Rather than get this lost in a different topic entirely I thought I would start another thread.
My solar tubes have been brilliant. I have checked the primary circuit pressure occasionally over about 10 (edit: almost exactly 15) years and topped it up once (but even that was only by a little bit to bring the pressure back up.)
As the tubes are on a single storey extension to the house I can get at them quite easily to wipe them if it looks as though a dust storm has coated them - I try to clean them if it looks bad, but I don't know how necessary it is. Washing with a hose is quite effective.
Clumps of moss have started to grow in the channels between the tubes and the stainless reflectors so I pull them out where I can reach them, and one day I shall take all the reflectors off to clean them and the tubes under them. Maybe I have done it once already. I doubt anybody else bothers with any of this though.
The kitchen ought to be completely rebuilt, so my plan would be to put the solar on the main roof first (with microbore tubing this time.)
If you are re-plumbing a house I would do it, but I can see that the costs of a new twin-coil cylinder might put people off when solar pv heating water via a normal immersion heater is mainstream now.
A