The Evacuated
Tube Solar Collector

An evacuated tube solar collector is an array of tubes.The vacuum tube solar is a second generation (more efficient) collector, the first generation is the flat plate (or flat panel) solar collector.

How are Solar Evacuated Tubes Built?

Each tube is built as co-centered rings. Going from the outer ring inside we find:

• Outer transparent glass tube
• Black absorbing material, attached to inner transparent glass tube
• The volume between the 2 glass tubes is evacuated (it explains the name I think…),so we can call it a vacuum tube solar collector
• Inside the inner tube there are two non-concentric pipes that flows anti freeze liquid (e.g. glycol). Greenhouse effect is playing here the same role as it played in the solar flat plate collector

The Advantages of the Vacuum Tube Solar Collector

The advantages of evacuated tubes are:

• Graceful degradation, in case of fault it is possible to replace only the damaged tube and until it is replaced the effect on performance is marginal
• Efficiency – more radiation is converted to useful heat because a circle exposes more angles to the sun, even when the is lower in the sky.
• The heat losses are minimized due to the vacuum (vacuum is an exteremely good heat insulator); as a matter of fact, one can touch the tube surface and not get burned.

Where Do You Need the Vacuum Tubes Collector?

Vacuum tube solar collectors have typically 20 to 30 circular tubes

Bellow is a schematic drawing of the solar evacuated tubes