the side of the evacuated tube that is not facing the sun, the optimised geometry of a highly reflective, weather-proof CPC (Compound Parabolic Concentrator) reflector concentrates direct and diffuse sunlight onto the absorber from almost all directions. This increases the efficiency of the evacuated tube collectors compared to conventional collectors. Especially under unfavourable conditions, e.g. during autumn and winter, when the sky is overcast, during morning and evening sun and when the roof surface does not face south.
|Type of construction ||For On-roof, Flat-roof and Façade mounting |
|Absorber type ||Vacuum insulated Tube, selective coating, U-Tube Construction |
|Measurement ||Height = 1.645m, Width = 1.555, Depth = 0.107m |
|Gross area ||2.57 m² |
|Absorber area ||2.359 m² |
|Aperture Area ||2.207 m² |
|Total Weight dry ||42 kg |
|Liquid content ||2.3 litres |
|Efficiency η0 ||64%, related to the aperture area |
|Heat loss coefficient a1 ||1.059 W/(m²K) |
|Heat loss coefficient a2 ||0.0045 W/(m²K²) |
| ||292 °C |
|Absorber coating ||Highly selective on Aluminium (eta plus_al) |
|Absorption ||96 % |
|Emission ||6% |
|Absorber Sheet ||Rolled Aluminium |
|Reflection Coating ||PVD -Coated |
|Hydraulic connection ||Series connection with collectors side-by-side |
|Collector connection ||¾” coupling nut, flat sealing |
|Max. operation pressure ||10 bar |
|Heat insulation ||Mineral wool |
|Collector case ||Aluminium frame, Powder Coated |
|Angle of inclination ||15 – 75° |
, solar vacuum tubes