@transparent doubt my kitchen scales will measure that, but in theory heat shouldn’t cross a vacuum so it must be the hot ones that are stuffed. Just so I can break them up in the bin and keep the good ones, although how good are the good one's?  I got my delivery and two spare and all intact. I was worried since I fear it would be a battle to get compensation. The driver said he was the third person to handle them. Meant to send thermal grease but forgot I think but I should get by

I'm suggesting that you weigh the tubes in order to confirm that the only fault is the loss of vacuum.

If all the tubes (hot & cold) still weigh the same, then the fault is likely to be with the copper inner-tubes.

Even if you can't weigh them separately on kitchen scales, you should still be able to make a lever-balance with the fulcrum in the centre.
Place a cold tube at one end and a hot one at the other....

You have two possible verification checks. Two cold tubes should balance, as should two hot tubes.
That will confirm that you're really measuring the weight of air rather than random variations in the weight of glass.

@transparent fitted the foil to the roof with spray contact glue, a bit sceptical whether I was wasting my time but half way through it I had to go and get my sunglasses, and that caught me off guard if I’m honest.  Will see how it goes and if a success look for a quality material. 

in relation to the tubes they all look fine, other than the damaged ones of course.  But out of interest I put them all outside for a bit and monitored the heat build up in the copper tips with my infrared thermometer. The ones with hot tubes are slow to build up temp and cooler at the tips than the ones with cool glass. Quite surprised how quickly they heated up at the tips but my take is, if the tubes are warm then the vacuum is either gone or deteriorated to allow thermal transfer to the outer tube.  No condensation in any and look identical to the ones where the tubes are cold on the outside. Perhaps I’m wrong though and holding onto the 15 tube just now. 

Posted by: @david999

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I put them all outside for a bit and monitored the heat build up in the copper tips with my infrared thermometer.

....Quite surprised how quickly they heated up at the tips....

At what angle?

I'm unsure what fluid is within the copper tube, but my understanding is that it changes density, thus rising up to the top when hot.
If you change the angle of the tube (wrt the direction of gravity) then the speed of heat transfer alters accordingly.

If you hold the tip of the copper inner-tube tightly in your hand, and allow the glass vacuum vessel to hang vertically, then it breaks...

... because you've just burnt your hand and dropped it! 😯 

@transparent I just stuck them all flat,  probably not ideal as you say but holding onto them for the meantime.  I have a thought of sticking them in a smaller unit for winter use and cover it  during summer, or something but I hate waste so figure out something.

no casualties fitting them although the wife managed to get covered in thermal grease. She usually gets fingers jammed somewhere and I get the blame 

If you've recovered 15 tubes which still seem to work, then you could consider using them in a greenhouse environment.

Even if they are now only half as efficient as they used to be, that would be ample to raise the temperature of a cultivation bed with water-pipe snaked below it.

Have a look on ebay or AliExpress to find a short manifold for the required diameter evacuated tube - 47mm?

A PV panel on the greenhouse would provide sufficient power to drive a 24v motor as a pump.
Of course, that would run faster on days with lots of sunshine... which is what you'd want anyway.

@transparent got me thinking, but no greenhouse. Got a garage though but heating it is not a great idea, the heat in fire stations rots the appliances, I never thought that but there you go.  Car is best under a canopy with air circulation.

What’s yours putting out today, it’s a clear sunny day and my 20 tube putting out 50c.  I thought a bit more but my angle is a bit shallow.  I felt the tubes and there is a bit of warmth at the base but nothing like before. 

Erm... I'm not quite sure of the temperature,
but the water's pretty warm today.

It's been a 'busy day at the office'

@transparent you're working way too hard. You need to take a break 🤣

@transparent nothing to beat working from home. 😂

When I installed my thermal solar years ago I thought that I should increase the capacity to compensate for winter.  Navitron at that time advised that more capacity would simply mean reaching the 30c during winter faster but unable to produce the 60c or more during summer and be an issue during summer producing too much heat.  Does that still apply?