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I have seen these solar thermal tubes but will a semi vacuum work? Answered

I have seen solar collectors with a black pipe inside a vacuum tube like these Ebay Tube
I want to know if this needs a complete vacuum or will a semi-vacuum work just as well, or at least help. 
Will even the smallest amount of air eliminate any benefit.



Best Answer 7 years ago

the vacuum prevents the heat energy escaping by conduction and convection so it lets only the radiant heat energy from the sun to enter and stops the heat escaping back out. A full vacuum completely eliminates heat loss by these 2 ways while a partial vacuum will reduce heat loss only by a percentage so even a semi-vacuum will help to raise the temp by a bit but not as much as a complete vacuum. hope this helps

Thanks, I just was wondering if it was sort of an all or nothing but I am glad that this will improve under less powerful vacuums.

Depending on how efficient you need your solar panel to be all you need is GOOD insulation - and I mean really good, behind the collector tubes. A good length of black collector tube, pople used to use old finned radiators painted matt black but modern black PVC water tubing is easier to work with.

On the front of the box you put triple or quadruple glazing. 2 old double glazing panels would do well one on top of the other.

This set up will easily raise 45 gals of water to boiling inside an hour in the UK on a normal sunny day. Don't forget to insulate your holding tank and provide a suitable control system to make sure the water in the solar collector doesn't boil or freeze or you get melt down!

What is this glazing thing I am really interested in doing this now.

See attached picture - There are web pages dedicated to building such systems. Example http://www.solarfriend.co.uk/

Your link doesn't work.