Im again curious why there is only one single post with the subject here, these tubes are incredibly efficient, simple to use and not all that expensive. 10 short tubes on Ebay for 100 Dollars to play with. The many many youtube videos utilizing them for different solar and energy and thermal work. There are Solar tube ovens, cooking over 400F, many applications, like utilizing it for the heat collector from the sun for the piston valve sleeve of a stirling engine.
China is super producing these, and yet.. nearly no information of them out there. There are systems self built video series for water heating on Youtube. The idea I have yet to see implemented as yet is including TEG's seebeck modules. Why no one has thought to work with such elements together is sad to me.
I mean in minutes you reach 220 plus fluid temperatures within these. There is even a short tube for sale at about 20 dollars for use as your own personal self heating thermos. The ovens are getting far over priced, 300 dollars and such. Its a rip off, but.. it comes with all the nifty items, the carrying case is a solar collecting curvature, the term escapes me( AH- parabolic troughs-sorry recalled it later), but.. in any Case these things are being used to create generated energy as well. These collectors have improved vastly in efficiency since the past. What I have noticed however.. is the very limiting nature of awareness and lack of USA sales. There seems to be a concerted effort to keep them out of the minds of people here and out of the marketplace.
So, in short I think there needs to be a full section of Your Solar area For Solar Evacuated Tube Collectors... the plethora of experimentation and products and so fourth out there.. REALLY need to be explored and seen as options. The reach for the free energy systems needs all the tools in the box, before people can realllly get to their goals.
Off soapbox,
cheers