ESTEC Solar Vacuum Tubes | Clean Energy

By: Clean Energy Ireland  05/12/2011
Keywords: 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°

Keywords: Clean Energy, solar vacuum tubes

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